repose_tree/

tree.rs

//! The main ViewTree structure.

use crate::{
    hash::{SubtreeHashBuilder, SubtreeHashes, ViewHashes, hash_view_facets},
    node::{LayoutCache, LayoutConstraints, NodeId, TreeNode, TreeStats},
    reconcile::ReconcileContext,
};
use repose_core::{Modifier, Rect, SubcomposeScope, View, ViewId, ViewKind};
use rustc_hash::{FxHashMap, FxHashSet};
use slotmap::Key;
use slotmap::SlotMap;
use smallvec::SmallVec;
use std::rc::Rc;
use std::sync::Arc;

/// A persistent view tree that supports incremental updates.
pub struct ViewTree {
    /// All nodes in the tree.
    nodes: SlotMap<NodeId, TreeNode>,

    /// The root node.
    root: Option<NodeId>,

    /// Nodes that need re-layout.
    dirty: FxHashSet<NodeId>,
    dirty_propagated: FxHashSet<NodeId>,

    paint_dirty: FxHashSet<NodeId>,
    paint_dirty_propagated: FxHashSet<NodeId>,

    /// Current generation (frame counter).
    generation: u64,

    /// Map from user-facing ViewId to internal NodeId.
    view_id_map: FxHashMap<ViewId, NodeId>,

    /// Every live node claiming each `ViewId`, in claim order. The first
    /// entry is the lookup owner.
    view_id_members: FxHashMap<ViewId, SmallVec<[NodeId; 2]>>,

    duplicate_view_ids: FxHashSet<ViewId>,

    /// Statistics from the last reconcile operation.
    pub stats: TreeStats,

    /// Nodes removed during the last update (needed to sync external systems like Taffy).
    pub removed_ids: Vec<NodeId>,

    pending_removals: Vec<NodeId>,
    removal_seen: FxHashSet<NodeId>,

    /// Root constraints to use when calling a `SubcomposeLayout`'s content
    /// closure during this frame. Set via [`ViewTree::set_subcompose_scope`]
    /// before calling [`ViewTree::update`].
    subcompose_scope: SubcomposeScope,

    /// Cache of (scope, subcomposed slots) for each `SubcomposeLayout` node.
    /// The closure is re-invoked only when the ancestor-derived scope
    /// changes or the node's content changes. Each cached slot view has its
    /// `Modifier::key` overwritten with its slot id.
    subcompose_cache: FxHashMap<NodeId, (SubcomposeScope, Arc<Vec<View>>)>,

    scope_invalidation_seen: FxHashSet<NodeId>,
}

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

fn rc_identity_changed<T: ?Sized>(old: &Option<Rc<T>>, new: &Option<Rc<T>>) -> bool {
    match (old, new) {
        (Some(old), Some(new)) => !Rc::ptr_eq(old, new),
        (None, None) => false,
        _ => true,
    }
}

fn arc_identity_changed<T: ?Sized>(old: &Option<Arc<T>>, new: &Option<Arc<T>>) -> bool {
    match (old, new) {
        (Some(old), Some(new)) => !Arc::ptr_eq(old, new),
        (None, None) => false,
        _ => true,
    }
}

#[derive(Clone, Copy, Default)]
struct IdentityChange {
    paint: bool,
    layout: bool,
    subcompose: bool,
}

impl IdentityChange {
    fn merge(&mut self, other: Self) {
        self.paint |= other.paint;
        self.layout |= other.layout;
        self.subcompose |= other.subcompose;
    }
}

fn focus_requester_changed(
    old: &Option<repose_core::FocusRequester>,
    new: &Option<repose_core::FocusRequester>,
) -> bool {
    match (old, new) {
        (Some(old), Some(new)) => !Rc::ptr_eq(&old.target, &new.target),
        (None, None) => false,
        _ => true,
    }
}

fn interaction_source_changed(
    old: &Option<repose_core::InteractionSource>,
    new: &Option<repose_core::InteractionSource>,
) -> bool {
    match (old, new) {
        (Some(old), Some(new)) => old.stable_id() != new.stable_id(),
        (None, None) => false,
        _ => true,
    }
}

fn text_selection_changed(
    old: &Option<repose_core::text::TextSelection>,
    new: &Option<repose_core::text::TextSelection>,
) -> bool {
    match (old, new) {
        (Some(old), Some(new)) => old.stable_id() != new.stable_id(),
        (None, None) => false,
        _ => true,
    }
}

fn scroll_axis_identity_changed(
    old: &repose_core::scroll::ScrollAxisBinding,
    new: &repose_core::scroll::ScrollAxisBinding,
) -> bool {
    rc_identity_changed(&old.on_scroll, &new.on_scroll)
        || rc_identity_changed(&old.set_viewport_main, &new.set_viewport_main)
        || rc_identity_changed(&old.set_content_main, &new.set_content_main)
        || rc_identity_changed(&old.get_offset_main, &new.get_offset_main)
        || rc_identity_changed(&old.set_offset_main, &new.set_offset_main)
        || rc_identity_changed(&old.tick, &new.tick)
        || rc_identity_changed(&old.set_nested_scroll_parent, &new.set_nested_scroll_parent)
}

fn scroll_identity_changed(
    old: &Option<repose_core::ScrollBinding>,
    new: &Option<repose_core::ScrollBinding>,
) -> bool {
    match (old, new) {
        (
            Some(repose_core::ScrollBinding::Vertical(old)),
            Some(repose_core::ScrollBinding::Vertical(new)),
        ) => scroll_axis_identity_changed(old, new),
        (
            Some(repose_core::ScrollBinding::Horizontal(old)),
            Some(repose_core::ScrollBinding::Horizontal(new)),
        ) => scroll_axis_identity_changed(old, new),
        (
            Some(repose_core::ScrollBinding::Both(old)),
            Some(repose_core::ScrollBinding::Both(new)),
        ) => {
            rc_identity_changed(&old.on_scroll, &new.on_scroll)
                || rc_identity_changed(&old.set_viewport_width, &new.set_viewport_width)
                || rc_identity_changed(&old.set_viewport_height, &new.set_viewport_height)
                || rc_identity_changed(&old.set_content_width, &new.set_content_width)
                || rc_identity_changed(&old.set_content_height, &new.set_content_height)
                || rc_identity_changed(&old.get_offset_xy, &new.get_offset_xy)
                || rc_identity_changed(&old.set_offset_xy, &new.set_offset_xy)
                || rc_identity_changed(&old.tick, &new.tick)
                || rc_identity_changed(&old.set_nested_scroll_parent, &new.set_nested_scroll_parent)
        }
        (None, None) => false,
        _ => true,
    }
}

fn cursor_identity_changed(
    old: &Option<repose_core::CursorIcon>,
    new: &Option<repose_core::CursorIcon>,
) -> bool {
    match (old, new) {
        (
            Some(repose_core::CursorIcon::Custom(old)),
            Some(repose_core::CursorIcon::Custom(new)),
        ) => !std::sync::Arc::ptr_eq(old, new) || old != new,
        (None, None) => false,
        _ => true,
    }
}

fn text_input_identity_change(
    old: Option<&repose_core::TextInputConfig>,
    new: Option<&repose_core::TextInputConfig>,
) -> IdentityChange {
    let (Some(old), Some(new)) = (old, new) else {
        return IdentityChange {
            paint: old.is_some() != new.is_some(),
            layout: old.is_some() != new.is_some(),
            subcompose: false,
        };
    };
    let mut change = IdentityChange::default();
    if rc_identity_changed(&old.on_change, &new.on_change)
        || rc_identity_changed(&old.on_submit, &new.on_submit)
        || rc_identity_changed(&old.on_text_layout, &new.on_text_layout)
        || rc_identity_changed(&old.focus_tracker, &new.focus_tracker)
        || interaction_source_changed(&old.interaction_source, &new.interaction_source)
    {
        change.paint = true;
    }
    if rc_identity_changed(&old.visual_transformation, &new.visual_transformation) {
        change.paint = true;
        change.layout = true;
    }
    match (&old.keyboard_actions, &new.keyboard_actions) {
        (Some(old), Some(new)) => {
            if rc_identity_changed(&old.on_done, &new.on_done)
                || rc_identity_changed(&old.on_go, &new.on_go)
                || rc_identity_changed(&old.on_next, &new.on_next)
                || rc_identity_changed(&old.on_previous, &new.on_previous)
                || rc_identity_changed(&old.on_search, &new.on_search)
                || rc_identity_changed(&old.on_send, &new.on_send)
            {
                change.paint = true;
            }
        }
        (None, None) => {}
        _ => change.paint = true,
    }
    change
}

