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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)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[cfg_attr(feature = "serde", serde(rename_all = "kebab-case"))]
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)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[cfg_attr(feature = "serde", serde(rename_all = "kebab-case"))]
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 {
            let area = if self.visible(r, &vis) {
                area
            } else {
                Rect::new(area.x + area.w / 2.0, area.y, 0.0, area.h)
            };
            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	#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
10	#[cfg_attr(feature = "serde", serde(rename_all = "kebab-case"))]
11	pub enum Axis {
12	Horizontal,
13	Vertical,
14	}
15
16	impl Axis {
17	pub fn other(self) -> Self {
18	match self {
19	Self::Horizontal => Self::Vertical,
20	Self::Vertical => Self::Horizontal,
21	}
22	}
23	}
24
25	#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
26	#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
27	#[cfg_attr(feature = "serde", serde(rename_all = "kebab-case"))]
28	pub enum Dir {
29	Left,
30	Right,
31	Up,
32	Down,
33	}
34
35	impl Dir {
36	pub fn axis(self) -> Axis {
37	match self {
38	Self::Left \| Self::Right => Axis::Horizontal,
39	Self::Up \| Self::Down => Axis::Vertical,
40	}
41	}
42
43	pub fn forward(self) -> bool {
44	matches!(self, Self::Right \| Self::Down)
45	}
46	}
47
48	const MIN_SHARE: f64 = 0.05;
49
50	#[derive(Clone, Debug)]
51	struct Child {
52	node: NodeId,
53	weight: f64,
54	}
55
56	#[derive(Clone, Debug)]
57	enum Kind<W> {
58	Leaf(W),
59	Container {
60	axis: Axis,
61	children: Vec<Child>,
62	expanded: Option<NodeId>,
63	},
64	}
65
66	#[derive(Clone, Debug)]
67	struct Node<W> {
68	parent: Option<NodeId>,
69	kind: Kind<W>,
70	}
71
72	/// One output's tiling tree. Every tiled window of every tag lives here, the
73	/// caller's visibility filter decides which ones take space.
74	///
75	/// Children run on the axis opposite their parent. Containers hold at least
76	/// two children, hidden ones included, and a container left with one child
77	/// is replaced by it.
78	#[derive(Clone, Debug)]
79	pub struct Tree<W> {
80	nodes: SlotMap<NodeId, Node<W>>,
81	root: Option<NodeId>,
82	leaves: HashMap<W, NodeId>,
83	stack: Axis,
84	}
85
86	impl<W: Copy + Eq + Hash> Default for Tree<W> {
87	fn default() -> Self {
88	Self {
89	nodes: SlotMap::with_key(),
90	root: None,
91	leaves: HashMap::new(),
92	stack: Axis::Vertical,
93	}
94	}
95	}
96
97	impl<W: Copy + Eq + Hash> Tree<W> {
98	/// The axis tag rows stack along.
99	pub fn stack_axis(&self) -> Axis {
100	self.stack
101	}
102
103	pub fn contains(&self, w: W) -> bool {
104	self.leaves.contains_key(&w)
105	}
106
107	pub fn is_empty(&self) -> bool {
108	self.root.is_none()
109	}
110
111	pub fn windows(&self) -> impl Iterator<Item = W> + '_ {
112	self.leaves.keys().copied()
113	}
114
115	/// Inserts `w` as the next sibling of `anchor`, or as a new row if
116	/// `anchor` is not in the tree.
117	pub fn insert_after(&mut self, w: W, anchor: W) {
118	let Some(&a) = self.leaves.get(&anchor) else {
119	return self.insert_row(w);
120	};
121	let n = self.new_leaf(w);
122	match self.position(a) {
123	Some((p, i)) if Some(p) == self.root && self.axis(p) == Some(self.stack) => {
124	let weight = self.unlink(p, i).weight;
125	let c = self.new_container(self.stack.other());
126	self.attach(c, 0, a, 1.0);
127	self.attach(c, 1, n, 1.0);
128	self.attach(p, i, c, weight);
129	}
130	Some((p, i)) => {
131	let weight = self.mean_weight(p);
132	self.attach(p, i + 1, n, weight);
133	}
134	None => {
135	let c = self.new_container(self.stack.other());
136	self.attach(c, 0, a, 1.0);
137	self.attach(c, 1, n, 1.0);
138	self.root = Some(c);
139	}
140	}
141	}
142
143	/// Appends `w` as a row of its own along the stacking axis.
