Rewrite srdwm in Rust: working X11 and Wayland backends, Lua config

The C++ prototype (moved to legacy-cpp/) was mostly a design skeleton:
X11 and Windows backends were partially real, Wayland created the
wlroots object graph but never wired a single event listener, macOS
was stub except monitor enumeration, and the Lua engine's srd.bind()
stored a key-combo string but never the actual closure. See
docs/PRIOR_ART.md for the full audit.

This replaces it with a Cargo workspace:

- srdwm-core: platform-independent window/workspace/monitor state,
  a real master-stack tiling layout, and SmartPlacement grid/cascade/
  snap-to-edge placement - fixing several bugs in the C++ version
  (hardcoded 2-column grid, cascade that never cascaded, snap-to-edge
  that always returned a fixed rect). 35 unit tests.
- srdwm-config: the srd Lua API via mlua, implementing the surface
  docs/DEFAULTS.md always documented but the C++ engine never actually
  built (srd.window.close()/focus(direction), srd.workspace.next(),
  real keybinding closures, require("srd") support). 10 unit tests.
- srdwm-x11: a real reparenting WM with a drawn title bar (buttons,
  drag, resize), verified live under Xephyr - frame placement and
  client offset match srdwm-core's computed geometry exactly, and the
  decoration renders correctly on screen.
- srdwm-wayland: a from-scratch smithay compositor (the C++ version
  had nothing working to port from) - runs via the winit backend,
  tracks xdg-shell toplevels through the same WindowManager and
  hit-testing code X11 uses, verified to start/render/run without
  crashing. Decorations are solid-color (no text yet); see
  docs/IMPLEMENTATION_STATUS.md for exact scope.
- srdwm-windows / srdwm-macos: structured, cfg-gated designs informed
  by komorebi/glazewm and yabai/AeroSpace respectively (see
  docs/PRIOR_ART.md), honestly marked as unbuilt/unverified since this
  sandbox has no Windows or macOS target.

1 files changed, 724 insertions, 0 deletions

diff --git a/crates/core/src/manager.rs b/crates/core/src/manager.rs
new file mode 100644
index 0000000..1fdd7eb
--- /dev/null
+++ b/crates/core/src/manager.rs
@@ -0,0 +1,724 @@
+use crate::geometry::Rect;
+use crate::layout::{Layout, MasterStackLayout, NoOpLayout, TilingConfig};
+use crate::monitor::{Monitor, MonitorId};
+use crate::placement::{PlacementConfig, SmartPlacement, MIN_WINDOW_HEIGHT, MIN_WINDOW_WIDTH};
+use crate::window::{ResizeEdge, TitlebarHit, Window, WindowId};
+use crate::workspace::{Workspace, WorkspaceId};
+use std::collections::HashMap;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Direction {
+    Left,
+    Right,
+    Up,
+    Down,
+}
+
+struct DragState {
+    window: WindowId,
+    start_x: i32,
+    start_y: i32,
+    orig: Rect,
+}
+
+struct ResizeState {
+    window: WindowId,
+    edge: ResizeEdge,
+    start_x: i32,
+    start_y: i32,
+    orig: Rect,
+}
+
+/// The platform-independent core of srdwm: owns window/workspace/monitor
+/// state and layout policy. Backends (X11, Wayland, ...) drive this via
+/// `add_window`/`remove_window`/input events, and apply the `Rect`s it
+/// computes back onto real surfaces.