fn modifier_identity_change(old: &Modifier, new: &Modifier) -> IdentityChange {
    let mut change = IdentityChange::default();
    macro_rules! paint_changed {
        ($($field:ident),+ $(,)?) => {
            if false $(|| rc_identity_changed(&old.$field, &new.$field))+ {
                change.paint = true;
            }
        };
    }
    macro_rules! layout_changed {
        ($($field:ident),+ $(,)?) => {
            if false $(|| rc_identity_changed(&old.$field, &new.$field))+ {
                change.layout = true;
            }
        };
    }
    paint_changed!(
        on_scroll,
        on_pointer_down,
        on_pointer_move,
        on_pointer_up,
        on_pointer_cancel,
        on_pointer_enter,
        on_pointer_leave,
        on_click,
        on_double_click,
        on_long_click,
        on_globally_positioned,
        on_size_changed,
        on_key_event,
        on_preview_key_event,
        on_ime,
        on_drag_start,
        on_drag_end,
        on_drag_enter,
        on_drag_over,
        on_drag_leave,
        on_drop,
        on_action,
        painter,
        indication,
        drag_preview,
        on_focus_changed,
    );
    layout_changed!(layout);
    if arc_identity_changed(&old.paint_callback, &new.paint_callback) {
        change.paint = true;
    }
    if focus_requester_changed(&old.focus_requester, &new.focus_requester)
        || interaction_source_changed(&old.interaction_source, &new.interaction_source)
        || text_selection_changed(&old.text_selection, &new.text_selection)
    {
        change.paint = true;
    }
    change.merge(text_input_identity_change(
        old.text_input.as_ref(),
        new.text_input.as_ref(),
    ));
    match (&old.nested_scroll_connection, &new.nested_scroll_connection) {
        (Some(old), Some(new)) => {
            if rc_identity_changed(&old.on_pre_scroll, &new.on_pre_scroll)
                || rc_identity_changed(&old.on_post_scroll, &new.on_post_scroll)
                || rc_identity_changed(&old.on_pre_fling, &new.on_pre_fling)
                || rc_identity_changed(&old.on_post_fling, &new.on_post_fling)
            {
                change.paint = true;
            }
        }
        (None, None) => {}
        _ => change.paint = true,
    }
    if scroll_identity_changed(&old.scroll, &new.scroll)
        || cursor_identity_changed(&old.cursor, &new.cursor)
        || old.scrollbar_style != new.scrollbar_style
    {
        change.paint = true;
    }
    change
}

fn view_identity_change(node: &TreeNode, view: &View) -> IdentityChange {
    let mut change = modifier_identity_change(&node.modifier, &view.modifier);
    if let (
        ViewKind::SubcomposeLayout { content: old },
        ViewKind::SubcomposeLayout { content: new },
    ) = (&node.kind, &view.kind)
        && !Arc::ptr_eq(old, new)
    {
        change.paint = true;
        change.layout = true;
        change.subcompose = true;
    }
    change
}

fn semantics_equal(
    old: Option<&repose_core::Semantics>,
    new: Option<&repose_core::Semantics>,
) -> bool {
    match (old, new) {
        (Some(old), Some(new)) => {
            old.role == new.role
                && old.label == new.label
                && old.focused == new.focused
                && old.enabled == new.enabled
                && old.selectable_group == new.selectable_group
                && old.checked == new.checked
                && old.selected == new.selected
                && old.value == new.value
        }
        (None, None) => true,
        _ => false,
    }
}

fn view_kind_equal(old: &ViewKind, new: &ViewKind) -> bool {
    match (old, new) {
        (
            ViewKind::SubcomposeLayout { content: old },
            ViewKind::SubcomposeLayout { content: new },
        ) => Arc::ptr_eq(old, new),
        (
            ViewKind::Text {
                text: old_text,
                color: old_color,
                font_size: old_font_size,
                soft_wrap: old_soft_wrap,
                max_lines: old_max_lines,
                overflow: old_overflow,
                font_family: old_font_family,
                annotations: old_annotations,
                text_align: old_text_align,
                font_weight: old_font_weight,
                font_style: old_font_style,
                text_decoration: old_text_decoration,
                letter_spacing: old_letter_spacing,
                line_height: old_line_height,
                url: old_url,
                font_variation_settings: old_font_variation_settings,
                draw_style: old_draw_style,
            },
            ViewKind::Text {
                text: new_text,
                color: new_color,
                font_size: new_font_size,
                soft_wrap: new_soft_wrap,
                max_lines: new_max_lines,
                overflow: new_overflow,
                font_family: new_font_family,
                annotations: new_annotations,
                text_align: new_text_align,
                font_weight: new_font_weight,
                font_style: new_font_style,
                text_decoration: new_text_decoration,
                letter_spacing: new_letter_spacing,
                line_height: new_line_height,
                url: new_url,
                font_variation_settings: new_font_variation_settings,
                draw_style: new_draw_style,
            },
        ) => {
            old_text == new_text
                && old_color == new_color
                && old_font_size == new_font_size
                && old_soft_wrap == new_soft_wrap
                && old_max_lines == new_max_lines
                && old_overflow == new_overflow
                && old_font_family == new_font_family
                && old_annotations == new_annotations
                && old_text_align == new_text_align
                && old_font_weight == new_font_weight
                && old_font_style == new_font_style
                && old_text_decoration == new_text_decoration
                && old_letter_spacing == new_letter_spacing
                && old_line_height == new_line_height
                && old_url == new_url
                && old_font_variation_settings == new_font_variation_settings
                && old_draw_style == new_draw_style
        }
        (
            ViewKind::Image {
                handle: old_handle,
                tint: old_tint,
                fit: old_fit,
                filter: old_filter,
                source_rect: old_source_rect,
                alignment: old_alignment,
            },
            ViewKind::Image {
                handle: new_handle,
                tint: new_tint,
                fit: new_fit,
                filter: new_filter,
                source_rect: new_source_rect,
                alignment: new_alignment,
            },
        ) => {
            old_handle == new_handle
                && old_tint == new_tint
                && old_fit == new_fit
                && old_filter == new_filter
                && old_source_rect == new_source_rect
                && old_alignment == new_alignment
        }
        _ => std::mem::discriminant(old) == std::mem::discriminant(new),
    }
}

fn next_dedup_key(
    original: u64,
    index: usize,
    parent_id: NodeId,
    new_seen_keys: &mut FxHashSet<u64>,
    keyed_children: &FxHashMap<u64, NodeId>,
) -> u64 {
    let mut candidate = (original.wrapping_mul(0x9E3779B97F4A7C15)
        ^ (index as u64).wrapping_add(0xBF58476D1CE4E5B9))
    .wrapping_add(parent_id.data().as_ffi());
    loop {
        if candidate != original
            && !new_seen_keys.contains(&candidate)
            && !keyed_children.contains_key(&candidate)
        {
            new_seen_keys.insert(candidate);
            return candidate;
        }
        candidate = candidate.wrapping_add(1);
        if candidate == 0 {
            candidate = 1;
        }
    }
}

impl ViewTree {
    /// Create a new empty tree.
    pub fn new() -> Self {
        Self {
            nodes: SlotMap::with_key(),
            root: None,
            dirty: FxHashSet::default(),
            dirty_propagated: FxHashSet::default(),
            paint_dirty: FxHashSet::default(),
            paint_dirty_propagated: FxHashSet::default(),
            generation: 0,
            view_id_map: FxHashMap::default(),
            view_id_members: FxHashMap::default(),
            duplicate_view_ids: FxHashSet::default(),
            stats: TreeStats::default(),
            removed_ids: Vec::new(),
            pending_removals: Vec::new(),
            removal_seen: FxHashSet::default(),
            subcompose_scope: SubcomposeScope::UNBOUNDED,
            subcompose_cache: FxHashMap::default(),
            scope_invalidation_seen: FxHashSet::default(),
        }
    }

    /// Set the constraints that will be passed to any `SubcomposeLayout`
    /// content closures during the next [`update`](Self::update) call.
    /// The scope is read once per reconcile of a `SubcomposeLayout` node. If
    /// you need different scopes at different depths, the closure itself is
    /// responsible for narrowing the values it receives.
    pub fn set_subcompose_scope(&mut self, scope: SubcomposeScope) {
        self.subcompose_scope = SubcomposeScope::new(
            scope.min_width,
            scope.max_width,
            scope.min_height,
            scope.max_height,
        );
    }

    /// Get the currently-set subcompose scope.
    pub fn subcompose_scope(&self) -> SubcomposeScope {
        self.subcompose_scope
    }

    /// Run a `SubcomposeLayout`'s content closure, returning the cached views
    /// when the scope is unchanged for this node.
    /// The caller is responsible for ensuring the cache is invalidated (e.g.
    /// on content change) via [`ViewTree::invalidate_subcompose_cache`].
    ///
    /// The closure must run whenever the scope differs from the scope the
    /// cached views were built for: the scope is derived from the previous
    /// frame's layout, so holding a stale result would keep feeding the tree a
    /// scope that no longer exists.
    ///
    /// The scope is computed by walking the node's ancestor chain and
    /// intersecting the root scope with each ancestor's `Modifier` width /
    /// height / min / max fields, plus the SubcomposeLayout's own modifier.
    /// Ancestors additionally narrow the scope by their own cached
    /// Taffy-computed size from the previous frame's layout pass.
    fn run_subcompose(
        &mut self,
        node_id: NodeId,
        content: &Arc<dyn Fn(&SubcomposeScope) -> Vec<(u64, View)>>,
    ) -> Arc<Vec<View>> {
        let raw_scope = self.compute_scope_for_node(node_id);
        let scope = SubcomposeScope::new(
            raw_scope.min_width,
            raw_scope.max_width,
            raw_scope.min_height,
            raw_scope.max_height,
        );
        if let Some((cached_scope, cached_slots)) = self.subcompose_cache.get(&node_id)
            && *cached_scope == scope
        {
            return Arc::clone(cached_slots);
        }
        let slots = content(&scope);
        let scope_key = format!("subcompose_{:?}", node_id);
        let mut views = Vec::with_capacity(slots.len());
        for (slot_id, mut view) in slots {
            view.modifier.key = Some(slot_id);
            view.scope_key = Some(scope_key.clone());
            view.modifier.repaint_boundary = true;
            views.push(view);
        }
        let views = Arc::new(views);
        let old_cache = self
            .subcompose_cache
            .insert(node_id, (scope, Arc::clone(&views)));
        drop(old_cache);
        views
    }