144	pub fn insert_row(&mut self, w: W) {
145	let n = self.new_leaf(w);
146	match self.root {
147	None => self.root = Some(n),
148	Some(r) if self.axis(r) == Some(self.stack) => {
149	let weight = self.mean_weight(r);
150	let end = self.children(r).len();
151	self.attach(r, end, n, weight);
152	}
153	Some(r) => {
154	let c = self.new_container(self.stack);
155	self.attach(c, 0, r, 1.0);
156	self.attach(c, 1, n, 1.0);
157	self.root = Some(c);
158	}
159	}
160	}
161
162	pub fn remove(&mut self, w: W) -> bool {
163	let Some(n) = self.leaves.remove(&w) else {
164	return false;
165	};
166	self.detach(n);
167	self.nodes.remove(n);
168	true
169	}
170
171	pub fn retain(&mut self, mut keep: impl FnMut(W) -> bool) {
172	let gone: Vec<W> = self.windows().filter(\|&w\| !keep(w)).collect();
173	for w in gone {
174	self.remove(w);
175	}
176	}
177
178	/// Moves a window one step in `dir`. Leaves swap slots with the next
179	/// visible sibling, enter a sibling container, or step out beside their
180	/// container. Hidden windows never move.
181	pub fn move_window(&mut self, w: W, dir: Dir, vis: impl Fn(W) -> bool) -> bool {
182	let Some(&n) = self.leaves.get(&w) else {
183	return false;
184	};
185	self.move_node(n, dir, &vis, true)
186	}
187
188	/// Moves the container holding `w` as a rigid block. A window sitting
189	/// directly in the root is its own block.
190	pub fn move_container(&mut self, w: W, dir: Dir, vis: impl Fn(W) -> bool) -> bool {
191	let Some(&n) = self.leaves.get(&w) else {
192	return false;
193	};
194	let block = self.nodes[n]
195	.parent
196	.filter(\|&p\| Some(p) != self.root)
197	.unwrap_or(n);
198	self.move_node(block, dir, &vis, false)
199	}
200
201	/// Moves a window to the end of the next visible lane in `dir`, stepping
202	/// up a level when its container has none that way. A lone window there
203	/// becomes a stack with it.
204	pub fn merge_window(&mut self, w: W, dir: Dir, vis: impl Fn(W) -> bool) -> bool {
205	let Some(&n) = self.leaves.get(&w) else {
206	return false;
207	};
208	let mut cur = n;
209	while let Some((p, i)) = self.position(cur) {
210	if self.axis(p) == Some(dir.axis())
211	&& let Some(j) = self.next_shown(p, i, dir, &vis)
212	{
213	self.join_lane(n, p, j);
214	return true;
215	}
216	cur = p;
217	}
218	false
219	}
220
221	/// Whether every container above `w` is expanded towards it.
222	pub fn maximized(&self, w: W) -> bool {
223	let Some(&leaf) = self.leaves.get(&w) else {
224	return false;
225	};
226	let mut cur = leaf;
227	let mut any = false;
228	while let Some(p) = self.nodes[cur].parent {
229	if self.expanded(p) != Some(cur) {
230	return false;
231	}
232	any = true;
233	cur = p;
234	}
235	any
236	}
237
238	/// Transposes the whole tree.
239	pub fn flip(&mut self) {
240	self.stack = self.stack.other();
241	for node in self.nodes.values_mut() {
242	if let Kind::Container { axis, .. } = &mut node.kind {
243	*axis = axis.other();
244	}
245	}
246	}
247
248	/// Toggles expansion for `count` levels of `w`'s ancestry, starting
249	/// `skip` levels up. Level 0 expands the window inside its container.
