Create module boundaries for `pane_grid` logic

6 files changed, 448 insertions, 412 deletions

diff --git a/native/src/widget/pane_grid.rs b/native/src/widget/pane_grid.rs
index 32dc4236..2272d32c 100644
--- a/native/src/widget/pane_grid.rs
+++ b/native/src/widget/pane_grid.rs
@@ -1,14 +1,24 @@
+mod direction;
+mod node;
+mod pane;
+mod split;
+mod state;
+
+pub use direction::Direction;
+pub use pane::Pane;
+pub use split::Split;
+pub use state::{Focus, State};
+
 use crate::{
     input::{keyboard, mouse, ButtonState},
-    layout, Clipboard, Element, Event, Hasher, Layout, Length, Point,
-    Rectangle, Size, Widget,
+    layout, Clipboard, Element, Event, Hasher, Layout, Length, Point, Size,
+    Widget,
 };
 
-use std::collections::HashMap;
-
 #[allow(missing_debug_implementations)]
 pub struct PaneGrid<'a, Message, Renderer> {
-    state: &'a mut Internal,
+    state: &'a mut state::Internal,
+    modifiers: &'a mut keyboard::ModifiersState,
     elements: Vec<(Pane, Element<'a, Message, Renderer>)>,
     width: Length,
     height: Length,
@@ -26,14 +36,14 @@ impl<'a, Message, Renderer> PaneGrid<'a, Message, Renderer> {
         ) -> Element<'a, Message, Renderer>,
     ) -> Self {
         let elements = {
-            let focused_pane = state.internal.focused_pane;
+            let focused_pane = state.internal.focused();
 
             state
                 .panes
                 .iter_mut()
                 .map(move |(pane, pane_state)| {
                     let focus = match focused_pane {
-                        FocusedPane::Some {
+                        state::FocusedPane::Some {
                             pane: focused_pane,
                             focus,
                         } if *pane == focused_pane => Some(focus),
@@ -47,6 +57,7 @@ impl<'a, Message, Renderer> PaneGrid<'a, Message, Renderer> {
 
         Self {
             state: &mut state.internal,
+            modifiers: &mut state.modifiers,
             elements,
             width: Length::Fill,
             height: Length::Fill,
@@ -117,7 +128,7 @@ where
         let limits = limits.width(self.width).height(self.height);
         let size = limits.resolve(Size::ZERO);
 
-        let regions = self.state.layout.regions(f32::from(self.spacing), size);
+        let regions = self.state.regions(f32::from(self.spacing), size);
 
         let children = self
             .elements
@@ -162,37 +173,24 @@ where
 
                     if let Some(((pane, _), _)) = clicked_region.next() {
                         match &self.on_drag {
-                            Some(on_drag) if self.state.modifiers.alt => {
-                                self.state.focused_pane = FocusedPane::Some {
-                                    pane: *pane,
-                                    focus: Focus::Dragging,
-                                };
+                            Some(on_drag) if self.modifiers.alt => {
+                                self.state.drag(pane);
 
                                 messages.push(on_drag(DragEvent::Picked {
                                     pane: *pane,
                                 }));
                             }
                             _ => {
-                                self.state.focused_pane = FocusedPane::Some {
-                                    pane: *pane,
-                                    focus: Focus::Idle,
-                                };
+                                self.state.focus(pane);
                             }
                         }
                     } else {
-                        self.state.focused_pane = FocusedPane::None;
+                        self.state.unfocus();
                     }
                 }
                 ButtonState::Released => {
-                    if let FocusedPane::Some {
-                        pane,
-                        focus: Focus::Dragging,
-                    } = self.state.focused_pane
-                    {
-                        self.state.focused_pane = FocusedPane::Some {
-                            pane,
-                            focus: Focus::Idle,
-                        };
+                    if let Some(pane) = self.state.dragged() {
+                        self.state.focus(&pane);
 
                         if let Some(on_drag) = &self.on_drag {
                             let mut dropped_region = self
@@ -219,17 +217,13 @@ where
                 }
             },
             Event::Keyboard(keyboard::Event::Input { modifiers, .. }) => {
-                self.state.modifiers = modifiers;
+                *self.modifiers = modifiers;
             }
             _ => {}
         }
 
-        match self.state.focused_pane {
-            FocusedPane::Some {
-                focus: Focus::Dragging,
-                ..
