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use monolith_planner::Rect;
use slotmap::{SlotMap, new_key_type};
use std::collections::HashMap;
use std::hash::Hash;

new_key_type! { pub struct NodeId; }

#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub enum Axis {
    Horizontal,
    Vertical,
}

impl Axis {
    pub fn other(self) -> Self {
        match self {
            Self::Horizontal => Self::Vertical,
            Self::Vertical => Self::Horizontal,
        }
    }
}

#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub enum Dir {
    Left,
    Right,
    Up,
    Down,
}

impl Dir {
    pub fn axis(self) -> Axis {
        match self {
            Self::Left | Self::Right => Axis::Horizontal,
            Self::Up | Self::Down => Axis::Vertical,
        }
    }

    pub fn forward(self) -> bool {
        matches!(self, Self::Right | Self::Down)
    }
}

const MIN_SHARE: f64 = 0.05;

#[derive(Clone, Debug)]
struct Child {
    node: NodeId,
    weight: f64,
}

#[derive(Clone, Debug)]
enum Kind<W> {
    Leaf(W),
    Container {
        axis: Axis,
        children: Vec<Child>,
        expanded: Option<NodeId>,
    },
}

#[derive(Clone, Debug)]
struct Node<W> {
    parent: Option<NodeId>,
    kind: Kind<W>,
}

/// One output's tiling tree. Every tiled window of every tag lives here, the
/// caller's visibility filter decides which ones take space.
///
/// Children run on the axis opposite their parent. Containers hold at least
/// two children, hidden ones included, and a container left with one child
/// is replaced by it.
#[derive(Clone, Debug)]
pub struct Tree<W> {
    nodes: SlotMap<NodeId, Node<W>>,
    root: Option<NodeId>,
    leaves: HashMap<W, NodeId>,
    stack: Axis,
}

impl<W: Copy + Eq + Hash> Default for Tree<W> {
    fn default() -> Self {
        Self {
            nodes: SlotMap::with_key(),
            root: None,
            leaves: HashMap::new(),
            stack: Axis::Vertical,
        }
    }
}

impl<W: Copy + Eq + Hash> Tree<W> {
    /// The axis tag rows stack along.
    pub fn stack_axis(&self) -> Axis {
        self.stack
    }

    pub fn contains(&self, w: W) -> bool {
        self.leaves.contains_key(&w)
    }

    pub fn is_empty(&self) -> bool {
        self.root.is_none()
    }

    pub fn windows(&self) -> impl Iterator<Item = W> + '_ {
        self.leaves.keys().copied()
    }

    /// Inserts `w` as the next sibling of `anchor`, or as a new row if
    /// `anchor` is not in the tree.
    pub fn insert_after(&mut self, w: W, anchor: W) {
        let Some(&a) = self.leaves.get(&anchor) else {
            return self.insert_row(w);
        };
        let n = self.new_leaf(w);
        match self.position(a) {
            Some((p, i)) if Some(p) == self.root && self.axis(p) == Some(self.stack) => {
                let weight = self.unlink(p, i).weight;
                let c = self.new_container(self.stack.other());
                self.attach(c, 0, a, 1.0);
                self.attach(c, 1, n, 1.0);
                self.attach(p, i, c, weight);
            }
            Some((p, i)) => {
                let weight = self.mean_weight(p);
                self.attach(p, i + 1, n, weight);
            }
            None => {
                let c = self.new_container(self.stack.other());
                self.attach(c, 0, a, 1.0);
                self.attach(c, 1, n, 1.0);
                self.root = Some(c);
            }
        }
    }

    /// Appends `w` as a row of its own along the stacking axis.
    pub fn insert_row(&mut self, w: W) {
        let n = self.new_leaf(w);
        match self.root {
            None => self.root = Some(n),
            Some(r) if self.axis(r) == Some(self.stack) => {
                let weight = self.mean_weight(r);
                let end = self.children(r).len();
                self.attach(r, end, n, weight);
            }
            Some(r) => {
                let c = self.new_container(self.stack);
                self.attach(c, 0, r, 1.0);
                self.attach(c, 1, n, 1.0);
                self.root = Some(c);
            }
        }
    }

    pub fn remove(&mut self, w: W) -> bool {
        let Some(n) = self.leaves.remove(&w) else {
            return false;
        };
        self.detach(n);
        self.nodes.remove(n);
        true
    }

    pub fn retain(&mut self, mut keep: impl FnMut(W) -> bool) {
        let gone: Vec<W> = self.windows().filter(|&w| !keep(w)).collect();
        for w in gone {
            self.remove(w);
        }
    }

    /// Moves a window one step in `dir`. Leaves swap slots with the next
    /// visible sibling, enter a sibling container, or step out beside their
    /// container. Hidden windows never move.
    pub fn move_window(&mut self, w: W, dir: Dir, vis: impl Fn(W) -> bool) -> bool {
        let Some(&n) = self.leaves.get(&w) else {
            return false;
        };
        self.move_node(n, dir, &vis, true)
    }

    /// Moves the container holding `w` as a rigid block. A window sitting
    /// directly in the root is its own block.
    pub fn move_container(&mut self, w: W, dir: Dir, vis: impl Fn(W) -> bool) -> bool {
        let Some(&n) = self.leaves.get(&w) else {
            return false;
        };
        let block = self.nodes[n]
            .parent
            .filter(|&p| Some(p) != self.root)
            .unwrap_or(n);
        self.move_node(block, dir, &vis, false)
    }

    /// Moves a window to the end of the next visible lane in `dir`, stepping
    /// up a level when its container has none that way. A lone window there
    /// becomes a stack with it.
    pub fn merge_window(&mut self, w: W, dir: Dir, vis: impl Fn(W) -> bool) -> bool {
        let Some(&n) = self.leaves.get(&w) else {
            return false;
        };
        let mut cur = n;
        while let Some((p, i)) = self.position(cur) {
            if self.axis(p) == Some(dir.axis())
                && let Some(j) = self.next_shown(p, i, dir, &vis)
            {
                self.join_lane(n, p, j);
                return true;
            }
            cur = p;
        }
        false
    }