250	pub fn toggle_expand(&mut self, w: W, skip: usize, count: usize) -> bool {
251	let Some(&leaf) = self.leaves.get(&w) else {
252	return false;
253	};
254	let mut path = Vec::new();
255	let mut cur = leaf;
256	while let Some(p) = self.nodes[cur].parent {
257	path.push((p, cur));
258	cur = p;
259	}
260	let path: Vec<_> = path.into_iter().skip(skip).take(count).collect();
261	if path.is_empty() {
262	return false;
263	}
264	let all = path.iter().all(\|&(p, c)\| self.expanded(p) == Some(c));
265	for (p, c) in path {
266	if let Kind::Container { expanded, .. } = &mut self.nodes[p].kind {
267	*expanded = (!all).then_some(c);
268	}
269	}
270	true
271	}
272
273	/// Grows `w` by `delta`, a fraction of the visible length of the nearest
274	/// container along `axis` where it has a visible sibling. Hidden siblings
275	/// keep their weights, and with them their share.
276	pub fn resize(&mut self, w: W, axis: Axis, delta: f64, vis: impl Fn(W) -> bool) -> bool {
277	let Some(&leaf) = self.leaves.get(&w) else {
278	return false;
279	};
280	let mut cur = leaf;
281	while let Some((p, i)) = self.position(cur) {
282	if self.axis(p) == Some(axis) {
283	let shown: Vec<usize> = (0..self.children(p).len())
284	.filter(\|&j\| self.visible(self.children(p)[j].node, &vis))
285	.collect();
286	if shown.len() >= 2 {
287	let children = self.children_mut(p);
288	let sum: f64 = shown.iter().map(\|&j\| children[j].weight).sum();
289	let old = children[i].weight;
290	let max = 1.0 - MIN_SHARE * (shown.len() - 1) as f64;
291	let new = (old / sum + delta).clamp(MIN_SHARE, max) * sum;
292	let scale = (sum - new) / (sum - old);
293	for j in shown {
294	children[j].weight = if j == i {
295	new
296	} else {
297	children[j].weight * scale
298	};
299	}
300	return true;
301	}
302	}
303	cur = p;
304	}
305	false
306	}
307
308	/// Lays the tree out in `area`. Hidden windows come back as zero-size
309	/// rects on the boundary where they would reappear.
310	pub fn arrange(&self, area: Rect, gap: f64, vis: impl Fn(W) -> bool) -> Vec<(W, Rect)> {
311	let mut out = Vec::with_capacity(self.leaves.len());
312	if let Some(r) = self.root {
313	let area = if self.visible(r, &vis) {
314	area
315	} else {
316	Rect::new(area.x + area.w / 2.0, area.y, 0.0, area.h)
317	};
318	self.place(r, area, gap, &vis, &mut out);
319	}
320	out
321	}
322
323	fn place(
324	&self,
325	n: NodeId,
326	r: Rect,
327	gap: f64,
328	vis: &impl Fn(W) -> bool,
329	out: &mut Vec<(W, Rect)>,
330	) {
331	let (axis, children, expanded) = match &self.nodes[n].kind {
332	Kind::Leaf(w) => return out.push((*w, r)),
333	Kind::Container {
334	axis,
335	children,
336	expanded,
337	} => (axis, children, expanded),
338	};
339	let shown: Vec<bool> = children.iter().map(\|c\| self.visible(c.node, vis)).collect();
340	let (start, len) = span(r, axis);
341	if let Some(e) = expanded.and_then(\|e\| children.iter().position(\|c\| c.node == e))
342	&& shown[e]
343	{
344	for (i, c) in children.iter().enumerate() {
345	let sub = match i.cmp(&e) {
346	std::cmp::Ordering::Equal => r,
347	std::cmp::Ordering::Less => with_span(r, axis, start, 0.0),
348	std::cmp::Ordering::Greater => with_span(r, axis, start + len, 0.0),
349	};
350	self.place(c.node, sub, gap, vis, out);
351	}
352	return;
353	}