-            } => {}
-            _ => {
+        if self.state.dragged().is_none() {
+            {
                 self.elements.iter_mut().zip(layout.children()).for_each(
                     |((_, pane), layout)| {
                         pane.widget.on_event(
@@ -253,18 +247,10 @@ where
         layout: Layout<'_>,
         cursor_position: Point,
     ) -> Renderer::Output {
-        let dragging = match self.state.focused_pane {
-            FocusedPane::Some {
-                pane,
-                focus: Focus::Dragging,
-            } => Some(pane),
-            _ => None,
-        };
-
         renderer.draw(
             defaults,
             &self.elements,
-            dragging,
+            self.state.dragged(),
             layout,
             cursor_position,
         )
@@ -276,7 +262,7 @@ where
         std::any::TypeId::of::<PaneGrid<'_, Message, Renderer>>().hash(state);
         self.width.hash(state);
         self.height.hash(state);
-        self.state.layout.hash(state);
+        self.state.hash_layout(state);
 
         for (_, element) in &self.elements {
             element.hash_layout(state);
@@ -284,374 +270,6 @@ where
     }
 }
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
-pub struct Pane(usize);
-
-impl Pane {
-    pub fn index(&self) -> usize {
-        self.0
-    }
-}
-
-#[derive(Debug)]
-pub struct State<T> {
-    panes: HashMap<Pane, T>,
-    internal: Internal,
-}
-
-#[derive(Debug)]
-struct Internal {
-    layout: Node,
-    last_pane: usize,
-    focused_pane: FocusedPane,
-    modifiers: keyboard::ModifiersState,
-}
-
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub enum Focus {
-    Idle,
-    Dragging,
-}
-
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
-enum FocusedPane {
-    None,
-    Some { pane: Pane, focus: Focus },
-}
-
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub enum Direction {
-    Up,
-    Down,
-    Left,
-    Right,
-}
-
-impl<T> State<T> {
-    pub fn new(first_pane_state: T) -> (Self, Pane) {
-        let first_pane = Pane(0);
-
-        let mut panes = HashMap::new();
-        let _ = panes.insert(first_pane, first_pane_state);
-
-        (
-            State {
-                panes,
-                internal: Internal {
-                    layout: Node::Pane(first_pane),
-                    last_pane: 0,
-                    focused_pane: FocusedPane::None,
-                    modifiers: keyboard::ModifiersState::default(),
-                },
-            },
-            first_pane,
-        )
-    }
-
-    pub fn len(&self) -> usize {
-        self.panes.len()
-    }
-
-    pub fn get_mut(&mut self, pane: &Pane) -> Option<&mut T> {
-        self.panes.get_mut(pane)
-    }
-
-    pub fn iter(&self) -> impl Iterator<Item = (&Pane, &T)> {
-        self.panes.iter()
-    }
-
-    pub fn iter_mut(&mut self) -> impl Iterator<Item = (&Pane, &mut T)> {
-        self.panes.iter_mut()
-    }
-
-    pub fn focused_pane(&self) -> Option<Pane> {
-        match self.internal.focused_pane {
-            FocusedPane::Some {
-                pane,
-                focus: Focus::Idle,
-            } => Some(pane),
-            FocusedPane::Some {
-                focus: Focus::Dragging,
-                ..
