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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_block(&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)
    }

    /// 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()) {
                if cur != n {
                    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;
                }
            }
            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 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_block(&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	/// Transposes the whole tree.
198	pub fn flip(&mut self) {
199	self.stack = self.stack.other();
200	for node in self.nodes.values_mut() {
201	if let Kind::Container { axis, .. } = &mut node.kind {
202	*axis = axis.other();
203	}
204	}
205	}
206
207	/// Toggles expansion for `count` levels of `w`'s ancestry, starting
208	/// `skip` levels up. Level 0 expands the window inside its container.
209	pub fn toggle_expand(&mut self, w: W, skip: usize, count: usize) -> bool {
210	let Some(&leaf) = self.leaves.get(&w) else {
211	return false;
212	};
213	let mut path = Vec::new();
214	let mut cur = leaf;
215	while let Some(p) = self.nodes[cur].parent {
216	path.push((p, cur));
217	cur = p;
218	}
219	let path: Vec<_> = path.into_iter().skip(skip).take(count).collect();
220	if path.is_empty() {
221	return false;
222	}
223	let all = path.iter().all(\|&(p, c)\| self.expanded(p) == Some(c));
224	for (p, c) in path {
225	if let Kind::Container { expanded, .. } = &mut self.nodes[p].kind {
226	*expanded = (!all).then_some(c);
227	}
228	}
229	true
230	}
231
232	/// Grows `w` by `delta`, a fraction of the visible length of the nearest
233	/// container along `axis` where it has a visible sibling. Hidden siblings
234	/// keep their weights, and with them their share.
235	pub fn resize(&mut self, w: W, axis: Axis, delta: f64, vis: impl Fn(W) -> bool) -> bool {
236	let Some(&leaf) = self.leaves.get(&w) else {
237	return false;
238	};
239	let mut cur = leaf;
240	while let Some((p, i)) = self.position(cur) {
241	if self.axis(p) == Some(axis) {
242	let shown: Vec<usize> = (0..self.children(p).len())
243	.filter(\|&j\| self.visible(self.children(p)[j].node, &vis))
244	.collect();
245	if shown.len() >= 2 {
246	let children = self.children_mut(p);
247	let sum: f64 = shown.iter().map(\|&j\| children[j].weight).sum();
248	let old = children[i].weight;
249	let max = 1.0 - MIN_SHARE * (shown.len() - 1) as f64;
250	let new = (old / sum + delta).clamp(MIN_SHARE, max) * sum;
251	let scale = (sum - new) / (sum - old);
252	for j in shown {
253	children[j].weight = if j == i {
254	new
255	} else {
256	children[j].weight * scale
257	};
258	}
259	return true;
260	}
261	}
262	cur = p;
263	}
264	false
265	}
266
267	/// Lays the tree out in `area`. Hidden windows come back as zero-size
268	/// rects on the boundary where they would reappear.
