compose_rust/

schema.rs

//! Closed Rust-side schema and metadata used for Kotlin code generation.

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct EnumVariantSchema {
    pub name: &'static str,
    pub tag: u16,
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum FieldType {
    Float,
    U32,
    U64,
    /// A `Paint`, either a `ColorRole` or a literal ARGB `Color`.
    Paint,
    /// A role enum, named so codegen can emit the matching Kotlin type.
    Role(&'static str),
    /// A word that is 0 or 1. Any other value is a protocol error, not a third state.
    Bool,
    /// An `f32` that has to be a number. NaN or an infinity is a protocol error, for a
    /// value that would otherwise turn a whole subtree into nothing on one side only.
    FiniteFloat,
}

/// Which half of which `u64` word of a modifier's value a field occupies.
///
/// Two `f32` share one `u64`: the low 32 bits hold the first value. Every modifier has the
/// `first` and `second` words; the words after them exist only for a modifier whose
/// schema entry gives it `extra_words`.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum FieldSlot {
    FirstLow,
    FirstHigh,
    First,
    SecondLow,
    SecondHigh,
    Second,
    ThirdLow,
    ThirdHigh,
    Third,
    FourthLow,
    FourthHigh,
    Fourth,
    FifthLow,
    FifthHigh,
    Fifth,
    SixthLow,
    SixthHigh,
    Sixth,
    SeventhLow,
    SeventhHigh,
    Seventh,
    EighthLow,
    EighthHigh,
    Eighth,
    NinthLow,
    NinthHigh,
    Ninth,
    TenthLow,
    TenthHigh,
    Tenth,
}

impl FieldSlot {
    /// Which word, counting from zero, and whether the field is that word's high half.
    pub const fn word(self) -> (usize, bool) {
        match self {
            Self::FirstLow | Self::First => (0, false),
            Self::FirstHigh => (0, true),
            Self::SecondLow | Self::Second => (1, false),
            Self::SecondHigh => (1, true),
            Self::ThirdLow | Self::Third => (2, false),
            Self::ThirdHigh => (2, true),
            Self::FourthLow | Self::Fourth => (3, false),
            Self::FourthHigh => (3, true),
            Self::FifthLow | Self::Fifth => (4, false),
            Self::FifthHigh => (4, true),
            Self::SixthLow | Self::Sixth => (5, false),
            Self::SixthHigh => (5, true),
            Self::SeventhLow | Self::Seventh => (6, false),
            Self::SeventhHigh => (6, true),
            Self::EighthLow | Self::Eighth => (7, false),
            Self::EighthHigh => (7, true),
            Self::NinthLow | Self::Ninth => (8, false),
            Self::NinthHigh => (8, true),
            Self::TenthLow | Self::Tenth => (9, false),
            Self::TenthHigh => (9, true),
        }
    }
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct FieldSchema {
    pub name: &'static str,
    pub ty: FieldType,
    pub slot: FieldSlot,
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct VariantSchema {
    pub name: &'static str,
    pub tag: u16,
    /// How many eight byte words this modifier's value takes beyond the two every
    /// `SetModifier` record carries. The record is `28 + 8 * extra_words` bytes long, fixed
    /// per tag, so a decoder knows the length from the tag before it reads the value.
    pub extra_words: u8,
    pub fields: &'static [FieldSchema],
}

/// The most words any modifier's value takes, the two every record has included.
pub const MAX_MODIFIER_WORDS: usize = 10;

/// The `extra_words` the schema gives a modifier tag, or `None` for a tag it does not list.
pub const fn modifier_extra_words(tag: u16) -> Option<u8> {
    let mut index = 0;
    while index < MODIFIER_SCHEMA.len() {
        if MODIFIER_SCHEMA[index].tag == tag {
            return Some(MODIFIER_SCHEMA[index].extra_words);
        }
        index += 1;
    }
    None
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum EventPayloadType {
    None,
    Text,
    ProtocolError,
    KeyDown,
    Range,
    /// One `f64`. Every value-carrying widget shares it, so the same concept has one
    /// name on the wire whether the value counts days or slides between two ends.
    Double,
    /// Width, height, classes, and three safe-area insets.
    WindowSize,
    /// One `u16`: the tag of the design system the Renderer resolved the theme to.
    DesignSystem,
    /// A `u32` saying what was pressed (0 for the body, 1 or 2 for an action button), then
    /// the notification's key as a string reference.
    NotificationActivation,
    /// One `u32`: the notification permission the Renderer last saw.
    NotificationPermission,
    /// One moment in a renderer-played animation: its id, what happened, the property and
    /// slot it plays on, the iteration, the elapsed time and the frame time.
    Animation,
    /// One `u32`: whether the platform asks for reduced motion.
    ReducedMotion,
    /// One committed edit to a code editor's document: the version it produced, the range
    /// it replaced in the document as it stood before, and the text that replaced it.
    CodeChange,
    /// A Host edit the Renderer would not apply: the request it answers, the version it
    /// was written against, the version the document had reached, and the range as sent.
    CodeEditRejected,
    /// A pointer resting on, or leaving, a place in a code editor: the decoration under it,
    /// where it is, and which of the two it was.
    CodeHover,
    /// The save shortcut, with the version of the document it was pressed on.
    CodeSave,
    /// The id the application gave one decoration, which was pressed or accepted.
    Decoration,
    /// One pointer happening inside a subscribed node: its kind, which pointer, where,
    /// which buttons and modifiers, the wheel deltas and when. A fixed 72-byte record.
    Pointer,
    /// Two `f32` and an `i32`: the whole zoom factor, the system's text size, and the
    /// application's zoom level.
    Zoom,
    /// Where a code editor's selection is: the document version and the two ends.
    CodeSelection,
    /// Which lines of a code editor are on screen, folded lines left out.
    CodeVisibleRange,
    /// One word, 0 or 1: whether a code editor holds the keyboard focus.
    CodeFocus,
    /// The line a fold starts on and whether it is now collapsed.
    CodeFold,
    /// One word, 0 or 1: whether an input method is composing in a code editor. The
    /// composed text is never part of it.
    CodeComposition,
    /// One word, 0 or 1: whether a window is the key window.
    WindowFocus,
    /// Where a window's outer frame is and how large it is: `x`, `y`, `width`, `height`,
    /// all `f32` in screen dp.
    WindowMove,
    /// A torn-off window being dragged: the phase, the pointer's screen position, and the
    /// window under the pointer.
    WindowDrag,
    /// A dragged window passing over a subscribed node: the kind, the dragged window, and
    /// the position inside the node.
    WindowDragOver,
    /// A window the platform or the user asked the application for: a request number, then
    /// the `RestoreKey` as a string reference. The one window event that carries a string.
    WindowRequest,
    /// What became of one file dialog: the request number, the status, the filter in use
    /// and the paths as one string reference.
    FileDialogResult,
    /// What one clipboard read found: the request number, the status word, the text's length
    /// in bytes, and the text as one string reference.
    ClipboardText,
    /// The one answer to an input or output request the Host made of the Renderer: the
    /// request number, an `IoStatus`, and the bytes it carries as one reference.
    IoAnswer,
    /// Files the Renderer holds handles for: the request number, the status, the filter in
    /// use, how they were delivered, the first handle number, then the names (NUL
    /// separated) and one kind letter per name, as two references.
    FileHandles,
    /// Where a scroll container is: the first visible item, the flags, then six `f64` in
    /// physical pixels (offset, furthest offset and viewport, x before y). A fixed 72-byte
    /// record.
    ScrollChanged,
    /// The size a node's size motion settled at: `width_dp` and `height_dp`, two `f32` in
    /// dp. A fixed 24-byte record.
    MotionFinished,
    /// Where a code editor's caret is drawn: the line and the column it stands at, then
    /// `x`, `y`, `width` and `height` as `f32` in the window's dp. A fixed 40-byte record.
    CodeCaretRect,
    /// The answer to one position query: the request number, a word that is 1 when the
    /// position is on screen and 0 when it is not, then the rectangle as in
    /// `CodeCaretRect`, all zero when there is none. A fixed 40-byte record.
    CodePositionRect,
    /// A pointer event over a code editor: the 72-byte `Pointer` record, then the line and
    /// the column of the text under the pointer, both `u32::MAX` where it is over none. A
    /// fixed 80-byte record.
    CodePointer,
    /// Every selection of a code editor, the primary first: the document version, then a
    /// reference to 16-byte records behind the record (anchor line, anchor column, active
    /// line, active column). A fixed 28-byte record and its selections.
    CodeSelections,
    /// What became of one grouped edit of a code editor: the request id, an
    /// `EditGroupStatus` word, the version the group was written against, the version the
    /// document is at now and the index of the edit that decided it (or, applied, how many
    /// edits went in). A fixed 36-byte record.
    CodeEditGroupResult,
    /// One `u32`: whether the system appearance is light (0) or dark (1).
    ColorScheme,
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct EventSchema {
    pub name: &'static str,
    pub tag: u16,
    pub payload: EventPayloadType,
}

/// Canonical schema text. Variant order is wire-significant and must only be appended to.
pub const SCHEMA_DESCRIPTOR: &str = concat!(
    "compose-rust/v1;",
    "widgets=Column,Row,Box,Text,TextField,Button,Spacer,LazyColumn,ScrollColumn,Image,Icon,Checkbox,RadioButton,Switch,Slider,ProgressIndicator,Divider,Card,Surface,Dialog,Menu,Tabs,TopAppBar,LazyRow,Tooltip,Canvas,DatePicker,TimePicker,Dropdown,Navigation,NavigationItem,Sheet,Scaffold,ScaffoldSlot,LazyGrid,FileDropTarget,ScrollRow,Chip,FloatingAction,Badge,SelectionContainer,SplitPane,CodeEditor,AbsoluteBox,Window,FlowRow,Popover;",
    "properties=text,placeholder,enabled,multiline,on_click,on_value_change,on_submit,on_focus_lost,on_key_down,item_count,item_key,on_range_requested,type_role,font_size,font_weight,line_height,letter_spacing,color,text_align,max_lines,overflow,arrangement,spacing,space_role,alignment,variant,asset,checked,steps,determinate,circular,vertical,open,on_dismiss,selected_index,commands,value,min,max,icon,slot,columns,min_column_width,spans,on_files_entered,on_files_dropped,section,count,collapsible,button_kind,decorations,syntax_spans,tab_width,on_edit_rejected,on_hover,on_save,on_decoration_click,folds,gutter_decorations,on_selection_change,font,word_break,overflow_wrap,tab_size,absolute_size,soft_wrap,span_fonts,on_visible_range_change,on_editor_focus_change,on_fold_change,on_composition_change,on_pointer,pointer_kinds,cursor,user_select,island_zoom,window_title,window_size,window_min_size,window_resizable,window_chrome,window_title_bar,window_icon,window_position,window_restore_key,window_zoom_level,drag_from_pointer,on_window_close_requested,on_window_focus_changed,on_window_moved,on_window_drag,on_window_unavailable,on_window_closed,on_window_drag_over,tear_off_key,on_focus_gained,on_key_up,accessible_name,track_color,thumb_color,active_track_color,container_color,check_color,control_size,report_size,scrim,bare,horizontal_spacing,vertical_spacing,horizontal_alignment,vertical_alignment,max_items_in_each_row,placement,align,offset_dp,line_numbers,gutter_min_width_dp,gutter_padding_dp,text_inset_dp,code_editor_colors,on_code_metrics,on_code_scrolled,compact_navigation,on_scroll_changed,collapse_below,snap,max_height_fraction,font_feature_settings,on_motion_finished,on_edit_group_result,on_caret_rect,on_key_preview,on_code_pointer,radio_group,minimap,view_zones,word_wrap,content_scale,thumb_size;",
    "modifiers=Empty,Padding,FillMaxWidth,FillMaxHeight,Width,Height,Size,Background,Clickable,PaddingRole,PaddingEach,Weight,Shape,ShapeRole,Border,Elevation,ObserveSize,Motion,Material,Offset,RequiredSize,BorderEach,CornerEach,Shadow,Clip,Alpha,Transform,Transform3D,MatchParentSize,WindowDrag,PressFeedback,Semantics,CornerCurve,BackgroundBrush;",
    "keys=Enter,Other;",
    "events=Clicked,TextChanged,TextSubmitted,FocusLost,ProtocolError,KeyDown,RangeRequested,ValueChanged,WindowSizeChanged,DesignSystemResolved,FilesEntered,FilesDropped,NotificationActivated,NotificationPermissionChanged,CodeChanged,CodeEditRejected,CodeHovered,CodeSaveRequested,DecorationActivated,AnimationEvent,ReducedMotionChanged,Pointer,ZoomChanged,SelectionChanged,VisibleRangeChanged,EditorFocusChanged,FoldChanged,CompositionChanged,WindowCloseRequested,WindowFocusChanged,WindowMoved,WindowDrag,WindowDragOver,WindowUnavailable,WindowClosed,WindowRequested,ApplicationReopen,FocusGained,KeyUp,FileDialogResult,CodeEditGroupResult,ClipboardText,CodeMetrics,CodeScrolled,IoAnswer,FileHandles,StorageLocation,ScrollChanged,MotionFinished,CaretRect,PositionRect,CodePointer,ColorSchemeChanged,SelectionsChanged;",
    "windowsizeclasses=Compact,Medium,Expanded;",
    "windowheightclasses=Compact,Medium,Expanded;",
    "commands=Create,SetProp,SetModifier,Insert,Move,Remove,SetText,AppendText,SetTheme,SetWindow,RegisterAsset,ReleaseAsset,ShowMessage,PostNotification,WithdrawNotification,RequestNotificationPermission,EditCode,StartAnimation,ControlAnimation,SetSelection,RevealRange,SetFolded,SetWindowTheme,FocusWindow,RequestFocus,ShowFileDialog,SetOverlayTokens,EditCodeGroup,SetClipboardText,ReadClipboard,SetScrollOffset,StorageCall,FileCall,ReleaseFileHandle,ScrollTo,ScrollIntoView,QueryPositionRect,InsertSnippet,SetSelections;",
    // The fields of the overlay tokens record in wire order. A field is only appended, and
    // appending one changes the record's length, so it is part of what the hash covers.
    "overlaytokens=sheet_corner_radius,dialog_corner_radius,popup_corner_radius,sheet_elevation,popup_elevation,dialog_elevation,sheet_padding,dialog_padding,popup_padding,scrim,toast_elevation,toast_corner_radius;",
    // The fields of the message record in wire order, appended to in the same way.
    "showmessage=handler_id,text,action,duration,vertical,horizontal,offset_dp"
);

const fn hash_bytes(mut hash: u64, bytes: &[u8]) -> u64 {
    let mut index = 0;
    while index < bytes.len() {
        hash ^= bytes[index] as u64;
        hash = hash.wrapping_mul(0x0000_0100_0000_01b3);
        index += 1;
    }
    hash
}

const fn hash_enum_schema(mut hash: u64, schema: &[EnumVariantSchema]) -> u64 {
    let mut index = 0;
    while index < schema.len() {
        hash = hash_bytes(hash, schema[index].name.as_bytes());
        hash = hash_bytes(hash, &schema[index].tag.to_le_bytes());
        index += 1;
    }
    hash
}

const fn schema_hash() -> u64 {
    let mut hash = hash_bytes(0xcbf2_9ce4_8422_2325_u64, SCHEMA_DESCRIPTOR.as_bytes());
    hash = hash_bytes(hash, crate::extensions::SCHEMA_DESCRIPTOR.as_bytes());
    hash = hash_bytes(hash, crate::measure::SCHEMA_DESCRIPTOR.as_bytes());
    hash = hash_enum_schema(hash, WIDGET_SCHEMA);
    hash = hash_enum_schema(hash, PROPERTY_SCHEMA);
    hash = hash_enum_schema(hash, KEY_SCHEMA);
    hash = hash_enum_schema(hash, WINDOW_SIZE_CLASS_SCHEMA);
    hash = hash_enum_schema(hash, WINDOW_HEIGHT_CLASS_SCHEMA);
    let mut role_index = 0;
    while role_index < ROLE_ENUM_SCHEMA.len() {
        hash = hash_bytes(hash, ROLE_ENUM_SCHEMA[role_index].name.as_bytes());
        hash = hash_enum_schema(hash, ROLE_ENUM_SCHEMA[role_index].variants);
        role_index += 1;
    }
    let mut index = 0;
    while index < MODIFIER_SCHEMA.len() {
        let modifier = MODIFIER_SCHEMA[index];
        hash = hash_bytes(hash, modifier.name.as_bytes());
        hash = hash_bytes(hash, &modifier.tag.to_le_bytes());
        hash = hash_bytes(hash, &[modifier.extra_words]);
        let mut field_index = 0;
        while field_index < modifier.fields.len() {
            let field = modifier.fields[field_index];
            hash = hash_bytes(hash, field.name.as_bytes());
            hash = hash_bytes(
                hash,
                &[match field.ty {
                    FieldType::Float => 1,
                    FieldType::U32 => 2,
                    FieldType::U64 => 3,
                    FieldType::Paint => 4,
                    FieldType::Role(_) => 5,
                    FieldType::Bool => 6,
                    FieldType::FiniteFloat => 7,
                }],
            );
            if let FieldType::Role(role) = field.ty {
                hash = hash_bytes(hash, role.as_bytes());
            }
            hash = hash_bytes(
                hash,
                &[match field.slot {
                    FieldSlot::FirstLow => 0,
                    FieldSlot::FirstHigh => 1,
                    FieldSlot::First => 2,
                    FieldSlot::SecondLow => 3,
                    FieldSlot::SecondHigh => 4,
                    FieldSlot::Second => 5,
                    FieldSlot::ThirdLow => 6,
                    FieldSlot::ThirdHigh => 7,
                    FieldSlot::Third => 8,
                    FieldSlot::FourthLow => 9,
                    FieldSlot::FourthHigh => 10,
                    FieldSlot::Fourth => 11,
                    FieldSlot::FifthLow => 12,
                    FieldSlot::FifthHigh => 13,
                    FieldSlot::Fifth => 14,
                    FieldSlot::SixthLow => 15,
                    FieldSlot::SixthHigh => 16,
                    FieldSlot::Sixth => 17,
                    FieldSlot::SeventhLow => 18,
                    FieldSlot::SeventhHigh => 19,
                    FieldSlot::Seventh => 20,
                    FieldSlot::EighthLow => 21,
                    FieldSlot::EighthHigh => 22,
                    FieldSlot::Eighth => 23,
                    FieldSlot::NinthLow => 24,
                    FieldSlot::NinthHigh => 25,
                    FieldSlot::Ninth => 26,
                    FieldSlot::TenthLow => 27,
                    FieldSlot::TenthHigh => 28,
                    FieldSlot::Tenth => 29,
                }],
            );
            field_index += 1;
        }
        index += 1;
    }
    index = 0;
    while index < crate::drawing::DRAW_COMMAND_SCHEMA.len() {
        let command = crate::drawing::DRAW_COMMAND_SCHEMA[index];
        hash = hash_bytes(hash, command.name.as_bytes());
        hash = hash_bytes(hash, &command.tag.to_le_bytes());
        let mut field_index = 0;
        while field_index < command.fields.len() {
            let field = command.fields[field_index];
            hash = hash_bytes(hash, field.name.as_bytes());
            hash = hash_bytes(hash, &[field.word]);
            hash = hash_bytes(
                hash,
                &[match field.ty {
                    crate::drawing::DrawFieldType::Float => 1,
                    crate::drawing::DrawFieldType::U32 => 2,
                    crate::drawing::DrawFieldType::Role(_) => 3,
                }],
            );
            if let crate::drawing::DrawFieldType::Role(role) = field.ty {
                hash = hash_bytes(hash, role.as_bytes());
            }
            field_index += 1;
        }
        index += 1;
    }
    index = 0;
    while index < EVENT_SCHEMA.len() {
        let event = EVENT_SCHEMA[index];
        hash = hash_bytes(hash, event.name.as_bytes());
        hash = hash_bytes(hash, &event.tag.to_le_bytes());
        hash = hash_bytes(
            hash,
            &[match event.payload {
                EventPayloadType::None => 0,
                EventPayloadType::Text => 1,
                EventPayloadType::ProtocolError => 2,
                EventPayloadType::KeyDown => 3,
                EventPayloadType::Range => 4,
                EventPayloadType::Double => 5,
                EventPayloadType::WindowSize => 6,
                EventPayloadType::DesignSystem => 7,
                EventPayloadType::NotificationActivation => 8,
                EventPayloadType::NotificationPermission => 9,
                EventPayloadType::Animation => 10,
                EventPayloadType::ReducedMotion => 11,
                EventPayloadType::CodeChange => 12,
                EventPayloadType::CodeEditRejected => 13,
                EventPayloadType::CodeHover => 14,
                EventPayloadType::CodeSave => 15,
                EventPayloadType::Decoration => 16,
                EventPayloadType::Pointer => 17,
                EventPayloadType::Zoom => 18,
                EventPayloadType::CodeSelection => 19,
                EventPayloadType::CodeVisibleRange => 20,
                EventPayloadType::CodeFocus => 21,
                EventPayloadType::CodeFold => 22,
                EventPayloadType::CodeComposition => 23,
                EventPayloadType::WindowFocus => 24,
                EventPayloadType::WindowMove => 25,
                EventPayloadType::WindowDrag => 26,
                EventPayloadType::WindowDragOver => 27,
                EventPayloadType::WindowRequest => 28,
                EventPayloadType::FileDialogResult => 29,
                EventPayloadType::ClipboardText => 30,
                EventPayloadType::IoAnswer => 31,
                EventPayloadType::FileHandles => 32,
                EventPayloadType::ScrollChanged => 33,
                EventPayloadType::MotionFinished => 34,
                EventPayloadType::CodeCaretRect => 35,
                EventPayloadType::CodePositionRect => 36,
                EventPayloadType::CodePointer => 37,
                EventPayloadType::CodeEditGroupResult => 38,
                EventPayloadType::ColorScheme => 39,
                EventPayloadType::CodeSelections => 40,
            }],
        );
        index += 1;
    }
    hash = crate::code::hash_record_schema(hash, crate::code::DECORATION_RECORD);
    hash = crate::code::hash_record_schema(hash, crate::code::SYNTAX_SPAN_RECORD);
    hash = crate::code::hash_record_schema(hash, crate::code::FOLD_RECORD);
    hash = crate::code::hash_record_schema(hash, crate::code::GUTTER_DECORATION_RECORD);
    hash = crate::code::hash_record_schema(hash, crate::code::CODE_EDITOR_COLORS_RECORD);
    hash = crate::code::hash_record_schema(hash, crate::code::VIEW_ZONE_RECORD);
    hash
}