+pub struct WindowManager {
+    windows: HashMap<WindowId, Window>,
+    order: Vec<WindowId>,
+    focused: Option<WindowId>,
+    monitors: Vec<Monitor>,
+    workspaces: Vec<Workspace>,
+    current_workspace: WorkspaceId,
+    next_workspace_id: WorkspaceId,
+    next_window_id: WindowId,
+    layouts: HashMap<String, Box<dyn Layout>>,
+    pub tiling: TilingConfig,
+    pub placement: PlacementConfig,
+    drag: Option<DragState>,
+    resize: Option<ResizeState>,
+}
+
+impl Default for WindowManager {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl WindowManager {
+    pub fn new() -> Self {
+        let mut layouts: HashMap<String, Box<dyn Layout>> = HashMap::new();
+        layouts.insert("tiling".into(), Box::new(MasterStackLayout));
+        layouts.insert("dynamic".into(), Box::new(NoOpLayout("dynamic")));
+        layouts.insert("floating".into(), Box::new(NoOpLayout("floating")));
+
+        Self {
+            windows: HashMap::new(),
+            order: Vec::new(),
+            focused: None,
+            monitors: Vec::new(),
+            workspaces: vec![Workspace::new(0, "1", "dynamic")],
+            current_workspace: 0,
+            next_workspace_id: 1,
+            next_window_id: 1,
+            layouts,
+            tiling: TilingConfig::default(),
+            placement: PlacementConfig::default(),
+            drag: None,
+            resize: None,
+        }
+    }
+
+    pub fn register_layout(&mut self, name: impl Into<String>, layout: Box<dyn Layout>) {
+        self.layouts.insert(name.into(), layout);
+    }
+
+    pub fn available_layouts(&self) -> Vec<&str> {
+        self.layouts.keys().map(String::as_str).collect()
+    }
+
+    // ---- Monitors ----------------------------------------------------
+
+    pub fn set_monitors(&mut self, monitors: Vec<Monitor>) {
+        self.monitors = monitors;
+    }
+
+    pub fn monitors(&self) -> &[Monitor] {
+        &self.monitors
+    }
+
+    pub fn primary_monitor(&self) -> Option<&Monitor> {
+        self.monitors.iter().find(|m| m.primary).or_else(|| self.monitors.first())
+    }
+
+    fn monitor_for(&self, id: MonitorId) -> Option<&Monitor> {
+        self.monitors.iter().find(|m| m.id == id).or_else(|| self.primary_monitor())
+    }
+
+    // ---- Windows -------------------------------------------------------
+
+    pub fn alloc_window_id(&mut self) -> WindowId {
+        let id = self.next_window_id;
+        self.next_window_id += 1;
+        id
+    }
+
+    /// Registers a window that a backend has already created. If the current
+    /// workspace's layout doesn't auto-tile ("dynamic"/"floating"), the
+    /// window's initial geometry is chosen via [`SmartPlacement`]; otherwise
+    /// it's left for the next `arrange_workspace` call to place.
+    pub fn add_window(&mut self, mut window: Window) -> WindowId {
+        let id = window.id;
+        window.workspace = self.current_workspace;
+        if let Some(monitor) = self.primary_monitor() {
+            window.monitor = monitor.id;
+            let layout_name = self.workspace(self.current_workspace).map(|w| w.layout.clone()).unwrap_or_default();
+            if layout_name != "tiling" {
+                let existing: Vec<Rect> = self.windows_on_workspace(self.current_workspace).map(|w| w.geometry).collect();
+                let size = (window.geometry.width, window.geometry.height);
+                window.geometry = SmartPlacement::place(monitor, &existing, size, &self.placement);
+            }
+        }
+        self.windows.insert(id, window);
+        self.order.push(id);
+        self.focused = Some(id);
+        id
+    }
+
+    pub fn remove_window(&mut self, id: WindowId) -> Option<Window> {
+        self.order.retain(|&w| w != id);
+        if self.focused == Some(id) {
+            self.focused = self.order.last().copied();
+        }
+        self.windows.remove(&id)
+    }
+
+    pub fn window(&self, id: WindowId) -> Option<&Window> {
+        self.windows.get(&id)
+    }
+
+    pub fn window_mut(&mut self, id: WindowId) -> Option<&mut Window> {
+        self.windows.get_mut(&id)
+    }
+
+    pub fn windows(&self) -> impl Iterator<Item = &Window> {
+        self.windows.values()
+    }
+
+    /// Windows in stacking order, topmost (most recently raised) last.
