use gpui::{
    AppContext as _, Context, Entity, InteractiveElement as _, IntoElement, Modifiers, MouseButton,
    MouseDownEvent, MouseMoveEvent, MouseUpEvent, ParentElement as _, Pixels, Render, Styled as _,
    TestAppContext, VisualTestContext, Window, div, point, px,
};
use gpui_native_layout::dock::{Dock, DockState, PanelDescriptor, SplitDirection};
use gpui_native_theme::Theme;

struct Panel {
    tag: &'static str,
}

impl Render for Panel {
    fn render(&mut self, _window: &mut Window, _cx: &mut Context<Self>) -> impl IntoElement {
        div()
            .size_full()
            .debug_selector(move || format!("panel-{}", self.tag))
    }
}

fn descriptor(tag: &'static str) -> PanelDescriptor {
    PanelDescriptor::new(tag, tag, move |_, cx| cx.new(|_| Panel { tag }).into())
}

struct Harness {
    dock: Entity<DockState>,
}

impl Render for Harness {
    fn render(
        &mut self,
        _window: &mut Window,
        _cx: &mut gpui::Context<Self>,
    ) -> impl gpui::IntoElement {
        div()
            .size_full()
            .child(Dock::new("test-dock", self.dock.clone()))
    }
}

fn dock_window(cx: &mut TestAppContext) -> (Entity<DockState>, VisualTestContext) {
    cx.update(Theme::init);
    let dock = cx.update(DockState::new);
    let dock_for_window = dock.clone();
    let window = cx.add_window(move |_, _| Harness {
        dock: dock_for_window,
    });
    let mut visual = VisualTestContext::from_window(window.into(), cx);
    redraw(&mut visual);
    (dock, visual)
}

fn redraw(visual: &mut VisualTestContext) {
    visual.update(|window, cx| {
        window.draw(cx).clear(cx);
    });
}

fn bounds(visual: &mut VisualTestContext, selector: &str) -> Option<gpui::Bounds<Pixels>> {
    visual.debug_bounds(Box::leak(selector.to_string().into_boxed_str()))
}

fn center_of(bounds: gpui::Bounds<Pixels>) -> gpui::Point<Pixels> {
    point(bounds.center().x, bounds.center().y)
}

fn press(visual: &mut VisualTestContext, at: gpui::Point<Pixels>, click_count: usize) {
    visual.simulate_event(MouseDownEvent {
        position: at,
        click_count,
        modifiers: Modifiers::default(),
        button: MouseButton::Left,
        first_mouse: false,
    });
    visual.simulate_event(MouseUpEvent {
        position: at,
        click_count,
        modifiers: Modifiers::default(),
        button: MouseButton::Left,
    });
}

fn drag(visual: &mut VisualTestContext, from: gpui::Point<Pixels>, to: gpui::Point<Pixels>) {
    visual.simulate_mouse_down(from, MouseButton::Left, Modifiers::default());
    visual.simulate_event(MouseMoveEvent {
        position: to,
        pressed_button: Some(MouseButton::Left),
        modifiers: Modifiers::default(),
    });
    visual.simulate_mouse_up(to, MouseButton::Left, Modifiers::default());
}

fn register(dock: &Entity<DockState>, tags: &[&'static str], cx: &mut TestAppContext) {
    cx.update(|cx| {
        dock.update(cx, |dock, cx| {
            for tag in tags {
                dock.register_panel(descriptor(tag), cx);
            }
        });
    });
}

fn open(visual: &mut VisualTestContext, dock: &Entity<DockState>, tag: &'static str) {
    visual.update(|window, cx| {
        dock.update(cx, |dock, cx| dock.open_panel(tag, window, cx));
    });
    redraw(visual);
}