/// Stable handshake hash of the complete ordered schema metadata.
pub const SCHEMA_HASH: u64 = schema_hash();
pub const PROTOCOL_VERSION: u16 = 1;

fn wire_name_eq(input: &str, schema_name: &str) -> bool {
    input
        .bytes()
        .filter(|byte| *byte != b'_')
        .map(|byte| byte.to_ascii_lowercase())
        .eq(schema_name.bytes().map(|byte| byte.to_ascii_lowercase()))
}

macro_rules! define_wire_enum {
    ($schema:ident, $name:ident { $($variant:ident = $tag:literal),+ $(,)? }) => {
        define_wire_enum!($schema, $name { $($variant = $tag),+ } unlisted {});
    };
    // `unlisted` variants exist in Rust and travel as their tag, but are not in the schema
    // table, so codegen mirrors no Kotlin enum entry for them and `TryFrom` does not
    // produce them. The one there is, `TypeRole::None`, is tag 0, which every role
    // decoder already reads as "no role", and an entry for it in the Kotlin enum would
    // shift every ordinal the Renderer indexes its token tables by.
    (
        $schema:ident,
        $name:ident { $($variant:ident = $tag:literal),+ $(,)? }
        unlisted { $($extra:ident = $extra_tag:literal),* $(,)? }
    ) => {
        #[derive(Clone, Copy, Debug, Eq, PartialEq)]
        #[repr(u16)]
        pub enum $name {
            $($extra = $extra_tag,)*
            $($variant = $tag),+
        }

        pub const $schema: &[EnumVariantSchema] = &[
            $(EnumVariantSchema { name: stringify!($variant), tag: $tag }),+
        ];

        impl From<$name> for u16 {
            fn from(value: $name) -> Self {
                value as Self
            }
        }

        impl TryFrom<u16> for $name {
            type Error = ();

            // Spelled `()` rather than `Self::Error`: a `ColorRole::Error` variant would
            // otherwise make the associated item ambiguous.
            fn try_from(value: u16) -> Result<Self, ()> {
                match value {
                    $($tag => Ok(Self::$variant),)+
                    _ => Err(()),
                }
            }
        }

        impl $name {
            // The unit error is the wire's own convention: a name either is a variant or is
            // not, and the caller reports which name it was.
            #[allow(dead_code, clippy::result_unit_err)]
            #[doc(hidden)]
            #[allow(clippy::result_unit_err)]
            pub fn from_name(value: &str) -> Result<Self, ()> {
                $(if wire_name_eq(value, stringify!($variant)) {
                    return Ok(Self::$variant);
                })+
                Err(())
            }
        }
    };
}

crate::extensions::define_widget_schema_with_extensions!(define_wire_enum; WIDGET_SCHEMA, WidgetKind {
    Column = 1,
    Row = 2,
    Box = 3,
    Text = 4,
    TextField = 5,
    Button = 6,
    Spacer = 7,
    LazyColumn = 8,
    ScrollColumn = 9,
    Image = 10,
    Icon = 11,
    // The selection controls and the indicators. Each one emits a state and a role and
    // nothing about how it is drawn: the tick, the track, the thumb and the sweep of an
    // indeterminate bar are the design system's.
    Checkbox = 12,
    RadioButton = 13,
    Switch = 14,
    Slider = 15,
    ProgressIndicator = 16,
    Divider = 17,
    Card = 18,
    Surface = 19,
    Dialog = 20,
    Menu = 21,
    Tabs = 22,
    TopAppBar = 23,
    LazyRow = 24,
    Tooltip = 25,
    // Drawing commands instead of child nodes. The command list is its only property.
    Canvas = 26,
    DatePicker = 27,
    TimePicker = 28,
    Dropdown = 29,
    // One declaration, three presentations. The Renderer picks a bottom bar, a rail or a
    // permanent drawer from the width it has already measured, so the same tree looks
    // native on a phone and on a desktop without the Host branching on the size class.
    Navigation = 30,
    // One destination. Its label and its icon are properties rather than children,
    // because a child tree would fix the arrangement the presentations need to differ in.
    NavigationItem = 31,
    // A temporary surface that slides in from an edge of the screen. Which edge is the
    // Renderer's decision, for the same reason the navigation presentation is.
    Sheet = 32,
    // The screen's frame. The application fills slots and the Renderer decides what each
    // one becomes on this platform and at this width, which is the same decision
    // `Navigation` already makes for itself, widened to the whole frame.
    Scaffold = 33,
    // One filled slot. A wrapper rather than a property on the slot's own root, because
    // an application may put any tree in a slot and the Renderer has to know which slot
    // it is looking at without reading into it.
    ScaffoldSlot = 34,
    // A lazy grid. The windowing protocol is the list's, unchanged: the Renderer asks for a
    // range of items and the Host materialises exactly that range. What the grid adds is
    // that the Renderer rounds the range it asks for to whole rows, because a row is what
    // it lays out, and how many items a row holds is its own decision when the columns
    // were given as a minimum width rather than a count.
    LazyGrid = 35,
    // A place files may be dropped. Being this widget is the willingness: a node that is
    // not one is never offered as a target, so the platform shows no drop cursor over it
    // and nothing is reported.
    FileDropTarget = 36,
    // The whole content with a horizontal scroll, which is a ScrollColumn turned on its
    // side. Every child is materialised and the scroll position is the Renderer's, so
    // nothing about scrolling crosses the boundary; a long horizontal list is a LazyRow.
    ScrollRow = 37,
    // A small token that is chosen or filters. It carries its label and whether it is
    // chosen, and the chosen state is the Host's: it changes only because the Host's own
    // click handler changed it. The shape is the design system's.
    Chip = 38,
    // The one action a screen is about. It carries an icon, a label and a click. Where it
    // goes and what it is drawn as is the design system's: a disc floating over the page
    // is one system's answer, a plus at the trailing end of the bar is another's, and an
    // accent button at the head of the command bar is a third.
    FloatingAction = 39,
    // A small mark on something else that says how many, that there is something new, or
    // one short word. With one child it is attached to that child; with none it stands on
    // its own, at the end of a row. Where it sits on the child, its shape, and how a large
    // count is shortened are the design system's: nothing here can ask for a corner or a
    // ceiling.
    Badge = 40,
    // A region whose text can be dragged over and copied, as one selection across every
    // Text inside it. Text outside one cannot be selected. The selection and the copy are
    // the Renderer's entirely, so nothing about either crosses the boundary.
    SelectionContainer = 41,
    // Two panes side by side, a side pane and a body, with a divider the user drags to
    // change the side pane's width. Exactly two children, the side pane first.
    //
    // The drag is the Renderer's, like a scroll position: nothing crosses the boundary
    // while it moves, and the width it ends on is reported once through the value change
    // event. How the divider looks and how far its grip reaches, the side pane's default
    // width, the body's minimum, and whether a narrow place shows the two panes side by
    // side, with the side pane laid over the body, or one at a time, are the design
    // system's answers.
    SplitPane = 42,
    // Several lines of code that the reader edits. The text, the caret, the selection,
    // the scroll position and the undo history are the Renderer's, the way a text field's
    // are, and the Host is told about each committed edit with the version it produced.
    // What the Host adds on top is said as ranges: colour runs for the syntax, and
    // decorations for diagnostics, lenses, hover anchors and inline suggestions. How any
    // of it is drawn, from the gutter to the weight of an underline, is the design
    // system's.
    CodeEditor = 43,
    // Children laid where the Host already put them. Each child is placed at its own
    // `Offset`, relative to this box, and no child moves or sizes another: the layout was
    // computed on the Host (an HTML engine, for instance) and laying it out a second time
    // here would only be a second answer that can disagree with the first. Later children
    // draw over earlier ones, so a stacking order is the child order.
    AbsoluteBox = 44,
    // A platform window, a child of the root and only of the root. The children of a
    // `Window` are that window's content. Putting one anywhere else, or moving a node from
    // one window into another, is a protocol error: Compose keeps one composition per
    // window and has no way to hand a node from one to the next.
    Window = 45,
    // A row that wraps. Children are measured at their own width and placed one after
    // another on a line; a child that does not fit in what is left of the line starts the
    // next one. A child wider than the whole line has the line to itself and is measured
    // at the line's width, so nothing runs out of the row.
    FlowRow = 46,
    // A floating box of any content attached to an anchor. The first child is the anchor
    // and is always drawn; the rest is the content, drawn only while the Host says it is
    // open. A `Menu` is the same shape with entries in it and a place the design system
    // fixes; here the Host names the side and the edge, and the Renderer keeps the box
    // inside the window by flipping it to the other side or sliding it along the edge.
    // 46 is held for a widget on another branch.
    Popover = 47,
});

#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
#[repr(u8)]
pub enum LoopMode {
    #[default]
    Renderer = 0,
    Platform = 1,
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct Selection {
    pub start: u32,
    pub end: u32,
}

// Compose key identities supported by the M0 schema.
define_wire_enum!(KEY_SCHEMA, Key {
    Enter = 1,
    // Any key the enum does not name. The event's `code` and `text` say which one.
    Other = 2,
    // Keys a menu, a list or an overlay acts on. Appended only: a tag never moves, so an
    // older Renderer that sends `Other` for these still decodes.
    Escape = 3,
    Tab = 4,
    Backspace = 5,
    Delete = 6,
    ArrowUp = 7,
    ArrowDown = 8,
    ArrowLeft = 9,
    ArrowRight = 10,
    Home = 11,
    End = 12,
    PageUp = 13,
    PageDown = 14,
    // The function keys and the key that opens a context menu, appended after the rest.
    F1 = 15,
    F2 = 16,
    F3 = 17,
    F4 = 18,
    F5 = 19,
    F6 = 20,
    F7 = 21,
    F8 = 22,
    F9 = 23,
    F10 = 24,
    F11 = 25,
    F12 = 26,
    ContextMenu = 27,
});

define_wire_enum!(WINDOW_SIZE_CLASS_SCHEMA, WindowSizeClass {
    Compact = 0,
    Medium = 1,
    Expanded = 2,
});

impl WindowSizeClass {
    /// The width in dp at which `Medium` begins, and the width at which `Expanded` does.
    ///
    /// These are the Material 3 window size class boundaries. Using different numbers
    /// would make the Compose components adapt at one width and the Rust layout branch at
    /// another, and that mismatch is visible on screen.
    pub const MEDIUM_MIN_WIDTH_DP: f32 = 600.0;
    pub const EXPANDED_MIN_WIDTH_DP: f32 = 840.0;

    /// The class a window of this width belongs to. Height does not take part.
    pub fn from_width_dp(width_dp: f32) -> Self {
        if width_dp >= Self::EXPANDED_MIN_WIDTH_DP {
            Self::Expanded
        } else if width_dp >= Self::MEDIUM_MIN_WIDTH_DP {
            Self::Medium
        } else {
            Self::Compact
        }
    }
}

define_wire_enum!(WINDOW_HEIGHT_CLASS_SCHEMA, WindowHeightClass {
    Compact = 0,
    Medium = 1,
    Expanded = 2,
});

impl WindowHeightClass {
    /// The height in dp at which `Medium` begins, and the height at which `Expanded` does.
    ///
    /// The same published table the width boundaries came from, so a layout that folds
    /// when it runs out of vertical room folds at the height Compose's own components
    /// treat as short.
    pub const MEDIUM_MIN_HEIGHT_DP: f32 = 480.0;
    pub const EXPANDED_MIN_HEIGHT_DP: f32 = 900.0;

    /// The class a window of this height belongs to. Width does not take part.
    pub fn from_height_dp(height_dp: f32) -> Self {
        if height_dp >= Self::EXPANDED_MIN_HEIGHT_DP {
            Self::Expanded
        } else if height_dp >= Self::MEDIUM_MIN_HEIGHT_DP {
            Self::Medium
        } else {
            Self::Compact
        }
    }
}

/// A role enum that codegen mirrors into Kotlin.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct RoleEnumSchema {
    pub name: &'static str,
    pub variants: &'static [EnumVariantSchema],
}

// An opaque ARGB colour. Gradients and image brushes are deliberately absent: they do not
// fit the two words a modifier variant has, and they would need resources to cross the
// boundary, which the fixed-layout records cannot carry.
#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
#[repr(transparent)]
pub struct Color(pub u32);

impl Color {
    /// An opaque colour from a 24-bit `0xRRGGBB` value.
    pub const fn rgb(value: u32) -> Self {
        Self(0xff00_0000 | (value & 0x00ff_ffff))
    }

    /// A colour from a full 32-bit `0xAARRGGBB` value.
    pub const fn argb(value: u32) -> Self {
        Self(value)
    }

    pub const fn to_argb(self) -> u32 {
        self.0
    }
}

// Semantic colour slots. The design system resolves them, inside the Renderer.
define_wire_enum!(COLOR_ROLE_SCHEMA, ColorRole {
    Primary = 1,
    OnPrimary = 2,
    Secondary = 3,
    OnSecondary = 4,
    Surface = 5,
    OnSurface = 6,
    SurfaceVariant = 7,
    OnSurfaceVariant = 8,
    Background = 9,
    OnBackground = 10,
    Outline = 11,
    OutlineVariant = 12,
    Error = 13,
    OnError = 14,
    // The layer a panel is made of: a thing raised off the page, holding the page's own
    // reading ink. It exists because `Surface` cannot do that job everywhere. Material 3
    // gives `Surface` and `Background` one value on purpose and expresses depth through
    // tonal containers instead, so a panel filled with `Surface` on a page of `Background`
    // is drawn, in the right colour, and is invisible. `SurfaceVariant` is not the answer
    // either: its ink pair is the muted secondary ink, so a panel holding primary content
    // would have to set that content half faded. This is the one role every design system
    // promises to make visible against the page, and `OnSurface` is what reads on it.
    SurfaceContainer = 15,
    // The third accent, and a quiet fill for each of the three.
    //
    // Two accents and a page say a button, a bar and a heading. They cannot say a grid of
    // subject tiles where the subject is the colour, a mood picker, or a panel of costs
    // beside a panel of totals. Those screens need fills that read as relatives of one
    // another, are not reading surfaces, and are quiet enough that body text sits on them.
    //
    // A container is a colour in the table rather than its accent at a lower opacity.
    // Opacity only means something once you know what is behind it, and a role has to
    // answer before anyone knows that. So each container is its own value and carries its
    // own ink, held to the body-text bound rather than the label bound, because the reason
    // it exists is that paragraphs land on it.
    //
    // The three containers are not required to be told apart from each other. Material 3's
    // baseline primary and secondary containers are neighbouring tones of one palette, and
    // that is its published scheme, not a mistake. A caller who needs three fills that
    // separate at a glance reaches for the tertiary pair.
    Tertiary = 16,
    OnTertiary = 17,
    PrimaryContainer = 18,
    OnPrimaryContainer = 19,
    SecondaryContainer = 20,
    OnSecondaryContainer = 21,
    TertiaryContainer = 22,
    OnTertiaryContainer = 23,
    // What a highlighter paints code with. A conversation shows code blocks and diffs, and
    // with only literals to paint them the same grey comment would be stamped into seven
    // systems and two schemes, which is how a light comment grey disappears on a dark page.
    // So a token kind is a role like any other, and each system answers it from the code
    // editor of its own platform.
    //
    // The split follows what tree-sitter's highlight names, VS Code's semantic token kinds
    // and TextMate scopes all agree on. Each of those divides more finely, and the finer
    // names fold into one of these (`keyword.return` is a keyword). A token that fits none
    // is left in the body ink rather than given a colour of its own.
    //
    // The fifteen syntax inks hold the body-text bound on the code block's panel, comments
    // included: a comment can be quieter in hue and lightness, but one nobody can read is
    // a comment that is not there.
    SyntaxKeyword = 24,
    SyntaxString = 25,
    SyntaxComment = 26,
    SyntaxNumber = 27,
    SyntaxConstant = 28,
    SyntaxType = 29,
    SyntaxFunction = 30,
    SyntaxVariable = 31,
    SyntaxProperty = 32,
    SyntaxOperator = 33,
    SyntaxPunctuation = 34,
    SyntaxTag = 35,
    SyntaxAttribute = 36,
    SyntaxEscape = 37,
    SyntaxMacro = 38,
    // A diff. The ink marks an added or removed line and its text; the container is the
    // whole line's background, drawn as the line node's own background; the emphasis is
    // the background behind the words that actually changed, drawn by the span. Added and
    // removed are never told apart by colour alone: the `+` and `-` at the head of a line
    // stay, because the two backgrounds can look the same to a red-green colour blind
    // reader.
    DiffAdded = 39,
    DiffRemoved = 40,
    DiffModified = 41,
    DiffAddedContainer = 42,
    DiffRemovedContainer = 43,
    DiffAddedEmphasis = 44,
    DiffRemovedEmphasis = 45,
});

/// How many colour roles there are, which is how many rows every token table has and how
/// many slots a palette carries per scheme.
pub const COLOR_ROLE_COUNT: usize = 45;

// The nine-rung type ladder every supported design system maps onto.
//
// `None` is text with no rung at all, which is what a page laid out by CSS draws: its size,
// weight, line height, letter spacing and font come from the text's own values and nothing
// from the design system. It is the only text that may name a font of its own. It is not
// in the schema table, because it is not a rung: see `define_wire_enum!`.
define_wire_enum!(TYPE_ROLE_SCHEMA, TypeRole {
    Display = 1,
    Headline = 2,
    Title = 3,
    Subtitle = 4,
    Body = 5,
    BodyStrong = 6,
    Label = 7,
    Caption = 8,
    Mono = 9,
} unlisted {
    None = 0,
});

// Where a line of text may break, as CSS `word-break` says it. `Normal` breaks where the
// language does: between words, and between syllables in Korean. `KeepAll` breaks only at
// spaces, which is how Korean prose is usually set. `BreakAll` breaks between any two
// characters.
define_wire_enum!(WORD_BREAK_SCHEMA, WordBreak {
    Normal = 1,
    KeepAll = 2,
    BreakAll = 3,
});

// Whether a word too long for its line may be broken inside, as CSS `overflow-wrap` says
// it. `Anywhere` also lets that break count when the narrowest width the text can take is
// worked out; `BreakWord` does not.
define_wire_enum!(OVERFLOW_WRAP_SCHEMA, OverflowWrap {
    Normal = 1,
    Anywhere = 2,
    BreakWord = 3,
});

// The families CSS names without naming a font. Which installed font each one is, is the
// platform's answer.
define_wire_enum!(GENERIC_FAMILY_SCHEMA, GenericFamily {
    SystemUi = 1,
    SansSerif = 2,
    Serif = 3,
    Monospace = 4,
});

// Corner roles. The radius is the design system's decision.
define_wire_enum!(SHAPE_ROLE_SCHEMA, ShapeRole {
    None = 1,
    ExtraSmall = 2,
    Small = 3,
    Medium = 4,
    Large = 5,
    Full = 6,
});

// How long a change takes and along which curve. A role rather than a duration, because
// Material's emphasized curve and Cupertino's spring are different answers to the same
// question, and a milliseconds figure from the application would settle it in the wrong
// place. A system asked to reduce motion answers every one of these instantly.
define_wire_enum!(MOTION_ROLE_SCHEMA, MotionRole {
    Instant = 1,
    Quick = 2,
    Standard = 3,
    Slow = 4,
    Emphasized = 5,
});

// What a surface is made of. Four roles rather than a blur radius, because Cupertino and
// Liquid Glass answer with blur, Material 3 with elevation and a tone laid over the
// surface, and the GNOME and KDE systems with an opaque fill. A radius from the
// application would be a blur instruction to systems that do not blur.
define_wire_enum!(MATERIAL_ROLE_SCHEMA, MaterialRole {
    Thin = 1,
    Regular = 2,
    Thick = 3,
    Chrome = 4,
});

// What a node is to assistive technology. Compose's own `Role` names, so the Renderer maps
// each one to the platform's. `None` leaves the role the widget already has.
define_wire_enum!(SEMANTICS_ROLE_SCHEMA, SemanticsRole {
    None = 1,
    Button = 2,
    Checkbox = 3,
    Switch = 4,
    RadioButton = 5,
    Tab = 6,
    Image = 7,
    DropdownList = 8,
    TabList = 9,
    Tree = 10,
    TreeItem = 11,
    Menu = 12,
    MenuItem = 13,
    TextBox = 14,
    Heading = 15,
    Navigation = 16,
    List = 17,
    ListItem = 18,
    Group = 19,
});

// Density roles, because dp density differs per design system.
define_wire_enum!(SPACE_ROLE_SCHEMA, SpaceRole {
    None = 1,
    Xs = 2,
    Sm = 3,
    Md = 4,
    Lg = 5,
    Xl = 6,
    Xxl = 7,
});

// `Start` and `End` follow the writing direction and swap in right-to-left text. `Left`
// and `Right` are physical, as CSS `text-align: left|right` is, and never swap.
define_wire_enum!(TEXT_ALIGN_SCHEMA, TextAlign {
    Start = 1,
    Center = 2,
    End = 3,
    Justify = 4,
    Left = 5,
    Right = 6,
});

define_wire_enum!(TEXT_OVERFLOW_SCHEMA, TextOverflow {
    Clip = 1,
    Ellipsis = 2,
    Visible = 3,
});

define_wire_enum!(ARRANGEMENT_SCHEMA, Arrangement {
    Start = 1,
    Center = 2,
    End = 3,
    SpaceBetween = 4,
    SpaceAround = 5,
    SpaceEvenly = 6,
});

define_wire_enum!(ALIGNMENT_SCHEMA, Alignment {
    TopStart = 1,
    TopCenter = 2,
    TopEnd = 3,
    CenterStart = 4,
    Center = 5,
    CenterEnd = 6,
    BottomStart = 7,
    BottomCenter = 8,
    BottomEnd = 9,
});

