cranpose_ui/modifier/

slices.rs

use std::{fmt, mem::size_of, rc::Rc};

use cranpose_foundation::{ModifierNodeChain, NodeCapabilities, PointerEvent, PointerEventKind};
use cranpose_ui_graphics::{
    ColorFilter, EdgeInsets, GraphicsLayer, LayerShape, PointerIcon, RenderEffect,
    RoundedCornerShape,
};

use super::{ModifierChainHandle, Point};
use crate::{
    draw::DrawCommand,
    modifier::{
        Modifier,
        scroll::{MotionContextAnimatedNode, TranslatedContentContextNode},
    },
    modifier_nodes::{
        BackgroundNode, ClipToBoundsNode, CornerShapeNode, DrawCommandNode, GraphicsLayerNode,
        PaddingNode, PointerIconNode, SelectableTextNode, WindowRectReporterNode,
    },
    text::{TextLayoutOptions, TextStyle},
    text_field_modifier_node::{TextFieldLayoutHandle, TextFieldModifierNode, TextPanResolver},
    text_modifier_node::{TextModifierNode, TextPreparedLayoutHandle},
};

/// Snapshot of modifier node slices that impact draw and pointer subsystems.
#[derive(Default)]
pub struct ModifierNodeSlices {
    draw_commands: Vec<DrawCommand>,
    layer_draw_boundary: Option<usize>,
    pointer_inputs: Vec<Rc<dyn Fn(PointerEvent)>>,
    pointer_input_sizes: Vec<Rc<std::cell::Cell<cranpose_ui_graphics::Size>>>,
    click_handlers: Vec<Rc<dyn Fn(Point)>>,
    pointer_icon: Option<PointerIcon>,
    clip_to_bounds: bool,
    motion_context_animated: bool,
    translated_content_context: bool,
    translated_content_context_identity: Option<usize>,
    translated_content_offset_reader: Option<Rc<dyn Fn() -> Point>>,
    text_content: Option<Rc<crate::text::AnnotatedString>>,
    text_style: Option<TextStyle>,
    text_layout_options: Option<TextLayoutOptions>,
    prepared_text_layout: Option<MeasuredTextLayoutSource>,
    text_pan: Option<TextPanResolver>,
    text_window_origin: Option<Rc<std::cell::Cell<Point>>>,
    viewport_window_rect: Option<Rc<dyn crate::modifier_nodes::WindowRectSink>>,
    graphics_layer: Option<GraphicsLayer>,
    graphics_layer_resolver: Option<Rc<dyn Fn() -> GraphicsLayer>>,
    corner_shape: Option<RoundedCornerShape>,
    chain_guard: Option<Rc<ChainGuard>>,
}

struct ChainGuard {
    _handle: ModifierChainHandle,
}

#[derive(Clone)]
enum MeasuredTextLayoutSource {
    Text(TextPreparedLayoutHandle),
    TextField(TextFieldLayoutHandle),
}

#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub struct ModifierNodeSlicesDebugStats {
    pub draw_command_count: usize,
    pub draw_command_capacity: usize,
    pub pointer_input_count: usize,
    pub pointer_input_capacity: usize,
    pub click_handler_count: usize,
    pub click_handler_capacity: usize,
    pub has_text_content: bool,
    pub has_text_style: bool,
    pub has_text_layout_options: bool,
    pub has_prepared_text_layout: bool,
    pub has_graphics_layer: bool,
    pub has_graphics_layer_resolver: bool,
    pub heap_bytes: usize,
}

impl Clone for ModifierNodeSlices {
    fn clone(&self) -> Self {
        Self {
            draw_commands: self.draw_commands.clone(),
            layer_draw_boundary: self.layer_draw_boundary,
            pointer_inputs: self.pointer_inputs.clone(),
            pointer_input_sizes: self.pointer_input_sizes.clone(),
            click_handlers: self.click_handlers.clone(),
            pointer_icon: self.pointer_icon.clone(),
            clip_to_bounds: self.clip_to_bounds,
            motion_context_animated: self.motion_context_animated,
            translated_content_context: self.translated_content_context,
            translated_content_context_identity: self.translated_content_context_identity,
            translated_content_offset_reader: self.translated_content_offset_reader.clone(),
            text_content: self.text_content.clone(),
            text_style: self.text_style.clone(),
            text_layout_options: self.text_layout_options,
            prepared_text_layout: self.prepared_text_layout.clone(),
            text_pan: self.text_pan.clone(),
            text_window_origin: self.text_window_origin.clone(),
            viewport_window_rect: self.viewport_window_rect.clone(),
            graphics_layer: self.graphics_layer.clone(),
            graphics_layer_resolver: self.graphics_layer_resolver.clone(),
            corner_shape: self.corner_shape,
            chain_guard: self.chain_guard.clone(),
        }
    }
}