-            } => None,
-            FocusedPane::None => None,
-        }
-    }
-
-    pub fn adjacent_pane(
-        &self,
-        pane: &Pane,
-        direction: Direction,
-    ) -> Option<Pane> {
-        let regions =
-            self.internal.layout.regions(0.0, Size::new(4096.0, 4096.0));
-
-        let current_region = regions.get(pane)?;
-
-        let target = match direction {
-            Direction::Left => {
-                Point::new(current_region.x - 1.0, current_region.y + 1.0)
-            }
-            Direction::Right => Point::new(
-                current_region.x + current_region.width + 1.0,
-                current_region.y + 1.0,
-            ),
-            Direction::Up => {
-                Point::new(current_region.x + 1.0, current_region.y - 1.0)
-            }
-            Direction::Down => Point::new(
-                current_region.x + 1.0,
-                current_region.y + current_region.height + 1.0,
-            ),
-        };
-
-        let mut colliding_regions =
-            regions.iter().filter(|(_, region)| region.contains(target));
-
-        let (pane, _) = colliding_regions.next()?;
-
-        Some(*pane)
-    }
-
-    pub fn focus(&mut self, pane: &Pane) {
-        self.internal.focused_pane = FocusedPane::Some {
-            pane: *pane,
-            focus: Focus::Idle,
-        };
-    }
-
-    pub fn split_vertically(&mut self, pane: &Pane, state: T) -> Option<Pane> {
-        self.split(Split::Vertical, pane, state)
-    }
-
-    pub fn split_horizontally(
-        &mut self,
-        pane: &Pane,
-        state: T,
-    ) -> Option<Pane> {
-        self.split(Split::Horizontal, pane, state)
-    }
-
-    pub fn split(
-        &mut self,
-        kind: Split,
-        pane: &Pane,
-        state: T,
-    ) -> Option<Pane> {
-        let node = self.internal.layout.find(pane)?;
-
-        let new_pane = {
-            self.internal.last_pane = self.internal.last_pane.checked_add(1)?;
-
-            Pane(self.internal.last_pane)
-        };
-
-        node.split(kind, new_pane);
-
-        let _ = self.panes.insert(new_pane, state);
-        self.focus(&new_pane);
-
-        Some(new_pane)
-    }
-
-    pub fn swap(&mut self, a: &Pane, b: &Pane) {
-        self.internal.layout.update(&|node| match node {
-            Node::Split { .. } => {}
-            Node::Pane(pane) => {
-                if pane == a {
-                    *node = Node::Pane(*b);
-                } else if pane == b {
-                    *node = Node::Pane(*a);
-                }
-            }
-        });
-    }
-
-    pub fn close(&mut self, pane: &Pane) -> Option<T> {
-        if let Some(sibling) = self.internal.layout.remove(pane) {
-            self.focus(&sibling);
-            self.panes.remove(pane)
-        } else {
-            None
-        }
-    }
-}
-
-#[derive(Debug, Clone, Hash)]
-enum Node {
-    Split {
-        kind: Split,
-        ratio: u32,
-        a: Box<Node>,
-        b: Box<Node>,
-    },
-    Pane(Pane),
-}
-
-impl Node {
-    fn find(&mut self, pane: &Pane) -> Option<&mut Node> {
-        match self {
-            Node::Split { a, b, .. } => {
-                a.find(pane).or_else(move || b.find(pane))
-            }
-            Node::Pane(p) => {
-                if p == pane {
-                    Some(self)
-                } else {
-                    None
-                }
-            }
-        }
-    }
-
-    fn split(&mut self, kind: Split, new_pane: Pane) {
-        *self = Node::Split {
-            kind,
-            ratio: 500_000,
-            a: Box::new(self.clone()),
-            b: Box::new(Node::Pane(new_pane)),
-        };
-    }
-
-    fn update(&mut self, f: &impl Fn(&mut Node)) {
-        match self {
-            Node::Split { a, b, .. } => {
-                a.update(f);