+    pub fn stacking_order(&self) -> impl Iterator<Item = &Window> {
+        self.order.iter().filter_map(|id| self.windows.get(id))
+    }
+
+    fn windows_on_workspace(&self, workspace: WorkspaceId) -> impl Iterator<Item = &Window> {
+        self.windows.values().filter(move |w| w.workspace == workspace)
+    }
+
+    pub fn raise_window(&mut self, id: WindowId) {
+        if let Some(pos) = self.order.iter().position(|&w| w == id) {
+            let id = self.order.remove(pos);
+            self.order.push(id);
+        }
+    }
+
+    // ---- Focus ----------------------------------------------------------
+
+    pub fn focused_window(&self) -> Option<&Window> {
+        self.focused.and_then(|id| self.windows.get(&id))
+    }
+
+    pub fn focused_id(&self) -> Option<WindowId> {
+        self.focused
+    }
+
+    pub fn focus_window(&mut self, id: WindowId) {
+        if self.windows.contains_key(&id) {
+            self.focused = Some(id);
+            self.raise_window(id);
+        }
+    }
+
+    fn cycle_focus(&mut self, forward: bool) {
+        let ids: Vec<WindowId> = self.windows_on_workspace(self.current_workspace).filter(|w| !w.minimized).map(|w| w.id).collect();
+        if ids.is_empty() {
+            self.focused = None;
+            return;
+        }
+        let cur_pos = self.focused.and_then(|f| ids.iter().position(|&i| i == f));
+        let next = match cur_pos {
+            None => 0,
+            Some(p) if forward => (p + 1) % ids.len(),
+            Some(p) => (p + ids.len() - 1) % ids.len(),
+        };
+        self.focus_window(ids[next]);
+    }
+
+    pub fn focus_next(&mut self) {
+        self.cycle_focus(true);
+    }
+
+    pub fn focus_previous(&mut self) {
+        self.cycle_focus(false);
+    }
+
+    /// Vim-style directional focus: picks the nearest window whose center
+    /// lies in `dir` relative to the focused window's center, on the same
+    /// workspace. Returns the newly focused window, if any.
+    pub fn focus_direction(&mut self, dir: Direction) -> Option<WindowId> {
+        let (fx, fy, fid) = {
+            let focused = self.focused_window()?;
+            let (fx, fy) = focused.geometry.center();
+            (fx, fy, focused.id)
+        };
+        let workspace = self.current_workspace;
+        let mut best: Option<(WindowId, i64)> = None;
+        for w in self.windows_on_workspace(workspace).filter(|w| w.id != fid && !w.minimized) {
+            let (cx, cy) = w.geometry.center();
+            let (dx, dy) = ((cx - fx) as i64, (cy - fy) as i64);
+            let matches = match dir {
+                Direction::Left => dx < 0,
+                Direction::Right => dx > 0,
+                Direction::Up => dy < 0,
+                Direction::Down => dy > 0,
+            };
+            if !matches {
+                continue;
+            }
+            // Distance biased toward the requested axis so a window that's
+            // mostly to the left (small |dy|) beats one that's diagonally
+            // placed, matching how i3/sway-style directional focus feels.
+            let (primary, secondary) = match dir {
+                Direction::Left | Direction::Right => (dx, dy),
+                Direction::Up | Direction::Down => (dy, dx),
+            };
+            let dist = primary * primary + secondary * secondary * 4;
+            if best.is_none_or(|(_, d)| dist < d) {
+                best = Some((w.id, dist));
+            }
+        }
+        let target = best.map(|(id, _)| id);
+        if let Some(id) = target {
+            self.focus_window(id);
+        }
+        target
+    }
+
+    // ---- Window operations ----------------------------------------------
+
+    pub fn close_window(&mut self, id: WindowId) {
+        log::info!("close_window({id})");
+    }
+
+    pub fn minimize_window(&mut self, id: WindowId) {
+        if let Some(w) = self.windows.get_mut(&id) {
+            w.minimized = true;
+        }
+        if self.focused == Some(id) {
+            self.cycle_focus(true);
+        }
+    }
+
+    pub fn restore_window(&mut self, id: WindowId) {
+        if let Some(w) = self.windows.get_mut(&id) {
+            w.minimized = false;
+        }
+    }
+
+    pub fn toggle_maximize(&mut self, id: WindowId) {
+        let monitor_geom = self.windows.get(&id).and_then(|w| self.monitor_for(w.monitor)).map(|m| m.geometry);
+        let Some(w) = self.windows.get_mut(&id) else { return };
+        if w.maximized {
+            if let Some(restore) = w.restore_geometry.take() {
+                w.geometry = restore;
+            }
+            w.maximized = false;
+        } else if let Some(geom) = monitor_geom {
+            w.restore_geometry = Some(w.geometry);
+            w.geometry = geom;
+            w.maximized = true;
+        }
+    }
+
+    pub fn toggle_floating(&mut self, id: WindowId) {
+        if let Some(w) = self.windows.get_mut(&id) {
+            w.floating = !w.floating;
+        }
+    }
+
+    pub fn is_floating(&self, id: WindowId) -> bool {
+        self.windows.get(&id).map(|w| w.floating).unwrap_or(false)
+    }
+
+    pub fn move_window(&mut self, id: WindowId, x: i32, y: i32) {
+        if let Some(w) = self.windows.get_mut(&id) {
+            w.geometry.x = x;
+            w.geometry.y = y;
+        }
+    }
+
+    pub fn resize_window(&mut self, id: WindowId, width: u32, height: u32) {
+        if let Some(w) = self.windows.get_mut(&id) {
+            w.geometry.width = width.max(MIN_WINDOW_WIDTH);
+            w.geometry.height = height.max(MIN_WINDOW_HEIGHT);
+        }
+    }
+
+    // ---- Hit testing ------------------------------------------------------
+
+    /// Topmost window whose frame contains `(x, y)`, along with what part of
+    /// its titlebar/border was hit (button, drag area, resize edge).
