mod dock;
mod invalid_panel;
mod panel;
mod resize_handle;
mod stack_panel;
mod state;
mod tab_bar;
mod tab_panel;
mod window_controls;

use std::sync::Arc;

use anyhow::Result;
pub use dock::*;
use gpui::prelude::FluentBuilder;
use gpui::{
    AnyElement, AnyView, App, AppContext, Axis, Bounds, Context, Edges, Entity, EntityId,
    EventEmitter, InteractiveElement as _, IntoElement, ParentElement as _, Pixels, Render,
    SharedString, Styled, Subscription, WeakEntity, Window, actions, div, px,
};
use gpui_component::{ElementExt, Placement};
pub use panel::*;
pub use stack_panel::*;
pub use state::*;
pub use tab_panel::*;

/// Initialize the dock, registering the [`PanelRegistry`] global.
///
/// Call this from your app entry point, before building any [`DockArea`].
/// It is idempotent, so it is safe to call alongside `gpui_component::init`.
pub fn init(cx: &mut App) {
    PanelRegistry::init(cx);
}

// Note: the action group name must not collide with gpui-component's own
// `dock::` actions, which are linked into the same binary while the app still
// depends on gpui-component (action names are registered globally per App).
actions!(signed_dock, [ToggleZoom, ClosePanel]);

/// Minimal i18n shim replacing gpui-component's `rust_i18n::t!()`.
///
/// The upstream dock used `t!("Dock.*")` keys; we keep the same keys but
/// resolve them to the English strings so the crate has no i18n dependency.
pub(crate) fn t(key: &'static str) -> &'static str {
    match key {
        "Dock.Unnamed" => "Unnamed",
        "Dock.Close" => "Close",
        "Dock.Zoom In" => "Zoom In",
        "Dock.Zoom Out" => "Zoom Out",
        "Dock.Collapse" => "Collapse",
        "Dock.Expand" => "Expand",
        _ => key,
    }
}

/// The fixed height of the tab bar, which doubles as the window title bar.
pub const TAB_BAR_HEIGHT: Pixels = px(44.);

/// A host-owned drag item, dragged into the dock by the application.
#[derive(Clone, Debug)]
pub struct AnyDrag {
    pub value: Arc<dyn std::any::Any + Send + Sync>,
}

impl AnyDrag {
    pub fn new<T: 'static + Send + Sync>(value: T) -> Self {
        Self {
            value: Arc::new(value),
        }
    }
}

pub enum DockEvent {
    /// The layout of the dock has changed, subscribers this to save the layout.
    ///
    /// This event is emitted when every time the layout of the dock has changed,
    /// So it emits may be too frequently, you may want to debounce the event.
    LayoutChanged,

    /// A host-owned drag item ([`AnyDrag`]) was dropped inside the dock.
    DragDrop { item: AnyDrag, target: DropTarget },
}

/// Where a host-owned drag landed, and how much the container can say about it.
#[derive(Clone, Debug)]
pub enum DropTarget {
    /// Dropped on a [`TabPanel`] in a split layout. A split layout has no free
    /// coordinates, so the container reports the panel and the edge it resolved
    /// from the cursor instead.
    ///
    /// `placement` is `None` for the centre zone, meaning merge into the tab
    /// group rather than split.
    Panel {
        tab_panel: Entity<TabPanel>,
        placement: Option<Placement>,
    },
}

/// The main area of the dock.
pub struct DockArea {
    id: SharedString,
    /// The version is used to special the default layout, this is like the `panel_version` in [`Panel`](Panel).
    version: Option<usize>,
    pub(crate) bounds: Bounds<Pixels>,

    /// The center view of the dock_area.
    center: DockItem,
    /// The left dock of the dock_area.
    left_dock: Option<Entity<Dock>>,

    /// The entity_id of the [`TabPanel`](TabPanel) where each toggle button should be displayed,
    toggle_button_panels: Edges<Option<EntityId>>,