fn merge_graphics_layers(base: GraphicsLayer, overlay: GraphicsLayer) -> GraphicsLayer {
    GraphicsLayer {
        alpha: (base.alpha * overlay.alpha).clamp(0.0, 1.0),
        scale: base.scale * overlay.scale,
        scale_x: base.scale_x * overlay.scale_x,
        scale_y: base.scale_y * overlay.scale_y,
        rotation_x: base.rotation_x + overlay.rotation_x,
        rotation_y: base.rotation_y + overlay.rotation_y,
        rotation_z: base.rotation_z + overlay.rotation_z,
        camera_distance: transform_frame(&base, &overlay).camera_distance,
        transform_origin: transform_frame(&base, &overlay).transform_origin,
        translation_x: base.translation_x + overlay.translation_x,
        translation_y: base.translation_y + overlay.translation_y,
        shadow_elevation: overlay.shadow_elevation,
        ambient_shadow_color: overlay.ambient_shadow_color,
        spot_shadow_color: overlay.spot_shadow_color,
        shape: merged_layer_shape(&base, &overlay),
        clip: base.clip || overlay.clip,
        compositing_strategy: overlay.compositing_strategy,
        blend_mode: overlay.blend_mode,
        color_filter: compose_color_filters(base.color_filter, overlay.color_filter),
        render_effect: compose_render_effects(base.render_effect, overlay.render_effect),
        backdrop_effect: overlay.backdrop_effect.or(base.backdrop_effect),
    }
}

/// Which of two stacked layers merged into one frames the merged transform:
/// the later layer when it rotates or scales itself, else the earlier one. A
/// layer that neither rotates nor scales, such as a glass surface under a
/// tilt, leaves its camera and pivot at their defaults, and those would
/// replace the tilt's own.
fn transform_frame<'a>(base: &'a GraphicsLayer, overlay: &'a GraphicsLayer) -> &'a GraphicsLayer {
    let transforms = |layer: &GraphicsLayer| {
        layer.rotation_x != 0.0
            || layer.rotation_y != 0.0
            || layer.rotation_z != 0.0
            || layer.scale != 1.0
            || layer.scale_x != 1.0
            || layer.scale_y != 1.0
    };
    if transforms(overlay) || !transforms(base) {
        overlay
    } else {
        base
    }
}

/// The shape of two stacked layers merged into one: the layer that clips
/// owns it, else the layer that carries the backdrop (its effect covers that
/// shape), else the later layer, whose default resets it like every other
/// parent-local field.
fn merged_layer_shape(base: &GraphicsLayer, overlay: &GraphicsLayer) -> LayerShape {
    if overlay.clip || (!base.clip && overlay.backdrop_effect.is_some()) {
        overlay.shape
    } else if base.clip || base.backdrop_effect.is_some() {
        base.shape
    } else {
        overlay.shape
    }
}

fn compose_render_effects(
    outer: Option<RenderEffect>,
    inner: Option<RenderEffect>,
) -> Option<RenderEffect> {
    match (outer, inner) {
        (None, None) => None,
        (Some(effect), None) | (None, Some(effect)) => Some(effect),
        (Some(outer_effect), Some(inner_effect)) => Some(inner_effect.then(outer_effect)),
    }
}

fn compose_color_filters(
    base: Option<ColorFilter>,
    overlay: Option<ColorFilter>,
) -> Option<ColorFilter> {
    match (base, overlay) {
        (None, None) => None,
        (Some(filter), None) | (None, Some(filter)) => Some(filter),
        (Some(filter), Some(next)) => Some(filter.compose(next)),
    }
}

impl ModifierNodeSlices {
    pub fn draw_commands(&self) -> &[DrawCommand] {
        &self.draw_commands
    }