    /// Whether every container above `w` is expanded towards it.
    pub fn maximized(&self, w: W) -> bool {
        let Some(&leaf) = self.leaves.get(&w) else {
            return false;
        };
        let mut cur = leaf;
        let mut any = false;
        while let Some(p) = self.nodes[cur].parent {
            if self.expanded(p) != Some(cur) {
                return false;
            }
            any = true;
            cur = p;
        }
        any
    }

    /// Transposes the whole tree.
    pub fn flip(&mut self) {
        self.stack = self.stack.other();
        for node in self.nodes.values_mut() {
            if let Kind::Container { axis, .. } = &mut node.kind {
                *axis = axis.other();
            }
        }
    }

    /// Toggles expansion for `count` levels of `w`'s ancestry, starting
    /// `skip` levels up. Level 0 expands the window inside its container.
    pub fn toggle_expand(&mut self, w: W, skip: usize, count: usize) -> bool {
        let Some(&leaf) = self.leaves.get(&w) else {
            return false;
        };
        let mut path = Vec::new();
        let mut cur = leaf;
        while let Some(p) = self.nodes[cur].parent {
            path.push((p, cur));
            cur = p;
        }
        let path: Vec<_> = path.into_iter().skip(skip).take(count).collect();
        if path.is_empty() {
            return false;
        }
        let all = path.iter().all(|&(p, c)| self.expanded(p) == Some(c));
        for (p, c) in path {
            if let Kind::Container { expanded, .. } = &mut self.nodes[p].kind {
                *expanded = (!all).then_some(c);
            }
        }
        true
    }

    /// Grows `w` by `delta`, a fraction of the visible length of the nearest
    /// container along `axis` where it has a visible sibling. Hidden siblings
    /// keep their weights, and with them their share.
    pub fn resize(&mut self, w: W, axis: Axis, delta: f64, vis: impl Fn(W) -> bool) -> bool {
        let Some(&leaf) = self.leaves.get(&w) else {
            return false;
        };
        let mut cur = leaf;
        while let Some((p, i)) = self.position(cur) {
            if self.axis(p) == Some(axis) {
                let shown: Vec<usize> = (0..self.children(p).len())
                    .filter(|&j| self.visible(self.children(p)[j].node, &vis))
                    .collect();
                if shown.len() >= 2 {
                    let children = self.children_mut(p);
                    let sum: f64 = shown.iter().map(|&j| children[j].weight).sum();
                    let old = children[i].weight;
                    let max = 1.0 - MIN_SHARE * (shown.len() - 1) as f64;
                    let new = (old / sum + delta).clamp(MIN_SHARE, max) * sum;
                    let scale = (sum - new) / (sum - old);
                    for j in shown {
                        children[j].weight = if j == i {
                            new
                        } else {
                            children[j].weight * scale
                        };
                    }
                    return true;
                }
            }
            cur = p;
        }
        false
    }

    /// Lays the tree out in `area`. Hidden windows come back as zero-size
    /// rects on the boundary where they would reappear.
    pub fn arrange(&self, area: Rect, gap: f64, vis: impl Fn(W) -> bool) -> Vec<(W, Rect)> {
        let mut out = Vec::with_capacity(self.leaves.len());
        if let Some(r) = self.root {
            self.place(r, area, gap, &vis, &mut out);
        }
        out
    }

    fn place(
        &self,
        n: NodeId,
        r: Rect,
        gap: f64,
        vis: &impl Fn(W) -> bool,
        out: &mut Vec<(W, Rect)>,
    ) {
        let (axis, children, expanded) = match &self.nodes[n].kind {
            Kind::Leaf(w) => return out.push((*w, r)),
            Kind::Container {
                axis,
                children,
                expanded,
            } => (*axis, children, *expanded),
        };
        let shown: Vec<bool> = children.iter().map(|c| self.visible(c.node, vis)).collect();
        let (start, len) = span(r, axis);
        if let Some(e) = expanded.and_then(|e| children.iter().position(|c| c.node == e))
            && shown[e]
        {
            for (i, c) in children.iter().enumerate() {
                let sub = match i.cmp(&e) {
                    std::cmp::Ordering::Equal => r,
                    std::cmp::Ordering::Less => with_span(r, axis, start, 0.0),
                    std::cmp::Ordering::Greater => with_span(r, axis, start + len, 0.0),
                };
                self.place(c.node, sub, gap, vis, out);
            }
            return;
        }
        let count = shown.iter().filter(|s| **s).count();
        let total: f64 = children
            .iter()
            .zip(&shown)
            .filter(|(_, s)| **s)
            .map(|(c, _)| c.weight)
            .sum();
        let gaps = count.saturating_sub(1) as f64;
        let gap = if gaps > 0.0 { gap.min(len / gaps) } else { gap };
        let avail = len - gap * gaps;
        let last = shown.iter().rposition(|s| *s);
        let mut pos = start;
        let mut seen = false;
        for (i, c) in children.iter().enumerate() {
            if shown[i] {
                if seen {
                    pos += gap;
                }
                let l = avail * c.weight / total;
                self.place(c.node, with_span(r, axis, pos, l), gap, vis, out);
                pos += l;
                seen = true;
            } else {
                let between = seen && last.is_some_and(|l| l > i);
                let at = if between { pos + gap / 2.0 } else { pos };
                self.place(c.node, with_span(r, axis, at, 0.0), gap, vis, out);
            }
        }
    }