// The neutral component variant names the design system styles.
define_wire_enum!(BUTTON_VARIANT_SCHEMA, ButtonVariant {
    Filled = 1,
    Tonal = 2,
    Outlined = 3,
    Text = 4,
    Operator = 5,
});

// What a button is, independently from the visual emphasis its variant carries.
define_wire_enum!(BUTTON_KIND_SCHEMA, ButtonKind {
    Standard = 1,
    ActionKey = 2,
});

// What the bytes behind an asset id are. A kind the Renderer cannot read is a reported
// protocol error, not a guess.
define_wire_enum!(ASSET_KIND_SCHEMA, AssetKind {
    Png = 1,
    Jpeg = 2,
    Svg = 3,
    VectorIcon = 4,
    // A font file, registered so that a type role can resolve to it. The bytes are the
    // font, which is why this is an asset and not a name: a name would put the check that
    // the font exists at run time on the reader's machine, and a missing one there is a
    // screen in the wrong typeface with nobody to tell.
    Font = 5,
    // A gradient or an image fill, registered so that any Paint may name it. The bytes
    // are the brush's own fixed layout rather than a file: nothing on any platform stores
    // a list of stops as a document, and a format would be a parser to write and keep.
    Brush = 6,
});

// How a brush carries on past the area it was given.
define_wire_enum!(TILE_MODE_SCHEMA, TileMode {
    // Stops at the edge and drags the last colour outwards, which is what a gradient
    // filling a surface wants.
    Clamp = 1,
    Repeat = 2,
    // Repeats, flipping every other copy, so the seams do not show.
    Mirror = 3,
});

// The closed set of icon meanings. An icon is addressed by what it is for, never by a
// system icon name: a name would defer the check that the icon exists to run time, and it
// would pin one platform's artwork into the protocol. The role is what lets the same
// declaration come out as SF Symbols under Cupertino and Material Symbols under Material 3.
define_wire_enum!(ICON_ROLE_SCHEMA, IconRole {
    Back = 1,
    Forward = 2,
    Close = 3,
    Search = 4,
    Add = 5,
    Check = 6,
    Settings = 7,
    More = 8,
    // The meanings a set of destinations needs before any other: where the application
    // starts, the list it is mostly about, and what has arrived.
    Home = 9,
    List = 10,
    Inbox = 11,
    // What a window's own bar needs: the button that opens everything this screen does
    // not have room for, and the one that goes back over what has already happened. Both
    // are in the reference bar of more than one sample, and neither is a destination, so
    // neither could be said with the three above.
    Menu = 12,
    History = 13,
    // What putting the samples beside the applications they are drawn from turned up: eight
    // meanings the set could not say. Each is a meaning rather than a picture, so a system
    // that draws sending as a paper aeroplane is still answering `Send`.
    //
    // None of them is an existing role used loosely. A composer's send was drawn with
    // `Forward` for a while, and an arrow pointing sideways says "on to the next one"
    // rather than "send this".
    Send = 14,
    Mic = 15,
    Image = 16,
    Video = 17,
    Library = 18,
    Sidebar = 19,
    Compose = 20,
    Collapse = 21,
});

// How long a transient message stays on screen. Closed, and deliberately short: a message
// that has to be acknowledged is a `Dialog`, so there is no indefinite duration. What the
// two names mean in milliseconds is the design system's decision.
define_wire_enum!(MESSAGE_DURATION_SCHEMA, MessageDuration {
    Short = 1,
    Long = 2,
});

// The edge a transient message is drawn along, where the application chose one. Tag 0 on the
// wire is "the design system's place", which is what a message that names no placement
// gets, so neither enum lists it.
define_wire_enum!(MESSAGE_VERTICAL_SCHEMA, MessageVertical {
    Top = 1,
    Bottom = 2,
});

// Where along that edge the message sits. Start and End follow the layout direction, the
// same way a `Row`'s do.
define_wire_enum!(MESSAGE_HORIZONTAL_SCHEMA, MessageHorizontal {
    Start = 1,
    Center = 2,
    End = 3,
});

/// Where a transient message is drawn, for an application that wants a place other than
/// the design system's.
///
/// Wherever it is, the message stays clear of the safe area and of the application's own
/// bars: a message at the bottom sits above a bottom tab bar, and one at the top below the
/// top bar.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct MessagePlacement {
    pub vertical: MessageVertical,
    pub horizontal: MessageHorizontal,
}

// How much a notification matters. Closed for the same reason a message's duration is: what
// it is worth in sound, in an Android channel's importance or in getting through Do Not
// Disturb is the platform's answer, so the Host has no way to send a sound file or a
// priority number.
define_wire_enum!(NOTIFICATION_IMPORTANCE_SCHEMA, NotificationImportance {
    Normal = 1,
    Urgent = 2,
});

// Whether a notification is shown while the application's window is the active one.
// `WhenInactive` is dropped by the Renderer when the window has focus: whether it has is
// the Renderer's state, and a Host that wanted to judge it would need every focus change
// sent across.
define_wire_enum!(NOTIFICATION_PRESENTATION_SCHEMA, NotificationPresentation {
    Always = 1,
    WhenInactive = 2,
});

// Whether this run may show notifications. `Unsupported` is a platform or a run that has
// no way to show one (no bundle identifier, no AppUserModelID, no notification daemon),
// which is an answer and not an error.
define_wire_enum!(NOTIFICATION_PERMISSION_SCHEMA, NotificationPermission {
    NotDetermined = 1,
    Granted = 2,
    Denied = 3,
    Unsupported = 4,
});

// The design systems of phase one. Later ones append variants here and nowhere else: a new
// design system is one variant plus one token table and rule implementation in the Renderer.
//
// `LiquidGlass` is the language macOS 26 and iOS 26 draw, and it sits beside `Cupertino`
// rather than replacing it: one draws grouped inset lists on a grey page, the other draws
// translucent floating capsules, and an application that wants one does not want the
// other. Tags are append only, so it lands after the Linux three even though it belongs
// next to `Cupertino` in any list a reader would write.
define_wire_enum!(DESIGN_SYSTEM_SCHEMA, DesignSystem {
    Material3 = 1,
    Cupertino = 2,
    Fluent = 3,
    Gnome = 4,
    Breeze = 5,
    Deepin = 6,
    LiquidGlass = 7,
});

// Light and dark selection. `FollowSystem` leaves the choice to the Renderer, which learns
// of a system change first and applies it without involving the Host.
define_wire_enum!(COLOR_SCHEME_SCHEMA, ColorScheme {
    Light = 1,
    Dark = 2,
    FollowSystem = 3,
});

// Which part of the screen's frame a `Scaffold` slot fills.
//
// What each one becomes is the Renderer's: a top bar may be the window's caption, an
// ordinary bar under the system title bar, or a large title that shrinks as the page
// scrolls; a bottom bar may be a bar, a rail or a permanent drawer; a floating action
// may float, sit in the toolbar, or fold into a menu. The application says which slot
// it filled and nothing about the answer.
define_wire_enum!(SLOT_ROLE_SCHEMA, SlotRole {
    TopBar = 1,
    BottomBar = 2,
    FloatingAction = 3,
    Content = 4,
});

// What a code editor decoration is: a mark under a range, a line of text above a line, a
// range that answers a resting pointer, and a suggestion shown in place. Each is what a
// language server or an extension host already speaks in, so an application can pass its
// answers through without inventing its own. After them, the two backgrounds a diff view
// is drawn with: a tint across whole lines, the width of the editor, and a stronger one
// over the characters that changed. Values are only appended.
define_wire_enum!(DECORATION_KIND_SCHEMA, DecorationKind {
    Underline = 1,
    CodeLens = 2,
    HoverAnchor = 3,
    GhostText = 4,
    LineBackground = 5,
    RangeBackground = 6,
});

// How serious an underlined diagnostic is. The four a language server reports, in its
// order. The colour each one gets is the design system's unless the application names a
// role, and how the mark is drawn, a squiggle or a straight line, is always the system's.
define_wire_enum!(SEVERITY_SCHEMA, Severity {
    Error = 1,
    Warning = 2,
    Information = 3,
    Hint = 4,
});

// Whether a pointer has come to rest over a place in a code editor or has left it. Two
// values, because the Host is told once on arriving and once on leaving and never while
// the pointer stays.
define_wire_enum!(HOVER_PHASE_SCHEMA, HoverPhase {
    Rest = 1,
    Leave = 2,
});

// What a mark beside the line numbers of a code editor looks like: a dot, a bar the height
// of the line, or one character the application names. The colour is a role or the design
// system's; the size and the placement of all three are always the system's.
define_wire_enum!(GUTTER_DECORATION_KIND_SCHEMA, GutterDecorationKind {
    Dot = 1,
    Bar = 2,
    Glyph = 3,
});

// The side of its anchor a `Popover` opens on. `Start` and `End` follow the layout
// direction. It is the side asked for: the Renderer opens on the opposite one when the
// content does not fit between the anchor and the window's edge.
define_wire_enum!(POPOVER_PLACEMENT_SCHEMA, PopoverPlacement {
    Top = 1,
    Bottom = 2,
    Start = 3,
    End = 4,
});

// Which edge of its anchor a `Popover` lines up with, along the side it opened on.
define_wire_enum!(POPOVER_ALIGN_SCHEMA, PopoverAlign {
    Start = 1,
    Center = 2,
    End = 3,
});

// Where `RevealRange` puts the range it brings into view: the least scroll that shows it,
// the middle of the view, or the top.
define_wire_enum!(REVEAL_ALIGN_SCHEMA, RevealAlign {
    Nearest = 1,
    Center = 2,
    Top = 3,
});

// The vocabulary of animations the Renderer plays on its own frame clock. Every one is a
// byte on the wire and every one starts at 1, so a zero is always a record the two sides
// disagree about.

// What an animation changes. Each has a place it is drawn from: the node's first `Alpha`,
// its `color` property, its first `Background`, its first `Transform`, and the colour of
// every side of its first `Border` or `BorderEach`. A container's `color` is the colour
// the text inside it inherits, so one animation on it recolours all of that text.
define_wire_enum!(ANIMATED_PROPERTY_SCHEMA, AnimatedProperty {
    Alpha = 1,
    Color = 2,
    Background = 3,
    Transform = 4,
    BorderColor = 5,
});

define_wire_enum!(PLAYBACK_DIRECTION_SCHEMA, PlaybackDirection {
    Normal = 1,
    Reverse = 2,
    Alternate = 3,
    AlternateReverse = 4,
});

define_wire_enum!(FILL_MODE_SCHEMA, FillMode {
    None = 1,
    Forwards = 2,
    Backwards = 3,
    Both = 4,
});

define_wire_enum!(PLAY_STATE_SCHEMA, PlayState {
    Running = 1,
    Paused = 2,
});

// How two colours are mixed: the way CSS's older colour syntax does, or in Oklab, the
// default of CSS Color 4's newer syntax.
define_wire_enum!(COLOR_INTERPOLATION_SCHEMA, ColorInterpolation {
    SrgbPremultiplied = 1,
    Oklab = 2,
});

define_wire_enum!(TIMING_KIND_SCHEMA, TimingKind {
    Linear = 1,
    CubicBezier = 2,
    Steps = 3,
});

define_wire_enum!(STEP_POSITION_SCHEMA, StepPosition {
    JumpStart = 1,
    JumpEnd = 2,
    JumpNone = 3,
    JumpBoth = 4,
});

define_wire_enum!(TRANSFORM_FUNCTION_KIND_SCHEMA, TransformFunctionKind {
    Translate = 1,
    Rotate = 2,
    Scale = 3,
    Skew = 4,
    Matrix = 5,
});

define_wire_enum!(ANIMATION_CONTROL_SCHEMA, AnimationControl {
    Pause = 1,
    Resume = 2,
    Cancel = 3,
});

define_wire_enum!(ANIMATION_EVENT_KIND_SCHEMA, AnimationEventKind {
    Ready = 1,
    Active = 2,
    Iteration = 3,
    End = 4,
});

define_wire_enum!(REDUCED_MOTION_SCHEMA, ReducedMotion {
    Off = 1,
    On = 2,
    Unknown = 3,
});

// Whether the system appearance is light or dark, as the Renderer reads it. Unlike
// `ColorScheme`, it has no `FollowSystem`: it is the answer that choice follows.
define_wire_enum!(SYSTEM_COLOR_SCHEME_SCHEMA, SystemColorScheme {
    Light = 0,
    Dark = 1,
});

define_wire_enum!(POINTER_KIND_SCHEMA, PointerKind {
    Move = 1,
    Enter = 2,
    Leave = 3,
    Down = 4,
    Up = 5,
    Cancel = 6,
    Wheel = 7,
    ContextMenu = 8,
});

define_wire_enum!(POINTER_TYPE_SCHEMA, PointerType {
    Mouse = 1,
    Touch = 2,
    Pen = 3,
});

define_wire_enum!(WHEEL_DELTA_MODE_SCHEMA, WheelDeltaMode {
    Pixel = 0,
    Line = 1,
    Page = 2,
});

// CSS `cursor` keywords, by name and in the order CSS lists them. `Auto` is "let the widget
// under the pointer decide".
define_wire_enum!(CURSOR_SCHEMA, Cursor {
    Auto = 0,
    Default = 1,
    Pointer = 2,
    Text = 3,
    VerticalText = 4,
    Crosshair = 5,
    Move = 6,
    Grab = 7,
    Grabbing = 8,
    NotAllowed = 9,
    NoDrop = 10,
    Wait = 11,
    Progress = 12,
    Help = 13,
    ContextMenu = 14,
    Cell = 15,
    Copy = 16,
    Alias = 17,
    AllScroll = 18,
    ZoomIn = 19,
    ZoomOut = 20,
    ColResize = 21,
    RowResize = 22,
    EResize = 23,
    NResize = 24,
    NeResize = 25,
    NwResize = 26,
    SResize = 27,
    SeResize = 28,
    SwResize = 29,
    WResize = 30,
    EwResize = 31,
    NsResize = 32,
    NeswResize = 33,
    NwseResize = 34,
    None = 35,
});

// CSS `user-select`, resolved by the Host. `Auto` follows the parent.
define_wire_enum!(USER_SELECT_SCHEMA, UserSelect {
    Auto = 0,
    None = 1,
    Text = 2,
    All = 3,
});

/// Every role enum codegen mirrors, in wire order. Appending is the only allowed edit.
pub const ROLE_ENUM_SCHEMA: &[RoleEnumSchema] = &[
    RoleEnumSchema {
        name: "ColorRole",
        variants: COLOR_ROLE_SCHEMA,
    },
    RoleEnumSchema {
        name: "TypeRole",
        variants: TYPE_ROLE_SCHEMA,
    },
    RoleEnumSchema {
        name: "ShapeRole",
        variants: SHAPE_ROLE_SCHEMA,
    },
    RoleEnumSchema {
        name: "MotionRole",
        variants: MOTION_ROLE_SCHEMA,
    },
    RoleEnumSchema {
        name: "TileMode",
        variants: TILE_MODE_SCHEMA,
    },
    RoleEnumSchema {
        name: "MaterialRole",
        variants: MATERIAL_ROLE_SCHEMA,
    },
    RoleEnumSchema {
        name: "SemanticsRole",
        variants: SEMANTICS_ROLE_SCHEMA,
    },
    RoleEnumSchema {
        name: "SpaceRole",
        variants: SPACE_ROLE_SCHEMA,
    },
    RoleEnumSchema {
        name: "TextAlign",
        variants: TEXT_ALIGN_SCHEMA,
    },
    RoleEnumSchema {
        name: "TextOverflow",
        variants: TEXT_OVERFLOW_SCHEMA,
    },
    RoleEnumSchema {
        name: "Arrangement",
        variants: ARRANGEMENT_SCHEMA,
    },
    RoleEnumSchema {
        name: "Alignment",
        variants: ALIGNMENT_SCHEMA,
    },
    RoleEnumSchema {
        name: "ButtonVariant",
        variants: BUTTON_VARIANT_SCHEMA,
    },
    RoleEnumSchema {
        name: "ButtonKind",
        variants: BUTTON_KIND_SCHEMA,
    },
    RoleEnumSchema {
        name: "DesignSystem",
        variants: DESIGN_SYSTEM_SCHEMA,
    },
    RoleEnumSchema {
        name: "ColorScheme",
        variants: COLOR_SCHEME_SCHEMA,
    },
    RoleEnumSchema {
        name: "AssetKind",
        variants: ASSET_KIND_SCHEMA,
    },
    RoleEnumSchema {
        name: "IconRole",
        variants: ICON_ROLE_SCHEMA,
    },
    RoleEnumSchema {
        name: "MessageDuration",
        variants: MESSAGE_DURATION_SCHEMA,
    },
    RoleEnumSchema {
        name: "MessageVertical",
        variants: MESSAGE_VERTICAL_SCHEMA,
    },
    RoleEnumSchema {
        name: "MessageHorizontal",
        variants: MESSAGE_HORIZONTAL_SCHEMA,
    },
    RoleEnumSchema {
        name: "Chrome",
        variants: CHROME_SCHEMA,
    },
    RoleEnumSchema {
        name: "TitleBar",
        variants: TITLE_BAR_SCHEMA,
    },
    RoleEnumSchema {
        name: "SlotRole",
        variants: SLOT_ROLE_SCHEMA,
    },
    RoleEnumSchema {
        name: "NotificationImportance",
        variants: NOTIFICATION_IMPORTANCE_SCHEMA,
    },
    RoleEnumSchema {
        name: "NotificationPresentation",
        variants: NOTIFICATION_PRESENTATION_SCHEMA,
    },
    RoleEnumSchema {
        name: "NotificationPermission",
        variants: NOTIFICATION_PERMISSION_SCHEMA,
    },
    RoleEnumSchema {
        name: "WordBreak",
        variants: WORD_BREAK_SCHEMA,
    },
    RoleEnumSchema {
        name: "OverflowWrap",
        variants: OVERFLOW_WRAP_SCHEMA,
    },
    RoleEnumSchema {
        name: "GenericFamily",
        variants: GENERIC_FAMILY_SCHEMA,
    },
    RoleEnumSchema {
        name: "AnimatedProperty",
        variants: ANIMATED_PROPERTY_SCHEMA,
    },
    RoleEnumSchema {
        name: "PlaybackDirection",
        variants: PLAYBACK_DIRECTION_SCHEMA,
    },
    RoleEnumSchema {
        name: "FillMode",
        variants: FILL_MODE_SCHEMA,
    },
    RoleEnumSchema {
        name: "PlayState",
        variants: PLAY_STATE_SCHEMA,
    },
    RoleEnumSchema {
        name: "ColorInterpolation",
        variants: COLOR_INTERPOLATION_SCHEMA,
    },
    RoleEnumSchema {
        name: "TimingKind",
        variants: TIMING_KIND_SCHEMA,
    },
    RoleEnumSchema {
        name: "StepPosition",
        variants: STEP_POSITION_SCHEMA,
    },
    RoleEnumSchema {
        name: "TransformFunctionKind",
        variants: TRANSFORM_FUNCTION_KIND_SCHEMA,
    },
    RoleEnumSchema {
        name: "AnimationControl",
        variants: ANIMATION_CONTROL_SCHEMA,
    },
    RoleEnumSchema {
        name: "AnimationEventKind",
        variants: ANIMATION_EVENT_KIND_SCHEMA,
    },
    RoleEnumSchema {
        name: "ReducedMotion",
        variants: REDUCED_MOTION_SCHEMA,
    },
    RoleEnumSchema {
        name: "SystemColorScheme",
        variants: SYSTEM_COLOR_SCHEME_SCHEMA,
    },
    RoleEnumSchema {
        name: "DecorationKind",
        variants: DECORATION_KIND_SCHEMA,
    },
    RoleEnumSchema {
        name: "Severity",
        variants: SEVERITY_SCHEMA,
    },
    RoleEnumSchema {
        name: "HoverPhase",
        variants: HOVER_PHASE_SCHEMA,
    },
    RoleEnumSchema {
        name: "GutterDecorationKind",
        variants: GUTTER_DECORATION_KIND_SCHEMA,
    },
    RoleEnumSchema {
        name: "RevealAlign",
        variants: REVEAL_ALIGN_SCHEMA,
    },
    RoleEnumSchema {
        name: "PointerKind",
        variants: POINTER_KIND_SCHEMA,
    },
    RoleEnumSchema {
        name: "PointerType",
        variants: POINTER_TYPE_SCHEMA,
    },
    RoleEnumSchema {
        name: "WheelDeltaMode",
        variants: WHEEL_DELTA_MODE_SCHEMA,
    },
    RoleEnumSchema {
        name: "Cursor",
        variants: CURSOR_SCHEMA,
    },
    RoleEnumSchema {
        name: "UserSelect",
        variants: USER_SELECT_SCHEMA,
    },
    RoleEnumSchema {
        name: "WindowMode",
        variants: WINDOW_MODE_SCHEMA,
    },
    RoleEnumSchema {
        name: "LastWindowClosed",
        variants: LAST_WINDOW_CLOSED_SCHEMA,
    },
    RoleEnumSchema {
        name: "FileDialogKind",
        variants: FILE_DIALOG_KIND_SCHEMA,
    },
    RoleEnumSchema {
        name: "FileDialogStatus",
        variants: FILE_DIALOG_STATUS_SCHEMA,
    },
    RoleEnumSchema {
        name: "EditGroupStatus",
        variants: EDIT_GROUP_STATUS_SCHEMA,
    },
    RoleEnumSchema {
        name: "CompactNavigation",
        variants: COMPACT_NAVIGATION_SCHEMA,
    },
    RoleEnumSchema {
        name: "Snap",
        variants: SNAP_SCHEMA,
    },
    RoleEnumSchema {
        name: "MinimapSide",
        variants: MINIMAP_SIDE_SCHEMA,
    },
    RoleEnumSchema {
        name: "WordWrapMode",
        variants: WORD_WRAP_MODE_SCHEMA,
    },
    RoleEnumSchema {
        name: "StorageOp",
        variants: STORAGE_OP_SCHEMA,
    },
    RoleEnumSchema {
        name: "IoStatus",
        variants: IO_STATUS_SCHEMA,
    },
    RoleEnumSchema {
        name: "FileDelivery",
        variants: FILE_DELIVERY_SCHEMA,
    },
    RoleEnumSchema {
        name: "FileOp",
        variants: FILE_OP_SCHEMA,
    },
    RoleEnumSchema {
        name: "HorizontalAlignment",
        variants: HORIZONTAL_ALIGNMENT_SCHEMA,
    },
    RoleEnumSchema {
        name: "VerticalAlignment",
        variants: VERTICAL_ALIGNMENT_SCHEMA,
    },
    RoleEnumSchema {
        name: "PopoverPlacement",
        variants: POPOVER_PLACEMENT_SCHEMA,
    },
    RoleEnumSchema {
        name: "PopoverAlign",
        variants: POPOVER_ALIGN_SCHEMA,
    },
    RoleEnumSchema {
        name: "ContentScale",
        variants: CONTENT_SCALE_SCHEMA,
    },
    RoleEnumSchema {
        name: "BackgroundRepeat",
        variants: BACKGROUND_REPEAT_SCHEMA,
    },
];