    /// How many leading [`draw_commands`](Self::draw_commands) come from
    /// modifiers chained before the node's graphics layer or clip. Those draw
    /// around the layer in the parent's space, outside its clip, alpha and
    /// transform, exactly as an outer `drawBehind` wraps a `graphicsLayer`.
    pub fn outer_draw_command_count(&self) -> usize {
        self.layer_draw_boundary.unwrap_or(0)
    }

    fn insert_background_draw(
        &mut self,
        insert_index: Option<usize>,
        precedes_layer: bool,
        command: DrawCommand,
    ) {
        let insert_index = insert_index.unwrap_or(0).min(self.draw_commands.len());
        self.draw_commands.insert(insert_index, command);
        if let Some(boundary) = self.layer_draw_boundary.as_mut()
            && precedes_layer
        {
            *boundary += 1;
        }
    }

    fn mark_layer_draw_boundary(&mut self) {
        if self.layer_draw_boundary.is_none() {
            self.layer_draw_boundary = Some(self.draw_commands.len());
        }
    }

    pub fn pointer_inputs(&self) -> &[Rc<dyn Fn(PointerEvent)>] {
        &self.pointer_inputs
    }

    /// Dispatches an event whose position is already local to this layout node.
    /// Consumed events stop propagation except for release and cancellation,
    /// which reach every handler so each can finish its active interaction.
    pub fn dispatch_pointer_event(&self, event: PointerEvent) {
        let terminal = matches!(event.kind, PointerEventKind::Up | PointerEventKind::Cancel);
        for handler in &self.pointer_inputs {
            if event.is_consumed() && !terminal {
                break;
            }
            handler(event.clone());
        }
        if event.kind == PointerEventKind::Down && !event.is_consumed() {
            for handler in &self.click_handlers {
                handler(event.position);
            }
        }
    }

    /// The write targets for this node's resolved size, one per pointer-input
    /// node that exposes a size to its handler. See
    /// [`ModifierNodeSlices::publish_pointer_input_size`].
    pub fn pointer_input_size_sinks(&self) -> &[Rc<std::cell::Cell<cranpose_ui_graphics::Size>>] {
        &self.pointer_input_sizes
    }

    /// Publishes this layout node's resolved size to every pointer-input
    /// handler attached to it, so `PointerInputScope::size()` reports the
    /// node's real dimensions.
    ///
    /// Called by every pass that resolves a node's geometry (the layout `place`
    /// passes and the per-frame scene build), so the size is current before any
    /// pointer event for that frame is dispatched and tracks resizes.
    ///
    /// `size` is the node's layout box — the same box the dispatched
    /// [`PointerEvent`] positions are made local to — so handlers can compare
    /// event coordinates against it directly.
    pub fn publish_pointer_input_size(&self, size: cranpose_ui_graphics::Size) {
        for sink in &self.pointer_input_sizes {
            sink.set(size);
        }
    }

    pub fn click_handlers(&self) -> &[Rc<dyn Fn(Point)>] {
        &self.click_handlers
    }

    /// The pointer's appearance over this node, when a `pointer_icon`
    /// modifier names one. The innermost declaration in the chain wins.
    pub fn pointer_icon(&self) -> Option<&PointerIcon> {
        self.pointer_icon.as_ref()
    }

    pub fn clip_to_bounds(&self) -> bool {
        self.clip_to_bounds
    }

    pub fn motion_context_animated(&self) -> bool {
        self.motion_context_animated
    }

    pub fn translated_content_context(&self) -> bool {
        self.translated_content_context
    }

    pub fn translated_content_context_identity(&self) -> Option<usize> {
        self.translated_content_context_identity
    }

    pub fn translated_content_offset(&self) -> Option<Point> {
        self.translated_content_offset_reader
            .as_ref()
            .map(|reader| reader())
    }

    pub fn text_content(&self) -> Option<&str> {
        self.text_content.as_ref().map(|a| a.text.as_str())
    }

    pub fn annotated_text(&self) -> Option<&crate::text::AnnotatedString> {
        self.text_content.as_deref()
    }

    pub fn text_style(&self) -> Option<&TextStyle> {
        self.text_style.as_ref()
    }

    pub fn text_layout_options(&self) -> Option<TextLayoutOptions> {
        self.text_layout_options
    }

    /// Returns the horizontal pan resolver for single-line text fields.
    ///
    /// The resolver takes the content viewport width (px) and returns the
    /// horizontal scroll offset that keeps the cursor visible. Renderers
    /// subtract this offset from the text origin so the glyphs pan together
    /// with the cursor and selection.
    pub fn text_pan_resolver(&self) -> Option<TextPanResolver> {
        self.text_pan.clone()
    }