    fn move_node(&mut self, n: NodeId, dir: Dir, vis: &impl Fn(W) -> bool, enter: bool) -> bool {
        let mut cur = n;
        while let Some((p, i)) = self.position(cur) {
            if self.axis(p) == Some(dir.axis()) {
                let hidden_lane = self
                    .adjacent(p, i, dir)
                    .filter(|&j| enter && !self.visible(self.children(p)[j].node, vis));
                if cur != n {
                    if let Some(j) = hidden_lane {
                        self.join_lane(n, p, j);
                    } else {
                        let at = if dir.forward() { i + 1 } else { i };
                        self.relocate(n, p, at);
                    }
                    return true;
                }
                if let Some(j) = self.next_shown(p, i, dir, vis) {
                    let sib = self.children(p)[j].node;
                    if enter && self.axis(sib).is_some() {
                        let end = self.children(sib).len();
                        self.relocate(n, sib, end);
                    } else {
                        let children = self.children_mut(p);
                        children[i].node = sib;
                        children[j].node = n;
                    }
                    return true;
                }
                if let Some(j) = hidden_lane {
                    self.join_lane(n, p, j);
                    return true;
                }
            }
            cur = p;
        }
        if cur == n || self.axis(cur) == Some(dir.axis()) {
            return false;
        }
        let (old, i) = self.position(n).expect("n is below the root");
        self.unlink(old, i);
        self.normalize(old);
        let r = self.root.expect("the rest of the tree survives");
        if self.axis(r) == Some(dir.axis()) {
            let weight = self.mean_weight(r);
            let at = if dir.forward() {
                self.children(r).len()
            } else {
                0
            };
            self.attach(r, at, n, weight);
        } else {
            let c = self.new_container(dir.axis());
            self.attach(c, 0, r, 1.0);
            let at = if dir.forward() {
                self.children(c).len()
            } else {
                0
            };
            self.attach(c, at, n, 1.0);
            self.root = Some(c);
        }
        true
    }

    fn next_shown(&self, p: NodeId, i: usize, dir: Dir, vis: &impl Fn(W) -> bool) -> Option<usize> {
        let children = self.children(p);
        if dir.forward() {
            (i + 1..children.len()).find(|&j| self.visible(children[j].node, vis))
        } else {
            (0..i).rev().find(|&j| self.visible(children[j].node, vis))
        }
    }

    fn adjacent(&self, p: NodeId, i: usize, dir: Dir) -> Option<usize> {
        let j = if dir.forward() {
            i + 1
        } else {
            i.checked_sub(1)?
        };
        (j < self.children(p).len()).then_some(j)
    }

    /// Moves `n` to the end of the lane at `p`'s child `j`. A lone window
    /// there becomes a lane of its own, perpendicular to `p`.
    fn join_lane(&mut self, n: NodeId, p: NodeId, j: usize) {
        let lane = self.children(p)[j].node;
        let lane = if self.axis(lane).is_some() {
            lane
        } else {
            let c = self.new_container(self.axis(p).expect("p is a container").other());
            self.children_mut(p)[j].node = c;
            self.nodes[c].parent = Some(p);
            if let Kind::Container { expanded, .. } = &mut self.nodes[p].kind
                && *expanded == Some(lane)
            {
                *expanded = Some(c);
            }
            self.attach(c, 0, lane, 1.0);
            c
        };
        let end = self.children(lane).len();
        self.relocate(n, lane, end);
    }

    fn relocate(&mut self, n: NodeId, p: NodeId, at: usize) {
        let (old, i) = self.position(n).expect("relocated nodes have a parent");
        let weight = self.mean_weight(p);
        let at = if old == p && i < at { at - 1 } else { at };
        self.unlink(old, i);
        self.attach(p, at, n, weight);
        self.normalize(old);
    }

    /// Places `node` among `p`'s children. A container running along `p`'s
    /// axis is dissolved into `p` so axes keep alternating.
    fn attach(&mut self, p: NodeId, at: usize, node: NodeId, weight: f64) {
        if self.axis(node) == self.axis(p) {
            let Some(Node {
                kind: Kind::Container { children, .. },
                ..
            }) = self.nodes.remove(node)
            else {
                unreachable!("only containers have an axis");
            };
            let total: f64 = children.iter().map(|c| c.weight).sum();
            for (k, c) in children.into_iter().enumerate() {
                self.nodes[c.node].parent = Some(p);
                let weight = weight * c.weight / total;
                self.children_mut(p).insert(
                    at + k,
                    Child {
                        node: c.node,
                        weight,
                    },
                );
            }
        } else {
            self.nodes[node].parent = Some(p);
            self.children_mut(p).insert(at, Child { node, weight });
        }
    }

    fn unlink(&mut self, p: NodeId, i: usize) -> Child {
        let Kind::Container {
            children, expanded, ..
        } = &mut self.nodes[p].kind
        else {
            unreachable!("parents are containers");
        };
        let child = children.remove(i);
        if *expanded == Some(child.node) {
            *expanded = None;
        }
        self.nodes[child.node].parent = None;
        child
    }

    fn detach(&mut self, n: NodeId) {
        match self.position(n) {
            Some((p, i)) => {
                self.unlink(p, i);
                self.normalize(p);
            }
            None => self.root = None,
        }
    }

    /// Repairs a container that lost a child.
    fn normalize(&mut self, c: NodeId) {
        if self.children(c).len() >= 2 {
            return;
        }
        let pos = self.position(c);
        let was_expanded = pos.is_some_and(|(p, _)| self.expanded(p) == Some(c));
        let Some(Node {
            kind: Kind::Container { children, .. },
            ..
        }) = self.nodes.remove(c)
        else {
            unreachable!("only containers are normalized");
        };
        let only = children.into_iter().next();
        match (only, pos) {
            (None, Some((p, i))) => {
                self.unlink_dead(p, i);
                self.normalize(p);
            }
            (None, None) => self.root = None,
            (Some(only), Some((p, i))) => {
                let weight = self.unlink_dead(p, i).weight;
                let leaf_like = self.axis(only.node) != self.axis(p);
                self.attach(p, i, only.node, weight);
                if was_expanded
                    && leaf_like
                    && let Kind::Container { expanded, .. } = &mut self.nodes[p].kind
                {
                    *expanded = Some(only.node);
                }
            }
            (Some(only), None) => {
                self.nodes[only.node].parent = None;
                self.root = Some(only.node);
            }
        }
    }