    /// Compute the `SubcomposeScope` visible to a `SubcomposeLayout` at
    /// `node_id`. Starts with the user-set root scope and intersects each
    /// ancestor's `Modifier` width / height / min / max / padding fields in
    /// root-to-leaf order. Each ancestor also narrows the scope by its cached
    /// Taffy-computed size from the previous frame's layout pass, so
    /// parent-dependent sizes are reflected in the scope after the first frame.
    ///
    /// The SubcomposeLayout's own measured size is deliberately excluded: a
    /// node's size is an outcome of its content, so feeding it back would let
    /// subcomposed content ratchet its own scope inward every frame.
    fn compute_scope_for_node(&self, node_id: NodeId) -> SubcomposeScope {
        let mut scope = self.subcompose_scope;
        let mut chain: SmallVec<[NodeId; 16]> = SmallVec::new();
        let mut current = Some(node_id);
        while let Some(id) = current {
            chain.push(id);
            match self.nodes.get(id) {
                Some(node) => current = node.parent,
                None => break,
            }
        }
        chain.reverse();
        for &ancestor_id in &chain {
            if let Some(node) = self.nodes.get(ancestor_id) {
                scope = intersect_scope_with_modifier(scope, &node.modifier);
                if ancestor_id == node_id {
                    continue;
                }
                if let Some(cache) = &node.layout_cache {
                    let w = cache.rect.w;
                    if w >= 0.0 && w.is_finite() {
                        scope.max_width = scope.max_width.min(repose_core::Dp(w));
                    }
                    let h = cache.rect.h;
                    if h >= 0.0 && h.is_finite() {
                        scope.max_height = scope.max_height.min(repose_core::Dp(h));
                    }
                }
            }
        }
        scope
    }

    /// Drop the cached subcomposed view for a single node. Call this when the
    /// `SubcomposeLayout`'s modifier or identity changes so the next
    /// reconciliation re-invokes the closure.
    pub fn invalidate_subcompose_cache(&mut self, node_id: NodeId) {
        let removed = self.subcompose_cache.remove(&node_id);
        drop(removed);
    }

    /// Get the current generation.
    pub fn generation(&self) -> u64 {
        self.generation
    }

    /// Get the root node ID.
    pub fn root(&self) -> Option<NodeId> {
        self.root
    }

    /// Get a node by ID.
    pub fn get(&self, id: NodeId) -> Option<&TreeNode> {
        self.nodes.get(id)
    }

    /// Get a mutable node by ID.
    pub fn get_mut(&mut self, id: NodeId) -> Option<&mut TreeNode> {
        self.nodes.get_mut(id)
    }

    /// Get a node by ViewId.
    pub fn get_by_view_id(&self, view_id: ViewId) -> Option<&TreeNode> {
        self.view_id_map
            .get(&view_id)
            .and_then(|id| self.nodes.get(*id))
    }

    /// Get the number of nodes in the tree.
    pub fn len(&self) -> usize {
        self.nodes.len()
    }

    /// Check if the tree is empty.
    pub fn is_empty(&self) -> bool {
        self.nodes.is_empty()
    }

    /// Check if a node is marked dirty.
    pub fn is_dirty(&self, id: NodeId) -> bool {
        self.dirty.contains(&id)
    }

    /// Get the set of dirty nodes.
    pub fn dirty_nodes(&self) -> &FxHashSet<NodeId> {
        &self.dirty
    }

    /// Clear the dirty set (after layout).
    pub fn clear_dirty(&mut self) {
        self.dirty.clear();
        self.dirty_propagated.clear();
    }

    pub fn paint_dirty_nodes(&self) -> &FxHashSet<NodeId> {
        &self.paint_dirty
    }

    pub fn clear_paint_dirty(&mut self) {
        self.paint_dirty.clear();
        self.paint_dirty_propagated.clear();
    }

    fn mark_paint_dirty(&mut self, node_id: NodeId) {
        let mut current = Some(node_id);
        while let Some(id) = current {
            if !self.paint_dirty_propagated.insert(id) {
                break;
            }
            self.paint_dirty.insert(id);
            current = self.nodes.get(id).and_then(|node| node.parent);
        }
    }

    fn mark_scope_descendants_dirty(&mut self, id: NodeId) {
        if !self.scope_invalidation_seen.insert(id) {
            return;
        }
        let mut stack: SmallVec<[NodeId; 16]> = SmallVec::new();
        stack.push(id);
        while let Some(current) = stack.pop() {
            let Some(node) = self.nodes.get(current) else {
                continue;
            };
            for &child in &node.children {
                if self
                    .nodes
                    .get(child)
                    .is_some_and(|child| child.scope_key.is_some())
                {
                    self.dirty.insert(child);
                }
                stack.push(child);
            }
        }
    }

    /// Mark a node as needing re-layout.
    pub fn mark_dirty(&mut self, id: NodeId) {
        let mut current = Some(id);
        while let Some(current_id) = current {
            if !self.dirty_propagated.insert(current_id) {
                break;
            }
            self.dirty.insert(current_id);
            current = self.nodes.get(current_id).and_then(|node| node.parent);
        }

        let needs_scope_invalidate = self.nodes.get(id).is_some_and(|node| {
            node.modifier.transform.is_some()
                || node.modifier.alpha.is_some()
                || node.modifier.graphics_layer.is_some()
        });
        if needs_scope_invalidate {
            self.mark_scope_descendants_dirty(id);
        }
    }

    /// Update the tree from a new View, performing incremental reconciliation.
    /// Returns the root NodeId.
    pub fn update(&mut self, new_root: &View) -> NodeId {
        self.removed_ids.clear();
        self.pending_removals.clear();
        self.removal_seen.clear();
        self.paint_dirty.clear();
        self.paint_dirty_propagated.clear();
        self.dirty_propagated.clear();
        self.scope_invalidation_seen.clear();

        self.generation += 1;
        self.stats = TreeStats::default();

        let mut ctx = ReconcileContext::new(self.generation);

        let root_id = if let Some(existing_root) = self.root {
            self.reconcile_node(existing_root, new_root, None, 0, 0, &mut ctx)
        } else {
            self.create_node(new_root, None, 0, 0, &mut ctx)
        };

        self.root = Some(root_id);
        self.collect_explicit_removals(&mut ctx);

        self.stats.total_nodes = self.nodes.len();
        self.stats.dirty_nodes = self.dirty.len();
        self.stats.reconciled_nodes = ctx.reconciled;
        self.stats.skipped_nodes = ctx.skipped;
        self.stats.created_nodes = ctx.created;
        self.stats.removed_nodes = ctx.removed;

        root_id
    }

    /// Reconcile an existing node with a new View.
    fn reconcile_node(
        &mut self,
        node_id: NodeId,
        view: &View,
        parent: Option<NodeId>,
        depth: u32,
        index_in_parent: u32,
        ctx: &mut ReconcileContext,
    ) -> NodeId {
        let hashes = hash_view_facets(view);
        let Some(node) = self.nodes.get(node_id) else {
            log::error!(
                "reconcile_node: node {:?} not found - creating fresh",
                node_id
            );
            return self.create_node(view, parent, depth, index_in_parent, ctx);
        };

        let old_hashes = ViewHashes {
            layout: node.layout_hash,
            measurement: node.measurement_hash,
            paint: node.paint_hash,
            semantics: node.semantics_hash,
        };
        let identity = view_identity_change(node, view);
        let old_subtree = SubtreeHashes {
            layout: node.layout_subtree_hash,
            measurement: node.measurement_subtree_hash,
            paint: node.paint_subtree_hash,
            semantics: node.semantics_subtree_hash,
        };
        let old_subtree_hash = node.subtree_hash;
        let old_scope_key = node.scope_key.clone();
        let old_view_id = node.view_id;
        let old_is_subcompose = matches!(&node.kind, ViewKind::SubcomposeLayout { .. });
        let new_is_subcompose = matches!(&view.kind, ViewKind::SubcomposeLayout { .. });
        let hashes_equal = old_hashes == hashes;
        let content_hash = hashes.combined();
        let content_changed = !hashes_equal;
        let view_semantics_changed =
            !hashes_equal && !semantics_equal(node.semantics.as_ref(), view.semantics.as_ref());
        let modifier_semantics_changed = !hashes_equal
            && !semantics_equal(
                node.modifier.semantics.as_ref(),
                view.modifier.semantics.as_ref(),
            );
        let scope_effect_changed = node.modifier.transform != view.modifier.transform
            || node.modifier.alpha != view.modifier.alpha
            || node.modifier.graphics_layer != view.modifier.graphics_layer;
        let kind_changed = !view_kind_equal(&node.kind, &view.kind);
        let modifier_changed = old_hashes.layout != hashes.layout
            || old_hashes.measurement != hashes.measurement
            || old_hashes.paint != hashes.paint
            || modifier_semantics_changed
            || identity.paint
            || identity.layout;
        let scope_changed = old_scope_key.as_deref() != view.scope_key.as_deref();
        let node_layout_changed = old_hashes.layout != hashes.layout
            || old_hashes.measurement != hashes.measurement
            || identity.layout
            || identity.subcompose
            || old_is_subcompose != new_is_subcompose;
        let subcompose_changed = identity.subcompose
            || (new_is_subcompose
                && (old_hashes.layout != hashes.layout
                    || old_hashes.measurement != hashes.measurement
                    || identity.layout))
            || old_is_subcompose != new_is_subcompose;
        if subcompose_changed {
            self.invalidate_subcompose_cache(node_id);
        }

        let view_id = self.compute_view_id(view, node_id, parent, index_in_parent);
        self.assign_view_id(
            node_id,
            old_view_id,
            view_id,
            view.id == 0,
            "reconcile_node",
        );