    /// The write target for the composited window origin of the text this
    /// node shows, if it is a `BasicTextField` or a `Text` inside a
    /// `SelectionContainer`. The layout pass writes the node's true on-screen
    /// top-left here so selection handles and pointers find the text across
    /// scroll.
    pub fn text_window_origin(&self) -> Option<Rc<std::cell::Cell<Point>>> {
        self.text_window_origin.clone()
    }

    /// The write target for a scroll container's composited window rect, if this
    /// node carries a `report_window_rect` modifier. The layout pass writes the
    /// node's true on-screen viewport rect here so a `BringIntoViewResponder`
    /// can scroll a focused field's caret above the soft keyboard.
    pub fn viewport_window_rect(&self) -> Option<Rc<dyn crate::modifier_nodes::WindowRectSink>> {
        self.viewport_window_rect.clone()
    }

    /// Returns the text layout this node's `Text` or text field produced when
    /// layout last measured it, laid out at the same width.
    ///
    /// A text field's layout is its current text wrapped at the width its
    /// caret and selection are placed on. `None` when the node carries no text,
    /// or carries a `Text` that has not been measured yet.
    pub fn measured_text_layout(&self) -> Option<Rc<crate::text::PreparedTextLayout>> {
        match self.prepared_text_layout.as_ref()? {
            MeasuredTextLayoutSource::Text(handle) => handle.measured_layout(),
            MeasuredTextLayoutSource::TextField(handle) => {
                Some(handle.measured_layout(self.text_style.as_ref()?))
            }
        }
    }

    pub fn graphics_layer(&self) -> Option<GraphicsLayer> {
        if let Some(resolve) = &self.graphics_layer_resolver {
            Some(resolve())
        } else {
            self.graphics_layer.clone()
        }
    }

    pub fn corner_shape(&self) -> Option<RoundedCornerShape> {
        self.corner_shape
    }

    fn push_graphics_layer(
        &mut self,
        layer: GraphicsLayer,
        resolver: Option<Rc<dyn Fn() -> GraphicsLayer>>,
    ) {
        let existing_snapshot = self.graphics_layer.clone();
        let next_snapshot = existing_snapshot.as_ref().map_or_else(
            || layer.clone(),
            |current| merge_graphics_layers(current.clone(), layer.clone()),
        );
        let existing_resolver = self.graphics_layer_resolver.clone();

        self.graphics_layer = Some(next_snapshot);
        self.graphics_layer_resolver = match (existing_resolver, resolver) {
            (None, None) => None,
            (Some(current_resolver), None) => Some(Rc::new(move || {
                merge_graphics_layers(current_resolver(), layer.clone())
            })),
            (None, Some(next_resolver)) => {
                let base = existing_snapshot.unwrap_or_default();
                Some(Rc::new(move || {
                    merge_graphics_layers(base.clone(), next_resolver())
                }))
            }
            (Some(current_resolver), Some(next_resolver)) => Some(Rc::new(move || {
                merge_graphics_layers(current_resolver(), next_resolver())
            })),
        };
    }

    pub fn with_chain_guard(mut self, handle: ModifierChainHandle) -> Self {
        self.chain_guard = Some(Rc::new(ChainGuard { _handle: handle }));
        self
    }

    pub fn debug_stats(&self) -> ModifierNodeSlicesDebugStats {
        let draw_command_bytes = self.draw_commands.capacity() * size_of::<DrawCommand>();
        let pointer_input_bytes =
            self.pointer_inputs.capacity() * size_of::<Rc<dyn Fn(PointerEvent)>>();
        let click_handler_bytes = self.click_handlers.capacity() * size_of::<Rc<dyn Fn(Point)>>();
        ModifierNodeSlicesDebugStats {
            draw_command_count: self.draw_commands.len(),
            draw_command_capacity: self.draw_commands.capacity(),
            pointer_input_count: self.pointer_inputs.len(),
            pointer_input_capacity: self.pointer_inputs.capacity(),
            click_handler_count: self.click_handlers.len(),
            click_handler_capacity: self.click_handlers.capacity(),
            has_text_content: self.text_content.is_some(),
            has_text_style: self.text_style.is_some(),
            has_text_layout_options: self.text_layout_options.is_some(),
            has_prepared_text_layout: self.prepared_text_layout.is_some(),
            has_graphics_layer: self.graphics_layer.is_some(),
            has_graphics_layer_resolver: self.graphics_layer_resolver.is_some(),
            heap_bytes: draw_command_bytes + pointer_input_bytes + click_handler_bytes,
        }
    }