/// Every place that takes a colour takes a `Paint`, so colour is expressed once.
///
/// Encoded as one `u64`: the high 32 bits are the kind, the low 32 bits are the value.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum Paint {
    Role(ColorRole),
    Literal(Color),
    /// A registered brush: a gradient, or a picture laid out as a fill.
    ///
    /// An id rather than the thing itself, because a list of stops does not fit the two
    /// words a modifier has and because a brush outlives the frame that draws it, which
    /// is what the asset path already exists for.
    Asset(u32),
}

const PAINT_KIND_ROLE: u64 = 1;
const PAINT_KIND_LITERAL: u64 = 2;
const PAINT_KIND_ASSET: u64 = 3;

impl Paint {
    pub const fn to_bits(self) -> u64 {
        match self {
            Self::Role(role) => (PAINT_KIND_ROLE << 32) | role as u64,
            Self::Literal(color) => (PAINT_KIND_LITERAL << 32) | color.0 as u64,
            Self::Asset(id) => (PAINT_KIND_ASSET << 32) | id as u64,
        }
    }

    pub fn from_bits(bits: u64) -> Option<Self> {
        let value = bits as u32;
        match bits >> 32 {
            PAINT_KIND_ROLE => Some(Self::Role(
                ColorRole::try_from(u16::try_from(value).ok()?).ok()?,
            )),
            PAINT_KIND_LITERAL => Some(Self::Literal(Color(value))),
            PAINT_KIND_ASSET => Some(Self::Asset(value)),
            _ => None,
        }
    }
}

// How the window wears its title bar.
//
// `Modern` runs content into the title bar area and is the default, because every desktop
// platform now expects it and a window with a separate system bar looks a decade old.
//
// `System` is the platform's ordinary bar, and it is kept deliberately. Some tool-shaped
// applications want one, and more importantly it is where an application goes when
// `Modern` turns out to be wrong on some machine: a default with no way out of it is a
// default that strands people.
define_wire_enum!(CHROME_SCHEMA, Chrome {
    Modern = 1,
    System = 2,
    FullSize = 3,
});

// Which of two title bars this window has. `Chrome` chooses who draws the caption; this
// chooses, inside that, what kind of window the caption belongs to.
//
// What each one means is not the same on every platform, and the numbers are never the
// Host's. On macOS the buttons sit further in and the window is rounded more; on Windows
// and Linux the caption is a different height and the buttons stay where that platform
// puts them.
define_wire_enum!(TITLE_BAR_SCHEMA, TitleBar {
    // What an application on that platform actually looks like now, which is why it is the
    // default.
    Normal = 1,
    // An ordinary window. For tool applications, for the places the other reads oddly, and
    // as the way back.
    Simple = 2,
});

// What a `Navigation` becomes in a compact window, where the application chose. Medium and
// Expanded stay the design system's answer whatever is chosen here.
//
// `Default` is no choice at all: the design system answers, which is a bottom bar on most
// of them and the put-away sidebar on Apple's desktop systems. It travels as tag 0, which
// is the same as not sending the property, so it is not in the schema table.
//
// `Sidebar` is the sidebar put away behind a toggle that brings it over the page, on every
// design system. `None` leaves the destinations off a compact window altogether, with
// nothing to call them: the application draws its own way to them. The name is Compose's
// `NavigationSuiteType.None`.
define_wire_enum!(COMPACT_NAVIGATION_SCHEMA, CompactNavigation {
    Sidebar = 1,
    None = 2,
} unlisted {
    Default = 0,
});

// Where a scroll container comes to rest once a drag or a fling ends.
//
// `None` is free scrolling: the container stops wherever the drag or the fling left it. It
// travels as tag 0, which is the same as not sending the property, so it is not in the
// schema table.
//
// `ItemStart` stops with the start edge of the nearest direct child on the start of the
// visible area, the way CSS `scroll-snap-type: mandatory` with `scroll-snap-align: start`
// does.
// Where a code editor breaks a long line, the mode part of the `WordWrap` property: at the
// edge of the view, at a number of columns, or at whichever of the two comes first. `Off`
// breaks no line, which is what an editor that never sets it does.
define_wire_enum!(WORD_WRAP_MODE_SCHEMA, WordWrapMode {
    Viewport = 1,
    Column = 2,
    Bounded = 3,
} unlisted {
    Off = 0,
});

// Which side of a code editor its minimap is drawn on: the whole document shrunk, with the
// part on screen marked, which a press or a drag scrolls to. `Off` draws none, which is what
// an editor that never sets it does.
define_wire_enum!(MINIMAP_SIDE_SCHEMA, MinimapSide {
    Right = 1,
    Left = 2,
} unlisted {
    Off = 0,
});

define_wire_enum!(SNAP_SCHEMA, Snap {
    ItemStart = 1,
} unlisted {
    None = 0,
});

// How an `Image` lays its picture into the box it was given, as Compose's `ContentScale`.
//
// `Fit` keeps the picture's proportions and shows all of it, centred, leaving the rest of
// the box empty. `Crop` keeps the proportions and covers the whole box, centred, cutting
// off what falls outside. `FillBounds` stretches the picture to the box in each direction
// on its own, which is CSS `object-fit: fill`. Not sending the property draws `Fit`.
define_wire_enum!(CONTENT_SCALE_SCHEMA, ContentScale {
    Fit = 1,
    Crop = 2,
    FillBounds = 3,
});

// How a `BackgroundBrush` repeats its rectangle across the node, as CSS
// `background-repeat` does: not at all, in both directions, along the width only, or
// along the height only. A repeat runs both ways from the rectangle, so a node is covered
// to its edges whichever corner the rectangle sits in.
define_wire_enum!(BACKGROUND_REPEAT_SCHEMA, BackgroundRepeat {
    NoRepeat = 1,
    Repeat = 2,
    RepeatX = 3,
    RepeatY = 4,
});

// How the application uses windows. `Single` is every application until now: the
// root's content fills the one window `SetWindow` describes. `Windows` is the multi-window
// mode, in which the root's children are `Window` nodes and `SetWindow` describes nothing
// but the mode.
define_wire_enum!(WINDOW_MODE_SCHEMA, WindowMode {
    Single = 0,
    Windows = 1,
});

// What happens when the last `Window` node is removed. `Exit` ends the renderer
// loop, `KeepRunning` leaves the process up with no window. Ignored by `Single`.
define_wire_enum!(LAST_WINDOW_CLOSED_SCHEMA, LastWindowClosed {
    Exit = 0,
    KeepRunning = 1,
});

// What a file dialog asks the user to pick. Closed: each kind is a different platform panel
// with different rules about how many paths come back, so a free-form set of flags would
// allow combinations no panel can honour.
define_wire_enum!(FILE_DIALOG_KIND_SCHEMA, FileDialogKind {
    OpenFile = 1,
    OpenFiles = 2,
    OpenFolder = 3,
    OpenFolders = 4,
    Save = 5,
});

// How a file dialog ended. `Unavailable` means this run has no way to show one, which is an
// answer and not an error, and is never used for a user's cancel.
define_wire_enum!(FILE_DIALOG_STATUS_SCHEMA, FileDialogStatus {
    Chosen = 1,
    Cancelled = 2,
    Unavailable = 3,
});

// What became of one grouped edit of a code editor. The group goes in whole or not at all,
// and each way it can stay out asks the application for something different: `Rejected`
// means the reader typed where it would have written, so read the document again and send
// it again; `TooOld` means the version it was written against is older than the editor
// remembers, so the application's copy has to be brought back in step; `Invalid` means the
// group itself makes no sense (edits that overlap, a range outside the document, a version
// from the future).
define_wire_enum!(EDIT_GROUP_STATUS_SCHEMA, EditGroupStatus {
    Applied = 1,
    Rejected = 2,
    Invalid = 3,
    TooOld = 4,
});

// How the files a Renderer holds handles for reached it. Closed, because what an
// application may do with a file depends on it: only a `Handle` can be written again.
define_wire_enum!(FILE_DELIVERY_SCHEMA, FileDelivery {
    // The file itself, in the file system. Writing it again changes the same file.
    Handle = 1,
    // A copy the browser handed over from a file input. It can only be read.
    Upload = 2,
    // A save that became a download. Each write is a new download.
    Download = 3,
});

// What one `FileCall` asks of a file the Renderer holds a handle for.
define_wire_enum!(FILE_OP_SCHEMA, FileOp {
    Read = 1,
    Write = 2,
    Entries = 3,
    Child = 4,
});

// What a `StorageCall` asks the Renderer to do with the application's storage. Closed: a
// Renderer that meets an operation it does not know cannot answer it truthfully.
define_wire_enum!(STORAGE_OP_SCHEMA, StorageOp {
    Read = 1,
    Write = 2,
    Remove = 3,
    Keys = 4,
});

// How one input or output request ended, as an `IoAnswer` says it. Shared by storage and by
// files picked on the web, so one answer reads the same whichever asked. Closed, so a word
// this side does not know is a record the two sides disagree on.
define_wire_enum!(IO_STATUS_SCHEMA, IoStatus {
    Ok = 1,
    NotFound = 2,
    QuotaExceeded = 3,
    Unavailable = 4,
    PermissionDenied = 5,
    Failed = 6,
    ReadOnly = 7,
    TooLarge = 8,
});

// Where the children of one line of a `FlowRow` sit along it, when they do not fill it.
define_wire_enum!(HORIZONTAL_ALIGNMENT_SCHEMA, HorizontalAlignment {
    Start = 1,
    Center = 2,
    End = 3,
});

// Where a child of a `FlowRow` sits inside the height of its line, when it is shorter
// than the tallest child on that line.
define_wire_enum!(VERTICAL_ALIGNMENT_SCHEMA, VerticalAlignment {
    Top = 1,
    Center = 2,
    Bottom = 3,
});

/// What an application may decide about its own window.
///
/// The window belongs to the Renderer, so this is short and stays short. What is here is
/// what an application knows and the Renderer cannot guess: what the window is called and
/// how large it should open. Nothing here names a colour or a corner, because those are
/// the design system's, and nothing here is read more than once.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct Window {
    pub chrome: Chrome,
    /// Which of the two title bars this window has.
    pub title_bar: TitleBar,
    /// What the window calls itself.
    ///
    /// Empty means the application said nothing, and the renderer uses its own name for
    /// it. It is not decoration: a desktop lists windows by this, and a window with no
    /// title of its own is listed under whatever the renderer happened to be called.
    pub title: &'static str,
    /// The picture the window wears, as an asset id, or zero for none.
    ///
    /// An id rather than a path or a name, because a path is a fact about the machine the
    /// application was built on and a name asks the toolkit to find something it may not
    /// have. Registering the bytes and referring to them is what every other picture in
    /// this protocol does.
    pub icon: u32,
    /// Zero means the Renderer chooses, which is what an application that said nothing
    /// gets. A size is in the same density independent pixels gestures are measured in.
    pub width: u16,
    pub height: u16,
    pub min_width: u16,
    pub min_height: u16,
    pub resizable: bool,
    /// The application's zoom level, where it asked for one.
    ///
    /// `None` leaves the level to the Renderer, which starts from what the reader chose
    /// last time. A level set here is applied, remembered and reported back the way one
    /// chosen with the keys is. Kept inside `-8..=8`.
    pub zoom_level: Option<i8>,
    /// Whether the implicit single window reports every whole-dp change of its size,
    /// not only a change of size class. Off by default. Windows made with `Window`
    /// nodes opt in through the node's `report_size` property instead.
    pub report_size: bool,
    /// One window (the default) or several. In the second the root's children are
    /// `Window` nodes and the rest of this record describes no window.
    pub mode: WindowMode,
    /// What to do when the last window goes. Only read in `WindowMode::Windows`.
    pub last_window_closed: LastWindowClosed,
}

impl Window {
    pub const fn new() -> Self {
        Self {
            chrome: Chrome::Modern,
            title_bar: TitleBar::Normal,
            title: "",
            icon: 0,
            width: 0,
            height: 0,
            min_width: 0,
            min_height: 0,
            resizable: true,
            zoom_level: None,
            report_size: false,
            mode: WindowMode::Single,
            last_window_closed: LastWindowClosed::Exit,
        }
    }

    /// Several windows, one per `Window` node under the root. With the default
    /// policy of the platform: a macOS application stays up with no window, the others
    /// exit.
    pub const fn with_windows(mut self) -> Self {
        self.mode = WindowMode::Windows;
        self.last_window_closed = if cfg!(target_os = "macos") {
            LastWindowClosed::KeepRunning
        } else {
            LastWindowClosed::Exit
        };
        self
    }

    /// What happens when the last window is removed. Only meaningful with
    /// [`Window::with_windows`].
    pub const fn with_last_window_closed(mut self, policy: LastWindowClosed) -> Self {
        self.last_window_closed = policy;
        self
    }

    /// Which of the two title bars this window has.
    ///
    /// `Normal` unless it is said otherwise, because that is the window an application on
    /// this platform has now. What the mode is worth in pixels is the design system's, so
    /// nothing here is a measurement.
    pub const fn with_title_bar(mut self, title_bar: TitleBar) -> Self {
        self.title_bar = title_bar;
        self
    }

    /// Names the window. A literal, because this is read once before the window is stood
    /// up and never again, so there is nothing for a computed title to change.
    pub const fn with_title(mut self, title: &'static str) -> Self {
        self.title = title;
        self
    }

    /// Dresses the window in an asset that was registered with [`AssetKind::Png`].
    pub const fn with_icon(mut self, asset_id: u32) -> Self {
        self.icon = asset_id;
        self
    }

    pub const fn chrome(self, chrome: Chrome) -> Self {
        self.with_chrome(chrome)
    }

    pub const fn with_chrome(mut self, chrome: Chrome) -> Self {
        self.chrome = chrome;
        self
    }

    pub const fn with_size(mut self, width: u16, height: u16) -> Self {
        self.width = width;
        self.height = height;
        self
    }

    pub const fn with_min_size(mut self, width: u16, height: u16) -> Self {
        self.min_width = width;
        self.min_height = height;
        self
    }

    pub const fn resizable(mut self, resizable: bool) -> Self {
        self.resizable = resizable;
        self
    }

    /// Asks the implicit single window to report every whole-dp change of its size.
    pub const fn with_report_size(mut self, report: bool) -> Self {
        self.report_size = report;
        self
    }

    /// Starts the window at an application zoom level, kept inside `-8..=8`.
    pub const fn with_zoom_level(mut self, level: i8) -> Self {
        self.zoom_level = Some(if level < -8 {
            -8
        } else if level > 8 {
            8
        } else {
            level
        });
        self
    }
}

impl Default for Window {
    fn default() -> Self {
        Self::new()
    }
}

/// A design system choice plus how it reacts to the host platform.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct Theme {
    pub design_system: DesignSystem,
    pub fallback: DesignSystem,
    pub color_scheme: ColorScheme,
    pub adaptive: bool,
    /// The font asset each type role resolves to, or zero for the system font.
    ///
    /// Per theme and not per node. A node that could name its own font would be a node
    /// deciding typography, and the whole point of roles is that it does not: an
    /// application changes what `Display` is made of, and every title changes with it.
    ///
    /// Indexed by the role's wire tag minus one, so the array and the enum cannot drift
    /// apart without the compiler saying so.
    pub fonts: [u32; TYPE_ROLE_COUNT],
    /// The application's own colours, laid over whichever design system is chosen.
    ///
    /// A reference to something that lives for the whole program, so that a theme stays
    /// `Copy` and can still be built in a `const`. The same palette goes onto every system
    /// an adaptive theme may pick, because a brand colour does not change with the
    /// platform. A palette built while the application runs is handed to `use_theme`,
    /// which owns it, so application code never has to give it that lifetime itself.
    pub palette: Option<&'static crate::palette::Palette>,
    /// Application-level overlay theme tokens for Dialog, Menu, Dropdown, and Sheet.
    pub overlay: Option<&'static OverlayTokens>,
}

/// How many type roles there are, which is how many font slots a theme carries.
pub const TYPE_ROLE_COUNT: usize = 9;

/// Application-level overlay theme tokens for Dialog, Menu, Dropdown, Sheet and the
/// transient message. Every measure is in dp, and 0 keeps the design system's own.
#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
pub struct OverlayTokens {
    pub sheet_corner_radius: u16,
    pub dialog_corner_radius: u16,
    pub popup_corner_radius: u16,
    pub sheet_elevation: u16,
    pub popup_elevation: u16,
    pub dialog_elevation: u16,
    pub sheet_padding: u16,
    pub dialog_padding: u16,
    pub popup_padding: u16,
    pub scrim: u32,
    /// How high the transient message floats, which is how much shadow it casts.
    pub toast_elevation: u16,
    /// The corner radius of the transient message.
    pub toast_corner_radius: u16,
}

impl OverlayTokens {
    pub const fn new() -> Self {
        Self {
            sheet_corner_radius: 0,
            dialog_corner_radius: 0,
            popup_corner_radius: 0,
            sheet_elevation: 0,
            popup_elevation: 0,
            dialog_elevation: 0,
            sheet_padding: 0,
            dialog_padding: 0,
            popup_padding: 0,
            scrim: 0,
            toast_elevation: 0,
            toast_corner_radius: 0,
        }
    }

    pub const fn sheet_corner_radius(mut self, radius: u16) -> Self {
        self.sheet_corner_radius = radius;
        self
    }

    pub const fn dialog_corner_radius(mut self, radius: u16) -> Self {
        self.dialog_corner_radius = radius;
        self
    }

    pub const fn popup_corner_radius(mut self, radius: u16) -> Self {
        self.popup_corner_radius = radius;
        self
    }

    pub const fn sheet_elevation(mut self, elevation: u16) -> Self {
        self.sheet_elevation = elevation;
        self
    }

    pub const fn popup_elevation(mut self, elevation: u16) -> Self {
        self.popup_elevation = elevation;
        self
    }

    pub const fn dialog_elevation(mut self, elevation: u16) -> Self {
        self.dialog_elevation = elevation;
        self
    }

    pub const fn sheet_padding(mut self, padding: u16) -> Self {
        self.sheet_padding = padding;
        self
    }

    pub const fn dialog_padding(mut self, padding: u16) -> Self {
        self.dialog_padding = padding;
        self
    }

    pub const fn popup_padding(mut self, padding: u16) -> Self {
        self.popup_padding = padding;
        self
    }

    pub const fn scrim(mut self, color: Color) -> Self {
        self.scrim = color.to_argb();
        self
    }

    pub const fn scrim_argb(mut self, argb: u32) -> Self {
        self.scrim = argb;
        self
    }

    /// The transient message's elevation in dp: a shadow under it the height of a surface
    /// that far up. A message is not a node and takes no Modifier, so this is where its
    /// shadow is set, once for the application.
    pub const fn toast_elevation(mut self, elevation: u16) -> Self {
        self.toast_elevation = elevation;
        self
    }

    /// The transient message's corner radius in dp.
    pub const fn toast_corner_radius(mut self, radius: u16) -> Self {
        self.toast_corner_radius = radius;
        self
    }
}

impl Theme {
    /// The same design system on every platform.
    pub const fn unified(design_system: DesignSystem) -> Self {
        Self {
            design_system,
            fallback: design_system,
            color_scheme: ColorScheme::FollowSystem,
            adaptive: false,
            fonts: [0; TYPE_ROLE_COUNT],
            palette: None,
            overlay: None,
        }
    }

    /// Follows the host platform. The fallback is required, so no platform is left undecided.
    pub const fn adaptive(fallback: DesignSystem) -> Self {
        Self {
            design_system: fallback,
            fallback,
            color_scheme: ColorScheme::FollowSystem,
            adaptive: true,
            fonts: [0; TYPE_ROLE_COUNT],
            palette: None,
            overlay: None,
        }
    }

    pub const fn with_color_scheme(mut self, color_scheme: ColorScheme) -> Self {
        self.color_scheme = color_scheme;
        self
    }

    /// Resolves one type role to a registered font, leaving every other role alone.
    ///
    /// The asset has to be registered before the theme that names it reaches the
    /// Renderer, the same way a picture does. An id that names nothing is reported and
    /// the role falls back to the system font, because a screen in the wrong typeface is
    /// better than no screen.
    ///
    /// `TypeRole::None` has no font slot: text with no role names its own font, so asking
    /// the theme to give it one changes nothing.
    pub const fn with_font(mut self, role: TypeRole, asset: u32) -> Self {
        if let TypeRole::None = role {
            return self;
        }
        self.fonts[role as usize - 1] = asset;
        self
    }