    /// Whether to show the toggle button.
    toggle_button_visible: bool,
    /// The top zoom view of the dock_area, if any.
    zoom_view: Option<AnyView>,

    /// Lock panels layout, but allow to resize.
    locked: bool,

    _subscriptions: Vec<Subscription>,
}

/// DockItem is a tree structure that represents the layout of the dock.
#[derive(Clone)]
pub enum DockItem {
    /// Split layout
    Split {
        axis: Axis,
        /// Self size, only used for build split panels
        size: Option<Pixels>,
        items: Vec<DockItem>,
        /// Items sizes
        sizes: Vec<Option<Pixels>>,
        view: Entity<StackPanel>,
    },
    /// Tab layout
    Tabs {
        /// Self size, only used for build split panels
        size: Option<Pixels>,
        items: Vec<Arc<dyn PanelView>>,
        active_ix: usize,
        view: Entity<TabPanel>,
    },
    /// Panel layout
    Panel {
        /// Self size, only used for build split panels
        size: Option<Pixels>,
        view: Arc<dyn PanelView>,
    },
}

impl std::fmt::Debug for DockItem {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            DockItem::Split {
                axis, items, sizes, ..
            } => f
                .debug_struct("Split")
                .field("axis", axis)
                .field("items", &items.len())
                .field("sizes", sizes)
                .finish(),
            DockItem::Tabs {
                items, active_ix, ..
            } => f
                .debug_struct("Tabs")
                .field("items", &items.len())
                .field("active_ix", active_ix)
                .finish(),
            DockItem::Panel { .. } => f.debug_struct("Panel").finish(),
        }
    }
}

impl DockItem {
    /// Get the size of the DockItem.
    fn get_size(&self) -> Option<Pixels> {
        match self {
            Self::Split { size, .. } => *size,
            Self::Tabs { size, .. } => *size,
            Self::Panel { size, .. } => *size,
        }
    }

    /// Set size for the DockItem.
    pub fn size(mut self, new_size: impl Into<Pixels>) -> Self {
        let new_size: Option<Pixels> = Some(new_size.into());
        match self {
            Self::Split { ref mut size, .. } => *size = new_size,
            Self::Tabs { ref mut size, .. } => *size = new_size,
            Self::Panel { ref mut size, .. } => *size = new_size,
        }
        self
    }

    /// Set active index for the DockItem, only valid for [`DockItem::Tabs`].
    pub fn active_index(mut self, new_active_ix: usize, cx: &mut App) -> Self {
        debug_assert!(
            matches!(self, Self::Tabs { .. }),
            "active_ix can only be set for DockItem::Tabs"
        );

        if let Self::Tabs {
            ref mut active_ix,
            ref mut view,
            ..
        } = self
        {
            *active_ix = new_active_ix;
            view.update(cx, |tab_panel, _| {
                tab_panel.active_ix = new_active_ix;
            });
        }
        self
    }

    /// Create DockItem::Split with given split layout.
    pub fn split(
        axis: Axis,
        items: Vec<DockItem>,
        dock_area: &WeakEntity<DockArea>,
        window: &mut Window,
        cx: &mut App,
    ) -> Self {
        let sizes = items.iter().map(|item| item.get_size()).collect();
        Self::split_with_sizes(axis, items, sizes, dock_area, window, cx)
    }

    /// Create DockItem with vertical split layout.
    pub fn v_split(
        items: Vec<DockItem>,
        dock_area: &WeakEntity<DockArea>,
        window: &mut Window,
        cx: &mut App,
    ) -> Self {
        Self::split(Axis::Vertical, items, dock_area, window, cx)
    }

    /// Create DockItem with horizontal split layout.
    pub fn h_split(
        items: Vec<DockItem>,
        dock_area: &WeakEntity<DockArea>,
        window: &mut Window,
        cx: &mut App,
    ) -> Self {
        Self::split(Axis::Horizontal, items, dock_area, window, cx)
    }