    /// Resets the slice collection for reuse, retaining vector capacity.
    pub fn clear(&mut self) {
        self.draw_commands.clear();
        self.layer_draw_boundary = None;
        self.pointer_inputs.clear();
        self.pointer_input_sizes.clear();
        self.click_handlers.clear();
        self.pointer_icon = None;
        self.clip_to_bounds = false;
        self.motion_context_animated = false;
        self.translated_content_context = false;
        self.translated_content_context_identity = None;
        self.translated_content_offset_reader = None;
        self.text_content = None;
        self.text_style = None;
        self.text_layout_options = None;
        self.prepared_text_layout = None;
        self.text_pan = None;
        self.graphics_layer = None;
        self.graphics_layer_resolver = None;
        self.corner_shape = None;
        self.chain_guard = None;
    }
}

impl fmt::Debug for ModifierNodeSlices {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("ModifierNodeSlices")
            .field("draw_commands", &self.draw_commands.len())
            .field("pointer_inputs", &self.pointer_inputs.len())
            .field("click_handlers", &self.click_handlers.len())
            .field("pointer_icon", &self.pointer_icon)
            .field("clip_to_bounds", &self.clip_to_bounds)
            .field("motion_context_animated", &self.motion_context_animated)
            .field(
                "translated_content_context",
                &self.translated_content_context,
            )
            .field(
                "translated_content_context_identity",
                &self.translated_content_context_identity,
            )
            .field(
                "translated_content_offset",
                &self.translated_content_offset(),
            )
            .field("text_content", &self.text_content)
            .field("text_style", &self.text_style)
            .field("text_layout_options", &self.text_layout_options)
            .field("prepared_text_layout", &self.prepared_text_layout.is_some())
            .field("graphics_layer", &self.graphics_layer)
            .field(
                "graphics_layer_resolver",
                &self.graphics_layer_resolver.is_some(),
            )
            .field("corner_shape", &self.corner_shape)
            .finish()
    }
}

/// Records `node`'s pointer icon when it declares one, leaving the icon already
/// collected in place when it does not.
///
/// The chain is walked head to tail, so the innermost declaration is the last
/// one written and the one that survives.
fn collect_pointer_icon(node: &dyn std::any::Any, slices: &mut ModifierNodeSlices) {
    if let Some(icon_node) = node.downcast_ref::<PointerIconNode>() {
        slices.pointer_icon = Some(icon_node.icon().clone());
    }
}

/// Collects modifier node slices directly from a reconciled [`ModifierNodeChain`].
pub fn collect_modifier_slices(chain: &ModifierNodeChain) -> ModifierNodeSlices {
    let mut slices = ModifierNodeSlices::default();
    collect_modifier_slices_into(chain, &mut slices);
    slices
}

/// Collects modifier node slices into an existing buffer to reuse allocations.
///
/// Single-pass: iterates the chain once instead of 4 separate capability-filtered
/// traversals, reducing per-node `RefCell::borrow()` overhead.
pub fn collect_modifier_slices_into(chain: &ModifierNodeChain, slices: &mut ModifierNodeSlices) {
    slices.clear();

    let caps = chain.capabilities();
    let has_pointer = caps.intersects(NodeCapabilities::POINTER_INPUT);
    let has_draw = caps.intersects(NodeCapabilities::DRAW);
    let has_layout = caps.intersects(NodeCapabilities::LAYOUT);

    if !has_pointer && !has_draw && !has_layout {
        return;
    }

    let mut background = BackgroundSlot::default();
    let mut padding = EdgeInsets::default();

    for node_ref in chain.head_to_tail() {
        let node_caps = node_ref.kind_set();

        node_ref.with_node(|node| {
            let any = node.as_any();

            if has_pointer
                && node_caps.intersects(NodeCapabilities::POINTER_INPUT)
                && let Some(pointer_node) = node.as_pointer_input_node()
            {
                if let Some(handler) = pointer_node.pointer_input_handler() {
                    slices.pointer_inputs.push(handler);
                }
                if let Some(sink) = pointer_node.layout_size_sink() {
                    slices.pointer_input_sizes.push(sink);
                }
                collect_pointer_icon(any, slices);
            }