+    pub fn hit_test(&self, x: i32, y: i32) -> Option<(WindowId, TitlebarHit)> {
+        for w in self.order.iter().rev().filter_map(|id| self.windows.get(id)) {
+            if w.minimized {
+                continue;
+            }
+            if let Some(hit) = ResizeEdge::hit_test(w.geometry, x, y) {
+                return Some((w.id, hit));
+            }
+        }
+        None
+    }
+
+    // ---- Drag / resize ------------------------------------------------------
+
+    pub fn start_drag(&mut self, id: WindowId, x: i32, y: i32) {
+        if let Some(w) = self.windows.get(&id) {
+            self.drag = Some(DragState { window: id, start_x: x, start_y: y, orig: w.geometry });
+            self.focus_window(id);
+        }
+    }
+
+    pub fn update_drag(&mut self, x: i32, y: i32) {
+        let Some(drag) = &self.drag else { return };
+        let (dx, dy) = (x - drag.start_x, y - drag.start_y);
+        let mut new_geom = drag.orig;
+        new_geom.x += dx;
+        new_geom.y += dy;
+
+        let monitor_bounds = self.windows.get(&drag.window).and_then(|w| self.monitor_for(w.monitor)).map(|m| m.geometry);
+        if let Some(bounds) = monitor_bounds {
+            new_geom.x = new_geom.x.clamp(bounds.x - new_geom.width as i32 + 40, bounds.right() - 40);
+            new_geom.y = new_geom.y.clamp(bounds.y, bounds.bottom() - 40);
+        }
+
+        if let Some(w) = self.windows.get_mut(&drag.window) {
+            w.geometry = new_geom;
+        }
+    }
+
+    /// Ends a drag, snapping into a Windows-Snap zone if the pointer ended up
+    /// near a monitor edge.
+    pub fn end_drag(&mut self) {
+        if let Some(drag) = self.drag.take() {
+            let snapped = self.windows.get(&drag.window).and_then(|w| {
+                self.monitor_for(w.monitor).and_then(|m| SmartPlacement::snap_zone(w.geometry, m, &self.placement))
+            });
+            if let (Some(zone), Some(w)) = (snapped, self.windows.get_mut(&drag.window)) {
+                w.geometry = zone;
+            }
+        }
+    }
+
+    pub fn is_dragging(&self) -> bool {
+        self.drag.is_some()
+    }
+
+    pub fn start_resize(&mut self, id: WindowId, edge: ResizeEdge, x: i32, y: i32) {
+        if let Some(w) = self.windows.get(&id) {
+            self.resize = Some(ResizeState { window: id, edge, start_x: x, start_y: y, orig: w.geometry });
+            self.focus_window(id);
+        }
+    }
+
+    pub fn update_resize(&mut self, x: i32, y: i32) {
+        let Some(r) = &self.resize else { return };
+        let (dx, dy) = (x - r.start_x, y - r.start_y);
+        let new_geom = r.edge.apply_delta(r.orig, dx, dy, MIN_WINDOW_WIDTH, MIN_WINDOW_HEIGHT);
+        if let Some(w) = self.windows.get_mut(&r.window) {
+            w.geometry = new_geom;
+        }
+    }
+
+    pub fn end_resize(&mut self) {
+        self.resize = None;
+    }
+
+    pub fn is_resizing(&self) -> bool {
+        self.resize.is_some()
+    }
+
+    // ---- Workspaces -----------------------------------------------------
+
+    pub fn add_workspace(&mut self, name: impl Into<String>, layout: impl Into<String>) -> WorkspaceId {
+        let id = self.next_workspace_id;
+        self.next_workspace_id += 1;
+        self.workspaces.push(Workspace::new(id, name, layout));
+        id
+    }
+
+    pub fn remove_workspace(&mut self, id: WorkspaceId) {
+        if self.workspaces.len() <= 1 {
+            return;
+        }
+        let fallback = self.workspaces.iter().map(|w| w.id).find(|&w| w != id).unwrap_or(0);
+        for w in self.windows.values_mut().filter(|w| w.workspace == id) {
+            w.workspace = fallback;
+        }
+        self.workspaces.retain(|w| w.id != id);
+        if self.current_workspace == id {
+            self.current_workspace = fallback;
+        }
+    }
+
+    pub fn switch_workspace(&mut self, id: WorkspaceId) {
+        if self.workspaces.iter().any(|w| w.id == id) {
+            self.current_workspace = id;
+        }
+    }
+
+    pub fn current_workspace(&self) -> WorkspaceId {