    /// Create DockItem with split layout, each item of panel have specified size.
    ///
    /// Please note that the `items` and `sizes` must have the same length.
    /// Set `None` in `sizes` to make the index of panel have auto size.
    pub fn split_with_sizes(
        axis: Axis,
        items: Vec<DockItem>,
        sizes: Vec<Option<Pixels>>,
        dock_area: &WeakEntity<DockArea>,
        window: &mut Window,
        cx: &mut App,
    ) -> Self {
        let stack_panel = cx.new(|cx| {
            let mut stack_panel = StackPanel::new(axis, window, cx);
            for (i, item) in items.iter().enumerate() {
                let view = item.view();
                let size = sizes.get(i).copied().flatten();
                stack_panel.add_panel(view.clone(), size, dock_area.clone(), window, cx)
            }

            stack_panel
        });

        window.defer(cx, {
            let stack_panel = stack_panel.clone();
            let dock_area = dock_area.clone();
            move |window, cx| {
                _ = dock_area.update(cx, |this, cx| {
                    this.subscribe_panel(&stack_panel, window, cx);
                });
            }
        });

        Self::Split {
            axis,
            size: None,
            items,
            sizes,
            view: stack_panel,
        }
    }

    /// Create DockItem with panel layout
    pub fn panel(panel: Arc<dyn PanelView>) -> Self {
        Self::Panel {
            size: None,
            view: panel,
        }
    }

    /// Create DockItem with tabs layout, items are displayed as tabs.
    ///
    /// The `active_ix` is the index of the active tab, if `None` the first tab is active.
    pub fn tabs(
        items: Vec<Arc<dyn PanelView>>,
        dock_area: &WeakEntity<DockArea>,
        window: &mut Window,
        cx: &mut App,
    ) -> Self {
        let mut new_items: Vec<Arc<dyn PanelView>> = vec![];
        for item in items.into_iter() {
            new_items.push(item)
        }
        Self::new_tabs(new_items, None, dock_area, window, cx)
    }

    pub fn tab<P: Panel>(
        item: Entity<P>,
        dock_area: &WeakEntity<DockArea>,
        window: &mut Window,
        cx: &mut App,
    ) -> Self {
        Self::new_tabs(vec![Arc::new(item.clone())], None, dock_area, window, cx)
    }

    fn new_tabs(
        items: Vec<Arc<dyn PanelView>>,
        active_ix: Option<usize>,
        dock_area: &WeakEntity<DockArea>,
        window: &mut Window,
        cx: &mut App,
    ) -> Self {
        let active_ix = active_ix.unwrap_or(0);
        let tab_panel = cx.new(|cx| {
            let mut tab_panel = TabPanel::new(None, dock_area.clone(), window, cx);
            for item in items.iter() {
                tab_panel.add_panel(item.clone(), window, cx)
            }
            tab_panel.active_ix = active_ix;
            tab_panel
        });

        Self::Tabs {
            size: None,
            items,
            active_ix,
            view: tab_panel,
        }
    }

    /// Returns the views of the dock item.
    pub fn view(&self) -> Arc<dyn PanelView> {
        match self {
            Self::Split { view, .. } => Arc::new(view.clone()),
            Self::Tabs { view, .. } => Arc::new(view.clone()),
            Self::Panel { view, .. } => view.clone(),
        }
    }

    /// Whether this dock item currently holds no visible panel.
    ///
    /// Walks the live panel entities, not `items`: [`Self::add_panel`] only
    /// pushes into them, nothing ever removes, and splitting does not touch
    /// them at all.
    ///
    /// A container is empty when every child is, so a fresh one is empty. A
    /// leaf counts as empty while it is hidden, matching the render path, which
    /// skips panels whose [`Panel::visible`] is `false`.
    pub fn is_empty(&self, cx: &App) -> bool {
        fn is_empty(panel: &Arc<dyn PanelView>, cx: &App) -> bool {
            let view = panel.view();

            if let Ok(stack) = view.clone().downcast::<StackPanel>() {
                return stack
                    .read(cx)
                    .panels
                    .iter()
                    .all(|panel| is_empty(panel, cx));
            }
            if let Ok(tabs) = view.clone().downcast::<TabPanel>() {
                return tabs.read(cx).panels.iter().all(|panel| is_empty(panel, cx));
            }