    /// Like `unlink`, for a child whose node is already gone.
    fn unlink_dead(&mut self, p: NodeId, i: usize) -> Child {
        let Kind::Container {
            children, expanded, ..
        } = &mut self.nodes[p].kind
        else {
            unreachable!("parents are containers");
        };
        let child = children.remove(i);
        if *expanded == Some(child.node) {
            *expanded = None;
        }
        child
    }

    fn new_leaf(&mut self, w: W) -> NodeId {
        let n = self.nodes.insert(Node {
            parent: None,
            kind: Kind::Leaf(w),
        });
        self.leaves.insert(w, n);
        n
    }

    fn new_container(&mut self, axis: Axis) -> NodeId {
        self.nodes.insert(Node {
            parent: None,
            kind: Kind::Container {
                axis,
                children: Vec::new(),
                expanded: None,
            },
        })
    }

    fn position(&self, n: NodeId) -> Option<(NodeId, usize)> {
        let p = self.nodes[n].parent?;
        let i = self.children(p).iter().position(|c| c.node == n)?;
        Some((p, i))
    }

    fn axis(&self, n: NodeId) -> Option<Axis> {
        match &self.nodes[n].kind {
            Kind::Container { axis, .. } => Some(*axis),
            Kind::Leaf(_) => None,
        }
    }

    fn expanded(&self, n: NodeId) -> Option<NodeId> {
        match &self.nodes[n].kind {
            Kind::Container { expanded, .. } => *expanded,
            Kind::Leaf(_) => None,
        }
    }

    fn children(&self, n: NodeId) -> &[Child] {
        match &self.nodes[n].kind {
            Kind::Container { children, .. } => children,
            Kind::Leaf(_) => &[],
        }
    }

    fn children_mut(&mut self, n: NodeId) -> &mut Vec<Child> {
        match &mut self.nodes[n].kind {
            Kind::Container { children, .. } => children,
            Kind::Leaf(_) => unreachable!("leaves have no children"),
        }
    }

    fn mean_weight(&self, p: NodeId) -> f64 {
        let children = self.children(p);
        if children.is_empty() {
            1.0
        } else {
            children.iter().map(|c| c.weight).sum::<f64>() / children.len() as f64
        }
    }

    fn visible(&self, n: NodeId, vis: &impl Fn(W) -> bool) -> bool {
        match &self.nodes[n].kind {
            Kind::Leaf(w) => vis(*w),
            Kind::Container { children, .. } => children.iter().any(|c| self.visible(c.node, vis)),
        }
    }

    #[cfg(test)]
    pub(crate) fn check(&self) {
        let reachable = match self.root {
            Some(r) => {
                assert!(self.nodes[r].parent.is_none());
                self.check_node(r)
            }
            None => 0,
        };
        assert_eq!(reachable, self.nodes.len(), "orphaned nodes");
        for (&w, &n) in &self.leaves {
            assert!(matches!(self.nodes[n].kind, Kind::Leaf(x) if x == w));
        }
    }

    #[cfg(test)]
    fn check_node(&self, n: NodeId) -> usize {
        match &self.nodes[n].kind {
            Kind::Leaf(_) => 1,
            Kind::Container {
                axis,
                children,
                expanded,
            } => {
                assert!(
                    children.len() >= 2,
                    "container with {} children",
                    children.len()
                );
                if let Some(e) = expanded {
                    assert!(children.iter().any(|c| c.node == *e));
                }
                let mut count = 1;
                for c in children {
                    assert!(c.weight > 0.0 && c.weight.is_finite());
                    assert_eq!(self.nodes[c.node].parent, Some(n));
                    assert_ne!(self.axis(c.node), Some(*axis), "axes must alternate");
                    count += self.check_node(c.node);
                }
                count
            }
        }
    }
}

fn span(r: Rect, axis: Axis) -> (f64, f64) {
    match axis {
        Axis::Horizontal => (r.x, r.w),
        Axis::Vertical => (r.y, r.h),
    }
}

fn with_span(r: Rect, axis: Axis, start: f64, len: f64) -> Rect {
    match axis {
        Axis::Horizontal => Rect::new(start, r.y, len, r.h),
        Axis::Vertical => Rect::new(r.x, start, r.w, len),
    }
}