        {
            let Some(node) = self.nodes.get_mut(node_id) else {
                log::error!("reconcile_node: node {:?} vanished mid-reconcile", node_id);
                return node_id;
            };
            node.parent = parent;
            node.depth = depth;
            node.generation = self.generation;
            if kind_changed {
                node.kind = view.kind.clone();
            }
            if modifier_changed {
                node.modifier = view.modifier.clone();
            }
            if view_semantics_changed {
                node.semantics = view.semantics.clone();
            }
            if scope_changed {
                node.scope_key = view.scope_key.clone();
            }
            node.user_key = view.modifier.key;
            if node_layout_changed {
                node.layout_cache = None;
            }
        }

        let new_children_hashes = if let ViewKind::SubcomposeLayout { content } = &view.kind {
            let subcomposed = self.run_subcompose(node_id, content);
            self.reconcile_children(node_id, subcomposed.as_slice(), depth, ctx)
        } else {
            self.reconcile_children(node_id, &view.children, depth, ctx)
        };
        let new_subtree = new_children_hashes.finish(hashes);
        let new_subtree_hash = new_subtree.combined();
        let layout_subtree_changed = old_subtree.layout != new_subtree.layout
            || old_subtree.measurement != new_subtree.measurement
            || identity.layout
            || identity.subcompose;
        let paint_subtree_changed =
            old_subtree.paint != new_subtree.paint || identity.paint || identity.subcompose;
        let semantics_subtree_changed = old_subtree.semantics != new_subtree.semantics;
        let subtree_changed = old_subtree_hash != new_subtree_hash || identity.subcompose;

        {
            let Some(node) = self.nodes.get_mut(node_id) else {
                log::error!("reconcile_node: node {:?} vanished mid-reconcile", node_id);
                return node_id;
            };
            if layout_subtree_changed {
                node.layout_cache = None;
            }
            node.content_hash = content_hash;
            node.layout_hash = hashes.layout;
            node.measurement_hash = hashes.measurement;
            node.paint_hash = hashes.paint;
            node.semantics_hash = hashes.semantics;
            node.subtree_hash = new_subtree_hash;
            node.layout_subtree_hash = new_subtree.layout;
            node.measurement_subtree_hash = new_subtree.measurement;
            node.paint_subtree_hash = new_subtree.paint;
            node.semantics_subtree_hash = new_subtree.semantics;

            if content_changed || identity.paint || identity.layout || identity.subcompose {
                ctx.reconciled += 1;
            } else if !subtree_changed {
                ctx.skipped += 1;
            }
        }

        if paint_subtree_changed || semantics_subtree_changed {
            self.mark_paint_dirty(node_id);
        }
        if layout_subtree_changed {
            self.mark_dirty(node_id);
        }
        if scope_effect_changed {
            self.mark_scope_descendants_dirty(node_id);
        }

        node_id
    }
    fn node_subtree_hashes(&self, node_id: NodeId) -> SubtreeHashes {
        self.nodes
            .get(node_id)
            .map_or_default(|node| SubtreeHashes {
                layout: node.layout_subtree_hash,
                measurement: node.measurement_subtree_hash,
                paint: node.paint_subtree_hash,
                semantics: node.semantics_subtree_hash,
            })
    }

    /// Reconcile children of a node.
    /// Returns the subtree hashes of all children (for computing parent's subtree hash).
    fn reconcile_children(
        &mut self,
        parent_id: NodeId,
        new_children: &[View],
        parent_depth: u32,
        ctx: &mut ReconcileContext,
    ) -> SubtreeHashBuilder {
        let child_depth = parent_depth + 1;
        let old_children: SmallVec<[NodeId; 4]> = self
            .nodes
            .get_mut(parent_id)
            .map(|node| std::mem::take(&mut node.children))
            .unwrap_or_default();

        let mut keyed_children: FxHashMap<u64, NodeId> = FxHashMap::default();
        let mut unkeyed_children: SmallVec<[NodeId; 4]> = SmallVec::new();
        for &child_id in &old_children {
            if let Some(node) = self.nodes.get(child_id) {
                match node.user_key {
                    Some(key) => {
                        keyed_children.entry(key).or_insert(child_id);
                    }
                    None => unkeyed_children.push(child_id),
                }
            }
        }

        let mut new_child_ids: SmallVec<[NodeId; 4]> = SmallVec::new();
        let mut child_hashes = SubtreeHashBuilder::new(new_children.len());
        let mut unkeyed_index = 0;
        let mut used_nodes: FxHashSet<NodeId> = FxHashSet::default();
        let mut new_seen_keys: FxHashSet<u64> = FxHashSet::default();

        for (i, new_child) in new_children.iter().enumerate() {
            let mut owned_child: Option<View>;
            let child_ref = if let Some(key) = new_child.modifier.key {
                if new_seen_keys.insert(key) {
                    new_child
                } else {
                    log::error!(
                        "reconcile_children: duplicate modifier.key={} in children of node {:?} - deduplicating (suffixing). Ensure get_key returns unique keys.",
                        key,
                        parent_id
                    );
                    let salt =
                        next_dedup_key(key, i, parent_id, &mut new_seen_keys, &keyed_children);
                    owned_child = Some(new_child.clone());
                    let child = owned_child.as_mut().expect("owned child inserted");
                    child.modifier.key = Some(salt);
                    child
                }
            } else {
                new_child
            };

            let is_subcompose = matches!(&child_ref.kind, ViewKind::SubcomposeLayout { .. });
            let child_id = if let Some(key) = child_ref.modifier.key {
                if let Some(&existing_id) = keyed_children.get(&key) {
                    if used_nodes.insert(existing_id) {
                        self.reconcile_node(
                            existing_id,
                            child_ref,
                            Some(parent_id),
                            child_depth,
                            i as u32,
                            ctx,
                        )
                    } else {
                        let salt =
                            next_dedup_key(key, i, parent_id, &mut new_seen_keys, &keyed_children);
                        let mut fresh = child_ref.clone();
                        fresh.modifier.key = Some(salt);
                        self.create_node(&fresh, Some(parent_id), child_depth, i as u32, ctx)
                    }
                } else if is_subcompose && unkeyed_index < unkeyed_children.len() {
                    let existing_id = unkeyed_children[unkeyed_index];
                    unkeyed_index += 1;
                    if used_nodes.insert(existing_id) {
                        self.reconcile_node(
                            existing_id,
                            child_ref,
                            Some(parent_id),
                            child_depth,
                            i as u32,
                            ctx,
                        )
                    } else {
                        self.create_node(child_ref, Some(parent_id), child_depth, i as u32, ctx)
                    }
                } else {
                    self.create_node(child_ref, Some(parent_id), child_depth, i as u32, ctx)
                }
            } else if let Some(&existing_id) = unkeyed_children.get(unkeyed_index) {
                unkeyed_index += 1;
                if used_nodes.insert(existing_id) {
                    self.reconcile_node(
                        existing_id,
                        child_ref,
                        Some(parent_id),
                        child_depth,
                        i as u32,
                        ctx,
                    )
                } else {
                    self.create_node(child_ref, Some(parent_id), child_depth, i as u32, ctx)
                }
            } else {
                self.create_node(child_ref, Some(parent_id), child_depth, i as u32, ctx)
            };

            new_child_ids.push(child_id);
            child_hashes.push(self.node_subtree_hashes(child_id));
        }

        for &old_child in &old_children {
            if !used_nodes.contains(&old_child) {
                self.mark_for_removal(old_child);
            }
        }

        if let Some(parent) = self.nodes.get_mut(parent_id) {
            parent.children = new_child_ids;
        }

        child_hashes
    }

    /// Create a new node from a View.
    fn create_node(
        &mut self,
        view: &View,
        parent: Option<NodeId>,
        depth: u32,
        index_in_parent: u32,
        ctx: &mut ReconcileContext,
    ) -> NodeId {
        let hashes = hash_view_facets(view);
        let content_hash = hashes.combined();

        let node_id = self.nodes.insert_with_key(|id| {
            TreeNode::new(
                id,
                0,
                view.kind.clone(),
                view.modifier.clone(),
                self.generation,
            )
        });
        ctx.created += 1;