            !panel.visible(cx)
        }

        is_empty(&self.view(), cx)
    }

    /// Find existing panel in the dock item.
    pub fn find_panel(&self, panel: Arc<dyn PanelView>) -> Option<Arc<dyn PanelView>> {
        match self {
            Self::Split { items, .. } => {
                items.iter().find_map(|item| item.find_panel(panel.clone()))
            }
            Self::Tabs { items, .. } => items.iter().find(|item| *item == &panel).cloned(),
            Self::Panel { view, .. } => Some(view.clone()),
        }
    }

    /// Add a panel to the dock item.
    pub fn add_panel(
        &mut self,
        panel: Arc<dyn PanelView>,
        dock_area: &WeakEntity<DockArea>,
        window: &mut Window,
        cx: &mut App,
    ) {
        match self {
            Self::Tabs { view, items, .. } => {
                items.push(panel.clone());
                view.update(cx, |tab_panel, cx| {
                    tab_panel.add_panel(panel, window, cx);
                });
            }
            Self::Split { view, items, .. } => {
                // Iter items to add panel to the first tabs
                for item in items.iter_mut() {
                    if let DockItem::Tabs { view, .. } = item {
                        view.update(cx, |tab_panel, cx| {
                            tab_panel.add_panel(panel.clone(), window, cx);
                        });
                        return;
                    }
                }

                // Unable to find tabs, create new tabs
                let new_item = Self::tabs(vec![panel.clone()], dock_area, window, cx);
                items.push(new_item.clone());
                view.update(cx, |stack_panel, cx| {
                    stack_panel.add_panel(new_item.view(), None, dock_area.clone(), window, cx);
                });
            }
            Self::Panel { .. } => {}
        }
    }

    /// Remove a panel from the dock item.
    pub fn remove_panel(&self, panel: Arc<dyn PanelView>, window: &mut Window, cx: &mut App) {
        match self {
            DockItem::Tabs { view, .. } => {
                view.update(cx, |tab_panel, cx| {
                    tab_panel.remove_panel(panel, window, cx);
                });
            }
            DockItem::Split { items, view, .. } => {
                // For each child item, set collapsed state
                for item in items {
                    item.remove_panel(panel.clone(), window, cx);
                }
                view.update(cx, |split, cx| {
                    split.remove_panel(panel, window, cx);
                });
            }
            DockItem::Panel { .. } => {}
        }
    }

    pub fn set_collapsed(&self, collapsed: bool, window: &mut Window, cx: &mut App) {
        match self {
            DockItem::Tabs { view, .. } => {
                view.update(cx, |tab_panel, cx| {
                    tab_panel.set_collapsed(collapsed, window, cx);
                });
            }
            DockItem::Split { items, .. } => {
                // For each child item, set collapsed state
                for item in items {
                    item.set_collapsed(collapsed, window, cx);
                }
            }
            DockItem::Panel { view, .. } => view.set_active(!collapsed, window, cx),
        }
    }

    /// Recursively traverses to find the left-most and top-most TabPanel.
    pub(crate) fn left_top_tab_panel(&self, cx: &App) -> Option<Entity<TabPanel>> {
        match self {
            DockItem::Tabs { view, .. } => Some(view.clone()),
            DockItem::Split { view, .. } => view.read(cx).left_top_tab_panel(true, cx),
            DockItem::Panel { .. } => None,
        }
    }
}

impl DockArea {
    pub fn new(
        id: impl Into<SharedString>,
        version: Option<usize>,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) -> Self {
        let stack_panel = cx.new(|cx| StackPanel::new(Axis::Horizontal, window, cx));