            if has_draw && node_caps.intersects(NodeCapabilities::DRAW) {
                collect_draw_node(node, padding, slices, &mut background);
            }

            if has_layout && node_caps.intersects(NodeCapabilities::LAYOUT) {
                if let Some(padding_node) = any.downcast_ref::<PaddingNode>() {
                    let p = padding_node.padding();
                    padding.left += p.left;
                    padding.top += p.top;
                    padding.right += p.right;
                    padding.bottom += p.bottom;
                }

                if let Some(motion_context_node) = any.downcast_ref::<MotionContextAnimatedNode>() {
                    slices.motion_context_animated = motion_context_node.is_active();
                }

                collect_window_geometry_sink(any, padding, slices);

                if let Some(translated_content_node) =
                    any.downcast_ref::<TranslatedContentContextNode>()
                {
                    slices.translated_content_context = translated_content_node.is_active();
                    slices.translated_content_context_identity =
                        Some(translated_content_node.identity());
                    slices.translated_content_offset_reader =
                        translated_content_node.content_offset_reader();
                }

                if let Some(text_node) = any.downcast_ref::<TextModifierNode>() {
                    slices.text_content = Some(text_node.annotated_text());
                    slices.text_style = Some(text_node.style().clone());
                    slices.text_layout_options = Some(text_node.options());
                    slices.prepared_text_layout = Some(MeasuredTextLayoutSource::Text(
                        text_node.prepared_layout_handle(),
                    ));
                }

                if let Some(text_field_node) = any.downcast_ref::<TextFieldModifierNode>() {
                    let text = text_field_node.text();
                    slices.text_content = Some(Rc::new(crate::text::AnnotatedString::from(text)));
                    slices.text_style = Some(text_field_node.style().clone());
                    slices.text_layout_options = Some(TextLayoutOptions::default());
                    slices.prepared_text_layout = Some(MeasuredTextLayoutSource::TextField(
                        text_field_node.layout_handle(),
                    ));
                    slices.text_pan = text_field_node.text_pan_resolver();
                    slices.text_window_origin = Some(text_field_node.window_origin_sink());

                    text_field_node.set_content_offset(padding.left);
                    text_field_node.set_content_y_offset(padding.top);
                }
            }
        });
    }

    background.insert_into(slices);
}

/// The chain's background as the walk finds it: the last background wins,
/// drawn at its place in the draw order, inside the padding declared before
/// it, in the latest corner shape.
#[derive(Default)]
struct BackgroundSlot {
    color: Option<crate::modifier::Color>,
    inset: EdgeInsets,
    insert_index: Option<usize>,
    precedes_layer: bool,
    corner_shape: Option<RoundedCornerShape>,
}

impl BackgroundSlot {
    fn insert_into(self, slices: &mut ModifierNodeSlices) {
        slices.corner_shape = self.corner_shape;
        let Some(color) = self.color else {
            return;
        };
        let (inset, corner_shape) = (self.inset, self.corner_shape);
        let draw_cmd = Rc::new(move |scope: &mut cranpose_ui_graphics::DrawScopeDefault| {
            use cranpose_ui_graphics::{CornerRadii, DrawScope as _};

            use crate::modifier::Brush;

            let rect = inset.inset_rect(scope.size());
            let brush = Brush::solid(color);
            if let Some(shape) = corner_shape {
                let radii: CornerRadii = shape.resolve(rect.width, rect.height);
                scope.draw_round_rect_at(rect, brush, radii);
            } else {
                scope.draw_rect_at(rect, brush);
            }
        });
        slices.insert_background_draw(
            self.insert_index,
            self.precedes_layer,
            DrawCommand::Behind(draw_cmd),
        );
    }
}