+        self.current_workspace
+    }
+
+    pub fn workspace(&self, id: WorkspaceId) -> Option<&Workspace> {
+        self.workspaces.iter().find(|w| w.id == id)
+    }
+
+    pub fn workspaces(&self) -> &[Workspace] {
+        &self.workspaces
+    }
+
+    pub fn move_window_to_workspace(&mut self, id: WindowId, workspace: WorkspaceId) {
+        if let Some(w) = self.windows.get_mut(&id) {
+            w.workspace = workspace;
+        }
+    }
+
+    /// Windows that should currently be shown to the user: those on the
+    /// active workspace of whichever monitor they're assigned to, and not minimized.
+    pub fn visible_windows(&self) -> impl Iterator<Item = &Window> {
+        self.windows.values().filter(|w| w.workspace == self.current_workspace && !w.minimized)
+    }
+
+    // ---- Layout -----------------------------------------------------------
+
+    pub fn set_layout(&mut self, workspace: WorkspaceId, layout_name: impl Into<String>) {
+        let layout_name = layout_name.into();
+        if let Some(w) = self.workspaces.iter_mut().find(|w| w.id == workspace) {
+            w.layout = layout_name;
+        }
+    }
+
+    pub fn layout_name(&self, workspace: WorkspaceId) -> Option<&str> {
+        self.workspace(workspace).map(|w| w.layout.as_str())
+    }
+
+    /// Recomputes geometry for all non-floating, non-minimized windows on
+    /// `workspace`, grouped by the monitor each window is assigned to, and
+    /// applies the results in place. Returns the changed `(id, Rect)` pairs
+    /// so a backend can push them to real surfaces.
+    pub fn arrange_workspace(&mut self, workspace: WorkspaceId) -> Vec<(WindowId, Rect)> {
+        let Some(layout_name) = self.workspace(workspace).map(|w| w.layout.clone()) else {
+            return Vec::new();
+        };
+        let Some(layout) = self.layouts.get(&layout_name) else {
+            log::warn!("unknown layout '{layout_name}' for workspace {workspace}");
+            return Vec::new();
+        };
+
+        // Grouped via `self.order` (insertion/stacking order), not
+        // `self.windows.values()`: HashMap iteration order is randomized
+        // per-process, which would make master/stack assignment reshuffle
+        // unpredictably every time this runs (it runs on every window
+        // create/destroy/keybinding).
+        let mut by_monitor: HashMap<MonitorId, Vec<WindowId>> = HashMap::new();
+        for &id in &self.order {
+            let Some(w) = self.windows.get(&id) else { continue };
+            if w.workspace == workspace && !w.minimized && !w.floating {
+                by_monitor.entry(w.monitor).or_default().push(id);
+            }
+        }
+
+        let mut monitor_ids: Vec<MonitorId> = by_monitor.keys().copied().collect();
+        monitor_ids.sort_unstable();
+
+        let mut changes = Vec::new();
+        for monitor_id in monitor_ids {
+            let ids = &by_monitor[&monitor_id];
+            let Some(monitor) = self.monitor_for(monitor_id).cloned() else { continue };
+            let placements = layout.arrange(ids, &monitor, &self.tiling);
+            for (id, rect) in placements {
+                if let Some(w) = self.windows.get_mut(&id) {
+                    w.geometry = rect;
+                }
+                changes.push((id, rect));
+            }
+        }
+        changes
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn wm_with_monitor() -> WindowManager {
+        let mut wm = WindowManager::new();
+        wm.set_monitors(vec![{
+            let mut m = Monitor::new(0, "primary", Rect::new(0, 0, 1920, 1080));
+            m.primary = true;
+            m
+        }]);
+        wm
+    }
+
+    #[test]
+    fn new_window_on_dynamic_workspace_uses_smart_placement() {
+        let mut wm = wm_with_monitor();
+        let id = wm.alloc_window_id();
+        let mut w = Window::new(id, "first");
+        w.geometry = Rect::new(0, 0, 400, 300);
+        wm.add_window(w);
+        let placed = wm.window(id).unwrap().geometry;
+        // Grid placement starts at grid_margin, not (0,0).