        let dock_item = DockItem::Split {
            axis: Axis::Horizontal,
            size: None,
            items: vec![],
            sizes: vec![],
            view: stack_panel.clone(),
        };

        let mut this = Self {
            id: id.into(),
            version,
            bounds: Bounds::default(),
            center: dock_item,
            left_dock: None,
            zoom_view: None,
            toggle_button_panels: Edges::default(),
            toggle_button_visible: true,
            locked: false,
            _subscriptions: vec![],
        };

        this.subscribe_panel(&stack_panel, window, cx);

        this
    }

    /// Return the bounds of the dock area.
    pub fn bounds(&self) -> Bounds<Pixels> {
        self.bounds
    }

    /// Set version of the dock area.
    pub fn set_version(&mut self, version: usize, _: &mut Window, cx: &mut Context<Self>) {
        self.version = Some(version);
        cx.notify();
    }

    /// Return the center dock item.
    pub fn center(&self) -> &DockItem {
        &self.center
    }

    /// Whether the center area currently holds no visible panel.
    ///
    /// See [`DockItem::is_empty`]. Ask a dock the same question with
    /// [`Dock::panel`].
    pub fn is_center_empty(&self, cx: &App) -> bool {
        self.center.is_empty(cx)
    }

    /// Return the left dock item.
    pub fn left_dock(&self) -> Option<&Entity<Dock>> {
        self.left_dock.as_ref()
    }

    /// Remove the left dock.
    pub fn remove_left_dock(&mut self, _: &mut Window, _: &mut Context<Self>) {
        self.left_dock = None;
    }

    /// The the DockItem as the center of the dock area.
    ///
    /// This is used to render at the Center of the DockArea.
    pub fn set_center(&mut self, center: DockItem, window: &mut Window, cx: &mut Context<Self>) {
        self.subscribe_item(&center, window, cx);
        self.center = center;
        self.update_toggle_button_tab_panels(window, cx);
        cx.notify();
    }

    pub fn set_left_dock(
        &mut self,
        panel: DockItem,
        size: Option<Pixels>,
        open: bool,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) {
        self.subscribe_item(&panel, window, cx);
        let weak_self = cx.entity().downgrade();
        self.left_dock = Some(cx.new(|cx| {
            let mut dock = Dock::left(weak_self.clone(), window, cx);
            if let Some(size) = size {
                dock.set_size(size, window, cx);
            }
            dock.set_panel(panel, window, cx);
            dock.set_open(open, window, cx);
            dock
        }));
        self.update_toggle_button_tab_panels(window, cx);
    }

    /// Set locked state of the dock area, if locked, the dock area cannot be split or move, but allows to resize panels.
    pub fn set_locked(&mut self, locked: bool, _window: &mut Window, _cx: &mut App) {
        self.locked = locked;
    }

    /// Determine if the dock area is locked.
    #[inline]
    pub fn is_locked(&self) -> bool {
        self.locked
    }

    /// Determine if the dock area has a dock at the given placement.
    pub fn has_dock(&self, placement: DockPlacement) -> bool {
        match placement {
            DockPlacement::Left => self.left_dock.is_some(),
            DockPlacement::Center | DockPlacement::Right | DockPlacement::Bottom => false,
        }
    }

    /// Determine if the dock at the given placement is open.
    pub fn is_dock_open(&self, placement: DockPlacement, cx: &App) -> bool {
        match placement {
            DockPlacement::Left => self
                .left_dock
                .as_ref()
                .map(|dock| dock.read(cx).is_open())
                .unwrap_or(false),
            DockPlacement::Center | DockPlacement::Right | DockPlacement::Bottom => false,
        }
    }

    /// Set the dock at the given placement to be open or closed.
    ///
    /// Only the left dock can be toggled.
    pub fn set_dock_collapsible(
        &mut self,
        collapsible_edges: Edges<bool>,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) {
        if let Some(left_dock) = self.left_dock.as_ref() {
            left_dock.update(cx, |dock, cx| {
                dock.set_collapsible(collapsible_edges.left, window, cx);
            });
        }
    }