#[test]
fn opening_a_panel_adds_its_tab_and_activates_it() {
    let mut cx = TestAppContext::single();
    let (dock, mut visual) = dock_window(&mut cx);
    register(&dock, &["inbox", "explore"], &mut cx);

    open(&mut visual, &dock, "inbox");
    assert!(
        bounds(&mut visual, "panel-inbox").is_some(),
        "opened panel missing"
    );
    assert!(
        bounds(&mut visual, "test-dock-pane-0-tabs-tab-inbox").is_some(),
        "tab missing"
    );

    open(&mut visual, &dock, "explore");
    assert!(bounds(&mut visual, "panel-explore").is_some());
    assert!(
        bounds(&mut visual, "panel-inbox").is_none(),
        "the inactive view must not render"
    );
    assert!(
        bounds(&mut visual, "test-dock-pane-0-tabs-tab-inbox").is_some(),
        "the strip keeps both tabs"
    );

    assert!(dock.read_with(&cx, |dock, _| dock.is_open("inbox")));
    assert!(dock.read_with(&cx, |dock, _| dock.is_open("explore")));
}

#[test]
fn clicking_a_tab_activates_its_panel() {
    let mut cx = TestAppContext::single();
    let (dock, mut visual) = dock_window(&mut cx);
    register(&dock, &["inbox", "explore"], &mut cx);
    open(&mut visual, &dock, "inbox");
    open(&mut visual, &dock, "explore");

    let tab = bounds(&mut visual, "test-dock-pane-0-tabs-tab-inbox").expect("inbox tab missing");
    press(&mut visual, center_of(tab), 1);
    redraw(&mut visual);

    assert!(bounds(&mut visual, "panel-inbox").is_some());
    assert!(bounds(&mut visual, "panel-explore").is_none());
}

#[test]
fn the_tab_close_control_closes_its_panel() {
    let mut cx = TestAppContext::single();
    let (dock, mut visual) = dock_window(&mut cx);
    register(&dock, &["inbox", "explore"], &mut cx);
    open(&mut visual, &dock, "inbox");
    open(&mut visual, &dock, "explore");

    let close = bounds(&mut visual, "test-dock-pane-0-tabs-close-inbox").expect("close missing");
    press(&mut visual, center_of(close), 1);
    redraw(&mut visual);

    assert!(bounds(&mut visual, "test-dock-pane-0-tabs-tab-inbox").is_none());
    assert!(bounds(&mut visual, "panel-explore").is_some());
}

#[test]
fn closing_the_active_tab_activates_the_neighbor() {
    let mut cx = TestAppContext::single();
    let (dock, mut visual) = dock_window(&mut cx);
    register(&dock, &["inbox", "explore"], &mut cx);
    open(&mut visual, &dock, "inbox");
    open(&mut visual, &dock, "explore");

    cx.update(|cx| {
        dock.update(cx, |dock, cx| dock.close_panel("explore", cx));
    });
    redraw(&mut visual);

    assert!(
        bounds(&mut visual, "panel-inbox").is_some(),
        "the neighbor tab should activate"
    );
    assert!(bounds(&mut visual, "test-dock-pane-0-tabs-tab-explore").is_none());
    assert!(bounds(&mut visual, "test-dock-pane-0-tabs-tab-inbox").is_some());
}

#[test]
fn splitting_moves_the_tab_and_closing_collapses() {
    let mut cx = TestAppContext::single();
    let (dock, mut visual) = dock_window(&mut cx);
    register(&dock, &["inbox", "explore"], &mut cx);
    open(&mut visual, &dock, "inbox");
    open(&mut visual, &dock, "explore");

    cx.update(|cx| {
        dock.update(cx, |dock, cx| {
            dock.split_panel("explore", SplitDirection::Right, cx)
        });
    });
    redraw(&mut visual);

    assert!(
        bounds(&mut visual, "resize-handle").is_some(),
        "the split renders a seam"
    );
    assert!(bounds(&mut visual, "test-dock-pane-0").is_some());
    assert!(bounds(&mut visual, "test-dock-pane-1").is_some());
    assert!(
        bounds(&mut visual, "panel-explore").is_some(),
        "the moved tab activates in its new pane"
    );