-                b.update(f);
-            }
-            _ => {}
-        }
-
-        f(self);
-    }
-
-    fn remove(&mut self, pane: &Pane) -> Option<Pane> {
-        match self {
-            Node::Split { a, b, .. } => {
-                if a.pane() == Some(*pane) {
-                    *self = *b.clone();
-                    Some(self.first_pane())
-                } else if b.pane() == Some(*pane) {
-                    *self = *a.clone();
-                    Some(self.first_pane())
-                } else {
-                    a.remove(pane).or_else(|| b.remove(pane))
-                }
-            }
-            Node::Pane(_) => None,
-        }
-    }
-
-    pub fn regions(
-        &self,
-        spacing: f32,
-        size: Size,
-    ) -> HashMap<Pane, Rectangle> {
-        let mut regions = HashMap::new();
-
-        self.compute_regions(
-            spacing / 2.0,
-            &Rectangle {
-                x: 0.0,
-                y: 0.0,
-                width: size.width,
-                height: size.height,
-            },
-            &mut regions,
-        );
-
-        regions
-    }
-
-    fn pane(&self) -> Option<Pane> {
-        match self {
-            Node::Split { .. } => None,
-            Node::Pane(pane) => Some(*pane),
-        }
-    }
-
-    fn first_pane(&self) -> Pane {
-        match self {
-            Node::Split { a, .. } => a.first_pane(),
-            Node::Pane(pane) => *pane,
-        }
-    }
-
-    fn compute_regions(
-        &self,
-        halved_spacing: f32,
-        current: &Rectangle,
-        regions: &mut HashMap<Pane, Rectangle>,
-    ) {
-        match self {
-            Node::Split { kind, ratio, a, b } => {
-                let ratio = *ratio as f32 / 1_000_000.0;
-                let (region_a, region_b) =
-                    kind.apply(current, ratio, halved_spacing);
-
-                a.compute_regions(halved_spacing, &region_a, regions);
-                b.compute_regions(halved_spacing, &region_b, regions);
-            }
-            Node::Pane(pane) => {
-                let _ = regions.insert(*pane, *current);
-            }
-        }
-    }
-}
-
-#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq)]
-pub enum Split {
-    Horizontal,
-    Vertical,
-}
-
-impl Split {
-    fn apply(
-        &self,
-        rectangle: &Rectangle,
-        ratio: f32,
-        halved_spacing: f32,
-    ) -> (Rectangle, Rectangle) {
-        match self {
-            Split::Horizontal => {
-                let width_left =
-                    (rectangle.width * ratio).round() - halved_spacing;
-                let width_right = rectangle.width - width_left - halved_spacing;
-
-                (
-                    Rectangle {
-                        width: width_left,
-                        ..*rectangle
-                    },
-                    Rectangle {
-                        x: rectangle.x + width_left + halved_spacing,
-                        width: width_right,
-                        ..*rectangle
-                    },
-                )
-            }
-            Split::Vertical => {
-                let height_top =
-                    (rectangle.height * ratio).round() - halved_spacing;
-                let height_bottom =
-                    rectangle.height - height_top - halved_spacing;
-
-                (
-                    Rectangle {
-                        height: height_top,
-                        ..*rectangle
-                    },
-                    Rectangle {
-                        y: rectangle.y + height_top + halved_spacing,
-                        height: height_bottom,
-                        ..*rectangle
-                    },
-                )
-            }
-        }
-    }
-}
-
 /// The renderer of a [`PaneGrid`].
