feat(core): n-ary tree ops — split, remove+collapse, ratios, move

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/spacesh-core/Cargo.toml

@@ -6,3 +6,4 @@ version.workspace = true
 [dependencies]
 alacritty_terminal.workspace = true
 serde.workspace = true
+spacesh-proto = { path = "../spacesh-proto" }

crates/spacesh-core/src/lib.rs

@@ -1,4 +1,5 @@
 pub mod grid;
+pub mod ops;
 pub mod snapshot;
 
 pub use grid::GridSurface;

crates/spacesh-core/src/ops.rs

@@ -0,0 +1,256 @@
+//! Pure algorithms over `spacesh_proto::LayoutNode`. No I/O.
+use spacesh_proto::layout::{LayoutNode, Orient};
+use spacesh_proto::ids::SurfaceId;
+
+/// Minimum ratio a panel may shrink to (5%).
+const MIN_RATIO: f32 = 0.05;
+
+/// Collect all surface ids in the tree, left-to-right.
+pub fn leaves(node: &LayoutNode) -> Vec<SurfaceId> {
+    let mut out = Vec::new();
+    collect(node, &mut out);
+    out
+}
+fn collect(node: &LayoutNode, out: &mut Vec<SurfaceId>) {
+    match node {
+        LayoutNode::Leaf { surface_id } => out.push(surface_id.clone()),
+        LayoutNode::Split { children, .. } => children.iter().for_each(|c| collect(c, out)),
+    }
+}
+
+/// Split the leaf `target` by inserting `new_id` as a sibling on `dir`.
+/// Returns true if the target was found and split.
+pub fn split_leaf(root: &mut LayoutNode, target: &SurfaceId, dir: Orient, after: bool, new_id: SurfaceId) -> bool {
+    // If root itself is the target leaf, replace it with a split.
+    if let LayoutNode::Leaf { surface_id } = root {
+        if surface_id == target {
+            let existing = root.clone();
+            let new_leaf = LayoutNode::leaf(new_id);
+            let children = if after { vec![existing, new_leaf] } else { vec![new_leaf, existing] };
+            *root = LayoutNode::Split { orient: dir, ratios: even(children.len()), children };
+            return true;
+        }
+        return false;
+    }
+    if let LayoutNode::Split { orient, ratios, children } = root {
+        // If a direct child is the target leaf AND this split matches `dir`, insert as sibling.
+        if *orient == dir {
+            if let Some(i) = children.iter().position(|c| is_leaf(c, target)) {
+                children.insert(i + if after { 1 } else { 0 }, LayoutNode::leaf(new_id));
+                *ratios = even(children.len());
+                return true;
+            }
+        }
+        // Otherwise recurse.
+        for c in children.iter_mut() {
+            if split_leaf(c, target, dir, after, new_id.clone()) {
+                return true;
+            }
+        }
+    }
+    false
+}
+
+/// Remove the leaf `target`. Collapses empty/now-single-child splits and promotes
+/// single children. Returns the new root (None if the tree became empty).
+pub fn remove_leaf(root: LayoutNode, target: &SurfaceId) -> Option<LayoutNode> {
+    match root {
+        LayoutNode::Leaf { surface_id } => {
+            if &surface_id == target { None } else { Some(LayoutNode::Leaf { surface_id }) }
+        }
+        LayoutNode::Split { orient, children, .. } => {
+            let kept: Vec<LayoutNode> = children
+                .into_iter()
+                .filter_map(|c| remove_leaf(c, target))
+                .collect();
+            match kept.len() {
+                0 => None,
+                1 => Some(kept.into_iter().next().unwrap()), // promote single child
+                n => Some(LayoutNode::Split { orient, ratios: even(n), children: kept }),
+            }
+        }
+    }
+}
+