    /// Resolves every type role but `Mono` to one registered font: the application's own
    /// typeface, set once for the whole screen.
    ///
    /// The font is usually a [`crate::FontStack`], so a role is set in the first family and
    /// each letter it lacks comes from the next, with the machine's fonts after the last.
    /// `Mono` is left alone because code set in a proportional face is columns that no
    /// longer line up; name a font for it with [`Theme::with_font`]. A role named before or
    /// after this with `with_font` keeps whichever was said last.
    pub const fn with_default_font(mut self, asset: u32) -> Self {
        let mut index = 0;
        while index < TYPE_ROLE_COUNT {
            if index != TypeRole::Mono as usize - 1 {
                self.fonts[index] = asset;
            }
            index += 1;
        }
        self
    }

    /// Lays the application's own colours over the design system.
    ///
    /// Only colour roles change. Shape, type, spacing, elevation, motion and how each
    /// component is drawn stay the design system's, so the same brand colour reads as
    /// that system's button rather than as a copy of another's. Both schemes go to the
    /// Renderer at once, so a switch between light and dark never asks the Host.
    pub const fn with_palette(mut self, palette: &'static crate::palette::Palette) -> Self {
        self.palette = Some(palette);
        self
    }

    /// Overrides overlay geometry, spacing, elevation and scrim for Dialog, Menu, Dropdown and Sheet.
    pub const fn with_overlay_tokens(mut self, overlay: &'static OverlayTokens) -> Self {
        self.overlay = Some(overlay);
        self
    }

    /// The font this role resolves to, or `None` for the system font.
    pub const fn font(&self, role: TypeRole) -> Option<u32> {
        if let TypeRole::None = role {
            return None;
        }
        match self.fonts[role as usize - 1] {
            0 => None,
            asset => Some(asset),
        }
    }
}

/// Saying nothing follows the host platform, with Material 3 where the platform has no look
/// of its own. The default used to be `unified(Material3)`, on the theory that a default
/// looking the same everywhere is more predictable. In practice that meant macOS showed a
/// Material screen with no configuration, which is the wrong first impression for a toolkit
/// that claims native desktop UI, and it meant nothing on the default path ever exercised
/// platform adaptation. A default that can be broken without anyone noticing is not
/// predictability. An application that wants one design system everywhere says
/// `Theme::unified(..)`, which is a clearer statement of that intent than silence was.
impl Default for Theme {
    fn default() -> Self {
        Self::adaptive(DesignSystem::Material3)
    }
}

#[derive(Clone, Debug, PartialEq)]
pub enum Modifier {
    Empty,
    Padding(f32),
    FillMaxWidth,
    FillMaxHeight,
    Width(f32),
    Height(f32),
    Size {
        width: f32,
        height: f32,
    },
    /// A `Paint`, not a raw ARGB. Colour has exactly one wire representation.
    Background(Paint),
    Clickable {
        handler_id: u64,
    },
    PaddingRole(SpaceRole),
    PaddingEach {
        start: f32,
        top: f32,
        end: f32,
        bottom: f32,
    },
    Weight(f32),
    Shape {
        top_start: f32,
        top_end: f32,
        bottom_end: f32,
        bottom_start: f32,
    },
    ShapeRole(ShapeRole),
    Border {
        width: f32,
        paint: Paint,
    },
    /// One dp value. How the shadow is drawn is the design system's rule: tonal lift plus a
    /// shadow, a wide soft shadow, or layered shadow plus a hairline stroke.
    Elevation(f32),
    /// Asks the Renderer to report this node's measured size, the way it reports the
    /// window's.
    ///
    /// The token is the application's own name for the node. A node id belongs to the
    /// Renderer and is never something the Host chose, so a screen that wants to know how
    /// wide one of its own containers ended up needs a name it gave itself. The Renderer
    /// does not read it.
    ///
    /// With `every_dp` off, a report goes out on the first measurement and then only when
    /// the node's width or height class changes. With it on, a report also goes out when
    /// the width or height, rounded to the nearest whole dp, changes inside one class, at
    /// most once a frame and carrying the last size. It rides in the second word, which
    /// was always zero before, so a record with it off is the same bytes it always was.
    ObserveSize {
        token: u32,
        every_dp: bool,
    },
    /// Which curve and length this node's changes run along.
    ///
    /// The node says how important the change is, not how long it takes. Appearing,
    /// disappearing, a selection moving and a size changing all read this.
    Motion(MotionRole),
    /// What this node's surface is made of.
    ///
    /// A role, so that a system which blurs blurs and a system which does not lifts its
    /// surface instead. Nothing here claims a particular effect was achieved.
    Material(MaterialRole),
    /// Where this node sits inside its parent, in dp from the parent's top left corner.
    ///
    /// The position a layout engine on the Host already computed. Left and right are the
    /// screen's, not the reading direction's: the Host's coordinates are physical, so a
    /// right-to-left page is not mirrored a second time here.
    Offset {
        x: f32,
        y: f32,
    },
    /// This node's size in dp, whatever its parent's constraints say. The size a layout
    /// engine on the Host already computed, which is not open to negotiation.
    RequiredSize {
        width: f32,
        height: f32,
    },
    /// A border whose four sides each have their own width and paint. A node whose four
    /// sides are the same uses `Border`.
    BorderEach {
        top: f32,
        right: f32,
        bottom: f32,
        left: f32,
        top_paint: Paint,
        right_paint: Paint,
        bottom_paint: Paint,
        left_paint: Paint,
    },
    /// A radius in dp for each corner, cut as plain circular arcs. The background, the
    /// border, the shadow and a `Clip` all follow it. A node with one radius for every
    /// corner uses `Shape`.
    CornerEach {
        top_left: f32,
        top_right: f32,
        bottom_right: f32,
        bottom_left: f32,
    },
    /// One shadow cast by this node's outline: an offset, a blur radius and a spread in dp,
    /// and its paint, drawn only outside the node as CSS draws `box-shadow`. Several
    /// shadows are several of these. A modifier list draws in its order, so a later shadow
    /// lies over an earlier one; CSS puts the first of its list on top, so a Host sends
    /// that list last to first.
    Shadow {
        x: f32,
        y: f32,
        blur: f32,
        spread: f32,
        paint: Paint,
    },
    /// Whether this node's content is cut to its outline: the `CornerEach` shape where it
    /// has one, its rectangle otherwise.
    Clip(bool),
    /// Marks this node as a window drag region or excludes it from one.
    WindowDrag(bool),
    /// The opacity of this node and everything in it, from 0 to 1, applied once to the
    /// whole group rather than to each child.
    Alpha(f32),
    /// Draws this node and everything in it through a 2D affine matrix, the way CSS
    /// `transform` does, without changing its layout. Pointer input follows the drawn
    /// shape.
    ///
    /// The matrix means what CSS `matrix(a, b, c, d, e, f)` means: a point `(x, y)` goes to
    /// `(a x + c y + e, b x + d y + f)`, with `e` and `f` in dp. The origin is a fraction of
    /// the node's measured size, `(0.5, 0.5)` being its centre, so it stays right when the
    /// size is decided on the Renderer's side. An origin given as a length is folded into
    /// the matrix by the Host, which then sends `(0, 0)`. A matrix with no inverse draws
    /// nothing and takes no input. No value may be NaN or infinite.
    Transform {
        a: f32,
        b: f32,
        c: f32,
        d: f32,
        e: f32,
        f: f32,
        origin_x: f32,
        origin_y: f32,
    },
    /// Draws this node and everything in it through a 4x4 matrix, the way CSS 3D
    /// `transform` does, without changing its layout. Pointer input follows the drawn
    /// shape.
    ///
    /// `m` is column-major, in the order of CSS `matrix3d(...)`: element `m[4 * column +
    /// row]`. A point `(x, y, z, 1)` goes to `M * (x, y, z, 1)`, and the screen position is
    /// the first two results divided by the fourth. Translations are in dp. A perspective
    /// term is already inside the matrix, so the Renderer is never sent one separately. The
    /// origin means what it means for [`Modifier::Transform`] and its z is zero.
    ///
    /// `backface_hidden` is CSS `backface-visibility: hidden`: a node whose back is turned
    /// to the viewer is not drawn and takes no input. A matrix with no inverse draws
    /// nothing. No value may be NaN or infinite.
    Transform3D {
        m: [f32; 16],
        origin_x: f32,
        origin_y: f32,
        backface_hidden: bool,
    },
    /// Matches the bounds of a Box parent without contributing to its size.
    MatchParentSize,
    /// Controls the scale and tint of a pressed surface.
    PressFeedback {
        scale: f32,
        tint_alpha: f32,
    },
    /// What this node is to assistive technology: its role, and whether it is checked or
    /// selected. `state` holds two tri-state fields, `SEMANTICS_CHECKED_SHIFT` and
    /// `SEMANTICS_SELECTED_SHIFT` bits up, each 0 for unset, 1 for off and 2 for on. The
    /// accessible name is the `AccessibleName` property, because a string does not fit in
    /// a modifier's words. Above those, `expanded`, `disabled` and `focused` are tri-state
    /// fields in the same encoding, `SEMANTICS_HIDDEN_BIT` leaves the node out of the
    /// accessibility tree, and the two action bits expose a click and a focus action.
    Semantics {
        role: SemanticsRole,
        state: u32,
    },
    /// How this node's rounded corners curve, from 0 to 1. 0 is a plain circular arc; above
    /// it the curve starts further along each side and its curvature changes continuously,
    /// as Figma's corner smoothing does (0.6 is what iOS looks like). The radius still
    /// comes from `Shape`, `ShapeRole` or `CornerEach`; this changes only the curve, and
    /// a node without a radius is not changed. A value outside 0..=1 is drawn as the nearer
    /// end and NaN as 0, so one bad shape cannot stop the program; see
    /// [`corner_smoothing`].
    CornerCurve {
        smoothing: f32,
    },
    /// A brush laid into a rectangle of this node and repeated across it, the way CSS
    /// draws one `background-image` layer with its `background-position`,
    /// `background-size` and `background-repeat`.
    ///
    /// `x`, `y`, `width` and `height` are the rectangle in dp from the node's top left
    /// corner, which is one tile: a gradient is measured against it, not against the node.
    /// `repeat` says which ways the tile repeats and `tile_width` and `tile_height` how far
    /// apart the copies are, in dp; a plain CSS repeat sends the rectangle's own size, and
    /// `space` or `round` the step the Host worked out. The layer is cut to the node's
    /// outline, its corners included. Several layers are several of these, the first
    /// drawn at the bottom, so a Host sends a CSS list last to first. A tile width or
    /// height of zero or less, and any value that is not a finite number, is refused.
    BackgroundBrush {
        x: f32,
        y: f32,
        width: f32,
        height: f32,
        paint: Paint,
        repeat: BackgroundRepeat,
        tile_width: f32,
        tile_height: f32,
    },
}

/// The smoothing a `CornerCurve` value draws with: clamped to 0..=1, NaN as 0.
pub fn corner_smoothing(smoothing: f32) -> f32 {
    if smoothing.is_nan() {
        0.0
    } else {
        smoothing.clamp(0.0, 1.0)
    }
}

/// Where the checked field sits in `Modifier::Semantics::state`.
pub const SEMANTICS_CHECKED_SHIFT: u32 = 0;
/// Where the selected field sits in `Modifier::Semantics::state`.
pub const SEMANTICS_SELECTED_SHIFT: u32 = 2;
/// Where the expanded field sits in `Modifier::Semantics::state`: 0 unset, 1 collapsed,
/// 2 expanded.
pub const SEMANTICS_EXPANDED_SHIFT: u32 = 4;
/// Where the disabled field sits in `Modifier::Semantics::state`: 0 unset, 1 enabled,
/// 2 disabled.
pub const SEMANTICS_DISABLED_SHIFT: u32 = 6;
/// Where the focused field sits in `Modifier::Semantics::state`: 0 unset, 1 not focused,
/// 2 focused.
pub const SEMANTICS_FOCUSED_SHIFT: u32 = 8;
/// The bit that excludes the node from the accessibility tree.
pub const SEMANTICS_HIDDEN_BIT: u32 = 1 << 10;
/// The bit that exposes a click action on the node.
pub const SEMANTICS_CLICK_ACTION_BIT: u32 = 1 << 11;
/// The bit that exposes a focus action on the node.
pub const SEMANTICS_FOCUS_ACTION_BIT: u32 = 1 << 12;
/// Every bit `Modifier::Semantics::state` may set.
pub const SEMANTICS_STATE_MASK: u32 = 0b1_1111_1111_1111;

impl Modifier {
    /// A border with a width and a paint for each side, in CSS order: top, right, bottom,
    /// left.
    ///
    /// Four equal sides are one `Border`, which is the record every node with an ordinary
    /// border already sends. `BorderEach` is written only where the sides differ, so a
    /// screen that never mixes them never sends the longer record.
    pub fn border_sides(widths: [f32; 4], paints: [Paint; 4]) -> Self {
        let [top, right, bottom, left] = widths;
        let [top_paint, right_paint, bottom_paint, left_paint] = paints;
        if widths.iter().all(|width| width.to_bits() == top.to_bits())
            && paints.iter().all(|paint| *paint == top_paint)
        {
            return Self::Border {
                width: top,
                paint: top_paint,
            };
        }
        Self::BorderEach {
            top,
            right,
            bottom,
            left,
            top_paint,
            right_paint,
            bottom_paint,
            left_paint,
        }
    }

    /// A radius for each corner, in CSS order: top left, top right, bottom right, bottom
    /// left.
    ///
    /// One radius for every corner is one `Shape`, the record an ordinary rounded node
    /// already sends. `CornerEach` is written only where the corners differ.
    pub fn corner_radii(radii: [f32; 4]) -> Self {
        let [top_left, top_right, bottom_right, bottom_left] = radii;
        if radii
            .iter()
            .all(|radius| radius.to_bits() == top_left.to_bits())
        {
            return Self::Shape {
                top_start: top_left,
                top_end: top_left,
                bottom_end: top_left,
                bottom_start: top_left,
            };
        }
        Self::CornerEach {
            top_left,
            top_right,
            bottom_right,
            bottom_left,
        }
    }
}

/// The timing function of one keyframe, which shapes the segment to the next one.
#[derive(Clone, Copy, Debug, PartialEq)]
pub enum Timing {
    Linear,
    /// CSS `cubic-bezier(x1, y1, x2, y2)`. Both `x` values are between 0 and 1.
    CubicBezier {
        x1: f32,
        y1: f32,
        x2: f32,
        y2: f32,
    },
    /// CSS `steps(count, position)`. `count` is at least 1, and at least 2 for `JumpNone`.
    Steps {
        count: u32,
        position: StepPosition,
    },
}

/// One CSS transform function: its kind and up to six values, the unused ones zero.
///
/// `Translate` is x and y in dp, `Rotate` degrees (not folded into one turn, so 0 to 720
/// is two turns), `Scale` x and y, `Skew` the x and y angles in degrees, and `Matrix` the
/// six values of CSS `matrix()`.
#[derive(Clone, Copy, Debug, PartialEq)]
pub struct TransformFunction {
    pub kind: TransformFunctionKind,
    pub values: [f32; 6],
}

impl TransformFunction {
    pub const fn translate(x: f32, y: f32) -> Self {
        Self {
            kind: TransformFunctionKind::Translate,
            values: [x, y, 0.0, 0.0, 0.0, 0.0],
        }
    }

    pub const fn rotate(degrees: f32) -> Self {
        Self {
            kind: TransformFunctionKind::Rotate,
            values: [degrees, 0.0, 0.0, 0.0, 0.0, 0.0],
        }
    }

    pub const fn scale(x: f32, y: f32) -> Self {
        Self {
            kind: TransformFunctionKind::Scale,
            values: [x, y, 0.0, 0.0, 0.0, 0.0],
        }
    }

    pub const fn skew(x_degrees: f32, y_degrees: f32) -> Self {
        Self {
            kind: TransformFunctionKind::Skew,
            values: [x_degrees, y_degrees, 0.0, 0.0, 0.0, 0.0],
        }
    }

    pub const fn matrix(a: f32, b: f32, c: f32, d: f32, e: f32, f: f32) -> Self {
        Self {
            kind: TransformFunctionKind::Matrix,
            values: [a, b, c, d, e, f],
        }
    }
}

/// What one keyframe holds, which has to be what its animation's property takes.
#[derive(Clone, Debug, PartialEq)]
pub enum KeyframeValue {
    Alpha(f32),
    /// For `Color`, `Background` and `BorderColor`. A role is resolved against the theme every frame.
    Paint(Paint),
    /// A list of functions, the same kinds in the same order in every keyframe.
    Transform(std::borrow::Cow<'static, [TransformFunction]>),
}

#[derive(Clone, Debug, PartialEq)]
pub struct Keyframe {
    /// Where in an iteration this keyframe stands, from 0 to 1.
    pub offset: f32,
    /// How the segment from this keyframe to the next is timed.
    pub timing: Timing,
    /// Starts from whatever the node shows the frame this animation begins, instead of
    /// `value`. Only the first keyframe may say so: it is how a CSS transition that
    /// changes course midway carries on from where it was without a jump.
    pub from_presented: bool,
    pub value: KeyframeValue,
}

/// Which moments of an animation are reported back as `AnimationEvent`s. None, the
/// default, means the animation plays to its end without a single call to the Host.
#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
pub struct AnimationEvents(pub u8);

impl AnimationEvents {
    pub const NONE: Self = Self(0);
    pub const READY: Self = Self(1);
    pub const ACTIVE: Self = Self(2);
    pub const ITERATION: Self = Self(4);
    pub const END: Self = Self(8);
    /// Every kind there is. A bit outside these is a record the sides disagree about.
    pub const ALL: Self = Self(1 | 2 | 4 | 8);

    pub const fn union(self, other: Self) -> Self {
        Self(self.0 | other.0)
    }

    pub const fn contains(self, other: Self) -> bool {
        self.0 & other.0 == other.0
    }
}

/// One animation the Renderer plays to its end on its own frame clock, described once.
///
/// The key is `(node_id, property, slot)`: a second animation with the same key replaces
/// the first, and of the ones in effect on one property the highest slot is what shows.
/// Timing follows Web Animations Level 1, which is what CSS transitions and animations
/// are defined by.
#[derive(Clone, Debug, PartialEq)]
pub struct Animation<'a> {
    pub node_id: u32,
    /// The Host's own name for the animation, returned in every event about it.
    pub animation_id: u32,
    pub property: AnimatedProperty,
    pub slot: u8,
    pub direction: PlaybackDirection,
    pub fill: FillMode,
    pub play_state: PlayState,
    /// For `Color`, `Background` and `BorderColor` only, and required there.
    pub interpolation: Option<ColorInterpolation>,
    /// On the Renderer's frame clock. Zero starts it on the first frame that draws it.
    pub start_time_nanos: u64,
    /// May be negative, which starts it partway through.
    pub delay_ms: f32,
    pub duration_ms: f32,
    /// Infinite for `infinite`.
    pub iterations: f32,
    /// For `Transform` only: the origin, as a fraction of the node's size.
    pub origin_x: f32,
    pub origin_y: f32,
    pub events: AnimationEvents,
    /// At least two, the first at offset 0 and the last at 1.
    pub keyframes: std::borrow::Cow<'a, [Keyframe]>,
}