 ///
 /// Your [renderer] will need to implement this trait before being
diff --git a/native/src/widget/pane_grid/direction.rs b/native/src/widget/pane_grid/direction.rs
new file mode 100644
index 00000000..0ee90557
--- /dev/null
+++ b/native/src/widget/pane_grid/direction.rs
@@ -0,0 +1,7 @@
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Direction {
+    Up,
+    Down,
+    Left,
+    Right,
+}
diff --git a/native/src/widget/pane_grid/node.rs b/native/src/widget/pane_grid/node.rs
new file mode 100644
index 00000000..a9aa7fdc
--- /dev/null
+++ b/native/src/widget/pane_grid/node.rs
@@ -0,0 +1,128 @@
+use crate::{
+    pane_grid::{Pane, Split},
+    Rectangle, Size,
+};
+
+use std::collections::HashMap;
+
+#[derive(Debug, Clone, Hash)]
+pub enum Node {
+    Split {
+        kind: Split,
+        ratio: u32,
+        a: Box<Node>,
+        b: Box<Node>,
+    },
+    Pane(Pane),
+}
+
+impl Node {
+    pub fn find(&mut self, pane: &Pane) -> Option<&mut Node> {
+        match self {
+            Node::Split { a, b, .. } => {
+                a.find(pane).or_else(move || b.find(pane))
+            }
+            Node::Pane(p) => {
+                if p == pane {
+                    Some(self)
+                } else {
+                    None
+                }
+            }
+        }
+    }
+
+    pub fn split(&mut self, kind: Split, new_pane: Pane) {
+        *self = Node::Split {
+            kind,
+            ratio: 500_000,
+            a: Box::new(self.clone()),
+            b: Box::new(Node::Pane(new_pane)),
+        };
+    }
+
+    pub fn update(&mut self, f: &impl Fn(&mut Node)) {
+        match self {
+            Node::Split { a, b, .. } => {
+                a.update(f);
+                b.update(f);
+            }
+            _ => {}
+        }
+
+        f(self);
+    }
+
+    pub fn remove(&mut self, pane: &Pane) -> Option<Pane> {
+        match self {
+            Node::Split { a, b, .. } => {
+                if a.pane() == Some(*pane) {
+                    *self = *b.clone();
+                    Some(self.first_pane())
+                } else if b.pane() == Some(*pane) {
+                    *self = *a.clone();
+                    Some(self.first_pane())
+                } else {
+                    a.remove(pane).or_else(|| b.remove(pane))
+                }
+            }
+            Node::Pane(_) => None,
+        }
+    }
+
+    pub fn regions(
+        &self,
+        spacing: f32,
+        size: Size,
+    ) -> HashMap<Pane, Rectangle> {
+        let mut regions = HashMap::new();
+
+        self.compute_regions(
+            spacing / 2.0,
+            &Rectangle {
+                x: 0.0,
+                y: 0.0,
+                width: size.width,
+                height: size.height,
+            },
+            &mut regions,
+        );
+
+        regions
+    }
+
+    pub fn pane(&self) -> Option<Pane> {
+        match self {
+            Node::Split { .. } => None,
+            Node::Pane(pane) => Some(*pane),
+        }
+    }
+
+    pub fn first_pane(&self) -> Pane {
+        match self {
+            Node::Split { a, .. } => a.first_pane(),
+            Node::Pane(pane) => *pane,
+        }
+    }
+
+    fn compute_regions(
+        &self,
+        halved_spacing: f32,
+        current: &Rectangle,
+        regions: &mut HashMap<Pane, Rectangle>,
+    ) {
+        match self {
+            Node::Split { kind, ratio, a, b } => {
+                let ratio = *ratio as f32 / 1_000_000.0;
+                let (region_a, region_b) =
+                    kind.apply(current, ratio, halved_spacing);
+
+                a.compute_regions(halved_spacing, &region_a, regions);
+                b.compute_regions(halved_spacing, &region_b, regions);
+            }
+            Node::Pane(pane) => {
+                let _ = regions.insert(*pane, *current);
+            }
+        }
+    }
+}
diff --git a/native/src/widget/pane_grid/pane.rs b/native/src/widget/pane_grid/pane.rs