+/// Set ratios on the split node addressed by `path` (child indices from root).
+/// Normalizes to sum 1.0 and clamps each to >= MIN_RATIO. Returns false if the
+/// path is invalid or the length does not match the node's child count.
+pub fn set_ratios(root: &mut LayoutNode, path: &[u32], ratios: &[f32]) -> bool {
+    let Some(node) = node_at_mut(root, path) else { return false };
+    if let LayoutNode::Split { ratios: r, children, .. } = node {
+        if ratios.len() != children.len() {
+            return false;
+        }
+        *r = normalize_clamp(ratios);
+        true
+    } else {
+        false
+    }
+}
+
+/// Move leaf `src` to sit on `edge` of leaf `target`. Returns the new root.
+/// No-op (returns the original) if src == target or either is missing.
+pub fn move_leaf(root: LayoutNode, src: &SurfaceId, target: &SurfaceId, edge: spacesh_proto::message::Edge) -> LayoutNode {
+    use spacesh_proto::message::Edge;
+    if src == target || !contains(&root, src) || !contains(&root, target) {
+        return root;
+    }
+    let Some(removed) = remove_leaf(root, src) else { return LayoutNode::leaf(src.clone()) };
+    let (orient, after) = match edge {
+        Edge::Left => (Orient::H, false),
+        Edge::Right => (Orient::H, true),
+        Edge::Top => (Orient::V, false),
+        Edge::Bottom => (Orient::V, true),
+    };
+    let mut root = removed;
+    split_leaf(&mut root, target, orient, after, src.clone());
+    root
+}
+
+// ---- helpers ----
+
+fn is_leaf(node: &LayoutNode, id: &SurfaceId) -> bool {
+    matches!(node, LayoutNode::Leaf { surface_id } if surface_id == id)
+}
+fn contains(node: &LayoutNode, id: &SurfaceId) -> bool {
+    leaves(node).iter().any(|s| s == id)
+}
+fn even(n: usize) -> Vec<f32> {
+    vec![1.0 / n as f32; n]
+}
+fn normalize_clamp(ratios: &[f32]) -> Vec<f32> {
+    // Two-pass: clamp all to MIN_RATIO, then normalize. If normalization would
+    // bring any value back below MIN_RATIO, pin those and redistribute the rest.
+    let n = ratios.len();
+    if n == 0 { return vec![]; }
+    let mut r: Vec<f32> = ratios.iter().map(|v| v.max(MIN_RATIO)).collect();
+    // Iteratively pin items that would end up below MIN_RATIO after normalization.
+    let mut pinned = vec![false; n];
+    for _ in 0..n {
+        let pin_sum: f32 = r.iter().zip(&pinned).filter(|(_, p)| **p).map(|(v, _)| *v).sum();
+        let free_sum: f32 = r.iter().zip(&pinned).filter(|(_, p)| !**p).map(|(v, _)| *v).sum();
+        let remaining = 1.0 - pin_sum;
+        let mut changed = false;
+        for i in 0..n {
+            if pinned[i] { continue; }
+            let normalized = if free_sum > 0.0 { r[i] / free_sum * remaining } else { remaining / n as f32 };
+            if normalized < MIN_RATIO {
+                r[i] = MIN_RATIO;
+                pinned[i] = true;
+                changed = true;
+            }
+        }
+        if !changed { break; }
+    }
+    // Final normalization of unpinned values.
+    let pin_sum: f32 = r.iter().zip(&pinned).filter(|(_, p)| **p).map(|(v, _)| *v).sum();
+    let free_sum: f32 = r.iter().zip(&pinned).filter(|(_, p)| !**p).map(|(v, _)| *v).sum();
+    let remaining = (1.0 - pin_sum).max(0.0);
+    let mut result = vec![0.0f32; n];
+    for i in 0..n {
+        if pinned[i] {
+            result[i] = r[i];
+        } else {
+            result[i] = if free_sum > 0.0 { r[i] / free_sum * remaining } else { remaining / n as f32 };
+        }
+    }
+    result
+}
+fn node_at_mut<'a>(root: &'a mut LayoutNode, path: &[u32]) -> Option<&'a mut LayoutNode> {
