use gpui::{
    Context, IntoElement, Modifiers, ParentElement as _, Render, ScrollDelta, ScrollEvent,
    ScrollHandle, SharedString, Styled as _, TestAppContext, VisualTestContext, Window, div, point,
    px,
};
use gpui_native_core::scroll_area::ScrollArea;
use gpui_native_theme::Theme;

struct Harness {
    scroll: ScrollHandle,
    rows: usize,
}

impl Render for Harness {
    fn render(&mut self, _window: &mut Window, _cx: &mut Context<Self>) -> impl IntoElement {
        div().size_full().child(
            ScrollArea::new("test-scroll")
                .handle(self.scroll.clone())
                .h(px(200.))
                .w(px(300.))
                .child(div().flex().flex_col().children((0..self.rows).map(|row| {
                    div()
                        .h(px(20.))
                        .child(SharedString::from(format!("row {row}")))
                }))),
        )
    }
}

/// A 300×200 scroll area over `rows` 20px rows, with the handle the test
/// can inspect directly.
fn scroll_area_window(rows: usize) -> (TestAppContext, VisualTestContext, ScrollHandle) {
    let mut cx = TestAppContext::single();
    cx.update(Theme::init);
    let handle = ScrollHandle::new();
    let handle_for_view = handle.clone();
    let window = cx.add_window(move |_, _| Harness {
        scroll: handle_for_view,
        rows,
    });
    let mut visual = VisualTestContext::from_window(window.into(), &cx);
    visual.update(|window, cx| {
        window.draw(cx).clear(cx);
    });
    (cx, visual, handle)
}

#[test]
fn wheel_scrolling_moves_the_offset_and_stays_inside_the_content() {
    let (_cx, mut visual, handle) = scroll_area_window(30);

    // 30 rows × 20px = 600px of content in a 200px viewport.
    visual.simulate_event(ScrollEvent {
        position: point(px(100.), px(100.)),
        delta: ScrollDelta::Pixels(point(px(0.), px(-60.))),
        modifiers: Modifiers::default(),
        ..Default::default()
    });

    let offset = handle.offset().y;
    assert_eq!(offset, px(-60.));

    // Wheeling far past the end clamps to the content.
    for _ in 0..10 {
        visual.simulate_event(ScrollEvent {
            position: point(px(100.), px(100.)),
            delta: ScrollDelta::Pixels(point(px(0.), px(-60.))),
            modifiers: Modifiers::default(),
            ..Default::default()
        });
    }
    // max_offset = 600 - 200 = 400.
    assert_eq!(handle.offset().y, px(-400.));
}

#[test]
fn the_content_starts_unscrolled_and_horizontal_axes_scroll_x() {
    let (_cx, mut visual, handle) = scroll_area_window(30);
    assert_eq!(handle.offset(), gpui::point(px(0.), px(0.)));

    // A vertical-only area ignores horizontal wheel deltas.
    visual.simulate_event(ScrollEvent {
        position: point(px(100.), px(100.)),
        delta: ScrollDelta::Pixels(point(px(-60.), px(0.))),
        modifiers: Modifiers::default(),
        ..Default::default()
    });
    assert_eq!(handle.offset().x, px(0.));
}

#[test]
fn the_thumb_paints_when_the_content_overflows() {
    let (_cx, _visual, handle) = scroll_area_window(30);
    // 30 rows × 20px in a 200px viewport: the thumb has something to report.
    assert!(handle.max_offset().y > px(0.));
}

/// The gallery's exact shell: a window-filling root, a window-filling scroll
/// area over padded flex-column content that towers past the viewport.
struct GalleryShell {
    scroll: ScrollHandle,
}

impl Render for GalleryShell {
    fn render(&mut self, _window: &mut Window, _cx: &mut Context<Self>) -> impl IntoElement {
        div().size_full().child(
            ScrollArea::new("gallery-scroll")
                .handle(self.scroll.clone())
                .size_full()
                .child(
                    div()
                        .p_6()
                        .flex()
                        .flex_col()
                        .gap_5()
                        .children((0..12).map(|section| {
                            div()
                                .h(px(220.))
                                .child(SharedString::from(format!("section {section}")))
                        })),
                ),
        )
    }
}

#[test]
fn a_gallery_style_window_fill_scroll_area_scrolls_tall_flex_content() {
    let mut cx = TestAppContext::single();
    cx.update(Theme::init);
    let handle = ScrollHandle::new();
    let handle_for_view = handle.clone();
    let window = cx.add_window(move |_, _| GalleryShell {
        scroll: handle_for_view,
    });
    let mut visual = VisualTestContext::from_window(window.into(), &cx);
    visual.update(|window, cx| {
        window.draw(cx).clear(cx);
    });

    // 12 sections × 220px + padding towers past the window; a wheel event
    // over the middle of the viewport must scroll the root area.
    visual.simulate_event(ScrollEvent {
        position: point(px(300.), px(300.)),
        delta: ScrollDelta::Pixels(point(px(0.), px(-60.))),
        modifiers: Modifiers::default(),
        ..Default::default()
    });
    assert_eq!(handle.offset().y, px(-60.));
    assert!(handle.max_offset().y > px(1000.));
}