1	use monolith_planner::Rect;
2	use slotmap::{SlotMap, new_key_type};
3	use std::collections::HashMap;
4	use std::hash::Hash;
5
6	new_key_type! { pub struct NodeId; }
7
8	#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
9	pub enum Axis {
10	Horizontal,
11	Vertical,
12	}
13
14	impl Axis {
15	pub fn other(self) -> Self {
16	match self {
17	Self::Horizontal => Self::Vertical,
18	Self::Vertical => Self::Horizontal,
19	}
20	}
21	}
22
23	#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
24	pub enum Dir {
25	Left,
26	Right,
27	Up,
28	Down,
29	}
30
31	impl Dir {
32	pub fn axis(self) -> Axis {
33	match self {
34	Self::Left \| Self::Right => Axis::Horizontal,
35	Self::Up \| Self::Down => Axis::Vertical,
36	}
37	}
38
39	pub fn forward(self) -> bool {
40	matches!(self, Self::Right \| Self::Down)
41	}
42	}
43
44	const MIN_SHARE: f64 = 0.05;
45
46	#[derive(Clone, Debug)]
47	struct Child {
48	node: NodeId,
49	weight: f64,
50	}
51
52	#[derive(Clone, Debug)]
53	enum Kind<W> {
54	Leaf(W),
55	Container {
56	axis: Axis,
57	children: Vec<Child>,
58	expanded: Option<NodeId>,
59	},
60	}
61
62	#[derive(Clone, Debug)]
63	struct Node<W> {
64	parent: Option<NodeId>,
65	kind: Kind<W>,
66	}
67
68	/// One output's tiling tree. Every tiled window of every tag lives here, the
69	/// caller's visibility filter decides which ones take space.
70	///
71	/// Children run on the axis opposite their parent. Containers hold at least
72	/// two children, hidden ones included, and a container left with one child
73	/// is replaced by it.
74	#[derive(Clone, Debug)]
75	pub struct Tree<W> {
76	nodes: SlotMap<NodeId, Node<W>>,
77	root: Option<NodeId>,
78	leaves: HashMap<W, NodeId>,
79	stack: Axis,
80	}
81
82	impl<W: Copy + Eq + Hash> Default for Tree<W> {
83	fn default() -> Self {
84	Self {
85	nodes: SlotMap::with_key(),
86	root: None,
87	leaves: HashMap::new(),
88	stack: Axis::Vertical,
89	}
90	}
91	}
92
93	impl<W: Copy + Eq + Hash> Tree<W> {
94	/// The axis tag rows stack along.
95	pub fn stack_axis(&self) -> Axis {
96	self.stack
97	}
98
99	pub fn contains(&self, w: W) -> bool {
100	self.leaves.contains_key(&w)
101	}
102
103	pub fn is_empty(&self) -> bool {
104	self.root.is_none()
105	}
106
107	pub fn windows(&self) -> impl Iterator<Item = W> + '_ {
108	self.leaves.keys().copied()
109	}
110
111	/// Inserts `w` as the next sibling of `anchor`, or as a new row if
112	/// `anchor` is not in the tree.
113	pub fn insert_after(&mut self, w: W, anchor: W) {
114	let Some(&a) = self.leaves.get(&anchor) else {
115	return self.insert_row(w);
116	};
117	let n = self.new_leaf(w);
118	match self.position(a) {
119	Some((p, i)) if Some(p) == self.root && self.axis(p) == Some(self.stack) => {
120	let weight = self.unlink(p, i).weight;
121	let c = self.new_container(self.stack.other());
122	self.attach(c, 0, a, 1.0);
123	self.attach(c, 1, n, 1.0);
124	self.attach(p, i, c, weight);
125	}
126	Some((p, i)) => {
127	let weight = self.mean_weight(p);
128	self.attach(p, i + 1, n, weight);
129	}
130	None => {
131	let c = self.new_container(self.stack.other());
132	self.attach(c, 0, a, 1.0);
133	self.attach(c, 1, n, 1.0);
134	self.root = Some(c);
135	}
136	}
137	}
138
139	/// Appends `w` as a row of its own along the stacking axis.
140	pub fn insert_row(&mut self, w: W) {
141	let n = self.new_leaf(w);
142	match self.root {
143	None => self.root = Some(n),
144	Some(r) if self.axis(r) == Some(self.stack) => {
145	let weight = self.mean_weight(r);
146	let end = self.children(r).len();
147	self.attach(r, end, n, weight);
148	}
149	Some(r) => {
150	let c = self.new_container(self.stack);
151	self.attach(c, 0, r, 1.0);
152	self.attach(c, 1, n, 1.0);
153	self.root = Some(c);
154	}
155	}
156	}
157
158	pub fn remove(&mut self, w: W) -> bool {
159	let Some(n) = self.leaves.remove(&w) else {
160	return false;
161	};
162	self.detach(n);
163	self.nodes.remove(n);
164	true
165	}
166
167	pub fn retain(&mut self, mut keep: impl FnMut(W) -> bool) {
168	let gone: Vec<W> = self.windows().filter(\|&w\| !keep(w)).collect();
169	for w in gone {
170	self.remove(w);
171	}
172	}
173
174	/// Moves a window one step in `dir`. Leaves swap slots with the next
175	/// visible sibling, enter a sibling container, or step out beside their
176	/// container. Hidden windows never move.
177	pub fn move_window(&mut self, w: W, dir: Dir, vis: impl Fn(W) -> bool) -> bool {
178	let Some(&n) = self.leaves.get(&w) else {
179	return false;
180	};
181	self.move_node(n, dir, &vis, true)
182	}
183
184	/// Moves the container holding `w` as a rigid block. A window sitting
185	/// directly in the root is its own block.
186	pub fn move_container(&mut self, w: W, dir: Dir, vis: impl Fn(W) -> bool) -> bool {
187	let Some(&n) = self.leaves.get(&w) else {
188	return false;
189	};
190	let block = self.nodes[n]
191	.parent
192	.filter(\|&p\| Some(p) != self.root)
193	.unwrap_or(n);
194	self.move_node(block, dir, &vis, false)
195	}
196