        {
            let node = self
                .nodes
                .get_mut(node_id)
                .expect("create_node: node just inserted");
            node.parent = parent;
            node.depth = depth;
            node.semantics = view.semantics.clone();
            node.content_hash = content_hash;
            node.layout_hash = hashes.layout;
            node.measurement_hash = hashes.measurement;
            node.paint_hash = hashes.paint;
            node.semantics_hash = hashes.semantics;
            node.user_key = view.modifier.key;
            node.scope_key = view.scope_key.clone();
        }

        let view_id = self.compute_view_id(view, node_id, parent, index_in_parent);
        self.assign_view_id(node_id, 0, view_id, view.id == 0, "create_node");

        let child_depth = depth + 1;
        let mut child_ids: SmallVec<[NodeId; 4]> = SmallVec::new();
        let subcomposed = if let ViewKind::SubcomposeLayout { content } = &view.kind {
            Some(self.run_subcompose(node_id, content))
        } else {
            None
        };
        let children_to_create = subcomposed
            .as_ref()
            .map_or(view.children.as_slice(), |views| views.as_slice());
        let mut child_hashes = SubtreeHashBuilder::new(children_to_create.len());
        for (i, child_view) in children_to_create.iter().enumerate() {
            let child_id = self.create_node(child_view, Some(node_id), child_depth, i as u32, ctx);
            child_ids.push(child_id);
            child_hashes.push(self.node_subtree_hashes(child_id));
        }

        let subtree = child_hashes.finish(hashes);
        let subtree_hash = subtree.combined();

        let node = self
            .nodes
            .get_mut(node_id)
            .expect("create_node: node just inserted");
        node.children = child_ids;
        node.subtree_hash = subtree_hash;
        node.layout_subtree_hash = subtree.layout;
        node.measurement_subtree_hash = subtree.measurement;
        node.paint_subtree_hash = subtree.paint;
        node.semantics_subtree_hash = subtree.semantics;
        self.dirty.insert(node_id);

        node_id
    }
    /// Compute a stable ViewId for a node.
    fn compute_view_id(
        &self,
        view: &View,
        _node_id: NodeId,
        parent: Option<NodeId>,
        index_in_parent: u32,
    ) -> ViewId {
        if view.id != 0 {
            return view.id;
        }

        let parent_id = parent
            .and_then(|p| self.nodes.get(p))
            .map(|n| n.view_id)
            .unwrap_or(0);

        let salt = match view.modifier.key {
            Some(key) => key.wrapping_mul(2).wrapping_add(1),
            None => (index_in_parent as u64).wrapping_mul(2),
        };

        let mut id = parent_id.wrapping_mul(31).wrapping_add(salt);
        id = id.wrapping_mul(0x9E3779B97F4A7C15);
        id ^= id >> 30;

        if id == 0 {
            id = 1;
        }

        id
    }

    /// Recompute the lookup owner and duplicate flag for one id from its
    /// member list. The first member owns the id; anything longer is a
    /// duplicate the user has to fix with unique `View.id`s.
    fn sync_view_id_owner(&mut self, view_id: ViewId) {
        let Some(members) = self.view_id_members.get(&view_id) else {
            self.view_id_map.remove(&view_id);
            self.duplicate_view_ids.remove(&view_id);
            return;
        };
        match members.split_first() {
            Some((owner, rest)) => {
                self.view_id_map.insert(view_id, *owner);
                if rest.is_empty() {
                    self.duplicate_view_ids.remove(&view_id);
                } else {
                    self.duplicate_view_ids.insert(view_id);
                }
            }
            None => {
                self.view_id_members.remove(&view_id);
                self.view_id_map.remove(&view_id);
                self.duplicate_view_ids.remove(&view_id);
            }
        }
    }

    fn claim_view_id(&mut self, node_id: NodeId, view_id: ViewId) {
        let members = self.view_id_members.entry(view_id).or_default();
        if !members.contains(&node_id) {
            members.push(node_id);
        }
        self.sync_view_id_owner(view_id);
    }

    fn release_view_id(&mut self, node_id: NodeId, view_id: ViewId) {
        let empty = match self.view_id_members.get_mut(&view_id) {
            Some(members) => {
                if let Some(index) = members.iter().position(|member| *member == node_id) {
                    members.remove(index);
                }
                members.is_empty()
            }
            None => return,
        };
        if empty {
            self.view_id_members.remove(&view_id);
        }
        self.sync_view_id_owner(view_id);
    }

    fn assign_view_id(
        &mut self,
        node_id: NodeId,
        old_view_id: ViewId,
        requested_view_id: ViewId,
        generated: bool,
        phase: &str,
    ) {
        let view_id = if generated {
            self.available_generated_view_id(node_id, requested_view_id)
        } else {
            requested_view_id
        };

        if old_view_id == view_id && self.view_id_map.get(&view_id).copied() == Some(node_id) {
            return;
        }

        if old_view_id != 0 && old_view_id != view_id {
            self.release_view_id(node_id, old_view_id);
        }

        if let Some(existing) = self
            .view_id_members
            .get(&view_id)
            .and_then(|m| m.first())
            .copied()
            && existing != node_id
        {
            log::error!(
                "{}: duplicate View.id {}; keeping the first node {:?}",
                phase,
                view_id,
                existing
            );
        }

        self.claim_view_id(node_id, view_id);

        if let Some(node) = self.nodes.get_mut(node_id) {
            node.view_id = view_id;
        }
    }

    fn available_generated_view_id(&self, node_id: NodeId, requested: ViewId) -> ViewId {
        if self
            .view_id_map
            .get(&requested)
            .is_none_or(|existing| *existing == node_id)
        {
            return requested;
        }

        let mut candidate = requested;
        loop {
            candidate = candidate.wrapping_add(1);
            if candidate == 0 {
                candidate = 1;
            }
            if self
                .view_id_map
                .get(&candidate)
                .is_none_or(|existing| *existing == node_id)
            {
                return candidate;
            }
        }
    }

    /// Mark a node and its descendants for removal.
    fn mark_for_removal(&mut self, node_id: NodeId) {
        if !self.removal_seen.insert(node_id) {
            return;
        }
        let Some((view_id, children)) = self.nodes.get_mut(node_id).map(|node| {
            node.generation = 0;
            let children = std::mem::take(&mut node.children);
            (node.view_id, children)
        }) else {
            return;
        };
        self.pending_removals.push(node_id);
        self.release_view_id(node_id, view_id);
        self.dirty.remove(&node_id);
        self.dirty_propagated.remove(&node_id);
        self.paint_dirty.remove(&node_id);
        self.paint_dirty_propagated.remove(&node_id);
        self.scope_invalidation_seen.remove(&node_id);
        let removed_cache = self.subcompose_cache.remove(&node_id);
        drop(removed_cache);
        for child_id in children {
            self.mark_for_removal(child_id);
        }
    }

    fn collect_explicit_removals(&mut self, ctx: &mut ReconcileContext) {
        let pending = std::mem::take(&mut self.pending_removals);
        for node_id in pending {
            if self.nodes.remove(node_id).is_none() {
                continue;
            }
            ctx.removed += 1;
            self.removed_ids.push(node_id);
        }
        self.removal_seen.clear();
    }

    /// Set cached layout for a node.
    pub fn set_layout(
        &mut self,
        id: NodeId,
        rect: Rect,
        screen_rect: Rect,
        constraints: LayoutConstraints,
    ) {
        if let Some(node) = self.nodes.get_mut(id) {
            node.layout_cache = Some(LayoutCache {
                rect,
                screen_rect,
                constraints,
                generation: self.generation,
            });
        }
    }

    /// Iterate over all nodes (parent before children).
    pub fn iter(&self) -> impl Iterator<Item = &TreeNode> {
        self.nodes.values()
    }

    /// Iterate over all nodes with their IDs.
    pub fn iter_with_ids(&self) -> impl Iterator<Item = (NodeId, &TreeNode)> {
        self.nodes.iter()
    }

    /// Walk the tree from root, calling `f` for each node.
    /// Returns early if `f` returns false.
    pub fn walk<F>(&self, mut f: F)
    where
        F: FnMut(&TreeNode, u32) -> bool,
    {
        if let Some(root_id) = self.root {
            self.walk_node(root_id, 0, &mut f);
        }
    }

    fn walk_node<F>(&self, id: NodeId, depth: u32, f: &mut F)
    where
        F: FnMut(&TreeNode, u32) -> bool,
    {
        if let Some(node) = self.nodes.get(id) {
            if !f(node, depth) {
                return;
            }

            for &child_id in &node.children {
                self.walk_node(child_id, depth + 1, f);
            }
        }
    }

    /// Get children of a node.
    pub fn children(&self, id: NodeId) -> Option<&[NodeId]> {
        self.nodes.get(id).map(|n| n.children.as_slice())
    }
}