const NO_FIELDS: &[FieldSchema] = &[];
const OBSERVE_SIZE_FIELDS: &[FieldSchema] = &[
    FieldSchema {
        name: "token",
        ty: FieldType::U32,
        slot: FieldSlot::FirstLow,
    },
    FieldSchema {
        name: "everyDp",
        ty: FieldType::Bool,
        slot: FieldSlot::Second,
    },
];
const VALUE_FLOAT_FIELD: &[FieldSchema] = &[FieldSchema {
    name: "value",
    ty: FieldType::Float,
    slot: FieldSlot::FirstLow,
}];
const SIZE_FIELDS: &[FieldSchema] = &[
    FieldSchema {
        name: "width",
        ty: FieldType::Float,
        slot: FieldSlot::FirstLow,
    },
    FieldSchema {
        name: "height",
        ty: FieldType::Float,
        slot: FieldSlot::SecondLow,
    },
];
const PAINT_FIELD: &[FieldSchema] = &[FieldSchema {
    name: "paint",
    ty: FieldType::Paint,
    slot: FieldSlot::First,
}];
const HANDLER_ID_FIELD: &[FieldSchema] = &[FieldSchema {
    name: "handlerId",
    ty: FieldType::U64,
    slot: FieldSlot::First,
}];
const SPACE_ROLE_FIELD: &[FieldSchema] = &[FieldSchema {
    name: "role",
    ty: FieldType::Role("SpaceRole"),
    slot: FieldSlot::FirstLow,
}];
const SHAPE_ROLE_FIELD: &[FieldSchema] = &[FieldSchema {
    name: "role",
    ty: FieldType::Role("ShapeRole"),
    slot: FieldSlot::FirstLow,
}];
const MOTION_ROLE_FIELD: &[FieldSchema] = &[FieldSchema {
    name: "role",
    ty: FieldType::Role("MotionRole"),
    slot: FieldSlot::FirstLow,
}];
const MATERIAL_ROLE_FIELD: &[FieldSchema] = &[FieldSchema {
    name: "role",
    ty: FieldType::Role("MaterialRole"),
    slot: FieldSlot::FirstLow,
}];
const PADDING_EACH_FIELDS: &[FieldSchema] = &[
    FieldSchema {
        name: "start",
        ty: FieldType::Float,
        slot: FieldSlot::FirstLow,
    },
    FieldSchema {
        name: "top",
        ty: FieldType::Float,
        slot: FieldSlot::FirstHigh,
    },
    FieldSchema {
        name: "end",
        ty: FieldType::Float,
        slot: FieldSlot::SecondLow,
    },
    FieldSchema {
        name: "bottom",
        ty: FieldType::Float,
        slot: FieldSlot::SecondHigh,
    },
];
const SHAPE_FIELDS: &[FieldSchema] = &[
    FieldSchema {
        name: "topStart",
        ty: FieldType::Float,
        slot: FieldSlot::FirstLow,
    },
    FieldSchema {
        name: "topEnd",
        ty: FieldType::Float,
        slot: FieldSlot::FirstHigh,
    },
    FieldSchema {
        name: "bottomEnd",
        ty: FieldType::Float,
        slot: FieldSlot::SecondLow,
    },
    FieldSchema {
        name: "bottomStart",
        ty: FieldType::Float,
        slot: FieldSlot::SecondHigh,
    },
];
const BORDER_FIELDS: &[FieldSchema] = &[
    FieldSchema {
        name: "width",
        ty: FieldType::Float,
        slot: FieldSlot::FirstLow,
    },
    FieldSchema {
        name: "paint",
        ty: FieldType::Paint,
        slot: FieldSlot::Second,
    },
];
const OFFSET_FIELDS: &[FieldSchema] = &[
    FieldSchema {
        name: "x",
        ty: FieldType::Float,
        slot: FieldSlot::FirstLow,
    },
    FieldSchema {
        name: "y",
        ty: FieldType::Float,
        slot: FieldSlot::SecondLow,
    },
];
const BORDER_EACH_FIELDS: &[FieldSchema] = &[
    FieldSchema {
        name: "top",
        ty: FieldType::Float,
        slot: FieldSlot::FirstLow,
    },
    FieldSchema {
        name: "right",
        ty: FieldType::Float,
        slot: FieldSlot::FirstHigh,
    },
    FieldSchema {
        name: "bottom",
        ty: FieldType::Float,
        slot: FieldSlot::SecondLow,
    },
    FieldSchema {
        name: "left",
        ty: FieldType::Float,
        slot: FieldSlot::SecondHigh,
    },
    FieldSchema {
        name: "topPaint",
        ty: FieldType::Paint,
        slot: FieldSlot::Third,
    },
    FieldSchema {
        name: "rightPaint",
        ty: FieldType::Paint,
        slot: FieldSlot::Fourth,
    },
    FieldSchema {
        name: "bottomPaint",
        ty: FieldType::Paint,
        slot: FieldSlot::Fifth,
    },
    FieldSchema {
        name: "leftPaint",
        ty: FieldType::Paint,
        slot: FieldSlot::Sixth,
    },
];
const CORNER_EACH_FIELDS: &[FieldSchema] = &[
    FieldSchema {
        name: "topLeft",
        ty: FieldType::Float,
        slot: FieldSlot::FirstLow,
    },
    FieldSchema {
        name: "topRight",
        ty: FieldType::Float,
        slot: FieldSlot::FirstHigh,
    },
    FieldSchema {
        name: "bottomRight",
        ty: FieldType::Float,
        slot: FieldSlot::SecondLow,
    },
    FieldSchema {
        name: "bottomLeft",
        ty: FieldType::Float,
        slot: FieldSlot::SecondHigh,
    },
];
const SHADOW_FIELDS: &[FieldSchema] = &[
    FieldSchema {
        name: "x",
        ty: FieldType::Float,
        slot: FieldSlot::FirstLow,
    },
    FieldSchema {
        name: "y",
        ty: FieldType::Float,
        slot: FieldSlot::FirstHigh,
    },
    FieldSchema {
        name: "blur",
        ty: FieldType::Float,
        slot: FieldSlot::SecondLow,
    },
    FieldSchema {
        name: "spread",
        ty: FieldType::Float,
        slot: FieldSlot::SecondHigh,
    },
    FieldSchema {
        name: "paint",
        ty: FieldType::Paint,
        slot: FieldSlot::Third,
    },
];
const TRANSFORM_FIELDS: &[FieldSchema] = &[
    FieldSchema {
        name: "a",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::FirstLow,
    },
    FieldSchema {
        name: "b",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::FirstHigh,
    },
    FieldSchema {
        name: "c",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::SecondLow,
    },
    FieldSchema {
        name: "d",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::SecondHigh,
    },
    FieldSchema {
        name: "e",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::ThirdLow,
    },
    FieldSchema {
        name: "f",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::ThirdHigh,
    },
    FieldSchema {
        name: "originX",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::FourthLow,
    },
    FieldSchema {
        name: "originY",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::FourthHigh,
    },
];
const TRANSFORM_3D_FIELDS: &[FieldSchema] = &[
    FieldSchema {
        name: "m0",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::FirstLow,
    },
    FieldSchema {
        name: "m1",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::FirstHigh,
    },
    FieldSchema {
        name: "m2",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::SecondLow,
    },
    FieldSchema {
        name: "m3",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::SecondHigh,
    },
    FieldSchema {
        name: "m4",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::ThirdLow,
    },
    FieldSchema {
        name: "m5",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::ThirdHigh,
    },
    FieldSchema {
        name: "m6",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::FourthLow,
    },
    FieldSchema {
        name: "m7",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::FourthHigh,
    },
    FieldSchema {
        name: "m8",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::FifthLow,
    },
    FieldSchema {
        name: "m9",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::FifthHigh,
    },
    FieldSchema {
        name: "m10",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::SixthLow,
    },
    FieldSchema {
        name: "m11",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::SixthHigh,
    },
    FieldSchema {
        name: "m12",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::SeventhLow,
    },
    FieldSchema {
        name: "m13",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::SeventhHigh,
    },
    FieldSchema {
        name: "m14",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::EighthLow,
    },
    FieldSchema {
        name: "m15",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::EighthHigh,
    },
    FieldSchema {
        name: "originX",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::NinthLow,
    },
    FieldSchema {
        name: "originY",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::NinthHigh,
    },
    FieldSchema {
        name: "backfaceHidden",
        ty: FieldType::Bool,
        slot: FieldSlot::Tenth,
    },
];
const ENABLED_FIELD: &[FieldSchema] = &[FieldSchema {
    name: "enabled",
    ty: FieldType::Bool,
    slot: FieldSlot::First,
}];

const PRESS_FEEDBACK_FIELDS: &[FieldSchema] = &[
    FieldSchema {
        name: "scale",
        ty: FieldType::Float,
        slot: FieldSlot::FirstLow,
    },
    FieldSchema {
        name: "tintAlpha",
        ty: FieldType::Float,
        slot: FieldSlot::FirstHigh,
    },
];

const CORNER_CURVE_FIELDS: &[FieldSchema] = &[FieldSchema {
    name: "smoothing",
    ty: FieldType::Float,
    slot: FieldSlot::FirstLow,
}];

const BACKGROUND_BRUSH_FIELDS: &[FieldSchema] = &[
    FieldSchema {
        name: "x",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::FirstLow,
    },
    FieldSchema {
        name: "y",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::FirstHigh,
    },
    FieldSchema {
        name: "width",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::SecondLow,
    },
    FieldSchema {
        name: "height",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::SecondHigh,
    },
    FieldSchema {
        name: "paint",
        ty: FieldType::Paint,
        slot: FieldSlot::Third,
    },
    FieldSchema {
        name: "repeat",
        ty: FieldType::Role("BackgroundRepeat"),
        slot: FieldSlot::FourthLow,
    },
    FieldSchema {
        name: "tile_width",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::FifthLow,
    },
    FieldSchema {
        name: "tile_height",
        ty: FieldType::FiniteFloat,
        slot: FieldSlot::FifthHigh,
    },
];

const SEMANTICS_FIELDS: &[FieldSchema] = &[
    FieldSchema {
        name: "role",
        ty: FieldType::Role("SemanticsRole"),
        slot: FieldSlot::FirstLow,
    },
    FieldSchema {
        name: "state",
        ty: FieldType::U32,
        slot: FieldSlot::SecondLow,
    },
];

pub const MODIFIER_SCHEMA: &[VariantSchema] = &[
    VariantSchema {
        name: "Empty",
        tag: 0,
        extra_words: 0,
        fields: NO_FIELDS,
    },
    VariantSchema {
        name: "Padding",
        tag: 1,
        extra_words: 0,
        fields: VALUE_FLOAT_FIELD,
    },
    VariantSchema {
        name: "FillMaxWidth",
        tag: 2,
        extra_words: 0,
        fields: NO_FIELDS,
    },
    VariantSchema {
        name: "FillMaxHeight",
        tag: 3,
        extra_words: 0,
        fields: NO_FIELDS,
    },
    VariantSchema {
        name: "Width",
        tag: 4,
        extra_words: 0,
        fields: VALUE_FLOAT_FIELD,
    },
    VariantSchema {
        name: "Height",
        tag: 5,
        extra_words: 0,
        fields: VALUE_FLOAT_FIELD,
    },
    VariantSchema {
        name: "Size",
        tag: 6,
        extra_words: 0,
        fields: SIZE_FIELDS,
    },
    VariantSchema {
        name: "Background",
        tag: 7,
        extra_words: 0,
        fields: PAINT_FIELD,
    },
    VariantSchema {
        name: "Clickable",
        tag: 8,
        extra_words: 0,
        fields: HANDLER_ID_FIELD,
    },
    VariantSchema {
        name: "PaddingRole",
        tag: 9,
        extra_words: 0,
        fields: SPACE_ROLE_FIELD,
    },
    VariantSchema {
        name: "PaddingEach",
        tag: 10,
        extra_words: 0,
        fields: PADDING_EACH_FIELDS,
    },
    VariantSchema {
        name: "Weight",
        tag: 11,
        extra_words: 0,
        fields: VALUE_FLOAT_FIELD,
    },
    VariantSchema {
        name: "Shape",
        tag: 12,
        extra_words: 0,
        fields: SHAPE_FIELDS,
    },
    VariantSchema {
        name: "ShapeRole",
        tag: 13,
        extra_words: 0,
        fields: SHAPE_ROLE_FIELD,
    },
    VariantSchema {
        name: "Border",
        tag: 14,
        extra_words: 0,
        fields: BORDER_FIELDS,
    },
    VariantSchema {
        name: "Elevation",
        tag: 15,
        extra_words: 0,
        fields: VALUE_FLOAT_FIELD,
    },
    VariantSchema {
        name: "ObserveSize",
        tag: 16,
        extra_words: 0,
        fields: OBSERVE_SIZE_FIELDS,
    },
    VariantSchema {
        name: "Motion",
        tag: 17,
        extra_words: 0,
        fields: MOTION_ROLE_FIELD,
    },
    VariantSchema {
        name: "Material",
        tag: 18,
        extra_words: 0,
        fields: MATERIAL_ROLE_FIELD,
    },
    // The elements an HTML and CSS screen is drawn with: boxes a layout engine on the Host
    // already placed and sized, and the decoration CSS gives them.
    VariantSchema {
        name: "Offset",
        tag: 19,
        extra_words: 0,
        fields: OFFSET_FIELDS,
    },
    VariantSchema {
        name: "RequiredSize",
        tag: 20,
        extra_words: 0,
        fields: SIZE_FIELDS,
    },
    // Four widths and four paints are six words, so the record is four words longer.
    VariantSchema {
        name: "BorderEach",
        tag: 21,
        extra_words: 4,
        fields: BORDER_EACH_FIELDS,
    },
    VariantSchema {
        name: "CornerEach",
        tag: 22,
        extra_words: 0,
        fields: CORNER_EACH_FIELDS,
    },
    // Four measurements and a paint are three words, one more than the record has.
    VariantSchema {
        name: "Shadow",
        tag: 23,
        extra_words: 1,
        fields: SHADOW_FIELDS,
    },
    VariantSchema {
        name: "Clip",
        tag: 24,
        extra_words: 0,
        fields: ENABLED_FIELD,
    },
    VariantSchema {
        name: "Alpha",
        tag: 25,
        extra_words: 0,
        fields: VALUE_FLOAT_FIELD,
    },
    // Eight `f32` are four words: the linear part, the translation, and the origin.
    VariantSchema {
        name: "Transform",
        tag: 26,
        extra_words: 2,
        fields: TRANSFORM_FIELDS,
    },
    // Sixteen matrix values, the origin and a flag are ten words, eight more than the two
    // every record has: 92 bytes.
    VariantSchema {
        name: "Transform3D",
        tag: 27,
        extra_words: 8,
        fields: TRANSFORM_3D_FIELDS,
    },
    VariantSchema {
        name: "MatchParentSize",
        tag: 31,
        extra_words: 0,
        fields: NO_FIELDS,
    },
    VariantSchema {
        name: "WindowDrag",
        tag: 32,
        extra_words: 0,
        fields: ENABLED_FIELD,
    },
    VariantSchema {
        name: "PressFeedback",
        tag: 33,
        extra_words: 0,
        fields: PRESS_FEEDBACK_FIELDS,
    },
    VariantSchema {
        name: "Semantics",
        tag: 34,
        extra_words: 0,
        fields: SEMANTICS_FIELDS,
    },
    // 28 to 30 were set aside for modifiers that have not landed, so the next free tag is
    // 35.
    VariantSchema {
        name: "CornerCurve",
        tag: 35,
        extra_words: 0,
        fields: CORNER_CURVE_FIELDS,
    },
    // 28, the first of the tags set aside above. The rectangle, the paint, the repeat and
    // the step take five words, three past the two every record has.
    VariantSchema {
        name: "BackgroundBrush",
        tag: 28,
        extra_words: 3,
        fields: BACKGROUND_BRUSH_FIELDS,
    },
];

#[derive(Clone, Debug, PartialEq)]
pub struct ColumnProps {
    pub enabled: bool,
}

#[derive(Clone, Debug, PartialEq)]
pub struct RowProps {
    pub enabled: bool,
}

#[derive(Clone, Debug, PartialEq)]
pub struct BoxProps {
    pub enabled: bool,
}

#[derive(Clone, Debug, PartialEq)]
pub struct TextProps<'a> {
    pub text: &'a str,
}

#[derive(Clone, Debug, PartialEq)]
pub struct TextFieldProps<'a> {
    pub placeholder: &'a str,
    pub enabled: bool,
    pub multiline: bool,
}

#[derive(Clone, Debug, PartialEq)]
pub struct ButtonProps<'a> {
    pub text: &'a str,
    pub enabled: bool,
}

#[derive(Clone, Debug, PartialEq)]
pub struct SpacerProps {
    pub width: f32,
    pub height: f32,
}