197	/// Moves a window to the end of the next visible lane in `dir`, stepping
198	/// up a level when its container has none that way. A lone window there
199	/// becomes a stack with it.
200	pub fn merge_window(&mut self, w: W, dir: Dir, vis: impl Fn(W) -> bool) -> bool {
201	let Some(&n) = self.leaves.get(&w) else {
202	return false;
203	};
204	let mut cur = n;
205	while let Some((p, i)) = self.position(cur) {
206	if self.axis(p) == Some(dir.axis())
207	&& let Some(j) = self.next_shown(p, i, dir, &vis)
208	{
209	self.join_lane(n, p, j);
210	return true;
211	}
212	cur = p;
213	}
214	false
215	}
216
217	/// Whether every container above `w` is expanded towards it.
218	pub fn maximized(&self, w: W) -> bool {
219	let Some(&leaf) = self.leaves.get(&w) else {
220	return false;
221	};
222	let mut cur = leaf;
223	let mut any = false;
224	while let Some(p) = self.nodes[cur].parent {
225	if self.expanded(p) != Some(cur) {
226	return false;
227	}
228	any = true;
229	cur = p;
230	}
231	any
232	}
233
234	/// Transposes the whole tree.
235	pub fn flip(&mut self) {
236	self.stack = self.stack.other();
237	for node in self.nodes.values_mut() {
238	if let Kind::Container { axis, .. } = &mut node.kind {
239	*axis = axis.other();
240	}
241	}
242	}
243
244	/// Toggles expansion for `count` levels of `w`'s ancestry, starting
245	/// `skip` levels up. Level 0 expands the window inside its container.
246	pub fn toggle_expand(&mut self, w: W, skip: usize, count: usize) -> bool {
247	let Some(&leaf) = self.leaves.get(&w) else {
248	return false;
249	};
250	let mut path = Vec::new();
251	let mut cur = leaf;
252	while let Some(p) = self.nodes[cur].parent {
253	path.push((p, cur));
254	cur = p;
255	}
256	let path: Vec<_> = path.into_iter().skip(skip).take(count).collect();
257	if path.is_empty() {
258	return false;
259	}
260	let all = path.iter().all(\|&(p, c)\| self.expanded(p) == Some(c));
261	for (p, c) in path {
262	if let Kind::Container { expanded, .. } = &mut self.nodes[p].kind {
263	*expanded = (!all).then_some(c);
264	}
265	}
266	true
267	}
268
269	/// Grows `w` by `delta`, a fraction of the visible length of the nearest
270	/// container along `axis` where it has a visible sibling. Hidden siblings
271	/// keep their weights, and with them their share.
272	pub fn resize(&mut self, w: W, axis: Axis, delta: f64, vis: impl Fn(W) -> bool) -> bool {
273	let Some(&leaf) = self.leaves.get(&w) else {
274	return false;
275	};
276	let mut cur = leaf;
277	while let Some((p, i)) = self.position(cur) {
278	if self.axis(p) == Some(axis) {
279	let shown: Vec<usize> = (0..self.children(p).len())
280	.filter(\|&j\| self.visible(self.children(p)[j].node, &vis))
281	.collect();
282	if shown.len() >= 2 {
283	let children = self.children_mut(p);
284	let sum: f64 = shown.iter().map(\|&j\| children[j].weight).sum();
285	let old = children[i].weight;
286	let max = 1.0 - MIN_SHARE * (shown.len() - 1) as f64;
287	let new = (old / sum + delta).clamp(MIN_SHARE, max) * sum;
288	let scale = (sum - new) / (sum - old);
289	for j in shown {
290	children[j].weight = if j == i {
291	new
292	} else {
293	children[j].weight * scale
294	};
295	}
296	return true;
297	}
298	}
299	cur = p;
300	}
301	false
302	}
303
304	/// Lays the tree out in `area`. Hidden windows come back as zero-size
305	/// rects on the boundary where they would reappear.
306	pub fn arrange(&self, area: Rect, gap: f64, vis: impl Fn(W) -> bool) -> Vec<(W, Rect)> {
307	let mut out = Vec::with_capacity(self.leaves.len());
308	if let Some(r) = self.root {
309	self.place(r, area, gap, &vis, &mut out);
310	}
311	out
312	}
313
314	fn place(
315	&self,
316	n: NodeId,
317	r: Rect,
318	gap: f64,
319	vis: &impl Fn(W) -> bool,
320	out: &mut Vec<(W, Rect)>,
321	) {
322	let (axis, children, expanded) = match &self.nodes[n].kind {
323	Kind::Leaf(w) => return out.push((*w, r)),
324	Kind::Container {
325	axis,
326	children,
327	expanded,
328	} => (axis, children, expanded),
329	};
330	let shown: Vec<bool> = children.iter().map(\|c\| self.visible(c.node, vis)).collect();
331	let (start, len) = span(r, axis);
332	if let Some(e) = expanded.and_then(\|e\| children.iter().position(\|c\| c.node == e))
333	&& shown[e]
334	{
335	for (i, c) in children.iter().enumerate() {
336	let sub = match i.cmp(&e) {
337	std::cmp::Ordering::Equal => r,
338	std::cmp::Ordering::Less => with_span(r, axis, start, 0.0),
339	std::cmp::Ordering::Greater => with_span(r, axis, start + len, 0.0),
340	};
341	self.place(c.node, sub, gap, vis, out);
342	}
343	return;
344	}
345	let count = shown.iter().filter(\|s\| **s).count();
346	let total: f64 = children
347	.iter()
348	.zip(&shown)
349	.filter(\|(_, s)\| **s)
350	.map(\|(c, _)\| c.weight)
351	.sum();
352	let gaps = count.saturating_sub(1) as f64;
353	let gap = if gaps > 0.0 { gap.min(len / gaps) } else { gap };
354	let avail = len - gap * gaps;
355	let last = shown.iter().rposition(\|s\| *s);
356	let mut pos = start;
357	let mut seen = false;