/// Intersect a `SubcomposeScope` with a `Modifier`'s size-related fields.
/// `Modifier::width` / `Modifier::height` are treated as exact sizes (the
/// resulting min and max both equal that value). Padding values reduce the
/// available content area (matching Compose semantics where padding offsets
/// the child constraints). `fill_max_w` / `fill_max_h` are layout-direction
/// hints resolved by Taffy and cannot produce a concrete size here. They
/// are handled by storing the Taffy-computed size after layout.
fn intersect_scope_with_modifier(scope: SubcomposeScope, modifier: &Modifier) -> SubcomposeScope {
    let mut s = scope;
    // `size()` sets both min and max to the same value (exact size).
    if let Some(sz) = modifier.size {
        s.min_width = s.min_width.max(sz.width);
        s.max_width = s.max_width.min(sz.width);
        s.min_height = s.min_height.max(sz.height);
        s.max_height = s.max_height.min(sz.height);
    }
    if let Some(w) = modifier.width {
        s.min_width = s.min_width.max(w);
        s.max_width = s.max_width.min(w);
    }
    if let Some(h) = modifier.height {
        s.min_height = s.min_height.max(h);
        s.max_height = s.max_height.min(h);
    }
    if let Some(mw) = modifier.min_width {
        s.min_width = s.min_width.max(mw);
    }
    if let Some(mh) = modifier.min_height {
        s.min_height = s.min_height.max(mh);
    }
    if let Some(mw) = modifier.max_width {
        s.max_width = s.max_width.min(mw);
    }
    if let Some(mh) = modifier.max_height {
        s.max_height = s.max_height.min(mh);
    }
    // Padding reduces the available content area (Compose semantics:
    // constraints are offset by the padding amount).
    if let Some(p) = modifier.padding {
        let total = p * 2.0;
        s.min_width = (s.min_width - total).max(repose_core::Dp::ZERO);
        s.max_width = (s.max_width - total).max(repose_core::Dp::ZERO);
        s.min_height = (s.min_height - total).max(repose_core::Dp::ZERO);
        s.max_height = (s.max_height - total).max(repose_core::Dp::ZERO);
    }
    if let Some(pv) = modifier.padding_values {
        let h_total = pv.left + pv.right;
        let v_total = pv.top + pv.bottom;
        s.min_width = (s.min_width - h_total).max(repose_core::Dp::ZERO);
        s.max_width = (s.max_width - h_total).max(repose_core::Dp::ZERO);
        s.min_height = (s.min_height - v_total).max(repose_core::Dp::ZERO);
        s.max_height = (s.max_height - v_total).max(repose_core::Dp::ZERO);
    }
    if let Some(required) = modifier.required_size {
        s.min_width = required.width.max(repose_core::Dp::ZERO);
        s.max_width = s.min_width;
        s.min_height = required.height.max(repose_core::Dp::ZERO);
        s.max_height = s.min_height;
    }
    if let Some(value) = modifier.required_min_width {
        s.min_width = value.max(repose_core::Dp::ZERO);
        if s.min_width > s.max_width {
            s.max_width = s.min_width;
        }
    }
    if let Some(value) = modifier.required_max_width {
        s.max_width = value.max(repose_core::Dp::ZERO);
        if s.min_width > s.max_width {
            s.min_width = s.max_width;
        }
    }
    if let Some(value) = modifier.required_min_height {
        s.min_height = value.max(repose_core::Dp::ZERO);
        if s.min_height > s.max_height {
            s.max_height = s.min_height;
        }
    }
    if let Some(value) = modifier.required_max_height {
        s.max_height = value.max(repose_core::Dp::ZERO);
        if s.min_height > s.max_height {
            s.min_height = s.max_height;
        }
    }
    if s.min_width > s.max_width {
        let coerced = s.max_width.max(repose_core::Dp::ZERO);
        s.min_width = coerced;
        s.max_width = coerced;
    }
    if s.min_height > s.max_height {
        let coerced = s.max_height.max(repose_core::Dp::ZERO);
        s.min_height = coerced;
        s.max_height = coerced;
    }
    SubcomposeScope::new(s.min_width, s.max_width, s.min_height, s.max_height)
}

#[cfg(test)]
mod tests {
    use super::*;
    use repose_core::{
        Color, Dp, DrawStyle, FontStyle, FontWeight, Modifier, Sp, SubcomposeScope, TextAlign,
        TextDecoration, UnitExt, View, ViewKind,
    };
    use std::rc::Rc;
    use std::sync::Arc;

    fn text_view(text: &str) -> View {
        View::new(
            0,
            ViewKind::Text {
                text: text.to_string(),
                color: Color::WHITE,
                font_size: 16.0.sp(),
                soft_wrap: true,
                max_lines: None,
                overflow: repose_core::TextOverflow::Visible,
                font_family: None,
                annotations: None,
                text_align: TextAlign::Unspecified,
                font_weight: FontWeight::NORMAL,
                font_style: FontStyle::Normal,
                text_decoration: TextDecoration::default(),
                letter_spacing: Sp::ZERO,
                line_height: Sp::ZERO,
                url: None,
                font_variation_settings: None,
                draw_style: DrawStyle::Fill,
            },
        )
    }

    fn box_view() -> View {
        View::new(0, ViewKind::Box)
    }

    #[test]
    fn test_create_tree() {
        let mut tree = ViewTree::new();

        let root = box_view().with_children(vec![text_view("Hello"), text_view("World")]);

        tree.update(&root);

        assert_eq!(tree.len(), 3); // box + 2 text
        assert!(tree.root().is_some());
    }

    #[test]
    fn test_unchanged_tree_skips() {
        let mut tree = ViewTree::new();

        let root = box_view().with_children(vec![text_view("Hello")]);

        tree.update(&root);
        let gen1 = tree.generation();

        tree.update(&root);
        let gen2 = tree.generation();

        assert_eq!(gen2, gen1 + 1);
        assert!(tree.stats.skipped_nodes > 0);
    }

    #[test]
    fn test_changed_content_reconciles() {
        let mut tree = ViewTree::new();

        let root1 = box_view().with_children(vec![text_view("Hello")]);

        tree.update(&root1);

        let root2 = box_view().with_children(vec![text_view("Changed")]);

        tree.update(&root2);

        assert!(tree.stats.reconciled_nodes > 0);
    }

    #[test]
    fn generated_view_ids_are_unique_and_stable() {
        let mut tree = ViewTree::new();
        let branch = |text: &str| box_view().with_children(vec![text_view(text)]);
        let root = box_view().with_children(vec![
            text_view("keyed").modifier(Modifier::new().key(1)),
            text_view("unkeyed"),
            branch("left"),
            branch("right"),
        ]);

        tree.update(&root);
        let first: Vec<(NodeId, u64)> = tree
            .iter_with_ids()
            .map(|(id, node)| (id, node.view_id))
            .collect();
        let unique: std::collections::HashSet<u64> = first.iter().map(|(_, id)| *id).collect();
        assert_eq!(unique.len(), first.len());
        for (node_id, view_id) in &first {
            assert_eq!(
                tree.get_by_view_id(*view_id).map(|node| node.id),
                Some(*node_id)
            );
        }

        tree.update(&root);
        let second: Vec<(NodeId, u64)> = tree
            .iter_with_ids()
            .map(|(id, node)| (id, node.view_id))
            .collect();
        assert_eq!(first, second);
    }

    #[test]
    fn duplicate_explicit_ids_keep_first_lookup_stable() {
        let mut tree = ViewTree::new();
        let mut first = text_view("first").modifier(Modifier::new().key(1));
        let mut second = text_view("second").modifier(Modifier::new().key(2));
        first.id = 42;
        second.id = 42;
        let root = box_view().with_children(vec![first.clone(), second.clone()]);
        let root_id = tree.update(&root);
        let first_id = tree.children(root_id).unwrap()[0];
        assert_eq!(tree.get_by_view_id(42).map(|node| node.id), Some(first_id));
        let root = box_view().with_children(vec![second]);
        tree.update(&root);
        let second_id = tree.children(tree.root().unwrap()).unwrap()[0];
        assert_eq!(tree.get_by_view_id(42).map(|node| node.id), Some(second_id));
    }

    #[test]
    fn replaced_text_selection_is_picked_up() {
        let mut tree = ViewTree::new();
        let first = repose_core::text::TextSelection::default();
        let second = repose_core::text::TextSelection::default();
        assert_ne!(first.stable_id(), second.stable_id());

        let root = box_view().with_children(vec![
            text_view("hi").modifier(Modifier::new().text_selection(first.clone())),
        ]);
        let node = tree.update(&root);
        let node = tree.children(node).unwrap()[0];
        tree.set_layout(
            node,
            Rect::default(),
            Rect::default(),
            crate::LayoutConstraints::default(),
        );
        tree.update(&root);
        assert!(tree.get(node).unwrap().has_valid_layout());

        let replaced = box_view().with_children(vec![
            text_view("hi").modifier(Modifier::new().text_selection(second.clone())),
        ]);
        tree.update(&replaced);

        let stored = &tree.get(node).unwrap().modifier.text_selection;
        assert_eq!(
            stored.as_ref().map(|selection| selection.stable_id()),
            Some(second.stable_id())
        );
        assert!(tree.paint_dirty_nodes().contains(&node));
        assert!(tree.get(node).unwrap().has_valid_layout());
    }