crate::extensions::define_property_schema_with_extensions!(define_wire_enum; PROPERTY_SCHEMA, PropertyKind {
    Text = 1,
    Placeholder = 2,
    Enabled = 3,
    Multiline = 4,
    OnClick = 5,
    OnValueChange = 6,
    OnSubmit = 7,
    OnFocusLost = 8,
    OnKeyDown = 9,
    ItemCount = 10,
    ItemKey = 11,
    OnRangeRequested = 12,
    TypeRole = 13,
    FontSize = 14,
    FontWeight = 15,
    LineHeight = 16,
    LetterSpacing = 17,
    Color = 18,
    TextAlign = 19,
    MaxLines = 20,
    Overflow = 21,
    Arrangement = 22,
    Spacing = 23,
    SpaceRole = 24,
    Alignment = 25,
    Variant = 26,
    // The id of an asset the Host registered. Image and Icon carry nothing else: the
    // bytes were copied into the Renderer's cache once, at registration.
    Asset = 28,
    // Whether a toggle is on. One boolean for all three of them: a selected radio button
    // and a switch that is on are the same fact, and the schema names a concept once.
    Checked = 32,
    // Discrete stops between a slider's two ends. Zero leaves it continuous.
    Steps = 33,
    // Whether a progress indicator knows how far along it is. When it does not, `Value`
    // is not read at all.
    Determinate = 34,
    // Which of the two forms a progress indicator takes. It picks a shape, not a size.
    Circular = 35,
    // A divider's axis, which is the only thing a divider carries.
    Vertical = 36,
    // Whether an overlay is showing. The Renderer owns the state; this seeds it and
    // carries changes that came from outside the Renderer.
    Open = 40,
    OnDismiss = 41,
    SelectedIndex = 42,
    // The Canvas drawing command list, a byte blob in the batch arena.
    Commands = 50,
    // The control's current value, in the widget's own unit: an epoch day count for a
    // date, minutes since midnight for a time, the chosen position for a Dropdown, a
    // position between the ends for a Slider, a fraction for a ProgressIndicator. One tag,
    // because "this control's value" is one concept whichever widget holds it.
    Value = 51,
    // The ends of the selectable range, in the same unit as `Value`.
    Min = 52,
    Max = 53,
    // The meaning of the icon a destination carries, as an `IconRole` tag. Tag 0 is "not
    // sent", so a destination without an icon is label only.
    Icon = 60,
    // Which slot of a Scaffold this subtree fills.
    Slot = 61,
    // How many columns a grid has, where the screen said a number.
    Columns = 62,
    // How narrow a column may get before the grid drops one, where the screen said a
    // width instead of a number. The Renderer divides its own width by this, which is the
    // same kind of judgement as a size class and for the same reason is not the Host's.
    MinColumnWidth = 63,
    // Runs of different treatment inside one string, as a blob of fixed-length records.
    // A Text that says nothing about runs carries none of this and travels as it always
    // did.
    Spans = 64,
    // A node that is willing to have files dropped on it. The handler is the willingness:
    // a node without one is never told that files are over it, which is what keeps a
    // screen from lighting up every container it has.
    OnFilesEntered = 65,
    OnFilesDropped = 66,
    // Which named group of a navigation's strip this destination belongs to. Neighbouring
    // destinations carrying the same string are one group and the string is its heading.
    //
    // 76 rather than 67, because 67 through 74 are reserved for the gestures and 75 for a
    // button's kind. A reservation is not a free tag.
    Section = 76,
    // How many a badge counts. Absent rather than zero when the badge is a dot or a word,
    // because "no count" and "a count of nothing" are different things to show.
    //
    // 80 opens a fresh block of ten for widget tags 40 onwards, after the last tag in use
    // anywhere, so two pieces of work landing in either order cannot collide.
    Count = 80,
    // Whether a split pane's side pane may be folded away by dragging past its minimum, or
    // by the keyboard, or by the platform's own show and hide sidebar command. Whether a
    // side pane can be hidden is a fact about the screen rather than about the design
    // system: a list of sessions can, a settings screen's list of sections cannot.
    //
    // 90 opens the split pane's block of ten, after the badge's.
    Collapsible = 90,
    // What a button is, as opposed to how loud it is: a plain button, or one key of a
    // dense grid of them. The variant still chooses the fill and the emphasis; this lets
    // the design system give the key its own calculator's silhouette, so the Host never
    // sends a radius or a shape role to get one.
    //
    // 75 was reserved for this when the gestures took 67 through 74, and stays here
    // rather than with its neighbours by number because this list is append only.
    ButtonKind = 75,
    // A code editor's own block, after the split pane's.
    //
    // The decorations over the document and the colour runs of its syntax, each a blob of
    // fixed-length records sent whole. Every record carries the document version its
    // range was written against, so a list computed while the reader kept typing still
    // lands where it was meant to.
    Decorations = 100,
    SyntaxSpans = 101,
    // How many columns a tab advances. Absent leaves it to the design system.
    TabWidth = 102,
    OnEditRejected = 103,
    OnHover = 104,
    OnSave = 105,
    // One listener for every decoration that can be pressed or accepted. The ids inside
    // the decoration blob are the application's own names for them, not handlers, so the
    // event carries the id and the application tells them apart.
    OnDecorationClick = 106,
    // The editor's additions: the stretches that can be folded and the marks beside the
    // line numbers, each a blob of fixed-length records sent whole, and the listener for
    // the selection moving. The other four listeners are in the block at 130.
    Folds = 107,
    GutterDecorations = 108,
    OnSelectionChange = 109,
    // The text a page laid out by CSS draws, which takes its letters from its own values
    // rather than from a rung of the type ladder. 110 opens the block for it.
    //
    // The fonts to try, in order, for text whose role is `TypeRole::None`: a list of up to
    // eight registered font assets, installed families by name and generic families, as a
    // blob. Text with a role ignores it, because its font is the theme's.
    Font = 110,
    // Where a line may break, and whether a word too long for its line may be broken
    // inside. The `WordBreak` and `OverflowWrap` roles.
    WordBreak = 111,
    OverflowWrap = 112,
    // How many spaces' width apart the tab stops are. Absent is eight. A tab advances to
    // the next stop, which only the side that measures the letters can work out.
    TabSize = 113,
    // Whether the sizes are CSS pixels, which the system's font scale does not enlarge.
    AbsoluteSize = 114,
    // Whether lines wrap at the width they are given. Absent is yes; `false` is CSS
    // `nowrap` and `pre`, whose lines run as long as their text.
    SoftWrap = 115,
    // The font each run of a `Text` with no role is set in, as a blob beside `Spans`
    // rather than inside its records: a run record keeps the 36 bytes it has always had,
    // and only text that names fonts carries this at all.
    SpanFonts = 116,
    // The rest of the code editor's listeners, in the first block free after the text and
    // pointer blocks. The visible lines changing, the editor gaining or losing focus, a
    // stretch folded or unfolded, and an input method starting or ending a composition.
    OnVisibleRangeChange = 130,
    OnEditorFocusChange = 131,
    OnFoldChange = 132,
    OnCompositionChange = 133,
    // The node's pointer subscription: the handler, and the kinds it wants as a bit mask
    // (`1 << (kind - 1)`). 67 was reserved for a gesture handler that was never sent, so
    // it is free to carry this one. It is listed here, after the newer blocks, because
    // this list is append only.
    OnPointer = 67,
    // 140 opens the block after the animation and HTML-text properties.
    PointerKinds = 140,
    // The cursor the platform shows over the node and whether its text can be selected.
    // The Host resolves CSS inheritance and sends the value for each node.
    Cursor = 141,
    UserSelect = 142,
    // How large an HTML island is drawn, as the f32 factor `k` (see `ZoomChanged`), on the
    // island's root `AbsoluteBox`. 120 opens the block for zoom. Absent is 1.
    IslandZoom = 120,
    // The window block, after the cursor block. Every one of them belongs to a
    // `Window` node except the last two, which can sit on any node.
    //
    // The title. A string.
    WindowTitle = 150,
    // The size when the window opens, width then height, two `f32` in dp as 8 bytes. A
    // later change resizes the window; a size the user chose is not given back.
    WindowSize = 151,
    // The smallest size, in the same 8 bytes.
    WindowMinSize = 152,
    WindowResizable = 153,
    // A `Chrome` tag and a `TitleBar` tag, as integers.
    WindowChrome = 154,
    WindowTitleBar = 155,
    // The asset id of the window's icon; zero is the application's own.
    WindowIcon = 156,
    // Where the window sits, x then y, two `f32` in screen dp as 8 bytes. Removing it
    // leaves the placement to the platform.
    WindowPosition = 157,
    // The application's stable name for the window, a string, which matches a window the
    // system brings back to the node that describes it.
    WindowRestoreKey = 158,
    // The window's own zoom level, an integer in -8..=8.
    WindowZoomLevel = 159,
    // Open the window under a pointer that is held down and follow it until it is let go:
    // `pointer_id` as a `u32`, then the anchor `x` and `y` as two `f32`, 12 bytes. Read
    // when the window opens and not again.
    DragFromPointer = 160,
    // The handlers of the window events, each the handler id as an integer.
    OnWindowCloseRequested = 161,
    OnWindowFocusChanged = 162,
    OnWindowMoved = 163,
    OnWindowDrag = 164,
    OnWindowUnavailable = 165,
    OnWindowClosed = 166,
    // Not window properties: any node may take them. A node that has the handler is told
    // when a dragged window passes over it, and a node that has the key can be pulled out
    // into a window of its own, named by it.
    OnWindowDragOver = 167,
    TearOffKey = 168,
    OnFocusGained = 117,
    OnKeyUp = 118,
    // The name assistive technology reads for a node, a string. On a widget it overrides
    // the visible label, and on an icon-only button it beats the name the icon's meaning
    // would give. 117 and 118 are reserved for another pending change, and 119 is the next
    // free number; 120 is `IslandZoom`.
    AccessibleName = 119,
    // Colours and size of the selection controls. A node that does not set one leaves
    // the design system's value, so a control that sends none draws as it always has.
    // The colours are `Paint` bits; the size is two f32 (width, height) in dp.
    // 120 is the island zoom, so these start at 121.
    TrackColor = 121,
    ThumbColor = 122,
    ActiveTrackColor = 123,
    ContainerColor = 124,
    CheckColor = 125,
    ControlSize = 126,
    // Opt in to a `WindowSizeChanged` whenever the window's width or height, rounded to
    // whole dp, changes, and not only when the size class does. A `Window` node's boolean;
    // absent is false.
    ReportSize = 127,
    // Scrim colour for modal overlays (Dialog, Sheet, Menu), as a `Paint` bit value.
    // A `Popover` draws no scrim unless it is asked to, so there it is also a boolean:
    // true draws the design system's scrim, and a `Paint` draws that colour.
    Scrim = 128,
    // A `TextField` or `Dropdown` drawn without the design system's frame (fill, line,
    // underline, corner clip, inner padding, minimum height, focus line). A boolean;
    // absent is false. A node `Background` or `Border` is still drawn.
    Bare = 169,
    // A `FlowRow`'s layout. The gap between children on one line and the gap between
    // lines, each a literal dp; where a line's children sit along it and where each child
    // sits inside its line's height, as `HorizontalAlignment` and `VerticalAlignment` tags;
    // and the most children one line may hold, an integer, absent for no limit. 169 is
    // taken by another pending property, so these start at 170.
    HorizontalSpacing = 170,
    VerticalSpacing = 171,
    HorizontalAlignment = 172,
    VerticalAlignment = 173,
    MaxItemsInEachRow = 174,
    // The popover block. All three belong to a `Popover`. 169 to 174 are held for
    // properties on other branches.
    //
    // The side of the anchor the content opens on, a `PopoverPlacement` tag. Absent is
    // `Bottom`.
    Placement = 175,
    // The edge of the anchor the content lines up with, a `PopoverAlign` tag. Absent is
    // `Start`.
    Align = 176,
    // The gap between the anchor and the content, an `f32` in dp. Absent leaves the gap
    // to the design system.
    OffsetDp = 177,
    // How a code editor is laid out and coloured where the application says so. A node
    // that sets none of them draws with the design system's values. 169 to 177 are
    // numbered for properties that are not here yet.
    //
    // Whether the line numbers are drawn, a boolean. Absent is yes.
    LineNumbers = 178,
    // The least width of the line number column with its padding, the padding on each side
    // of a line number, and the space between the gutter and the text. Each an f32 in dp.
    GutterMinWidthDp = 179,
    GutterPaddingDp = 180,
    TextInsetDp = 181,
    // One colour record as a blob: a `ColorRole` for each of the container, the gutter, a
    // line number, the current line's number and the current line. Zero leaves a slot to
    // the design system.
    CodeEditorColors = 182,
    // The handlers of the editor's row height and of its scroll offset.
    OnCodeMetrics = 183,
    OnCodeScrolled = 184,
    // What a `Navigation` becomes in a compact window, as a `CompactNavigation` tag. Absent
    // or 0 leaves it to the design system.
    CompactNavigation = 185,
    // The handler a scroll container reports its position to, the handler id as an
    // integer. One handler shared by every scroll container rather than one widget's
    // block, so it takes the number after the last one in use: 169 to 184 are held by
    // properties other requirements have numbered.
    OnScrollChanged = 186,
    // The width in dp, an f32, below which a split pane shows one pane at a time instead of
    // its size class deciding. At or above it the split pane never stacks, and the design
    // system still chooses between two columns and a side pane laid over the body. Absent
    // or 0 keeps the size class's own line. The next place in the split pane's block after
    // `Collapsible`.
    CollapseBelow = 91,
    // Where a `ScrollRow` or `ScrollColumn` comes to rest, as a `Snap` tag. Absent or 0 is
    // free scrolling. 187 is held by a property on another branch.
    Snap = 188,
    // The tallest a `Sheet` grows, as an `f32` fraction of the window's height above 0 and
    // at most 1. Below it the sheet is as tall as its content; at it the content scrolls.
    // Absent leaves the height to the design system. 187 is held by a property on another
    // branch.
    MaxHeightFraction = 189,
    // OpenType features for a `Text` or a `TextField`, such as tabular figures. A blob of
    // 8-byte records, at most 16: the four tag bytes, then the value as a little-endian
    // u32. A tag that comes twice takes the later value. Absent, or empty, is no features.
    // 187 to 191 are held by properties other requirements have numbered.
    FontFeatureSettings = 192,
    // The handler a node's size motion reports to once it settles, the handler id as an
    // integer. Any node may take it, so it is numbered after the last one in use rather
    // than inside a widget's block: 187 to 192 are held by properties other requirements
    // have numbered.
    OnMotionFinished = 193,
    // The handler a code editor reports what became of each grouped edit to, the handler id
    // as an integer: one `CodeEditGroupResult` for every `EditCodeGroup`.
    OnEditGroupResult = 194,
    // The handler a code editor tells where its caret is drawn. 190 and 191 are held by
    // properties on other branches.
    OnCaretRect = 195,
    // The handler a code editor offers each key press to before it handles the key itself.
    // It hears the `KeyDown` record a key handler does, and a press it consumes is not the
    // editor's. Never while an input method is composing.
    OnKeyPreview = 196,
    // The handler a code editor sends its pointer events to, each with the place in the
    // text under the pointer. The kinds it hears are the `PointerKinds` mask's.
    OnCodePointer = 197,
    // Whether a `Column` or a `Row` is a group of radio buttons, a boolean. Such a group is
    // one stop for Tab, its arrow keys move between the radio buttons inside it, and
    // assistive technology hears it as a radio group. Absent is no.
    RadioGroup = 198,
    // Whether a code editor draws a minimap beside its text, and on which side, as a
    // `MinimapSide` tag. Absent or 0 draws none. 199 and 200 are held by the editor's view
    // zones and its word wrap.
    Minimap = 201,
    // A code editor's view zones, rows after a line that are not text, as a blob of
    // fixed-length records sent whole, with the text they show behind them.
    ViewZones = 199,
    // Where a code editor breaks a line too long for it onto the rows below, as an integer:
    // the `WordWrapMode` tag in the low 16 bits and the column count above them. Absent or
    // 0 breaks no line.
    WordWrap = 200,
    // How an `Image` lays its picture into its box, as a `ContentScale` tag. Absent or 0
    // is `Fit`, which is how every picture was drawn before there was a choice. 37 is the
    // next place in the 28 to 39 block, after the divider's `Vertical`.
    ContentScale = 37,
    // The diameter in dp a Slider draws its thumb at, an f32. Absent is the design system's
    // size. The track and the area that takes a press stay as they are.
    ThumbSize = 202,
});

#[derive(Clone, Debug, PartialEq)]
pub enum EventPayload<'a> {
    Clicked,
    TextChanged(&'a str),
    TextSubmitted(&'a str),
    FocusLost,
    ProtocolError {
        code: u32,
        message: &'a str,
    },
    KeyDown {
        key: Key,
        shift_key: bool,
        ctrl_key: bool,
        alt_key: bool,
        meta_key: bool,
        /// True when the event comes from a held key repeating.
        repeat: bool,
        /// The physical key as a USB HID usage value, the same on every layout.
        code: u32,
        /// The DOM `key` string, such as `"ArrowDown"` or `"a"`.
        text: &'a str,
    },
    /// The Renderer asks the Host to materialise the visible item range.
    RangeRequested {
        start: u32,
        count: u32,
    },
    /// A control's new value, in the widget's own unit: an epoch count for a picker, a
    /// position for a slider, 0.0 or 1.0 for a toggle. The Renderer decided how the user
    /// reached it, so nothing about calendars, wheels, tracks or thumbs crosses here.
    ///
    /// One `f64` holds all of them: integers up to 2^53 survive it exactly, so splitting
    /// the event in two would only give the same concept two names.
    ValueChanged(f64),
    /// The window, or one observed node, moved into a different size class. The Renderer
    /// measures it and sends this only when a class changes, never on every layout pass.
    /// A `node_id` of 0 is the window; anything else is the node that asked to be
    /// measured.
    WindowSizeChanged {
        width_dp: f32,
        height_dp: f32,
        class: WindowSizeClass,
        height_class: WindowHeightClass,
        safe_area_top: f32,
        safe_area_leading: f32,
        safe_area_trailing: f32,
    },
    /// Files are over a node that said it would take them. Nothing about what they are:
    /// the platforms disagree about what is knowable before a drop, and a screen that
    /// only needs to light up does not need to know.
    FilesEntered,
    /// Files were let go over a node. The paths arrive together, separated by a byte no
    /// path on any of the three desktops may contain.
    FilesDropped(&'a str),
    /// The Renderer resolved the theme and this is what it chose. Sent once and then
    /// only when the answer changes, the same way a size class is.
    DesignSystemResolved(DesignSystem),
    /// The Renderer lost its node table and asks for the whole tree again. A recreated
    /// Activity is the case that produces it.
    Resync,
    /// The platform brought the UI back. Timers and animations resume.
    LifecycleStart,
    /// The platform stopped the UI. Timers and animations are suppressed, so a process
    /// that is not on screen is not asked to draw.
    LifecycleStop,
    /// The user pressed a notification the application posted. `action` is 0 for the body
    /// and 1 or 2 for an action button; `key` is the name the application gave it.
    ///
    /// A name rather than a handler, because a notification outlives the component that
    /// posted it by hours and a callback dies with its scope.
    NotificationActivated {
        action: u32,
        key: &'a str,
    },
    /// Whether notifications may be shown, sent once after start and then only when the
    /// answer changes.
    NotificationPermissionChanged(NotificationPermission),
    /// One committed edit to a code editor's document.
    ///
    /// The range is in the document as it stood before the edit, and `version` is the
    /// version the edit produced. Lines and columns count from zero and columns are UTF-16
    /// code units, which is what a language server counts in, so the event can be handed
    /// to one unchanged. Text still being composed by an input method never arrives here:
    /// only what the reader committed does.
    CodeChanged {
        version: u32,
        start_line: u32,
        start_column: u32,
        end_line: u32,
        end_column: u32,
        text: &'a str,
    },
    /// An edit the Host asked for and the Renderer did not apply, because the reader had
    /// changed the same place since the version the edit was written against.
    CodeEditRejected {
        request_id: u32,
        base_version: u32,
        current_version: u32,
        start_line: u32,
        start_column: u32,
        end_line: u32,
        end_column: u32,
    },
    /// A pointer came to rest over a place in a code editor, or left it. `decoration` is
    /// the id of the hover anchor under it, or zero where there is none.
    CodeHovered {
        decoration: u64,
        line: u32,
        column: u32,
        phase: HoverPhase,
    },
    /// The reader pressed the platform's save shortcut on a code editor.
    CodeSaveRequested {
        version: u32,
    },
    /// A decoration was pressed or accepted, named by the id the application gave it.
    DecorationActivated {
        decoration: u64,
    },
    /// Something happened to an animation the Renderer is playing, sent only for the kinds
    /// the animation asked for. It names the node the animation plays on and no handler.
    AnimationEvent {
        animation_id: u32,
        kind: AnimationEventKind,
        property: AnimatedProperty,
        slot: u8,
        /// The iteration the animation was in at that moment.
        iteration: u32,
        /// What CSS reports as `elapsedTime`: active time, without the delay, in ms.
        elapsed_ms: f32,
        /// The frame the moment happened in; for `Ready`, the start time it was given.
        time_nanos: u64,
    },
    /// Whether the platform asks for reduced motion, sent once after start and then only
    /// when the answer changes.
    ReducedMotionChanged(ReducedMotion),
    /// Whether the system appearance is light or dark, sent once before the first frame and
    /// then only when it changes. It is sent whatever the theme's `color_scheme` is.
    ColorSchemeChanged(SystemColorScheme),
    /// A pointer did something inside a node that subscribed to it. Coordinates are in dp
    /// from the node's top left corner, `buttons` is what is held now and `button` is the
    /// one that caused a `Down` or an `Up`. `timestamp_nanos` is on the frame time's clock.
    Pointer {
        kind: PointerKind,
        pointer_id: u32,
        pointer_type: PointerType,
        x: f32,
        y: f32,
        buttons: u32,
        button: u32,
        modifiers: u32,
        click_count: u32,
        delta_x: f32,
        delta_y: f32,
        delta_mode: WheelDeltaMode,
        timestamp_nanos: u64,
    },
    /// How large the Renderer is drawing: `k = os × 1.2^level`. Sent once at start and
    /// again whenever any of the three changes. A move to a screen of another density
    /// changes none of them and is not reported.
    ZoomChanged {
        k: f32,
        os: f32,
        level: i32,
    },
    /// The selection of a code editor moved, or an edit moved it. `version` is the document
    /// version it is read against, the same series `CodeChanged` counts, and an edit's
    /// change always arrives first. Columns are UTF-16 units and never fall between the
    /// two halves of a pair.
    SelectionChanged {
        version: u32,
        anchor_line: u32,
        anchor_column: u32,
        active_line: u32,
        active_column: u32,
    },
    /// The lines of a code editor that are on screen changed. Folded lines are skipped, so
    /// `first_line` and `last_line` are the first and last lines the reader can see.
    VisibleRangeChanged {
        version: u32,
        first_line: u32,
        last_line: u32,
    },
    /// A code editor gained or lost the keyboard focus.
    EditorFocusChanged {
        focused: bool,
    },
    /// The reader folded or unfolded the stretch that starts on `start_line`.
    FoldChanged {
        start_line: u32,
        collapsed: bool,
    },
    /// An input method started or ended a composition in a code editor. What is being
    /// composed stays in the Renderer: only the fact crosses.
    CompositionChanged {
        composing: bool,
    },
    /// The user asked to close a window. The window stays until the application removes its
    /// `Window` node. Delivered to the node.
    WindowCloseRequested,
    /// A window became the key window or stopped being it.
    WindowFocusChanged {
        focused: bool,
    },
    /// A window's outer frame moved or changed size, in screen dp. At most once a frame.
    WindowMoved {
        x: f32,
        y: f32,
        width: f32,
        height: f32,
    },
    /// A torn-off window being dragged. `phase` is 1 for a move, 2 for the end and 3 for a
    /// cancel; `over_window` is the node id of the window under the pointer, or 0.
    WindowDrag {
        phase: u32,
        screen_x: f32,
        screen_y: f32,
        over_window: u32,
    },
    /// A dragged window passing over a node that has `OnWindowDragOver`. `kind` is 1 for
    /// enter, 2 for move, 3 for leave and 4 for drop, `window` is the dragged window's node
    /// id, and the position is inside the node, in dp.
    WindowDragOver {
        kind: u32,
        window: u32,
        x: f32,
        y: f32,
    },
    /// A window that could not be opened here: the platform has no second window, or it
    /// refused. Delivered once, to the node.
    WindowUnavailable,
    /// The platform closed a window without asking. The window is already gone.
    WindowClosed,
    /// A window the application has no node for yet, with the `RestoreKey` it was made
    /// under (empty for a new one) and a request number. Delivered to the root.
    WindowRequested {
        key: &'a str,
        request: u32,
    },
    /// The user opened the application again while it had no window. Delivered to the
    /// root.
    ApplicationReopen,
    /// The node or a descendant inside it gained keyboard focus.
    FocusGained,
    /// A key was released while the node held focus.
    KeyUp {
        key: Key,
        shift_key: bool,
        ctrl_key: bool,
        alt_key: bool,
        meta_key: bool,
        /// Always false: a release does not repeat. Present so a key-up carries the same
        /// fields as a key-down.
        repeat: bool,
        /// The physical key as a USB HID usage value, the same on every layout.
        code: u32,
        /// The DOM `key` string, such as `"ArrowDown"` or `"a"`.
        text: &'a str,
    },
    /// The height of one row of a code editor in physical pixels, as it is drawn. Sent when
    /// the editor is first drawn and whenever the height changes.
    CodeMetrics {
        line_height_px: f64,
    },
    /// How far a code editor is scrolled down, in physical pixels. At most once a frame.
    CodeScrolled {
        offset_px: f64,
    },
    /// A file dialog ended. `request` is the number the Host gave it, `filter` is the
    /// position of the filter in use (`u32::MAX` when there is none) and `paths` holds the
    /// chosen paths separated by one NUL byte, empty unless the status is `Chosen`.
    /// Delivered to the Host itself, with no node and no handler.
    FileDialogResult {
        request: u32,
        status: FileDialogStatus,
        filter: u32,
        paths: &'a str,
    },
    /// One clipboard read ended. `request` is the number the Host gave it, `status` is a
    /// word from `clipboard::read_status`, `len` is the text's length in UTF-8 bytes and
    /// `text` the text itself, empty unless the status is text. Delivered to the Host itself,
    /// with no node and no handler.
    ClipboardText {
        request: u32,
        status: u32,
        len: u32,
        text: &'a str,
    },
    /// The one answer to an input or output request: a storage operation the browser
    /// carried out, or an operation on a file picked on the web. `request` is the number
    /// the Host gave it, and `data` is what the operation hands back: a value or a file
    /// that was read, or the keys joined by NUL, and nothing for an operation that only
    /// writes. Delivered to the Host itself, with no node and no handler.
    IoAnswer {
        request: u32,
        status: IoStatus,
        data: &'a [u8],
    },
    /// Files the Renderer now holds handles for: the answer to a file dialog that was
    /// chosen, or to a folder's `Entries` or `Child`. The handles are `first_handle`,
    /// `first_handle + 1` and so on, one per name. `names` holds the names separated by one
    /// NUL byte and `kinds` one letter per name, `f` for a file and `d` for a folder.
    /// `filter` is the position of the filter in use, `u32::MAX` when there is none.
    /// Delivered to the Host itself, with no node and no handler.
    FileHandles {
        request: u32,
        status: FileDialogStatus,
        filter: u32,
        delivery: FileDelivery,
        first_handle: u32,
        names: &'a str,
        kinds: &'a str,
    },
    /// Where the application's storage lives on a platform whose Host cannot work it out
    /// from the environment: Android's application files directory, which only a
    /// `Context` knows. Sent once by that Renderer at start. Delivered to the Host itself.
    StorageLocation(&'a str),
    /// Where a scroll container is, reported by the Renderer to the node's
    /// `OnScrollChanged` handler: at most once a frame while it moves, and once more with
    /// `settled` when it stops. Every length is in physical pixels, the unit the Renderer
    /// scrolls in, so a value read here and sent back in a `ScrollTo` is the same place.
    ///
    /// In a lazy list `item` is the first visible item and the main-axis offset is the
    /// distance into that item; the list does not know its whole length, so its main-axis
    /// `max` is `-1.0`. Elsewhere `item` is 0.
    ScrollChanged {
        item: u32,
        /// The movement ended: a drag, a fling or an animation came to rest.
        settled: bool,
        /// The container can still scroll towards the start of its main axis.
        can_scroll_backward: bool,
        /// The container can still scroll towards the end of its main axis.
        can_scroll_forward: bool,
        x_px: f64,
        y_px: f64,
        max_x_px: f64,
        max_y_px: f64,
        viewport_width_px: f64,
        viewport_height_px: f64,
    },
    /// A node's size motion came to rest, reported to the node's `OnMotionFinished`
    /// handler with the size it settled at, in dp.
    ///
    /// Sent once for each run that reaches its target: a run that is interrupted by a new
    /// target sends nothing, and only the one that settles does. The first layout and a
    /// layout that leaves the size as it was send nothing, and neither does a node removed
    /// while its size is moving. Under reduced motion the size changes in one frame and
    /// this arrives in that frame.
    MotionFinished {
        width_dp: f32,
        height_dp: f32,
    },
    /// Where a code editor draws its caret, in the window's dp with the scroll and the zoom
    /// already in it. At most once a frame, when the caret or the view moves.
    CaretRect {
        line: u32,
        column: u32,
        rect: crate::code::CodeRect,
    },
    /// The answer to one `QueryPositionRect`, carrying the request number the Host gave
    /// it. `None` where the position is not on screen.
    PositionRect {
        request: u32,
        rect: Option<crate::code::CodeRect>,
    },
    /// A pointer event over a code editor: every field a `Pointer` event has, with the same
    /// meaning and the same rules, and the place in the text under the pointer. `position`
    /// is `None` where the pointer is not over a character: over the gutter, past the end
    /// of a line or below the last one.
    CodePointer {
        kind: PointerKind,
        pointer_id: u32,
        pointer_type: PointerType,
        x: f32,
        y: f32,
        buttons: u32,
        button: u32,
        modifiers: u32,
        click_count: u32,
        delta_x: f32,
        delta_y: f32,
        delta_mode: WheelDeltaMode,
        timestamp_nanos: u64,
        position: Option<crate::code::Position>,
    },
    /// Every selection of a code editor, the primary first, read against `version`: sent
    /// while there is more than one, and once more when it comes back to one, to the same
    /// listener as `SelectionChanged`, which goes on reporting the primary alone.
    /// `selections` is 16-byte records, which [`crate::code::SelectionsChange`] reads.
    SelectionsChanged {
        version: u32,
        selections: &'a [u8],
    },
    /// What became of one `EditCodeGroup`, sent exactly once for each. `current_version`
    /// is the version after the last change the group made where it went in, and the
    /// document's version where it did not. `index` is the position in the group, as sent,
    /// of the edit that kept it out, or the number of edits that went in.
    CodeEditGroupResult {
        request_id: u32,
        status: EditGroupStatus,
        base_version: u32,
        current_version: u32,
        index: u32,
    },
}