269	pub fn arrange(&self, area: Rect, gap: f64, vis: impl Fn(W) -> bool) -> Vec<(W, Rect)> {
270	let mut out = Vec::with_capacity(self.leaves.len());
271	if let Some(r) = self.root {
272	self.place(r, area, gap, &vis, &mut out);
273	}
274	out
275	}
276
277	fn place(
278	&self,
279	n: NodeId,
280	r: Rect,
281	gap: f64,
282	vis: &impl Fn(W) -> bool,
283	out: &mut Vec<(W, Rect)>,
284	) {
285	let (axis, children, expanded) = match &self.nodes[n].kind {
286	Kind::Leaf(w) => return out.push((*w, r)),
287	Kind::Container {
288	axis,
289	children,
290	expanded,
291	} => (axis, children, expanded),
292	};
293	let shown: Vec<bool> = children.iter().map(\|c\| self.visible(c.node, vis)).collect();
294	let (start, len) = span(r, axis);
295	if let Some(e) = expanded.and_then(\|e\| children.iter().position(\|c\| c.node == e))
296	&& shown[e]
297	{
298	for (i, c) in children.iter().enumerate() {
299	let sub = match i.cmp(&e) {
300	std::cmp::Ordering::Equal => r,
301	std::cmp::Ordering::Less => with_span(r, axis, start, 0.0),
302	std::cmp::Ordering::Greater => with_span(r, axis, start + len, 0.0),
303	};
304	self.place(c.node, sub, gap, vis, out);
305	}
306	return;
307	}
308	let count = shown.iter().filter(\|s\| **s).count();
309	let total: f64 = children
310	.iter()
311	.zip(&shown)
312	.filter(\|(_, s)\| **s)
313	.map(\|(c, _)\| c.weight)
314	.sum();
315	let gaps = count.saturating_sub(1) as f64;
316	let gap = if gaps > 0.0 { gap.min(len / gaps) } else { gap };
317	let avail = len - gap * gaps;
318	let last = shown.iter().rposition(\|s\| *s);
319	let mut pos = start;
320	let mut seen = false;
321	for (i, c) in children.iter().enumerate() {
322	if shown[i] {
323	if seen {
324	pos += gap;
325	}
326	let l = avail * c.weight / total;
327	self.place(c.node, with_span(r, axis, pos, l), gap, vis, out);
328	pos += l;
329	seen = true;
330	} else {
331	let between = seen && last.is_some_and(\|l\| l > i);
332	let at = if between { pos + gap / 2.0 } else { pos };
333	self.place(c.node, with_span(r, axis, at, 0.0), gap, vis, out);
334	}
335	}
336	}
337
338	fn move_node(&mut self, n: NodeId, dir: Dir, vis: &impl Fn(W) -> bool, enter: bool) -> bool {
339	let mut cur = n;
340	while let Some((p, i)) = self.position(cur) {
341	if self.axis(p) == Some(dir.axis()) {
342	if cur != n {
343	let at = if dir.forward() { i + 1 } else { i };
344	self.relocate(n, p, at);
345	return true;
346	}
347	if let Some(j) = self.next_shown(p, i, dir, vis) {
348	let sib = self.children(p)[j].node;
349	if enter && self.axis(sib).is_some() {
350	let end = self.children(sib).len();
351	self.relocate(n, sib, end);
352	} else {
353	let children = self.children_mut(p);
354	children[i].node = sib;
355	children[j].node = n;
356	}
357	return true;
358	}
359	}
360	cur = p;
361	}
362	if cur == n \|\| self.axis(cur) == Some(dir.axis()) {
363	return false;
364	}
365	let (old, i) = self.position(n).expect("n is below the root");
366	self.unlink(old, i);
367	self.normalize(old);
368	let r = self.root.expect("the rest of the tree survives");
369	if self.axis(r) == Some(dir.axis()) {
370	let weight = self.mean_weight(r);
371	let at = if dir.forward() {
372	self.children(r).len()
373	} else {
374	0
375	};
376	self.attach(r, at, n, weight);
377	} else {
378	let c = self.new_container(dir.axis());
379	self.attach(c, 0, r, 1.0);
380	let at = if dir.forward() {
381	self.children(c).len()
382	} else {
383	0
384	};
385	self.attach(c, at, n, 1.0);
386	self.root = Some(c);
387	}
388	true
389	}
390
391	fn next_shown(&self, p: NodeId, i: usize, dir: Dir, vis: &impl Fn(W) -> bool) -> Option<usize> {
392	let children = self.children(p);
393	if dir.forward() {
394	(i + 1..children.len()).find(\|&j\| self.visible(children[j].node, vis))
395	} else {
396	(0..i).rev().find(\|&j\| self.visible(children[j].node, vis))
397	}
398	}
399
400	fn relocate(&mut self, n: NodeId, p: NodeId, at: usize) {
401	let (old, i) = self.position(n).expect("relocated nodes have a parent");
402	let weight = self.mean_weight(p);
403	let at = if old == p && i < at { at - 1 } else { at };
404	self.unlink(old, i);
405	self.attach(p, at, n, weight);
406	self.normalize(old);
407	}
408
409	/// Places `node` among `p`'s children. A container running along `p`'s
410	/// axis is dissolved into `p` so axes keep alternating.