    /// Determine if the dock at the given placement is collapsible.
    pub fn is_dock_collapsible(&self, placement: DockPlacement, cx: &App) -> bool {
        match placement {
            DockPlacement::Left => self
                .left_dock
                .as_ref()
                .map(|dock| dock.read(cx).collapsible)
                .unwrap_or(false),
            DockPlacement::Center | DockPlacement::Right | DockPlacement::Bottom => false,
        }
    }

    /// Toggle the dock at the given placement.
    pub fn toggle_dock(
        &self,
        placement: DockPlacement,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) {
        if let DockPlacement::Left = placement
            && let Some(dock) = self.left_dock.as_ref()
        {
            dock.update(cx, |view, cx| {
                view.toggle_open(window, cx);
            })
        }
    }

    /// Set the visibility of the toggle button.
    pub fn set_toggle_button_visible(&mut self, visible: bool, _: &mut Context<Self>) {
        self.toggle_button_visible = visible;
    }

    /// Add a panel item to the dock area at the given placement.
    ///
    /// - [`DockPlacement::Left`] adds the panel to the left dock (creating it
    ///   if needed).
    /// - [`DockPlacement::Center`] adds the panel as a tab in the center.
    /// - [`DockPlacement::Right`] and [`DockPlacement::Bottom`] split the
    ///   center so the panel lands on the given side of the existing center
    ///   content.
    pub fn add_panel(
        &mut self,
        panel: Arc<dyn PanelView>,
        placement: DockPlacement,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) {
        let weak_self = cx.entity().downgrade();
        match placement {
            DockPlacement::Left => {
                if let Some(dock) = self.left_dock.as_ref() {
                    dock.update(cx, |dock, cx| dock.add_panel(panel, window, cx))
                } else {
                    self.set_left_dock(
                        DockItem::tabs(vec![panel], &weak_self, window, cx),
                        None,
                        true,
                        window,
                        cx,
                    );
                }
            }
            DockPlacement::Right | DockPlacement::Bottom => {
                self.add_panel_to_center_side(panel, placement, window, cx);
            }
            DockPlacement::Center => {
                self.center
                    .add_panel(panel, &cx.entity().downgrade(), window, cx);
            }
        }
    }

    /// Split the center so the new panel lands on the given side of the
    /// existing center content (right of it for [`DockPlacement::Right`],
    /// below it for [`DockPlacement::Bottom`]).
    ///
    /// The existing center keeps its place. Repeating adds with the same axis
    /// appends further tab groups to the split; a different axis wraps the
    /// current center in a new split. An empty center is added to directly.
    fn add_panel_to_center_side(
        &mut self,
        panel: Arc<dyn PanelView>,
        placement: DockPlacement,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) {
        debug_assert!(matches!(
            placement,
            DockPlacement::Right | DockPlacement::Bottom
        ));

        let weak_self = cx.entity().downgrade();

        if self.center.is_empty(cx) {
            self.center.add_panel(panel, &weak_self, window, cx);
        } else if let DockItem::Split {
            axis,
            size: _,
            items,
            sizes,
            view,
        } = &mut self.center
            && *axis == placement.axis()
        {
            // The center is already split along this axis: append a new tab group.
            let new_item = DockItem::tabs(vec![panel], &weak_self, window, cx);
            items.push(new_item.clone());
            sizes.push(None);
            view.update(cx, |stack, cx| {
                stack.add_panel(new_item.view(), None, weak_self.clone(), window, cx);
            });
        } else {
            // Wrap the existing center in a new split.
            let existing = self.center.clone();
            let new_item = DockItem::tabs(vec![panel], &weak_self, window, cx);
            let items = vec![existing, new_item];
            let sizes = vec![None; items.len()];
            self.center =
                DockItem::split_with_sizes(placement.axis(), items, sizes, &weak_self, window, cx);
        }