+        assert_eq!(placed.x, wm.placement.grid_margin as i32);
+    }
+
+    #[test]
+    fn tiling_workspace_arranges_two_windows_side_by_side() {
+        let mut wm = wm_with_monitor();
+        wm.set_layout(wm.current_workspace(), "tiling");
+        let a = wm.alloc_window_id();
+        wm.add_window(Window::new(a, "a"));
+        let b = wm.alloc_window_id();
+        wm.add_window(Window::new(b, "b"));
+
+        wm.arrange_workspace(wm.current_workspace());
+        let ra = wm.window(a).unwrap().geometry;
+        let rb = wm.window(b).unwrap().geometry;
+        assert!(!ra.overlaps(&rb));
+        assert_eq!(ra.y, rb.y);
+        assert!(ra.x < rb.x);
+    }
+
+    #[test]
+    fn floating_window_is_skipped_by_tiling_arrange() {
+        let mut wm = wm_with_monitor();
+        wm.set_layout(wm.current_workspace(), "tiling");
+        let a = wm.alloc_window_id();
+        wm.add_window(Window::new(a, "a"));
+        wm.toggle_floating(a);
+        let before = wm.window(a).unwrap().geometry;
+        wm.arrange_workspace(wm.current_workspace());
+        assert_eq!(wm.window(a).unwrap().geometry, before);
+    }
+
+    #[test]
+    fn focus_cycles_forward_and_wraps() {
+        let mut wm = wm_with_monitor();
+        let a = wm.alloc_window_id();
+        wm.add_window(Window::new(a, "a"));
+        let b = wm.alloc_window_id();
+        wm.add_window(Window::new(b, "b"));
+        // `b` was added last, so it's focused.
+        assert_eq!(wm.focused_id(), Some(b));
+        wm.focus_next();
+        assert_eq!(wm.focused_id(), Some(a));
+        wm.focus_next();
+        assert_eq!(wm.focused_id(), Some(b));
+    }
+
+    #[test]
+    fn minimized_window_is_skipped_by_focus_cycling() {
+        let mut wm = wm_with_monitor();
+        let a = wm.alloc_window_id();
+        wm.add_window(Window::new(a, "a"));
+        let b = wm.alloc_window_id();
+        wm.add_window(Window::new(b, "b"));
+        wm.minimize_window(a);
+        wm.focus_window(b);
+        wm.focus_next();
+        assert_eq!(wm.focused_id(), Some(b), "only unminimized window should ever be focused");
+    }
+
+    #[test]
+    fn drag_moves_window_by_pointer_delta() {
+        let mut wm = wm_with_monitor();
+        // "tiling" layout leaves add_window's requested geometry alone;
+        // "dynamic"/"floating" would override it via SmartPlacement, which
+        // these tests aren't exercising.