    #[test]
    fn explicit_id_change_releases_the_old_id() {
        let mut tree = ViewTree::new();
        let mut view = text_view("first").modifier(Modifier::new().key(1));
        view.id = 7;
        let root = box_view().with_children(vec![view.clone()]);
        let child = tree.update(&root);
        let child = tree.children(child).unwrap()[0];
        assert_eq!(tree.get_by_view_id(7).map(|node| node.id), Some(child));

        let mut renamed = view;
        renamed.id = 9;
        tree.update(&box_view().with_children(vec![renamed]));
        let child = tree.children(tree.root().unwrap()).unwrap()[0];

        assert_eq!(tree.get_by_view_id(7).map(|node| node.id), None);
        assert_eq!(tree.get_by_view_id(9).map(|node| node.id), Some(child));
    }

    #[test]
    fn test_keyed_children_stable() {
        let mut tree = ViewTree::new();

        // Initial: A, B, C
        let root1 = box_view().with_children(vec![
            text_view("A").modifier(Modifier::new().key(1)),
            text_view("B").modifier(Modifier::new().key(2)),
            text_view("C").modifier(Modifier::new().key(3)),
        ]);

        tree.update(&root1);

        let _b_view_id = tree
            .root()
            .and_then(|r| tree.children(r))
            .and_then(|c| c.get(1).copied())
            .and_then(|id| tree.get(id))
            .map(|n| n.view_id);

        // Reorder: C, A, B
        let root2 = box_view().with_children(vec![
            text_view("C").modifier(Modifier::new().key(3)),
            text_view("A").modifier(Modifier::new().key(1)),
            text_view("B").modifier(Modifier::new().key(2)),
        ]);

        tree.update(&root2);

        // B should have same view_id (key-based stability)
        // Note: Implementation detail - the node may be reused
        assert_eq!(tree.len(), 4); // Still 4 nodes (box + 3 text)
    }

    fn subcompose_view<F>(f: F) -> View
    where
        F: Fn(&SubcomposeScope) -> View + 'static,
    {
        let content: Arc<dyn Fn(&SubcomposeScope) -> Vec<(u64, View)>> =
            Arc::new(move |scope| vec![(0, f(scope))]);
        View {
            id: 0,
            kind: ViewKind::SubcomposeLayout { content },
            modifier: Modifier::default(),
            children: Vec::new(),
            scope_key: None,
            semantics: None,
        }
    }

    #[test]
    fn callback_identity_updates_handlers_without_layout_reset() {
        let mut tree = ViewTree::new();
        let calls = Arc::new(std::sync::atomic::AtomicUsize::new(0));
        let content_calls = calls.clone();
        let content: Arc<dyn Fn(&SubcomposeScope) -> Vec<(u64, View)>> = Arc::new(move |_| {
            content_calls.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
            vec![(0, text_view("callback"))]
        });
        let make = |callback: Rc<dyn Fn()>| {
            let callback = callback.clone();
            View {
                id: 0,
                kind: ViewKind::SubcomposeLayout {
                    content: content.clone(),
                },
                modifier: Modifier::new().on_click(move || callback()),
                children: Vec::new(),
                scope_key: None,
                semantics: None,
            }
        };
        let root = make(Rc::new(|| {}));
        let root_id = tree.update(&root);
        tree.set_layout(
            root_id,
            Rect {
                x: 0.0,
                y: 0.0,
                w: 100.0,
                h: 100.0,
            },
            Rect {
                x: 0.0,
                y: 0.0,
                w: 100.0,
                h: 100.0,
            },
            crate::LayoutConstraints::default(),
        );
        let root = make(Rc::new(|| {}));
        tree.update(&root);
        let calls_before = calls.load(std::sync::atomic::Ordering::SeqCst);
        tree.update(&root);
        assert!(tree.get(root_id).unwrap().has_valid_layout());
        assert_eq!(
            calls.load(std::sync::atomic::Ordering::SeqCst),
            calls_before
        );
        let calls_before = calls.load(std::sync::atomic::Ordering::SeqCst);
        let root = make(Rc::new(|| {}));
        tree.update(&root);
        assert!(tree.get(root_id).unwrap().has_valid_layout());
        assert_eq!(
            calls.load(std::sync::atomic::Ordering::SeqCst),
            calls_before
        );
        assert!(tree.paint_dirty_nodes().contains(&root_id));
    }

    #[test]
    fn test_subcompose_invokes_content() {
        let mut tree = ViewTree::new();
        let counter = Arc::new(std::sync::atomic::AtomicUsize::new(0));
        let counter2 = counter.clone();

        let root = box_view().with_children(vec![subcompose_view(move |_scope| {
            counter2.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
            text_view("from subcompose")
        })]);

        tree.update(&root);

        assert_eq!(counter.load(std::sync::atomic::Ordering::SeqCst), 1);
        assert_eq!(tree.len(), 3); // box + subcompose + text
    }

    #[test]
    fn test_subcompose_receives_scope() {
        let mut tree = ViewTree::new();
        let captured = Arc::new(std::sync::Mutex::new(None));
        let captured2 = captured.clone();

        let root = box_view().with_children(vec![subcompose_view(move |scope| {
            *captured2.lock().unwrap() = Some(*scope);
            text_view("hi")
        })]);

        tree.set_subcompose_scope(SubcomposeScope::new(Dp(0.0), Dp(360.0), Dp(0.0), Dp(640.0)));
        tree.update(&root);

        let observed = captured.lock().unwrap().expect("scope captured");
        assert_eq!(observed.max_width, Dp(360.0));
        assert_eq!(observed.max_height, Dp(640.0));
        assert_eq!(observed.min_width, Dp(0.0));
        assert_eq!(observed.min_height, Dp(0.0));
    }

    #[test]
    fn zero_subcompose_bounds_are_real() {
        let mut tree = ViewTree::new();
        let captured = Arc::new(std::sync::Mutex::new(None));
        let captured2 = captured.clone();
        let root = box_view().with_children(vec![subcompose_view(move |scope| {
            *captured2.lock().unwrap() = Some(*scope);
            text_view("zero")
        })]);
        tree.set_subcompose_scope(SubcomposeScope::new(Dp(0.0), Dp(0.0), Dp(0.0), Dp(0.0)));
        tree.update(&root);
        let scope = captured.lock().unwrap().unwrap();
        assert_eq!(scope.min_width, Dp(0.0));
        assert_eq!(scope.max_width, Dp(0.0));
        assert_eq!(scope.min_height, Dp(0.0));
        assert_eq!(scope.max_height, Dp(0.0));
    }

    #[test]
    fn test_subcompose_re_invokes_on_update() {
        let mut tree = ViewTree::new();
        let counter = Arc::new(std::sync::atomic::AtomicUsize::new(0));
        let counter2 = counter.clone();

        let root = box_view().with_children(vec![subcompose_view(move |_scope| {
            counter2.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
            text_view("hi")
        })]);

        tree.update(&root);
        tree.update(&root);
        tree.update(&root);

        // Closure should run only on the first update; subsequent updates hit
        // the cache because the scope and content are unchanged.
        assert_eq!(counter.load(std::sync::atomic::Ordering::SeqCst), 1);
    }

    #[test]
    fn test_subcompose_reruns_on_scope_change() {
        let mut tree = ViewTree::new();
        let counter = Arc::new(std::sync::atomic::AtomicUsize::new(0));
        let counter2 = counter.clone();

        let root = box_view().with_children(vec![subcompose_view(move |_scope| {
            counter2.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
            text_view("hi")
        })]);

        tree.set_subcompose_scope(SubcomposeScope::new(Dp(0.0), Dp(100.0), Dp(0.0), Dp(100.0)));
        tree.update(&root);
        assert_eq!(counter.load(std::sync::atomic::Ordering::SeqCst), 1);

        // Same scope: cache hit.
        tree.update(&root);
        assert_eq!(counter.load(std::sync::atomic::Ordering::SeqCst), 1);

        // Scope changed: closure re-runs.
        tree.set_subcompose_scope(SubcomposeScope::new(Dp(0.0), Dp(200.0), Dp(0.0), Dp(200.0)));
        tree.update(&root);
        assert_eq!(counter.load(std::sync::atomic::Ordering::SeqCst), 2);
    }

    #[test]
    fn test_subcompose_settles_on_final_scope() {
        let mut tree = ViewTree::new();
        let root = box_view().with_children(vec![subcompose_view(|scope| {
            text_view("content").modifier(Modifier::new().width(scope.max_width))
        })]);

        for width in [100.0f32, 200.0, 300.0, 400.0, 500.0, 500.0, 500.0, 500.0] {
            tree.set_subcompose_scope(SubcomposeScope::new(Dp(0.0), Dp(width), Dp(0.0), Dp(width)));
            tree.update(&root);
        }

        let sub_id = tree.children(tree.root().unwrap()).unwrap()[0];
        let child_id = tree.children(sub_id).unwrap()[0];
        assert_eq!(
            tree.get(child_id).unwrap().modifier.width,
            Some(Dp(500.0)),
            "closure must end up holding the scope that settled"
        );
    }