        self.update_toggle_button_tab_panels(window, cx);
        cx.notify();
    }

    /// Remove panel from the DockArea at the given placement.
    pub fn remove_panel(
        &mut self,
        panel: Arc<dyn PanelView>,
        placement: DockPlacement,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) {
        match placement {
            DockPlacement::Left => {
                if let Some(dock) = self.left_dock.as_mut() {
                    dock.update(cx, |dock, cx| {
                        dock.remove_panel(panel, window, cx);
                    });
                }
            }
            DockPlacement::Center => {
                self.center.remove_panel(panel, window, cx);
            }
            DockPlacement::Right | DockPlacement::Bottom => {
                // The panel lives in the center; splits are part of it.
                self.center.remove_panel(panel, window, cx);
            }
        }
        cx.notify();
    }

    /// Remove a panel from all docks.
    pub fn remove_panel_from_all_docks(
        &mut self,
        panel: Arc<dyn PanelView>,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) {
        self.remove_panel(panel.clone(), DockPlacement::Center, window, cx);
        self.remove_panel(panel.clone(), DockPlacement::Left, window, cx);
    }

    /// Load the state of the DockArea from the DockAreaState.
    ///
    /// See also [DockeArea::dump].
    pub fn load(
        &mut self,
        state: DockAreaState,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) -> Result<()> {
        self.version = state.version;
        let weak_self = cx.entity().downgrade();

        if let Some(left_dock_state) = state.left_dock {
            self.left_dock = Some(left_dock_state.to_dock(weak_self.clone(), window, cx));
        }

        self.center = state.center.to_item(weak_self, window, cx);
        self.update_toggle_button_tab_panels(window, cx);
        Ok(())
    }

    /// Dump the dock panels layout to PanelState.
    ///
    /// See also [DockArea::load].
    pub fn dump(&self, cx: &App) -> DockAreaState {
        let root = self.center.view();
        let center = root.dump(cx);

        let left_dock = self
            .left_dock
            .as_ref()
            .map(|dock| DockState::new(dock.clone(), cx));

        DockAreaState {
            version: self.version,
            center,
            left_dock,
        }
    }

    /// Subscribe event on the panels
    #[allow(clippy::only_used_in_recursion)]
    fn subscribe_item(&mut self, item: &DockItem, window: &mut Window, cx: &mut Context<Self>) {
        match item {
            DockItem::Split { items, view, .. } => {
                for item in items {
                    self.subscribe_item(item, window, cx);
                }

                self._subscriptions.push(cx.subscribe_in(
                    view,
                    window,
                    move |_, _, event, window, cx| {
                        if let PanelEvent::LayoutChanged = event {
                            cx.spawn_in(window, async move |view, window| {
                                _ = view.update_in(window, |view, window, cx| {
                                    view.update_toggle_button_tab_panels(window, cx)
                                });
                            })
                            .detach();
                            cx.emit(DockEvent::LayoutChanged);
                        }
                    },
                ));
            }
            DockItem::Tabs { .. } => {
                // We subscribe to the tab panel event in StackPanel's insert_panel
            }
            DockItem::Panel { .. } => {
                // Not supported
            }
        }
    }

    /// Subscribe zoom event on the panel
    pub(crate) fn subscribe_panel<P: Panel>(
        &mut self,
        view: &Entity<P>,
        window: &mut Window,
        cx: &mut Context<DockArea>,
    ) {
        let subscription =
            cx.subscribe_in(
                view,
                window,
                move |_, panel, event, window, cx| match event {
                    PanelEvent::ZoomIn => {
                        let panel = panel.clone();
                        cx.spawn_in(window, async move |view, window| {
                            _ = view.update_in(window, |view, window, cx| {
                                view.set_zoomed_in(panel, window, cx);
                                cx.notify();
                            });
                        })
                        .detach();
                    }
                    PanelEvent::ZoomOut => cx
                        .spawn_in(window, async move |view, window| {
                            _ = view.update_in(window, |view, window, cx| {
                                view.set_zoomed_out(window, cx);
                            });
                        })
                        .detach(),
                    PanelEvent::LayoutChanged => {
                        cx.spawn_in(window, async move |view, window| {
                            _ = view.update_in(window, |view, window, cx| {
                                view.update_toggle_button_tab_panels(window, cx)
                            });
                        })
                        .detach();
                        cx.emit(DockEvent::LayoutChanged);
                    }
                },
            );