new file mode 100644
index 00000000..cfca3b03
--- /dev/null
+++ b/native/src/widget/pane_grid/pane.rs
@@ -0,0 +1,2 @@
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct Pane(pub(super) usize);
diff --git a/native/src/widget/pane_grid/split.rs b/native/src/widget/pane_grid/split.rs
new file mode 100644
index 00000000..ca9ed5e1
--- /dev/null
+++ b/native/src/widget/pane_grid/split.rs
@@ -0,0 +1,54 @@
+use crate::Rectangle;
+
+#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq)]
+pub enum Split {
+    Horizontal,
+    Vertical,
+}
+
+impl Split {
+    pub(super) fn apply(
+        &self,
+        rectangle: &Rectangle,
+        ratio: f32,
+        halved_spacing: f32,
+    ) -> (Rectangle, Rectangle) {
+        match self {
+            Split::Horizontal => {
+                let width_left =
+                    (rectangle.width * ratio).round() - halved_spacing;
+                let width_right = rectangle.width - width_left - halved_spacing;
+
+                (
+                    Rectangle {
+                        width: width_left,
+                        ..*rectangle
+                    },
+                    Rectangle {
+                        x: rectangle.x + width_left + halved_spacing,
+                        width: width_right,
+                        ..*rectangle
+                    },
+                )
+            }
+            Split::Vertical => {
+                let height_top =
+                    (rectangle.height * ratio).round() - halved_spacing;
+                let height_bottom =
+                    rectangle.height - height_top - halved_spacing;
+
+                (
+                    Rectangle {
+                        height: height_top,
+                        ..*rectangle
+                    },
+                    Rectangle {
+                        y: rectangle.y + height_top + halved_spacing,
+                        height: height_bottom,
+                        ..*rectangle
+                    },
+                )
+            }
+        }
+    }
+}
diff --git a/native/src/widget/pane_grid/state.rs b/native/src/widget/pane_grid/state.rs
new file mode 100644
index 00000000..130c7e34
--- /dev/null
+++ b/native/src/widget/pane_grid/state.rs
@@ -0,0 +1,227 @@
+use crate::{
+    input::keyboard,
+    pane_grid::{node::Node, Direction, Pane, Split},
+    Hasher, Point, Rectangle, Size,
+};
+
+use std::collections::HashMap;
+
+#[derive(Debug)]
+pub struct State<T> {
+    pub(super) panes: HashMap<Pane, T>,
+    pub(super) internal: Internal,
+    pub(super) modifiers: keyboard::ModifiersState,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Focus {
+    Idle,
+    Dragging,
+}
+
+impl<T> State<T> {
+    pub fn new(first_pane_state: T) -> (Self, Pane) {
+        let first_pane = Pane(0);
+
+        let mut panes = HashMap::new();
+        let _ = panes.insert(first_pane, first_pane_state);
+
+        (
+            State {
+                panes,
+                internal: Internal {
+                    layout: Node::Pane(first_pane),
+                    last_pane: 0,
+                    focused_pane: FocusedPane::None,
+                },
+                modifiers: keyboard::ModifiersState::default(),
+            },
+            first_pane,
+        )
+    }
+
+    pub fn len(&self) -> usize {
+        self.panes.len()
+    }
+
+    pub fn get_mut(&mut self, pane: &Pane) -> Option<&mut T> {
+        self.panes.get_mut(pane)
+    }
+
+    pub fn iter(&self) -> impl Iterator<Item = (&Pane, &T)> {
+        self.panes.iter()
+    }
+
+    pub fn iter_mut(&mut self) -> impl Iterator<Item = (&Pane, &mut T)> {
+        self.panes.iter_mut()
+    }
+
+    pub fn focused_pane(&self) -> Option<Pane> {
+        match self.internal.focused_pane {
+            FocusedPane::Some {
+                pane,
+                focus: Focus::Idle,
+            } => Some(pane),
+            FocusedPane::Some {
+                focus: Focus::Dragging,
+                ..