358	for (i, c) in children.iter().enumerate() {
359	if shown[i] {
360	if seen {
361	pos += gap;
362	}
363	let l = avail * c.weight / total;
364	self.place(c.node, with_span(r, axis, pos, l), gap, vis, out);
365	pos += l;
366	seen = true;
367	} else {
368	let between = seen && last.is_some_and(\|l\| l > i);
369	let at = if between { pos + gap / 2.0 } else { pos };
370	self.place(c.node, with_span(r, axis, at, 0.0), gap, vis, out);
371	}
372	}
373	}
374
375	fn move_node(&mut self, n: NodeId, dir: Dir, vis: &impl Fn(W) -> bool, enter: bool) -> bool {
376	let mut cur = n;
377	while let Some((p, i)) = self.position(cur) {
378	if self.axis(p) == Some(dir.axis()) {
379	let hidden_lane = self
380	.adjacent(p, i, dir)
381	.filter(\|&j\| enter && !self.visible(self.children(p)[j].node, vis));
382	if cur != n {
383	if let Some(j) = hidden_lane {
384	self.join_lane(n, p, j);
385	} else {
386	let at = if dir.forward() { i + 1 } else { i };
387	self.relocate(n, p, at);
388	}
389	return true;
390	}
391	if let Some(j) = self.next_shown(p, i, dir, vis) {
392	let sib = self.children(p)[j].node;
393	if enter && self.axis(sib).is_some() {
394	let end = self.children(sib).len();
395	self.relocate(n, sib, end);
396	} else {
397	let children = self.children_mut(p);
398	children[i].node = sib;
399	children[j].node = n;
400	}
401	return true;
402	}
403	if let Some(j) = hidden_lane {
404	self.join_lane(n, p, j);
405	return true;
406	}
407	}
408	cur = p;
409	}
410	if cur == n \|\| self.axis(cur) == Some(dir.axis()) {
411	return false;
412	}
413	let (old, i) = self.position(n).expect("n is below the root");
414	self.unlink(old, i);
415	self.normalize(old);
416	let r = self.root.expect("the rest of the tree survives");
417	if self.axis(r) == Some(dir.axis()) {
418	let weight = self.mean_weight(r);
419	let at = if dir.forward() {
420	self.children(r).len()
421	} else {
422	0
423	};
424	self.attach(r, at, n, weight);
425	} else {
426	let c = self.new_container(dir.axis());
427	self.attach(c, 0, r, 1.0);
428	let at = if dir.forward() {
429	self.children(c).len()
430	} else {
431	0
432	};
433	self.attach(c, at, n, 1.0);
434	self.root = Some(c);
435	}
436	true
437	}
438
439	fn next_shown(&self, p: NodeId, i: usize, dir: Dir, vis: &impl Fn(W) -> bool) -> Option<usize> {
440	let children = self.children(p);
441	if dir.forward() {
442	(i + 1..children.len()).find(\|&j\| self.visible(children[j].node, vis))
443	} else {
444	(0..i).rev().find(\|&j\| self.visible(children[j].node, vis))
445	}
446	}
447
448	fn adjacent(&self, p: NodeId, i: usize, dir: Dir) -> Option<usize> {
449	let j = if dir.forward() {
450	i + 1
451	} else {
452	i.checked_sub(1)?
453	};
454	(j < self.children(p).len()).then_some(j)
455	}
456
457	/// Moves `n` to the end of the lane at `p`'s child `j`. A lone window
458	/// there becomes a lane of its own, perpendicular to `p`.
459	fn join_lane(&mut self, n: NodeId, p: NodeId, j: usize) {
460	let lane = self.children(p)[j].node;
461	let lane = if self.axis(lane).is_some() {
462	lane
463	} else {
464	let c = self.new_container(self.axis(p).expect("p is a container").other());
465	self.children_mut(p)[j].node = c;
466	self.nodes[c].parent = Some(p);
467	if let Kind::Container { expanded, .. } = &mut self.nodes[p].kind
468	&& *expanded == Some(lane)
469	{
470	*expanded = Some(c);
471	}
472	self.attach(c, 0, lane, 1.0);
473	c
474	};
475	let end = self.children(lane).len();
476	self.relocate(n, lane, end);
477	}
478
479	fn relocate(&mut self, n: NodeId, p: NodeId, at: usize) {
480	let (old, i) = self.position(n).expect("relocated nodes have a parent");
481	let weight = self.mean_weight(p);
482	let at = if old == p && i < at { at - 1 } else { at };
483	self.unlink(old, i);
484	self.attach(p, at, n, weight);
485	self.normalize(old);
486	}
487
488	/// Places `node` among `p`'s children. A container running along `p`'s
489	/// axis is dissolved into `p` so axes keep alternating.
490	fn attach(&mut self, p: NodeId, at: usize, node: NodeId, weight: f64) {
491	if self.axis(node) == self.axis(p) {
492	let Some(Node {
493	kind: Kind::Container { children, .. },
494	..
495	}) = self.nodes.remove(node)
496	else {
497	unreachable!("only containers have an axis");
498	};
499	let total: f64 = children.iter().map(\|c\| c.weight).sum();
500	for (k, c) in children.into_iter().enumerate() {
501	self.nodes[c.node].parent = Some(p);
502	let weight = weight * c.weight / total;
503	self.children_mut(p).insert(
504	at + k,
505	Child {
506	node: c.node,
507	weight,
508	},
509	);
510	}
511	} else {
512	self.nodes[node].parent = Some(p);
513	self.children_mut(p).insert(at, Child { node, weight });
514	}
515	}
516
517	fn unlink(&mut self, p: NodeId, i: usize) -> Child {
518	let Kind::Container {
519	children, expanded, ..
520	} = &mut self.nodes[p].kind
521	else {
522	unreachable!("parents are containers");
523	};
524	let child = children.remove(i);
525	if *expanded == Some(child.node) {
526	*expanded = None;
527	}