    #[test]
    fn test_subcompose_scope_ignores_own_measured_size() {
        let mut tree = ViewTree::new();
        let captured = Arc::new(std::sync::Mutex::new(SubcomposeScope::UNBOUNDED));
        let captured2 = captured.clone();
        let root = box_view().with_children(vec![subcompose_view(move |scope| {
            *captured2.lock().unwrap() = *scope;
            text_view("hi")
        })]);

        tree.set_subcompose_scope(SubcomposeScope::new(
            Dp(0.0),
            Dp(1000.0),
            Dp(0.0),
            Dp(1000.0),
        ));
        let root_id = tree.update(&root);
        let sub_id = tree.children(root_id).unwrap()[0];

        let narrow = Rect {
            x: 0.0,
            y: 0.0,
            w: 120.0,
            h: 40.0,
        };
        tree.set_layout(sub_id, narrow, narrow, crate::LayoutConstraints::default());
        tree.update(&root);

        assert_eq!(captured.lock().unwrap().max_width, Dp(1000.0));
    }

    #[test]
    fn test_subcompose_reruns_on_content_change() {
        let mut tree = ViewTree::new();
        let counter = Arc::new(std::sync::atomic::AtomicUsize::new(0));
        let c1 = counter.clone();

        let root1 = box_view().with_children(vec![subcompose_view(move |_scope| {
            c1.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
            text_view("hi")
        })]);

        tree.update(&root1);
        assert_eq!(counter.load(std::sync::atomic::Ordering::SeqCst), 1);

        // Same content: cache hit.
        tree.update(&root1);
        assert_eq!(counter.load(std::sync::atomic::Ordering::SeqCst), 1);

        // Changed modifier: closure re-runs.
        let c2 = counter.clone();
        let root2 = box_view().with_children(vec![
            subcompose_view(move |_scope| {
                c2.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
                text_view("hi")
            })
            .modifier(Modifier::new().padding(4.0.dp())),
        ]);

        tree.update(&root2);
        assert_eq!(counter.load(std::sync::atomic::Ordering::SeqCst), 2);
    }

    #[test]
    fn test_subcompose_cache_drops_on_node_removal() {
        let mut tree = ViewTree::new();
        tree.set_subcompose_scope(SubcomposeScope::new(Dp(0.0), Dp(100.0), Dp(0.0), Dp(100.0)));

        // First root has a SubcomposeLayout child.
        let counter = Arc::new(std::sync::atomic::AtomicUsize::new(0));
        let c1 = counter.clone();
        let root_with_sub = box_view().with_children(vec![subcompose_view(move |_scope| {
            c1.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
            text_view("hi")
        })]);

        tree.update(&root_with_sub);
        assert_eq!(counter.load(std::sync::atomic::Ordering::SeqCst), 1);

        // Swap to a root without the SubcomposeLayout - the old node should be
        // garbage-collected and its cache entry dropped.
        let root_no_sub = box_view().with_children(vec![text_view("plain")]);
        tree.update(&root_no_sub);
        assert_eq!(tree.len(), 2);

        // Bring the SubcomposeLayout back - it must run the closure again
        // because the cache entry was dropped during GC.
        let c2 = counter.clone();
        let root_with_sub_again = box_view().with_children(vec![subcompose_view(move |_scope| {
            c2.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
            text_view("hi")
        })]);

        tree.update(&root_with_sub_again);
        assert_eq!(counter.load(std::sync::atomic::Ordering::SeqCst), 2);
    }

    fn multi_slot_view<F>(f: F) -> View
    where
        F: Fn(&SubcomposeScope) -> Vec<(u64, View)> + 'static,
    {
        let content: Arc<dyn Fn(&SubcomposeScope) -> Vec<(u64, View)>> = Arc::new(f);
        View {
            id: 0,
            kind: ViewKind::SubcomposeLayout { content },
            modifier: Modifier::default(),
            children: Vec::new(),
            scope_key: None,
            semantics: None,
        }
    }

    #[test]
    fn test_subcompose_multi_slot_produces_multiple_children() {
        let mut tree = ViewTree::new();
        let root = box_view().with_children(vec![multi_slot_view(|_scope| {
            vec![
                (0, text_view("a")),
                (1, text_view("b")),
                (2, text_view("c")),
            ]
        })]);

        tree.update(&root);

        // box + subcompose + 3 texts
        assert_eq!(tree.len(), 5);
        let sub_id = tree
            .root()
            .and_then(|r| tree.children(r))
            .and_then(|c| c.first().copied())
            .expect("subcompose node");
        let sub_children = tree.children(sub_id).expect("subcompose has children");
        assert_eq!(sub_children.len(), 3);
    }

    #[test]
    fn test_subcompose_multi_slot_preserves_identity_across_removal() {
        let mut tree = ViewTree::new();

        // 3 slots: 0, 1, 2
        let root3 = box_view().with_children(vec![multi_slot_view(|_scope| {
            vec![
                (0, text_view("a")),
                (1, text_view("b")),
                (2, text_view("c")),
            ]
        })]);
        tree.update(&root3);

        let sub_id = tree
            .root()
            .and_then(|r| tree.children(r))
            .and_then(|c| c.first().copied())
            .expect("subcompose node");
        let before = tree.children(sub_id).expect("children").to_vec();
        let a_node = before[0];
        let b_node = before[1];
        let c_node = before[2];

        // 2 slots: 0, 2 (middle removed). The Modifier change (padding) forces
        // the subcompose cache to invalidate so the new closure runs.
        let root2 = box_view().with_children(vec![
            multi_slot_view(|_scope| vec![(0, text_view("a")), (2, text_view("c"))])
                .modifier(Modifier::new().padding(4.0.dp())),
        ]);
        tree.update(&root2);

        let after = tree.children(sub_id).expect("children after");
        assert_eq!(after.len(), 2);
        // Slot 0 (a) and slot 2 (c) should keep their NodeId.
        assert_eq!(after[0], a_node);
        assert_eq!(after[1], c_node);
        // Slot 1 (b) should be gone.
        assert!(tree.get(b_node).is_none());
    }

    #[test]
    fn test_subcompose_ancestor_modifier_narrows_scope() {
        let mut tree = ViewTree::new();
        tree.set_subcompose_scope(SubcomposeScope::new(
            Dp(0.0),
            Dp(1000.0),
            Dp(0.0),
            Dp(1000.0),
        ));

        let captured = Arc::new(std::sync::Mutex::new(SubcomposeScope::UNBOUNDED));
        let cap2 = captured.clone();

        // SubcomposeLayout inside a Box with width(200.dp) - the closure should
        // see max_width == 200.
        let sub = multi_slot_view(move |scope| {
            *cap2.lock().unwrap() = *scope;
            vec![(0, text_view("hi"))]
        });
        let root = box_view()
            .modifier(Modifier::new().width(200.0.dp()))
            .with_children(vec![sub]);

        tree.update(&root);

        let observed = *captured.lock().unwrap();
        assert_eq!(observed.max_width, Dp(200.0));
    }

    #[test]
    fn test_subcompose_chained_ancestor_constraints_intersect() {
        let mut tree = ViewTree::new();
        tree.set_subcompose_scope(SubcomposeScope::new(
            Dp(0.0),
            Dp(1000.0),
            Dp(0.0),
            Dp(1000.0),
        ));

        let captured = Arc::new(std::sync::Mutex::new(SubcomposeScope::UNBOUNDED));
        let cap2 = captured.clone();

        let sub = multi_slot_view(move |scope| {
            *cap2.lock().unwrap() = *scope;
            vec![(0, text_view("hi"))]
        });
        // Box(width=400) -> Box(max_width=300) -> SubcomposeLayout.
        // The intersection should give max_width = 300.
        let root = box_view()
            .modifier(Modifier::new().width(400.0.dp()))
            .with_children(vec![
                box_view()
                    .modifier(Modifier::new().max_width(300.0.dp()))
                    .with_children(vec![sub]),
            ]);

        tree.update(&root);

        let observed = *captured.lock().unwrap();
        assert_eq!(observed.max_width, Dp(300.0));
    }

    #[test]
    // Test-only: the view is shared across closures on one thread; Arc is structural.
    #[allow(clippy::arc_with_non_send_sync)]
    fn test_subcompose_nested_layouts_inherit_narrowed_scope() {
        let mut tree = ViewTree::new();
        tree.set_subcompose_scope(SubcomposeScope::new(
            Dp(0.0),
            Dp(1000.0),
            Dp(0.0),
            Dp(1000.0),
        ));

        let outer_captured = Arc::new(std::sync::Mutex::new(SubcomposeScope::UNBOUNDED));
        let inner_captured = Arc::new(std::sync::Mutex::new(SubcomposeScope::UNBOUNDED));
        let outer2 = outer_captured.clone();
        let inner2 = inner_captured.clone();

        // Outer SubcomposeLayout(width=400) hosts an inner SubcomposeLayout.
        // The inner closure should observe max_width = 400, not 1000.
        let inner = Arc::new(multi_slot_view(move |scope| {
            *inner2.lock().unwrap() = *scope;
            vec![(0, text_view("inner"))]
        }));
        let inner_clone = inner.clone();
        let outer = multi_slot_view(move |scope| {
            *outer2.lock().unwrap() = *scope;
            vec![(0, (*inner_clone).clone())]
        })
        .modifier(Modifier::new().width(400.0.dp()));
        let root = box_view().with_children(vec![outer]);

        tree.update(&root);

        let outer_obs = *outer_captured.lock().unwrap();
        let inner_obs = *inner_captured.lock().unwrap();
        assert_eq!(outer_obs.max_width, Dp(400.0));
        assert_eq!(inner_obs.max_width, Dp(400.0));
    }
}