    // Closing the new pane's only tab collapses its split.
    cx.update(|cx| {
        dock.update(cx, |dock, cx| dock.close_panel("explore", cx));
    });
    redraw(&mut visual);

    assert!(bounds(&mut visual, "resize-handle").is_none());
    assert!(bounds(&mut visual, "test-dock-pane-1").is_none());
    assert!(bounds(&mut visual, "test-dock-pane-0").is_some());
    assert!(bounds(&mut visual, "panel-inbox").is_some());
}

#[test]
fn splitting_at_a_target_pane_places_the_new_pane_there() {
    let mut cx = TestAppContext::single();
    let (dock, mut visual) = dock_window(&mut cx);
    register(&dock, &["inbox", "explore"], &mut cx);
    open(&mut visual, &dock, "inbox");
    open(&mut visual, &dock, "explore");
    cx.update(|cx| {
        dock.update(cx, |dock, cx| {
            dock.split_panel("explore", SplitDirection::Right, cx)
        });
    });
    redraw(&mut visual);

    // Move inbox into a new pane left of explore's pane (pane 1), not beside
    // inbox's own (pane 0, which empties and collapses).
    cx.update(|cx| {
        dock.update(cx, |dock, cx| {
            dock.split_panel_at("inbox", "explore", SplitDirection::Left, cx)
        });
    });
    redraw(&mut visual);

    let moved = bounds(&mut visual, "test-dock-pane-3").expect("the new pane missing");
    let target = bounds(&mut visual, "test-dock-pane-1").expect("target pane missing");
    assert!(
        moved.right() <= target.left(),
        "the new pane must sit left of the anchored pane"
    );
    assert!(bounds(&mut visual, "test-dock-pane-0").is_none());
}

#[test]
fn dragging_the_seam_resizes_and_double_click_resets() {
    let mut cx = TestAppContext::single();
    let (dock, mut visual) = dock_window(&mut cx);
    register(&dock, &["inbox", "explore"], &mut cx);
    open(&mut visual, &dock, "inbox");
    open(&mut visual, &dock, "explore");
    cx.update(|cx| {
        dock.update(cx, |dock, cx| {
            dock.split_panel("explore", SplitDirection::Right, cx)
        });
    });
    redraw(&mut visual);

    let before_0 = bounds(&mut visual, "test-dock-pane-0").expect("pane 0 missing");
    let before_1 = bounds(&mut visual, "test-dock-pane-1").expect("pane 1 missing");
    let seam = bounds(&mut visual, "resize-handle").expect("seam missing");

    drag(
        &mut visual,
        center_of(seam),
        center_of(seam) + point(px(40.), px(0.)),
    );
    let grown = bounds(&mut visual, "test-dock-pane-0").expect("pane 0 missing");
    let shrunk = bounds(&mut visual, "test-dock-pane-1").expect("pane 1 missing");
    assert!(
        grown.size.width > before_0.size.width,
        "the seam leads pane 0"
    );
    assert!(shrunk.size.width < before_1.size.width, "pane 1 gives way");

    // Double-clicking the seam restores the default ratio.
    let seam = bounds(&mut visual, "resize-handle").expect("seam missing");
    press(&mut visual, center_of(seam), 2);
    redraw(&mut visual);
    let reset_0 = bounds(&mut visual, "test-dock-pane-0").expect("pane 0 missing");
    let reset_1 = bounds(&mut visual, "test-dock-pane-1").expect("pane 1 missing");
    // The flex split may round an odd-pixel span by a hair.
    assert!((reset_0.size.width - reset_1.size.width).abs() <= px(1.));

    // A huge drag clamps instead of vanishing a side.
    let seam = bounds(&mut visual, "resize-handle").expect("seam missing");
    drag(
        &mut visual,
        center_of(seam),
        center_of(seam) + point(px(2000.), px(0.)),
    );
    let clamped = bounds(&mut visual, "test-dock-pane-1").expect("clamped pane missing");
    assert!(clamped.size.width > px(0.));
}

#[test]
fn dragging_a_tab_to_a_pane_edge_splits_it() {
    let mut cx = TestAppContext::single();
    let (dock, mut visual) = dock_window(&mut cx);
    register(&dock, &["inbox", "explore"], &mut cx);
    open(&mut visual, &dock, "inbox");
    open(&mut visual, &dock, "explore");