        self._subscriptions.push(subscription);
    }

    /// Returns the ID of the dock area.
    pub fn id(&self) -> SharedString {
        self.id.clone()
    }

    pub fn set_zoomed_in<P: Panel>(
        &mut self,
        panel: Entity<P>,
        _: &mut Window,
        cx: &mut Context<Self>,
    ) {
        self.zoom_view = Some(panel.into());
        cx.notify();
    }

    pub fn set_zoomed_out(&mut self, _: &mut Window, cx: &mut Context<Self>) {
        self.zoom_view = None;
        cx.notify();
    }

    fn render_items(&self, _window: &mut Window, _cx: &mut Context<Self>) -> AnyElement {
        match &self.center {
            DockItem::Split { view, .. } => view.clone().into_any_element(),
            DockItem::Tabs { view, .. } => view.clone().into_any_element(),
            DockItem::Panel { view, .. } => view.clone().view().into_any_element(),
        }
    }

    pub fn update_toggle_button_tab_panels(&mut self, _: &mut Window, cx: &mut Context<Self>) {
        // The left dock's toggle button lives in the center's top-left tab panel.
        self.toggle_button_panels.left = self
            .center
            .left_top_tab_panel(cx)
            .map(|view| view.entity_id());
    }
}
impl EventEmitter<DockEvent> for DockArea {}
impl Render for DockArea {
    fn render(&mut self, window: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
        let view = cx.entity().clone();

        div()
            .id("dock-area")
            .relative()
            .size_full()
            .overflow_hidden()
            .on_prepaint(move |bounds, _, cx| view.update(cx, |r, _| r.bounds = bounds))
            .map(|this| {
                if let Some(zoom_view) = self.zoom_view.clone() {
                    this.child(zoom_view)
                } else {
                    // render dock
                    this.child(
                        div()
                            .flex()
                            .flex_row()
                            .h_full()
                            // Left dock
                            .when_some(self.left_dock.clone(), |this, dock| {
                                this.child(div().flex().flex_none().child(dock))
                            })
                            // Center
                            .child(
                                div()
                                    .flex_1()
                                    .overflow_hidden()
                                    .child(self.render_items(window, cx)),
                            ),
                    )
                }
            })
    }
}

#[cfg(test)]
mod tests {
    use gpui::TestAppContext;

    use super::*;

    #[gpui::test]
    fn split_with_sizes_adds_each_child_once(cx: &mut TestAppContext) {
        cx.update(|cx| {
            cx.set_global(gpui_component::Theme::default());
            cx.open_window(Default::default(), |window, cx| {
                let dock_area = cx.new(|cx| DockArea::new("test-dock", None, window, cx));
                let weak_dock_area = dock_area.downgrade();
                let children = vec![
                    DockItem::tabs(Vec::new(), &weak_dock_area, window, cx),
                    DockItem::tabs(Vec::new(), &weak_dock_area, window, cx),
                ];

                let split = DockItem::split_with_sizes(
                    Axis::Horizontal,
                    children,
                    vec![None, None],
                    &weak_dock_area,
                    window,
                    cx,
                );

                let DockItem::Split { view, .. } = split else {
                    unreachable!("split_with_sizes must return DockItem::Split");
                };
                assert_eq!(view.read(cx).panels_len(), 2);

                cx.new(|cx| gpui_component::Root::new(dock_area, window, cx))
            })
            .unwrap();
        });
    }
}