411	fn attach(&mut self, p: NodeId, at: usize, node: NodeId, weight: f64) {
412	if self.axis(node) == self.axis(p) {
413	let Some(Node {
414	kind: Kind::Container { children, .. },
415	..
416	}) = self.nodes.remove(node)
417	else {
418	unreachable!("only containers have an axis");
419	};
420	let total: f64 = children.iter().map(\|c\| c.weight).sum();
421	for (k, c) in children.into_iter().enumerate() {
422	self.nodes[c.node].parent = Some(p);
423	let weight = weight * c.weight / total;
424	self.children_mut(p).insert(
425	at + k,
426	Child {
427	node: c.node,
428	weight,
429	},
430	);
431	}
432	} else {
433	self.nodes[node].parent = Some(p);
434	self.children_mut(p).insert(at, Child { node, weight });
435	}
436	}
437
438	fn unlink(&mut self, p: NodeId, i: usize) -> Child {
439	let Kind::Container {
440	children, expanded, ..
441	} = &mut self.nodes[p].kind
442	else {
443	unreachable!("parents are containers");
444	};
445	let child = children.remove(i);
446	if *expanded == Some(child.node) {
447	*expanded = None;
448	}
449	self.nodes[child.node].parent = None;
450	child
451	}
452
453	fn detach(&mut self, n: NodeId) {
454	match self.position(n) {
455	Some((p, i)) => {
456	self.unlink(p, i);
457	self.normalize(p);
458	}
459	None => self.root = None,
460	}
461	}
462
463	/// Repairs a container that lost a child.
464	fn normalize(&mut self, c: NodeId) {
465	if self.children(c).len() >= 2 {
466	return;
467	}
468	let pos = self.position(c);
469	let was_expanded = pos.is_some_and(\|(p, _)\| self.expanded(p) == Some(c));
470	let Some(Node {
471	kind: Kind::Container { children, .. },
472	..
473	}) = self.nodes.remove(c)
474	else {
475	unreachable!("only containers are normalized");
476	};
477	let only = children.into_iter().next();
478	match (only, pos) {
479	(None, Some((p, i))) => {
480	self.unlink_dead(p, i);
481	self.normalize(p);
482	}
483	(None, None) => self.root = None,
484	(Some(only), Some((p, i))) => {
485	let weight = self.unlink_dead(p, i).weight;
486	let leaf_like = self.axis(only.node) != self.axis(p);
487	self.attach(p, i, only.node, weight);
488	if was_expanded
489	&& leaf_like
490	&& let Kind::Container { expanded, .. } = &mut self.nodes[p].kind
491	{
492	*expanded = Some(only.node);
493	}
494	}
495	(Some(only), None) => {
496	self.nodes[only.node].parent = None;
497	self.root = Some(only.node);
498	}
499	}
500	}
501
502	/// Like `unlink`, for a child whose node is already gone.
503	fn unlink_dead(&mut self, p: NodeId, i: usize) -> Child {
504	let Kind::Container {
505	children, expanded, ..