354	let count = shown.iter().filter(\|s\| **s).count();
355	let total: f64 = children
356	.iter()
357	.zip(&shown)
358	.filter(\|(_, s)\| **s)
359	.map(\|(c, _)\| c.weight)
360	.sum();
361	let gaps = count.saturating_sub(1) as f64;
362	let gap = if gaps > 0.0 { gap.min(len / gaps) } else { gap };
363	let avail = len - gap * gaps;
364	let last = shown.iter().rposition(\|s\| *s);
365	let mut pos = start;
366	let mut seen = false;
367	for (i, c) in children.iter().enumerate() {
368	if shown[i] {
369	if seen {
370	pos += gap;
371	}
372	let l = avail * c.weight / total;
373	self.place(c.node, with_span(r, axis, pos, l), gap, vis, out);
374	pos += l;
375	seen = true;
376	} else {
377	let between = seen && last.is_some_and(\|l\| l > i);
378	let at = if between { pos + gap / 2.0 } else { pos };
379	self.place(c.node, with_span(r, axis, at, 0.0), gap, vis, out);
380	}
381	}
382	}
383
384	fn move_node(&mut self, n: NodeId, dir: Dir, vis: &impl Fn(W) -> bool, enter: bool) -> bool {
385	let mut cur = n;
386	while let Some((p, i)) = self.position(cur) {
387	if self.axis(p) == Some(dir.axis()) {
388	let hidden_lane = self
389	.adjacent(p, i, dir)
390	.filter(\|&j\| enter && !self.visible(self.children(p)[j].node, vis));
391	if cur != n {
392	if let Some(j) = hidden_lane {
393	self.join_lane(n, p, j);
394	} else {
395	let at = if dir.forward() { i + 1 } else { i };
396	self.relocate(n, p, at);
397	}
398	return true;
399	}
400	if let Some(j) = self.next_shown(p, i, dir, vis) {
401	let sib = self.children(p)[j].node;
402	if enter && self.axis(sib).is_some() {
403	let end = self.children(sib).len();
404	self.relocate(n, sib, end);
405	} else {
406	let children = self.children_mut(p);
407	children[i].node = sib;
408	children[j].node = n;
409	}
410	return true;
411	}
412	if let Some(j) = hidden_lane {
413	self.join_lane(n, p, j);
414	return true;
415	}
416	}
417	cur = p;
418	}
419	if cur == n \|\| self.axis(cur) == Some(dir.axis()) {
420	return false;
421	}
422	let (old, i) = self.position(n).expect("n is below the root");
423	self.unlink(old, i);
424	self.normalize(old);
425	let r = self.root.expect("the rest of the tree survives");
426	if self.axis(r) == Some(dir.axis()) {
427	let weight = self.mean_weight(r);
428	let at = if dir.forward() {
429	self.children(r).len()
430	} else {
431	0
432	};
433	self.attach(r, at, n, weight);
434	} else {
435	let c = self.new_container(dir.axis());
436	self.attach(c, 0, r, 1.0);
437	let at = if dir.forward() {
438	self.children(c).len()
439	} else {
440	0
441	};
442	self.attach(c, at, n, 1.0);
443	self.root = Some(c);
444	}
445	true
446	}
447
448	fn next_shown(&self, p: NodeId, i: usize, dir: Dir, vis: &impl Fn(W) -> bool) -> Option<usize> {
449	let children = self.children(p);
450	if dir.forward() {
451	(i + 1..children.len()).find(\|&j\| self.visible(children[j].node, vis))
452	} else {
453	(0..i).rev().find(\|&j\| self.visible(children[j].node, vis))
454	}
455	}
456
457	fn adjacent(&self, p: NodeId, i: usize, dir: Dir) -> Option<usize> {
458	let j = if dir.forward() {
459	i + 1
460	} else {
461	i.checked_sub(1)?
462	};
463	(j < self.children(p).len()).then_some(j)
464	}
465
466	/// Moves `n` to the end of the lane at `p`'s child `j`. A lone window
467	/// there becomes a lane of its own, perpendicular to `p`.