/// A rectangle in physical pixels, for [`ScrollTarget`].
#[derive(Clone, Copy, Debug, Default, PartialEq)]
pub struct Rect {
    pub x_px: f64,
    pub y_px: f64,
    pub width_px: f64,
    pub height_px: f64,
}

impl Rect {
    pub const fn new(x_px: f64, y_px: f64, width_px: f64, height_px: f64) -> Self {
        Self {
            x_px,
            y_px,
            width_px,
            height_px,
        }
    }
}

/// A request to scroll a container to an offset, written by `Batch::scroll_to`.
///
/// An axis left `None` is not touched, so setting one axis never sends a stale value for
/// the other. The Renderer keeps each value inside the range the content allows, and
/// ignores the request while the user is dragging or flinging the container.
#[derive(Clone, Copy, Debug, Default, PartialEq)]
pub struct ScrollTo {
    pub x_px: Option<f64>,
    pub y_px: Option<f64>,
    /// In a lazy list, the item the offset is measured from. 0 everywhere else.
    pub item: u32,
    pub animate: bool,
}

/// How a rectangle is brought into view along one axis: CSS's `block` and `inline` values,
/// and `Keep` for an axis that must not move.
#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
#[repr(u16)]
pub enum ScrollAlign {
    /// The axis does not move.
    #[default]
    Keep = 0,
    Start = 1,
    Center = 2,
    End = 3,
    /// No movement when the rectangle is already in view, otherwise the smallest one that
    /// shows it. A rectangle larger than the viewport is aligned to its start.
    Nearest = 4,
}

/// What a `ScrollIntoView` rectangle is measured from.
#[derive(Clone, Copy, Debug, PartialEq)]
pub enum ScrollTarget {
    /// The container's content: the origin is the content's top left at offset zero. Not
    /// for a lazy list, which has no content coordinates.
    Content(Rect),
    /// A descendant node of the container: the origin is that node's top left, and a
    /// rectangle with no width and no height means the whole node.
    Node(u32, Rect),
    /// An item of a lazy list by its index: the origin is the item's start, and a rectangle
    /// with no width and no height means the whole item.
    Item(u32, Rect),
}

/// A request to bring a rectangle into view in one container, written by
/// `Batch::scroll_into_view`.
#[derive(Clone, Copy, Debug, PartialEq)]
pub struct ScrollIntoView {
    pub target: ScrollTarget,
    pub align_x: ScrollAlign,
    pub align_y: ScrollAlign,
    pub animate: bool,
}

/// The bits of a `ScrollTo` record's flags word.
pub mod scroll_to_flags {
    pub const ANIMATE: u32 = 1;
    pub const X: u32 = 1 << 1;
    pub const Y: u32 = 1 << 2;
}

/// The values of a `ScrollIntoView` record's target kind.
pub mod scroll_target_kind {
    pub const CONTENT: u16 = 0;
    pub const NODE: u16 = 1;
    pub const ITEM: u16 = 2;
}

/// The bit of a `ScrollIntoView` record's flags.
pub mod scroll_into_view_flags {
    pub const ANIMATE: u16 = 1;
}

/// The bits of a `ScrollChanged` event's flags word.
pub mod scroll_changed_flags {
    pub const SETTLED: u32 = 1;
    pub const CAN_SCROLL_BACKWARD: u32 = 1 << 1;
    pub const CAN_SCROLL_FORWARD: u32 = 1 << 2;
    /// Every bit that has a meaning. Any other bit set is a protocol error.
    pub const KNOWN: u32 = SETTLED | CAN_SCROLL_BACKWARD | CAN_SCROLL_FORWARD;
}

pub const EVENT_SCHEMA: &[EventSchema] = &[
    EventSchema {
        name: "Clicked",
        tag: 1,
        payload: EventPayloadType::None,
    },
    EventSchema {
        name: "TextChanged",
        tag: 2,
        payload: EventPayloadType::Text,
    },
    EventSchema {
        name: "TextSubmitted",
        tag: 3,
        payload: EventPayloadType::Text,
    },
    EventSchema {
        name: "FocusLost",
        tag: 4,
        payload: EventPayloadType::None,
    },
    EventSchema {
        name: "ProtocolError",
        tag: 5,
        payload: EventPayloadType::ProtocolError,
    },
    EventSchema {
        name: "KeyDown",
        tag: 6,
        payload: EventPayloadType::KeyDown,
    },
    EventSchema {
        name: "RangeRequested",
        tag: 7,
        payload: EventPayloadType::Range,
    },
    EventSchema {
        name: "ValueChanged",
        // Tag 8 is the pointer event and 9 to 15 are reserved for the gesture events.
        tag: 16,
        payload: EventPayloadType::Double,
    },
    EventSchema {
        name: "WindowSizeChanged",
        tag: 17,
        payload: EventPayloadType::WindowSize,
    },
    // The three below address the Host itself rather than a node, so they carry no handler
    // and the Host answers them before it looks one up.
    EventSchema {
        name: "Resync",
        tag: 18,
        payload: EventPayloadType::None,
    },
    EventSchema {
        name: "LifecycleStart",
        tag: 19,
        payload: EventPayloadType::None,
    },
    EventSchema {
        name: "LifecycleStop",
        tag: 20,
        payload: EventPayloadType::None,
    },
    // Addressed to the Host rather than to a node, like the three above: it is a fact
    // about the window, not something that happened inside it.
    EventSchema {
        name: "DesignSystemResolved",
        tag: 21,
        payload: EventPayloadType::DesignSystem,
    },
    EventSchema {
        name: "FilesEntered",
        tag: 22,
        payload: EventPayloadType::None,
    },
    // One string for however many paths, which is the string convention unchanged. A
    // second way of carrying a list would be a second thing to keep in step.
    EventSchema {
        name: "FilesDropped",
        tag: 23,
        payload: EventPayloadType::Text,
    },
    // Both address the Host itself, like the resolved design system: a notification is not
    // in the tree, so there is no node and no handler to name.
    EventSchema {
        name: "NotificationActivated",
        tag: 24,
        payload: EventPayloadType::NotificationActivation,
    },
    EventSchema {
        name: "NotificationPermissionChanged",
        tag: 25,
        payload: EventPayloadType::NotificationPermission,
    },
    EventSchema {
        name: "CodeChanged",
        tag: 26,
        payload: EventPayloadType::CodeChange,
    },
    EventSchema {
        name: "CodeEditRejected",
        tag: 27,
        payload: EventPayloadType::CodeEditRejected,
    },
    EventSchema {
        name: "CodeHovered",
        tag: 28,
        payload: EventPayloadType::CodeHover,
    },
    EventSchema {
        name: "CodeSaveRequested",
        tag: 29,
        payload: EventPayloadType::CodeSave,
    },
    EventSchema {
        name: "DecorationActivated",
        tag: 30,
        payload: EventPayloadType::Decoration,
    },
    EventSchema {
        name: "AnimationEvent",
        tag: 31,
        payload: EventPayloadType::Animation,
    },
    // About the platform rather than a node, like the notification permission.
    EventSchema {
        name: "ReducedMotionChanged",
        tag: 32,
        payload: EventPayloadType::ReducedMotion,
    },
    // Tag 8 is the pointer event and 9 stays reserved. It is listed last because this table
    // is append only, not because its tag is the highest.
    EventSchema {
        name: "Pointer",
        tag: 8,
        payload: EventPayloadType::Pointer,
    },
    // Tags 26 to 32 are taken by events other requirements have numbered.
    EventSchema {
        name: "ZoomChanged",
        tag: 33,
        payload: EventPayloadType::Zoom,
    },
    EventSchema {
        name: "SelectionChanged",
        tag: 34,
        payload: EventPayloadType::CodeSelection,
    },
    EventSchema {
        name: "VisibleRangeChanged",
        tag: 35,
        payload: EventPayloadType::CodeVisibleRange,
    },
    EventSchema {
        name: "EditorFocusChanged",
        tag: 36,
        payload: EventPayloadType::CodeFocus,
    },
    EventSchema {
        name: "FoldChanged",
        tag: 37,
        payload: EventPayloadType::CodeFold,
    },
    EventSchema {
        name: "CompositionChanged",
        tag: 38,
        payload: EventPayloadType::CodeComposition,
    },
    EventSchema {
        name: "WindowCloseRequested",
        tag: 39,
        payload: EventPayloadType::None,
    },
    EventSchema {
        name: "WindowFocusChanged",
        tag: 40,
        payload: EventPayloadType::WindowFocus,
    },
    EventSchema {
        name: "WindowMoved",
        tag: 41,
        payload: EventPayloadType::WindowMove,
    },
    EventSchema {
        name: "WindowDrag",
        tag: 42,
        payload: EventPayloadType::WindowDrag,
    },
    EventSchema {
        name: "WindowDragOver",
        tag: 43,
        payload: EventPayloadType::WindowDragOver,
    },
    EventSchema {
        name: "WindowUnavailable",
        tag: 44,
        payload: EventPayloadType::None,
    },
    EventSchema {
        name: "WindowClosed",
        tag: 45,
        payload: EventPayloadType::None,
    },
    EventSchema {
        name: "WindowRequested",
        tag: 46,
        payload: EventPayloadType::WindowRequest,
    },
    EventSchema {
        name: "ApplicationReopen",
        tag: 47,
        payload: EventPayloadType::None,
    },
    EventSchema {
        name: "FocusGained",
        tag: 48,
        payload: EventPayloadType::None,
    },
    EventSchema {
        name: "KeyUp",
        tag: 49,
        payload: EventPayloadType::KeyDown,
    },
    // Like the notification events this addresses the Host itself: a dialog is not in the tree, so there is no
    // node and no handler to name, and the request number finds the callback.
    EventSchema {
        name: "FileDialogResult",
        tag: 50,
        payload: EventPayloadType::FileDialogResult,
    },
    // What became of a grouped edit of a code editor, reported to the editor's own handler.
    EventSchema {
        name: "CodeEditGroupResult",
        tag: 51,
        payload: EventPayloadType::CodeEditGroupResult,
    },
    // Tags 52 and 53 are held by events other requirements have numbered. Like a file
    // dialog's end, a clipboard read addresses the Host itself and is found by its request
    // number.
    EventSchema {
        name: "ClipboardText",
        tag: 56,
        payload: EventPayloadType::ClipboardText,
    },
    // The answer to a storage operation, and to a file operation on the web.
    EventSchema {
        name: "IoAnswer",
        tag: 57,
        payload: EventPayloadType::IoAnswer,
    },
    // Files a dialog, or a folder, handed the Renderer handles for.
    EventSchema {
        name: "FileHandles",
        tag: 58,
        payload: EventPayloadType::FileHandles,
    },
    // Android's files directory, which the Host cannot find on its own. A string, like a
    // text change, so it needs no payload type of its own.
    EventSchema {
        name: "StorageLocation",
        tag: 59,
        payload: EventPayloadType::Text,
    },
    // Where a scroll container is, reported to the node's own handler.
    EventSchema {
        name: "ScrollChanged",
        tag: 60,
        payload: EventPayloadType::ScrollChanged,
    },
    // 51 to 53 are numbered for events that are not here yet. Both of these carry one
    // `f64` of physical pixels, the shape `ValueChanged` has.
    EventSchema {
        name: "CodeMetrics",
        tag: 54,
        payload: EventPayloadType::Double,
    },
    EventSchema {
        name: "CodeScrolled",
        tag: 55,
        payload: EventPayloadType::Double,
    },
    // A node's size motion settled, reported to the node's own handler. 61 and 62 are
    // numbered for events that are not here yet.
    EventSchema {
        name: "MotionFinished",
        tag: 63,
        payload: EventPayloadType::MotionFinished,
    },
    // Where a code editor's caret is drawn,
    // and the answer to a question about where a position is.
    EventSchema {
        name: "CaretRect",
        tag: 64,
        payload: EventPayloadType::CodeCaretRect,
    },
    EventSchema {
        name: "PositionRect",
        tag: 65,
        payload: EventPayloadType::CodePositionRect,
    },
    // A pointer over a code editor, with the place in the text under it.
    EventSchema {
        name: "CodePointer",
        tag: 66,
        payload: EventPayloadType::CodePointer,
    },
    // About the platform rather than a node, like the reduced motion setting.
    EventSchema {
        name: "ColorSchemeChanged",
        tag: 52,
        payload: EventPayloadType::ColorScheme,
    },
    // Every selection of a code editor, to its selection listener.
    EventSchema {
        name: "SelectionsChanged",
        tag: 67,
        payload: EventPayloadType::CodeSelections,
    },
];

/// One argument of a boundary operation.
///
/// The set is deliberately tiny, because only primitives, pointers and lengths cross the
/// boundary. Every platform binding can then be generated from the same list.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum BoundaryParam {
    /// A readable byte range. It arrives as a direct byte buffer and a length on Android,
    /// as a pointer and a length on desktop.
    Bytes { name: &'static str },
    /// A 64-bit platform frame timestamp.
    Nanos { name: &'static str },
}

impl BoundaryParam {
    pub const fn name(self) -> &'static str {
        match self {
            Self::Bytes { name } | Self::Nanos { name } => name,
        }
    }
}

/// One logical boundary operation, stated without saying which side calls it.
///
/// `symbol` is the Host's C export. Every platform binding, the GraalVM function
/// declarations, the Android shims and the browser's imports and trampoline, is a rendering
/// of this table, which is why none of them is written by hand.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct BoundaryOp {
    /// Direction-neutral name, in PascalCase.
    pub name: &'static str,
    pub symbol: &'static str,
    pub params: &'static [BoundaryParam],
    /// Whether the operation answers with a mutation batch.
    pub returns_batch: bool,
    /// Whether the call may skip the runtime's thread state transition on Android. That
    /// is only sound for a call that cannot run long, because the thread stays runnable
    /// and the garbage collector cannot suspend it while the call is in flight. A call
    /// that runs the VirtualDom can run long.
    pub fast: bool,
}

pub const BOUNDARY_SCHEMA: &[BoundaryOp] = &[
    BoundaryOp {
        name: "Init",
        symbol: "compose_rust_host_init",
        params: &[BoundaryParam::Bytes { name: "handshake" }],
        returns_batch: true,
        fast: false,
    },
    BoundaryOp {
        name: "DispatchEvent",
        symbol: "compose_rust_host_dispatch_event",
        params: &[BoundaryParam::Bytes { name: "event" }],
        returns_batch: true,
        fast: false,
    },
    BoundaryOp {
        name: "RenderFrame",
        symbol: "compose_rust_host_render_frame",
        params: &[BoundaryParam::Nanos {
            name: "frameTimeNanos",
        }],
        returns_batch: true,
        fast: false,
    },
    BoundaryOp {
        name: "ReleaseBatch",
        symbol: "compose_rust_host_release_batch",
        params: &[],
        returns_batch: false,
        fast: true,
    },
    BoundaryOp {
        name: "Shutdown",
        symbol: "compose_rust_host_shutdown",
        params: &[],
        returns_batch: false,
        fast: false,
    },
];

/// The JVM class the Android shims bind to. The Kotlin file is generated under the same
/// name, so the two sides cannot drift.
pub const ANDROID_BRIDGE_CLASS: &str = "dev/darkpyonix/composerust/ui/platform/HostBridge";

// ---------------------------------------------------------------------------------------
// The browser's shared linear memory.
//
// One `WebAssembly.Memory` holds both modules' data. The Kotlin module defines and exports
// it, because a Kotlin/Wasm module has no way to import one, and the Rust module is linked
// with `--import-memory` so that the arena the Host writes is the arena the Renderer reads.
// Nothing below crosses the boundary as data: these are the addresses and offsets both
// generated halves are written against.
// ---------------------------------------------------------------------------------------

/// The first address that belongs to the Rust module.
///
/// Below it is the Kotlin module's `kotlin.wasm.unsafe` allocator; at and above it are the
/// Rust module's data, stack and heap, which the linker is told with `--global-base`. Two
/// allocators handing out addresses in one memory is the hazard: an overlap does not crash,
/// it draws the wrong screen, so the Renderer checks which side of this line its own
/// addresses fall on before it makes the first boundary call.
pub const WEB_RUST_REGION_BASE: u32 = 4 * 1024 * 1024;

/// One field of the `MutationBatch` record the Host writes into the shared memory.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct WebBatchField {
    /// PascalCase, so the generated Kotlin constant reads as a name rather than an offset.
    pub name: &'static str,
    pub offset: u32,
    pub width: u32,
    pub description: &'static str,
}

/// `MutationBatch` as a wasm32 target lays it out.
///
/// The offsets are written down rather than read from `offset_of!` because codegen runs on
/// the machine that generates, not the machine that runs: a 64-bit host makes the same
/// `#[repr(C)]` struct 24 bytes with an 8 byte pointer. The generated wasm glue asserts
/// this table against the real layout, so a compiler that disagrees stops that build
/// instead of producing a Renderer that reads the wrong four bytes.
pub const WEB_BATCH_FIELDS: &[WebBatchField] = &[
    WebBatchField {
        name: "Address",
        offset: 0,
        width: 4,
        description: "where the batch starts, as an address in the shared memory",
    },
    WebBatchField {
        name: "Length",
        offset: 4,
        width: 4,
        description: "the batch's length in bytes",
    },
    WebBatchField {
        name: "Result",
        offset: 8,
        width: 8,
        description: "the handler's synchronous result",
    },
];

/// How long that record is, including the padding `#[repr(C)]` adds before the result.
pub const WEB_BATCH_BYTES: u32 = 16;

/// How much room the Host lends the Renderer to encode one event into.
///
/// The same figure the Android connection allocates for the same job. An event that would
/// not fit is refused by the encoder rather than truncated.
pub const WEB_EVENT_BUFFER_BYTES: u32 = 4096;

/// The largest event buffer the Host lends a browser Renderer.
///
/// An event that does not fit in the first buffer is encoded into a larger one the Host
/// lends on request, doubling each time, and this is where the doubling stops. An event
/// larger than this is refused rather than cut short: a single event that large is a bug
/// in whatever produced it, and lending without a ceiling would turn that bug into running
/// out of memory. The other platforms grow their own buffers to the same ceiling.
pub const WEB_EVENT_BUFFER_MAX_BYTES: u32 = 64 * 1024 * 1024;

/// The Host export a browser Renderer borrows a larger event buffer from.
///
/// It is setup, like `compose_rust_host_web_start`, not a boundary operation: the
/// Renderer calls it only when an event outgrows the buffer it has, and keeps what it gets.
/// It goes through the trampoline like the boundary operations, in the slot after theirs.
pub const WEB_LEND_EVENT_BUFFER_SYMBOL: &str = "compose_rust_host_web_lend_event_buffer";

/// Where the event buffer starts inside the block `compose_rust_host_web_start` reports.
///
/// The out record comes first, at offset zero, and the event buffer follows it.
pub const WEB_EVENT_BUFFER_OFFSET: u32 = WEB_BATCH_BYTES;

/// The extra Host export a browser needs, because a page has no library loader.
///
/// It does what `JNI_OnLoad` does on Android, registering the root component and installing
/// the renderer API, and it answers with the address of the block above.
pub const WEB_START_SYMBOL: &str = "compose_rust_host_web_start";

/// The wasm import module the Host's frame request comes from.
///
/// This direction has no JavaScript on it: the page hands Kotlin's exported function object
/// straight to the Rust instantiation, which the engine binds as a wasm-to-wasm call. It can,
/// because Rust is instantiated second and Kotlin's exports already exist by then.
pub const WEB_RENDERER_IMPORT_MODULE: &str = "compose_rust_renderer";

/// The global the loader publishes the trampoline's table under.
///
/// The loader creates the table and the Renderer's generated `installHost` fills it with the
/// Host's exports. That body is a `@JsFun`, inlined into the import object module Kotlin
/// generates, so the only name it can reach the loader's table through is a property of the
/// global object. Nothing reads it on a call: a call goes through the table from wasm.
pub const WEB_TABLE_GLOBAL: &str = "__composeRustHostTable";

/// The global the loader module publishes the compiled Host module under.
///
/// Besides the trampoline, compiling is all the page does, and the reason the page has to
/// do it at all is that compiling is asynchronous while the boundary is not: the fetch has
/// to have finished before the Renderer's `main` runs. Everything after it, the memory, the
/// Host's imports, the entry point and filling the table, is in the generated Kotlin,
/// because only the Renderer's own module can name them.
pub const WEB_MODULE_GLOBAL: &str = "__composeRustHostModule";