/// Collects what a draw-capable node contributes, drawn inside `padding`, the
/// layout padding declared before it.
/// Where layout reports a node's window geometry: a scroll viewport's rect,
/// or the origin of a selectable text, whose content starts after `padding`.
fn collect_window_geometry_sink(
    any: &dyn std::any::Any,
    padding: EdgeInsets,
    slices: &mut ModifierNodeSlices,
) {
    if let Some(reporter) = any.downcast_ref::<WindowRectReporterNode>() {
        slices.viewport_window_rect = Some(reporter.window_rect_sink());
    }
    if let Some(selectable) = any.downcast_ref::<SelectableTextNode>() {
        slices.text_window_origin = Some(selectable.geometry().node_origin_sink());
        selectable.geometry().set_content_offset(Point {
            x: padding.left,
            y: padding.top,
        });
    }
}

fn collect_draw_node(
    node: &dyn cranpose_foundation::ModifierNode,
    padding: EdgeInsets,
    slices: &mut ModifierNodeSlices,
    background: &mut BackgroundSlot,
) {
    let any = node.as_any();
    if let Some(bg_node) = any.downcast_ref::<BackgroundNode>() {
        background.color = Some(bg_node.color());
        background.inset = padding;
        background.insert_index = Some(slices.draw_commands.len());
        background.precedes_layer = slices.layer_draw_boundary.is_none();
        if bg_node.shape().is_some() {
            background.corner_shape = bg_node.shape();
        }
    }

    if let Some(shape_node) = any.downcast_ref::<CornerShapeNode>() {
        background.corner_shape = Some(shape_node.shape());
    }

    if let Some(commands) = any.downcast_ref::<DrawCommandNode>() {
        slices.draw_commands.extend(
            commands
                .observed_commands()
                .into_iter()
                .map(|command| inset_draw_command(command, padding)),
        );
    }

    if let Some(draw_node) = node.as_draw_node() {
        collect_draw_closures(draw_node, padding, slices);
    }

    if let Some(layer_node) = any.downcast_ref::<GraphicsLayerNode>() {
        slices.mark_layer_draw_boundary();
        slices.push_graphics_layer(layer_node.layer_snapshot(), layer_node.layer_resolver());
    }

    if any.is::<ClipToBoundsNode>() {
        slices.mark_layer_draw_boundary();
        slices.clip_to_bounds = true;
    }
}

/// A draw node's behind and overlay closures, or what its `draw` records
/// when it has no overlay closure.
fn collect_draw_closures(
    draw_node: &dyn cranpose_foundation::DrawModifierNode,
    padding: EdgeInsets,
    slices: &mut ModifierNodeSlices,
) {
    if let Some(closure) = draw_node.create_behind_draw_closure() {
        slices
            .draw_commands
            .push(inset_draw_command(DrawCommand::Behind(closure), padding));
    }
    if let Some(closure) = draw_node.create_draw_closure() {
        slices
            .draw_commands
            .push(inset_draw_command(DrawCommand::Overlay(closure), padding));
        return;
    }
    use cranpose_ui_graphics::{DrawScope as _, DrawScopeDefault};
    let mut scope = DrawScopeDefault::with_text_measurer(
        crate::modifier::Size {
            width: 0.0,
            height: 0.0,
        },
        crate::text::AppContextTextMeasurer::shared(),
    );
    draw_node.draw(&mut scope);
    let primitives = scope.into_primitives();
    if primitives.is_empty() {
        return;
    }
    let draw_cmd = Rc::new(move |scope: &mut DrawScopeDefault| {
        scope.push_recorded(primitives.clone());
    });
    slices
        .draw_commands
        .push(inset_draw_command(DrawCommand::Overlay(draw_cmd), padding));
}

/// `command` drawn where a draw modifier after `padding` draws: in the node's
/// rect shrunk by that padding, as Compose places it.
fn inset_draw_command(command: DrawCommand, padding: EdgeInsets) -> DrawCommand {
    if padding.is_zero() {
        return command;
    }
    let inset = |draw: crate::draw::DrawCommandFn| -> crate::draw::DrawCommandFn {
        Rc::new(move |scope: &mut cranpose_ui_graphics::DrawScopeDefault| {
            scope.inset(padding, |inner| draw(inner));
        })
    };
    match command {
        DrawCommand::Behind(draw) => DrawCommand::Behind(inset(draw)),
        DrawCommand::WithContent(draw) => DrawCommand::WithContent(inset(draw)),
        DrawCommand::Overlay(draw) => DrawCommand::Overlay(inset(draw)),
    }
}

/// Collects modifier node slices by instantiating a temporary node chain from a [`Modifier`].
pub fn collect_slices_from_modifier(modifier: &Modifier) -> ModifierNodeSlices {
    let mut handle = ModifierChainHandle::new();
    let _ = handle.update(modifier);
    collect_modifier_slices(handle.chain()).with_chain_guard(handle)
}

#[cfg(test)]
#[path = "tests/slices_tests.rs"]
mod tests;