    // Drag explore's tab onto the right edge band of the pane's content.
    let tab = bounds(&mut visual, "test-dock-pane-0-tabs-tab-explore").expect("tab missing");
    let content = bounds(&mut visual, "test-dock-content-0").expect("content missing");
    let drop_at = point(
        content.right() - content.size.width * 0.125,
        content.center().y,
    );

    visual.simulate_mouse_down(center_of(tab), MouseButton::Left, Modifiers::default());
    // Past the drag threshold, the drag starts and the drop zones mount.
    visual.simulate_event(MouseMoveEvent {
        position: center_of(tab) + point(px(8.), px(2.)),
        pressed_button: Some(MouseButton::Left),
        modifiers: Modifiers::default(),
    });
    redraw(&mut visual);
    visual.simulate_event(MouseMoveEvent {
        position: drop_at,
        pressed_button: Some(MouseButton::Left),
        modifiers: Modifiers::default(),
    });
    visual.simulate_mouse_up(drop_at, MouseButton::Left, Modifiers::default());
    redraw(&mut visual);

    assert!(
        bounds(&mut visual, "resize-handle").is_some(),
        "the drop should have split the pane"
    );
    assert!(
        bounds(&mut visual, "test-dock-pane-1-tabs-tab-explore").is_some(),
        "the dragged tab lives in the new pane"
    );
    assert!(bounds(&mut visual, "panel-explore").is_some());
}

#[test]
fn moving_a_panel_merges_panes_and_collapses_the_source() {
    let mut cx = TestAppContext::single();
    let (dock, mut visual) = dock_window(&mut cx);
    register(&dock, &["inbox", "explore"], &mut cx);
    open(&mut visual, &dock, "inbox");
    open(&mut visual, &dock, "explore");
    cx.update(|cx| {
        dock.update(cx, |dock, cx| {
            dock.split_panel("explore", SplitDirection::Right, cx)
        });
    });
    redraw(&mut visual);

    cx.update(|cx| {
        dock.update(cx, |dock, cx| dock.move_panel("explore", "inbox", cx));
    });
    redraw(&mut visual);

    assert!(
        bounds(&mut visual, "resize-handle").is_none(),
        "the emptied source pane collapses"
    );
    assert!(bounds(&mut visual, "test-dock-pane-0-tabs-tab-inbox").is_some());
    assert!(bounds(&mut visual, "test-dock-pane-0-tabs-tab-explore").is_some());
    assert!(
        bounds(&mut visual, "panel-explore").is_some(),
        "the moved tab activates in its new pane"
    );
}

#[test]
fn close_others_keeps_one_and_close_pane_empties() {
    let mut cx = TestAppContext::single();
    let (dock, mut visual) = dock_window(&mut cx);
    register(&dock, &["inbox", "explore", "settings"], &mut cx);
    open(&mut visual, &dock, "inbox");
    open(&mut visual, &dock, "explore");
    open(&mut visual, &dock, "settings");

    cx.update(|cx| {
        dock.update(cx, |dock, cx| dock.close_others("inbox", cx));
    });
    redraw(&mut visual);

    assert!(bounds(&mut visual, "test-dock-pane-0-tabs-tab-inbox").is_some());
    assert!(bounds(&mut visual, "test-dock-pane-0-tabs-tab-explore").is_none());
    assert!(bounds(&mut visual, "test-dock-pane-0-tabs-tab-settings").is_none());
    assert!(bounds(&mut visual, "panel-inbox").is_some());

    cx.update(|cx| {
        dock.update(cx, |dock, cx| dock.close_pane("inbox", cx));
    });
    redraw(&mut visual);

    assert!(bounds(&mut visual, "test-dock-pane-0-tabs-tab-inbox").is_none());
    assert!(
        bounds(&mut visual, "panel-inbox").is_none(),
        "the emptied pane renders nothing"
    );

    // The dock is reusable: opening again fills the empty root pane.
    open(&mut visual, &dock, "inbox");
    assert!(bounds(&mut visual, "test-dock-pane-0-tabs-tab-inbox").is_some());
}