468	fn join_lane(&mut self, n: NodeId, p: NodeId, j: usize) {
469	let lane = self.children(p)[j].node;
470	let lane = if self.axis(lane).is_some() {
471	lane
472	} else {
473	let c = self.new_container(self.axis(p).expect("p is a container").other());
474	self.children_mut(p)[j].node = c;
475	self.nodes[c].parent = Some(p);
476	if let Kind::Container { expanded, .. } = &mut self.nodes[p].kind
477	&& *expanded == Some(lane)
478	{
479	*expanded = Some(c);
480	}
481	self.attach(c, 0, lane, 1.0);
482	c
483	};
484	let end = self.children(lane).len();
485	self.relocate(n, lane, end);
486	}
487
488	fn relocate(&mut self, n: NodeId, p: NodeId, at: usize) {
489	let (old, i) = self.position(n).expect("relocated nodes have a parent");
490	let weight = self.mean_weight(p);
491	let at = if old == p && i < at { at - 1 } else { at };
492	self.unlink(old, i);
493	self.attach(p, at, n, weight);
494	self.normalize(old);
495	}
496
497	/// Places `node` among `p`'s children. A container running along `p`'s
498	/// axis is dissolved into `p` so axes keep alternating.
499	fn attach(&mut self, p: NodeId, at: usize, node: NodeId, weight: f64) {
500	if self.axis(node) == self.axis(p) {
501	let Some(Node {
502	kind: Kind::Container { children, .. },
503	..
504	}) = self.nodes.remove(node)
505	else {
506	unreachable!("only containers have an axis");
507	};
508	let total: f64 = children.iter().map(\|c\| c.weight).sum();
509	for (k, c) in children.into_iter().enumerate() {
510	self.nodes[c.node].parent = Some(p);
511	let weight = weight * c.weight / total;
512	self.children_mut(p).insert(
513	at + k,
514	Child {
515	node: c.node,
516	weight,
517	},
518	);
519	}
520	} else {
521	self.nodes[node].parent = Some(p);
522	self.children_mut(p).insert(at, Child { node, weight });
523	}
524	}
525
526	fn unlink(&mut self, p: NodeId, i: usize) -> Child {
527	let Kind::Container {
528	children, expanded, ..
529	} = &mut self.nodes[p].kind
530	else {
531	unreachable!("parents are containers");
532	};
533	let child = children.remove(i);
534	if *expanded == Some(child.node) {
535	*expanded = None;
536	}
537	self.nodes[child.node].parent = None;
538	child
539	}
540
541	fn detach(&mut self, n: NodeId) {
542	match self.position(n) {
543	Some((p, i)) => {
544	self.unlink(p, i);
545	self.normalize(p);
546	}
547	None => self.root = None,
548	}
549	}
550
551	/// Repairs a container that lost a child.
552	fn normalize(&mut self, c: NodeId) {
553	if self.children(c).len() >= 2 {
554	return;
555	}
556	let pos = self.position(c);
557	let was_expanded = pos.is_some_and(\|(p, _)\| self.expanded(p) == Some(c));
558	let Some(Node {
559	kind: Kind::Container { children, .. },
560	..
561	}) = self.nodes.remove(c)
562	else {
563	unreachable!("only containers are normalized");
564	};
565	let only = children.into_iter().next();
566	match (only, pos) {
567	(None, Some((p, i))) => {
568	self.unlink_dead(p, i);
569	self.normalize(p);
570	}
571	(None, None) => self.root = None,
572	(Some(only), Some((p, i))) => {
573	let weight = self.unlink_dead(p, i).weight;
574	let leaf_like = self.axis(only.node) != self.axis(p);
575	self.attach(p, i, only.node, weight);
576	if was_expanded
577	&& leaf_like
578	&& let Kind::Container { expanded, .. } = &mut self.nodes[p].kind
579	{
580	*expanded = Some(only.node);
581	}
582	}
583	(Some(only), None) => {
584	self.nodes[only.node].parent = None;
585	self.root = Some(only.node);
586	}
587	}
588	}
589
590	/// Like `unlink`, for a child whose node is already gone.
591	fn unlink_dead(&mut self, p: NodeId, i: usize) -> Child {
592	let Kind::Container {
593	children, expanded, ..