+            } => None,
+            FocusedPane::None => None,
+        }
+    }
+
+    pub fn adjacent_pane(
+        &self,
+        pane: &Pane,
+        direction: Direction,
+    ) -> Option<Pane> {
+        let regions =
+            self.internal.layout.regions(0.0, Size::new(4096.0, 4096.0));
+
+        let current_region = regions.get(pane)?;
+
+        let target = match direction {
+            Direction::Left => {
+                Point::new(current_region.x - 1.0, current_region.y + 1.0)
+            }
+            Direction::Right => Point::new(
+                current_region.x + current_region.width + 1.0,
+                current_region.y + 1.0,
+            ),
+            Direction::Up => {
+                Point::new(current_region.x + 1.0, current_region.y - 1.0)
+            }
+            Direction::Down => Point::new(
+                current_region.x + 1.0,
+                current_region.y + current_region.height + 1.0,
+            ),
+        };
+
+        let mut colliding_regions =
+            regions.iter().filter(|(_, region)| region.contains(target));
+
+        let (pane, _) = colliding_regions.next()?;
+
+        Some(*pane)
+    }
+
+    pub fn focus(&mut self, pane: &Pane) {
+        self.internal.focus(pane);
+    }
+
+    pub fn split_vertically(&mut self, pane: &Pane, state: T) -> Option<Pane> {
+        self.split(Split::Vertical, pane, state)
+    }
+
+    pub fn split_horizontally(
+        &mut self,
+        pane: &Pane,
+        state: T,
+    ) -> Option<Pane> {
+        self.split(Split::Horizontal, pane, state)
+    }
+
+    pub fn split(
+        &mut self,
+        kind: Split,
+        pane: &Pane,
+        state: T,
+    ) -> Option<Pane> {
+        let node = self.internal.layout.find(pane)?;
+
+        let new_pane = {
+            self.internal.last_pane = self.internal.last_pane.checked_add(1)?;
+
+            Pane(self.internal.last_pane)
+        };
+
+        node.split(kind, new_pane);
+
+        let _ = self.panes.insert(new_pane, state);
+        self.focus(&new_pane);
+
+        Some(new_pane)
+    }
+
+    pub fn swap(&mut self, a: &Pane, b: &Pane) {
+        self.internal.layout.update(&|node| match node {
+            Node::Split { .. } => {}
+            Node::Pane(pane) => {
+                if pane == a {
+                    *node = Node::Pane(*b);
+                } else if pane == b {
+                    *node = Node::Pane(*a);
+                }
+            }
+        });
+    }
+
+    pub fn close(&mut self, pane: &Pane) -> Option<T> {
+        if let Some(sibling) = self.internal.layout.remove(pane) {
+            self.focus(&sibling);
+            self.panes.remove(pane)
+        } else {
+            None
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct Internal {
+    layout: Node,
+    last_pane: usize,
+    focused_pane: FocusedPane,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum FocusedPane {
+    None,
+    Some { pane: Pane, focus: Focus },
+}
+
+impl Internal {
+    pub fn focused(&self) -> FocusedPane {
+        self.focused_pane
+    }
+    pub fn dragged(&self) -> Option<Pane> {
+        match self.focused_pane {
+            FocusedPane::Some {
+                pane,
+                focus: Focus::Dragging,
+            } => Some(pane),
+            _ => None,
+        }
+    }
+
+    pub fn regions(
+        &self,
+        spacing: f32,
+        size: Size,
+    ) -> HashMap<Pane, Rectangle> {
+        self.layout.regions(spacing, size)
+    }
+
+    pub fn focus(&mut self, pane: &Pane) {
+        self.focused_pane = FocusedPane::Some {
+            pane: *pane,
+            focus: Focus::Idle,
+        };
+    }
+
+    pub fn drag(&mut self, pane: &Pane) {
+        self.focused_pane = FocusedPane::Some {
+            pane: *pane,
+            focus: Focus::Dragging,
+        };
+    }
+
+    pub fn unfocus(&mut self) {
+        self.focused_pane = FocusedPane::None;
+    }
+
+    pub fn hash_layout(&self, hasher: &mut Hasher) {
+        use std::hash::Hash;
+
+        self.layout.hash(hasher);
+    }
+}