+    let mut cur = root;
+    for &idx in path {
+        match cur {
+            LayoutNode::Split { children, .. } => {
+                cur = children.get_mut(idx as usize)?;
+            }
+            LayoutNode::Leaf { .. } => return None,
+        }
+    }
+    Some(cur)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    fn sid(s: &str) -> SurfaceId { SurfaceId(s.into()) }
+
+    #[test]
+    fn split_root_leaf_creates_split() {
+        let mut root = LayoutNode::leaf(sid("s_1"));
+        assert!(split_leaf(&mut root, &sid("s_1"), Orient::H, true, sid("s_2")));
+        assert_eq!(leaves(&root), vec![sid("s_1"), sid("s_2")]);
+    }
+
+    #[test]
+    fn split_same_orient_appends_as_sibling() {
+        let mut root = LayoutNode::Split {
+            orient: Orient::H, ratios: vec![0.5, 0.5],
+            children: vec![LayoutNode::leaf(sid("s_1")), LayoutNode::leaf(sid("s_2"))],
+        };
+        split_leaf(&mut root, &sid("s_2"), Orient::H, true, sid("s_3"));
+        // 3 children in one row, even ratios.
+        match &root {
+            LayoutNode::Split { children, ratios, .. } => {
+                assert_eq!(children.len(), 3);
+                assert!((ratios.iter().sum::<f32>() - 1.0).abs() < 1e-5);
+            }
+            _ => panic!(),
+        }
+        assert_eq!(leaves(&root), vec![sid("s_1"), sid("s_2"), sid("s_3")]);
+    }
+
+    #[test]
+    fn remove_promotes_single_child() {
+        let root = LayoutNode::Split {
+            orient: Orient::H, ratios: vec![0.5, 0.5],
+            children: vec![LayoutNode::leaf(sid("s_1")), LayoutNode::leaf(sid("s_2"))],
+        };
+        let after = remove_leaf(root, &sid("s_2")).unwrap();
+        assert_eq!(after, LayoutNode::leaf(sid("s_1"))); // split collapsed to the surviving leaf
+    }
+
+    #[test]
+    fn remove_last_leaf_returns_none() {
+        let root = LayoutNode::leaf(sid("s_1"));
+        assert!(remove_leaf(root, &sid("s_1")).is_none());
+    }
+
+    #[test]
+    fn set_ratios_normalizes_and_clamps() {
+        let mut root = LayoutNode::Split {
+            orient: Orient::H, ratios: vec![0.5, 0.5],
+            children: vec![LayoutNode::leaf(sid("s_1")), LayoutNode::leaf(sid("s_2"))],
+        };
+        assert!(set_ratios(&mut root, &[], &[0.0, 1.0]));
+        if let LayoutNode::Split { ratios, .. } = &root {
+            assert!(ratios[0] >= MIN_RATIO);
+            assert!((ratios.iter().sum::<f32>() - 1.0).abs() < 1e-5);
+        }
+    }
+
+    #[test]
+    fn set_ratios_wrong_len_rejected() {
+        let mut root = LayoutNode::Split {
+            orient: Orient::H, ratios: vec![0.5, 0.5],
+            children: vec![LayoutNode::leaf(sid("s_1")), LayoutNode::leaf(sid("s_2"))],
+        };
+        assert!(!set_ratios(&mut root, &[], &[1.0]));
+    }
+
+    #[test]
+    fn move_leaf_to_right_of_target() {
+        let root = LayoutNode::Split {
+            orient: Orient::V, ratios: vec![0.5, 0.5],
+            children: vec![LayoutNode::leaf(sid("s_1")), LayoutNode::leaf(sid("s_2"))],
+        };
+        let after = move_leaf(root, &sid("s_1"), &sid("s_2"), spacesh_proto::message::Edge::Right);
+        assert_eq!(leaves(&after), vec![sid("s_2"), sid("s_1")]);
+    }
+
+    #[test]
+    fn move_onto_self_is_noop() {
+        let root = LayoutNode::leaf(sid("s_1"));
+        let after = move_leaf(root.clone(), &sid("s_1"), &sid("s_1"), spacesh_proto::message::Edge::Right);
+        assert_eq!(after, root);
+    }
+}