594	} = &mut self.nodes[p].kind
595	else {
596	unreachable!("parents are containers");
597	};
598	let child = children.remove(i);
599	if *expanded == Some(child.node) {
600	*expanded = None;
601	}
602	child
603	}
604
605	fn new_leaf(&mut self, w: W) -> NodeId {
606	let n = self.nodes.insert(Node {
607	parent: None,
608	kind: Kind::Leaf(w),
609	});
610	self.leaves.insert(w, n);
611	n
612	}
613
614	fn new_container(&mut self, axis: Axis) -> NodeId {
615	self.nodes.insert(Node {
616	parent: None,
617	kind: Kind::Container {
618	axis,
619	children: Vec::new(),
620	expanded: None,
621	},
622	})
623	}
624
625	fn position(&self, n: NodeId) -> Option<(NodeId, usize)> {
626	let p = self.nodes[n].parent?;
627	let i = self.children(p).iter().position(\|c\| c.node == n)?;
628	Some((p, i))
629	}
630
631	fn axis(&self, n: NodeId) -> Option<Axis> {
632	match &self.nodes[n].kind {
633	Kind::Container { axis, .. } => Some(*axis),
634	Kind::Leaf(_) => None,
635	}
636	}
637
638	fn expanded(&self, n: NodeId) -> Option<NodeId> {
639	match &self.nodes[n].kind {
640	Kind::Container { expanded, .. } => *expanded,
641	Kind::Leaf(_) => None,
642	}
643	}
644
645	fn children(&self, n: NodeId) -> &[Child] {
646	match &self.nodes[n].kind {
647	Kind::Container { children, .. } => children,
648	Kind::Leaf(_) => &[],
649	}
650	}
651
652	fn children_mut(&mut self, n: NodeId) -> &mut Vec<Child> {
653	match &mut self.nodes[n].kind {
654	Kind::Container { children, .. } => children,
655	Kind::Leaf(_) => unreachable!("leaves have no children"),
656	}
657	}
658
659	fn mean_weight(&self, p: NodeId) -> f64 {
660	let children = self.children(p);
661	if children.is_empty() {
662	1.0
663	} else {
664	children.iter().map(\|c\| c.weight).sum::<f64>() / children.len() as f64
665	}
666	}
667
668	fn visible(&self, n: NodeId, vis: &impl Fn(W) -> bool) -> bool {
669	match &self.nodes[n].kind {
670	Kind::Leaf(w) => vis(*w),
671	Kind::Container { children, .. } => children.iter().any(\|c\| self.visible(c.node, vis)),
672	}
673	}
674
675	#[cfg(test)]
676	pub(crate) fn check(&self) {
677	let reachable = match self.root {
678	Some(r) => {
679	assert!(self.nodes[r].parent.is_none());
680	self.check_node(r)
681	}
682	None => 0,
683	};
684	assert_eq!(reachable, self.nodes.len(), "orphaned nodes");
685	for (&w, &n) in &self.leaves {
686	assert!(matches!(self.nodes[n].kind, Kind::Leaf(x) if x == w));
687	}
688	}
689
690	#[cfg(test)]
691	fn check_node(&self, n: NodeId) -> usize {
692	match &self.nodes[n].kind {
693	Kind::Leaf(_) => 1,
694	Kind::Container {
695	axis,
696	children,
697	expanded,
698	} => {
699	assert!(
700	children.len() >= 2,
701	"container with {} children",
702	children.len()
703	);
704	if let Some(e) = expanded {
705	assert!(children.iter().any(\|c\| c.node == *e));
706	}
707	let mut count = 1;
708	for c in children {
709	assert!(c.weight > 0.0 && c.weight.is_finite());
710	assert_eq!(self.nodes[c.node].parent, Some(n));
711	assert_ne!(self.axis(c.node), Some(*axis), "axes must alternate");
712	count += self.check_node(c.node);
713	}
714	count
715	}
716	}
717	}
718	}
719
720	fn span(r: Rect, axis: Axis) -> (f64, f64) {
721	match axis {
722	Axis::Horizontal => (r.x, r.w),
723	Axis::Vertical => (r.y, r.h),
724	}
725	}
726
727	fn with_span(r: Rect, axis: Axis, start: f64, len: f64) -> Rect {
728	match axis {
729	Axis::Horizontal => Rect::new(start, r.y, len, r.h),
730	Axis::Vertical => Rect::new(r.x, start, r.w, len),
731	}
732	}