528	self.nodes[child.node].parent = None;
529	child
530	}
531
532	fn detach(&mut self, n: NodeId) {
533	match self.position(n) {
534	Some((p, i)) => {
535	self.unlink(p, i);
536	self.normalize(p);
537	}
538	None => self.root = None,
539	}
540	}
541
542	/// Repairs a container that lost a child.
543	fn normalize(&mut self, c: NodeId) {
544	if self.children(c).len() >= 2 {
545	return;
546	}
547	let pos = self.position(c);
548	let was_expanded = pos.is_some_and(\|(p, _)\| self.expanded(p) == Some(c));
549	let Some(Node {
550	kind: Kind::Container { children, .. },
551	..
552	}) = self.nodes.remove(c)
553	else {
554	unreachable!("only containers are normalized");
555	};
556	let only = children.into_iter().next();
557	match (only, pos) {
558	(None, Some((p, i))) => {
559	self.unlink_dead(p, i);
560	self.normalize(p);
561	}
562	(None, None) => self.root = None,
563	(Some(only), Some((p, i))) => {
564	let weight = self.unlink_dead(p, i).weight;
565	let leaf_like = self.axis(only.node) != self.axis(p);
566	self.attach(p, i, only.node, weight);
567	if was_expanded
568	&& leaf_like
569	&& let Kind::Container { expanded, .. } = &mut self.nodes[p].kind
570	{
571	*expanded = Some(only.node);
572	}
573	}
574	(Some(only), None) => {
575	self.nodes[only.node].parent = None;
576	self.root = Some(only.node);
577	}
578	}
579	}
580
581	/// Like `unlink`, for a child whose node is already gone.
582	fn unlink_dead(&mut self, p: NodeId, i: usize) -> Child {
583	let Kind::Container {
584	children, expanded, ..
585	} = &mut self.nodes[p].kind
586	else {
587	unreachable!("parents are containers");
588	};
589	let child = children.remove(i);
590	if *expanded == Some(child.node) {
591	*expanded = None;
592	}
593	child
594	}
595
596	fn new_leaf(&mut self, w: W) -> NodeId {
597	let n = self.nodes.insert(Node {
598	parent: None,
599	kind: Kind::Leaf(w),
600	});
601	self.leaves.insert(w, n);
602	n
603	}
604
605	fn new_container(&mut self, axis: Axis) -> NodeId {
606	self.nodes.insert(Node {
607	parent: None,
608	kind: Kind::Container {
609	axis,
610	children: Vec::new(),
611	expanded: None,
612	},
613	})
614	}
615
616	fn position(&self, n: NodeId) -> Option<(NodeId, usize)> {
617	let p = self.nodes[n].parent?;
618	let i = self.children(p).iter().position(\|c\| c.node == n)?;
619	Some((p, i))
620	}
621
622	fn axis(&self, n: NodeId) -> Option<Axis> {
623	match &self.nodes[n].kind {
624	Kind::Container { axis, .. } => Some(*axis),
625	Kind::Leaf(_) => None,
626	}
627	}
628
629	fn expanded(&self, n: NodeId) -> Option<NodeId> {
630	match &self.nodes[n].kind {
631	Kind::Container { expanded, .. } => *expanded,
632	Kind::Leaf(_) => None,
633	}
634	}
635
636	fn children(&self, n: NodeId) -> &[Child] {
637	match &self.nodes[n].kind {
638	Kind::Container { children, .. } => children,
639	Kind::Leaf(_) => &[],
640	}
641	}
642
643	fn children_mut(&mut self, n: NodeId) -> &mut Vec<Child> {
644	match &mut self.nodes[n].kind {
645	Kind::Container { children, .. } => children,
646	Kind::Leaf(_) => unreachable!("leaves have no children"),
647	}
648	}
649
650	fn mean_weight(&self, p: NodeId) -> f64 {
651	let children = self.children(p);
652	if children.is_empty() {
653	1.0
654	} else {
655	children.iter().map(\|c\| c.weight).sum::<f64>() / children.len() as f64
656	}
657	}
658
659	fn visible(&self, n: NodeId, vis: &impl Fn(W) -> bool) -> bool {
660	match &self.nodes[n].kind {
661	Kind::Leaf(w) => vis(*w),
662	Kind::Container { children, .. } => children.iter().any(\|c\| self.visible(c.node, vis)),
663	}
664	}
665
666	#[cfg(test)]
667	pub(crate) fn check(&self) {
668	let reachable = match self.root {
669	Some(r) => {
670	assert!(self.nodes[r].parent.is_none());
671	self.check_node(r)
672	}
673	None => 0,
674	};
675	assert_eq!(reachable, self.nodes.len(), "orphaned nodes");
676	for (&w, &n) in &self.leaves {
677	assert!(matches!(self.nodes[n].kind, Kind::Leaf(x) if x == w));
678	}
679	}
680
681	#[cfg(test)]
682	fn check_node(&self, n: NodeId) -> usize {
683	match &self.nodes[n].kind {
684	Kind::Leaf(_) => 1,
685	Kind::Container {
686	axis,
687	children,
688	expanded,
689	} => {
690	assert!(
691	children.len() >= 2,
692	"container with {} children",
693	children.len()
694	);
695	if let Some(e) = expanded {
696	assert!(children.iter().any(\|c\| c.node == *e));
697	}
698	let mut count = 1;
699	for c in children {
700	assert!(c.weight > 0.0 && c.weight.is_finite());
701	assert_eq!(self.nodes[c.node].parent, Some(n));
702	assert_ne!(self.axis(c.node), Some(*axis), "axes must alternate");
703	count += self.check_node(c.node);
704	}
705	count
706	}
707	}
708	}
709	}
710
711	fn span(r: Rect, axis: Axis) -> (f64, f64) {
712	match axis {
713	Axis::Horizontal => (r.x, r.w),
714	Axis::Vertical => (r.y, r.h),
715	}
716	}
717
718	fn with_span(r: Rect, axis: Axis, start: f64, len: f64) -> Rect {
719	match axis {
720	Axis::Horizontal => Rect::new(start, r.y, len, r.h),
721	Axis::Vertical => Rect::new(r.x, start, r.w, len),
722	}
723	}