+        wm.set_layout(wm.current_workspace(), "tiling");
+        let a = wm.alloc_window_id();
+        let mut w = Window::new(a, "a");
+        w.geometry = Rect::new(300, 300, 400, 300);
+        wm.add_window(w);
+        wm.start_drag(a, 310, 310);
+        wm.update_drag(360, 340);
+        let g = wm.window(a).unwrap().geometry;
+        assert_eq!((g.x, g.y), (350, 330));
+        wm.end_drag();
+        assert!(!wm.is_dragging());
+    }
+
+    #[test]
+    fn drag_ending_near_edge_snaps_to_half_screen() {
+        let mut wm = wm_with_monitor();
+        wm.set_layout(wm.current_workspace(), "tiling");
+        let a = wm.alloc_window_id();
+        let mut w = Window::new(a, "a");
+        w.geometry = Rect::new(500, 500, 400, 300);
+        wm.add_window(w);
+        wm.start_drag(a, 510, 510);
+        wm.update_drag(20, 510); // drag far left, within snap threshold of edge 0
+        wm.end_drag();
+        let g = wm.window(a).unwrap().geometry;
+        assert_eq!(g, Rect::new(0, 0, 960, 1080));
+    }
+
+    #[test]
+    fn resize_from_bottom_right_grows_size_only() {
+        let mut wm = wm_with_monitor();
+        wm.set_layout(wm.current_workspace(), "tiling");
+        let a = wm.alloc_window_id();
+        let mut w = Window::new(a, "a");
+        w.geometry = Rect::new(100, 100, 300, 200);
+        wm.add_window(w);
+        wm.start_resize(a, ResizeEdge::BottomRight, 400, 300);
+        wm.update_resize(450, 340);
+        let g = wm.window(a).unwrap().geometry;
+        assert_eq!(g, Rect::new(100, 100, 350, 240));
+        wm.end_resize();
+        assert!(!wm.is_resizing());
+    }
+
+    #[test]
+    fn toggle_maximize_restores_original_geometry() {
+        let mut wm = wm_with_monitor();
+        let a = wm.alloc_window_id();
+        let mut w = Window::new(a, "a");
+        w.geometry = Rect::new(50, 50, 300, 200);
+        wm.add_window(w);
+        let original = wm.window(a).unwrap().geometry;
+        wm.toggle_maximize(a);
+        assert_eq!(wm.window(a).unwrap().geometry, Rect::new(0, 0, 1920, 1080));
+        wm.toggle_maximize(a);
+        assert_eq!(wm.window(a).unwrap().geometry, original);
+    }
+
+    #[test]
+    fn directional_focus_picks_nearest_window_in_that_direction() {
+        let mut wm = wm_with_monitor();
+        wm.set_layout(wm.current_workspace(), "tiling");
+        let center = wm.alloc_window_id();
+        let mut wc = Window::new(center, "center");
+        wc.geometry = Rect::new(500, 500, 100, 100);
+        wm.add_window(wc);
+        let left = wm.alloc_window_id();
+        let mut wl = Window::new(left, "left");
+        wl.geometry = Rect::new(0, 500, 100, 100);
+        wm.add_window(wl);
+        let right = wm.alloc_window_id();
+        let mut wr = Window::new(right, "right");
+        wr.geometry = Rect::new(1000, 500, 100, 100);
+        wm.add_window(wr);
+
+        wm.focus_window(center);
+        assert_eq!(wm.focus_direction(Direction::Left), Some(left));
+        assert_eq!(wm.focused_id(), Some(left));
+
+        wm.focus_window(center);
+        assert_eq!(wm.focus_direction(Direction::Right), Some(right));
+    }
+
+    #[test]
+    fn hit_test_prefers_topmost_window() {
+        let mut wm = wm_with_monitor();
+        wm.set_layout(wm.current_workspace(), "tiling");
+        let a = wm.alloc_window_id();
+        let mut wa = Window::new(a, "a");
+        wa.geometry = Rect::new(0, 0, 400, 300);
+        wm.add_window(wa);
+        let b = wm.alloc_window_id();
+        let mut wb = Window::new(b, "b");
+        wb.geometry = Rect::new(0, 0, 400, 300); // fully overlapping, added later -> on top
+        wm.add_window(wb);
+
+        let (hit_id, hit) = wm.hit_test(200, 10).unwrap();
+        assert_eq!(hit_id, b);
+        assert_eq!(hit, TitlebarHit::Drag);
+    }
+
+    #[test]
+    fn moving_window_to_another_workspace_removes_it_from_current() {
+        let mut wm = wm_with_monitor();
+        let a = wm.alloc_window_id();
+        wm.add_window(Window::new(a, "a"));
+        let ws2 = wm.add_workspace("2", "dynamic");
+        wm.move_window_to_workspace(a, ws2);
+        assert_eq!(wm.visible_windows().count(), 0);
+        wm.switch_workspace(ws2);
+        assert_eq!(wm.visible_windows().count(), 1);
+    }
+
+    #[test]
+    fn removing_a_workspace_reassigns_its_windows() {
+        let mut wm = wm_with_monitor();
+        let ws2 = wm.add_workspace("2", "dynamic");
+        wm.switch_workspace(ws2);
+        let a = wm.alloc_window_id();
+        wm.add_window(Window::new(a, "a"));
+        wm.remove_workspace(ws2);
+        assert_ne!(wm.window(a).unwrap().workspace, ws2);
+        assert!(wm.workspace(ws2).is_none());
+    }
+}