506	} = &mut self.nodes[p].kind
507	else {
508	unreachable!("parents are containers");
509	};
510	let child = children.remove(i);
511	if *expanded == Some(child.node) {
512	*expanded = None;
513	}
514	child
515	}
516
517	fn new_leaf(&mut self, w: W) -> NodeId {
518	let n = self.nodes.insert(Node {
519	parent: None,
520	kind: Kind::Leaf(w),
521	});
522	self.leaves.insert(w, n);
523	n
524	}
525
526	fn new_container(&mut self, axis: Axis) -> NodeId {
527	self.nodes.insert(Node {
528	parent: None,
529	kind: Kind::Container {
530	axis,
531	children: Vec::new(),
532	expanded: None,
533	},
534	})
535	}
536
537	fn position(&self, n: NodeId) -> Option<(NodeId, usize)> {
538	let p = self.nodes[n].parent?;
539	let i = self.children(p).iter().position(\|c\| c.node == n)?;
540	Some((p, i))
541	}
542
543	fn axis(&self, n: NodeId) -> Option<Axis> {
544	match &self.nodes[n].kind {
545	Kind::Container { axis, .. } => Some(*axis),
546	Kind::Leaf(_) => None,
547	}
548	}
549
550	fn expanded(&self, n: NodeId) -> Option<NodeId> {
551	match &self.nodes[n].kind {
552	Kind::Container { expanded, .. } => *expanded,
553	Kind::Leaf(_) => None,
554	}
555	}
556
557	fn children(&self, n: NodeId) -> &[Child] {
558	match &self.nodes[n].kind {
559	Kind::Container { children, .. } => children,
560	Kind::Leaf(_) => &[],
561	}
562	}
563
564	fn children_mut(&mut self, n: NodeId) -> &mut Vec<Child> {
565	match &mut self.nodes[n].kind {
566	Kind::Container { children, .. } => children,
567	Kind::Leaf(_) => unreachable!("leaves have no children"),
568	}
569	}
570
571	fn mean_weight(&self, p: NodeId) -> f64 {
572	let children = self.children(p);
573	if children.is_empty() {
574	1.0
575	} else {
576	children.iter().map(\|c\| c.weight).sum::<f64>() / children.len() as f64
577	}
578	}
579
580	fn visible(&self, n: NodeId, vis: &impl Fn(W) -> bool) -> bool {
581	match &self.nodes[n].kind {
582	Kind::Leaf(w) => vis(*w),
583	Kind::Container { children, .. } => children.iter().any(\|c\| self.visible(c.node, vis)),
584	}
585	}
586
587	#[cfg(test)]
588	pub(crate) fn check(&self) {
589	let reachable = match self.root {
590	Some(r) => {
591	assert!(self.nodes[r].parent.is_none());
592	self.check_node(r)
593	}
594	None => 0,
595	};
596	assert_eq!(reachable, self.nodes.len(), "orphaned nodes");
597	for (&w, &n) in &self.leaves {
598	assert!(matches!(self.nodes[n].kind, Kind::Leaf(x) if x == w));
599	}
600	}
601
602	#[cfg(test)]
603	fn check_node(&self, n: NodeId) -> usize {
604	match &self.nodes[n].kind {
605	Kind::Leaf(_) => 1,
606	Kind::Container {
607	axis,
608	children,
609	expanded,
610	} => {
611	assert!(
612	children.len() >= 2,
613	"container with {} children",
614	children.len()
615	);
616	if let Some(e) = expanded {
617	assert!(children.iter().any(\|c\| c.node == *e));
618	}
619	let mut count = 1;
620	for c in children {
621	assert!(c.weight > 0.0 && c.weight.is_finite());
622	assert_eq!(self.nodes[c.node].parent, Some(n));
623	assert_ne!(self.axis(c.node), Some(*axis), "axes must alternate");
624	count += self.check_node(c.node);
625	}
626	count
627	}
628	}
629	}
630	}
631
632	fn span(r: Rect, axis: Axis) -> (f64, f64) {
633	match axis {
634	Axis::Horizontal => (r.x, r.w),
635	Axis::Vertical => (r.y, r.h),
636	}
637	}
638
639	fn with_span(r: Rect, axis: Axis, start: f64, len: f64) -> Rect {
640	match axis {
641	Axis::Horizontal => Rect::new(start, r.y, len, r.h),
642	Axis::Vertical => Rect::new(r.x, start, r.w, len),
643	}
644	}