//! Layer 1 of docs/RUST.md's "Three test layers", for the transcript's
//! own edges: the real screen over the real fixture, under a header bar
//! like the bench app's, driven by `iris::harness`.
//!
//! What these are about is docs/IRIS_TODO.md's 2026-09-07 phone report --
//! rows scrolled above the viewport still drawn, over the header, and a
//! blank band where the row straddling the top edge should be. Both are
//! one rule (`LazySpan::intersects_viewport`): a row is drawn if any part of
//! it is inside the list's own box, and nothing outside that box reaches
//! the screen.

use ai_app::ui::fixture::{PHONE_FRAME_MS, PHONE_SCALE, phone_size};
use iris::harness::Harness;
use iris::prelude::*;

/// A header band above the transcript, as `bench_client.rs` puts one --
/// the surface the rows were drawing over on the phone. Its exact height
/// does not matter; what matters is that the list's own box does not
/// start at the top of the window, so "above the viewport" and "off the
/// screen" are different places.
const HEADER_H: f32 = 300.0;
const HEADER: UiColor = UiColor::new(28, 28, 34, 255);

fn opened() -> (Harness, ai_app::ui::TranscriptScreen) {
    let mut h = Harness::new(phone_size(), PHONE_SCALE);
    let (opened, tree) = ai_app::ui::fixture::build_screen(&mut h.rsc).expect("the fixture folds");
    let content = WidgetPtr::new().add(&mut h.rsc);
    content(&mut h.rsc).set(tree);
    let root = (rect(HEADER).height(abs(HEADER_H)), content.height(rest(1)))
        .span(Dir::DOWN)
        .add_strong(&mut h.rsc)
        .any();
    h.state.set_root(root);
    h.frame(0);
    h.frame(PHONE_FRAME_MS);
    (h, opened.screen)
}

/// The list's own on-screen box, in window pixels.
fn list_box(h: &Harness, screen: &ai_app::ui::TranscriptScreen) -> PixelRegion {
    h.render
        .window_region(&screen.list.id(), &h.rsc)
        .expect("the list is on screen")
}

/// Every row the list drew this frame, as `(top, bottom)` window pixels,
/// topmost first. A `LazySpan`'s direct children are exactly its rows, and
/// `draw_inner`'s old-children diffing means a row it did not place this
/// frame is not among them.
fn drawn_rows(h: &Harness, screen: &ai_app::ui::TranscriptScreen) -> Vec<(f32, f32)> {
    let mut rows: Vec<(f32, f32)> = h
        .render
        .active
        .get(&screen.list.id())
        .expect("the list is drawn")
        .children
        .iter()
        .filter_map(|id| h.render.window_region(id, &h.rsc))
        .map(|px| (px.top_left.y, px.bot_right.y))
        .collect();
    rows.sort_by(|a, b| a.0.total_cmp(&b.0));
    rows
}

/// Scrolls `amount` and runs the frame it asks for, returning the time of
/// the next one. **Positive walks back through older rows** -- the
/// finger's own direction, and `Scroll::scroll`'s, which is the one
/// convention a delta has anywhere in iris since the transcript's scroll
/// position lives in the `LazySpan`'s own `ScrollController`.
/// It used to be the opposite here, because a `LazySpan`'s anchor offset
/// ran the other way.
fn scrolled(h: &mut Harness, screen: &ai_app::ui::TranscriptScreen, amount: f32, t: u64) -> u64 {
    (screen.list)(&mut h.rsc).scroll(amount);
    h.frame(t);
    t + PHONE_FRAME_MS
}

/// (a) of docs/IRIS_TODO.md's reproduction: with a row across the top
/// edge, that row is placed -- the viewport's first pixel belongs to
/// something. A rule that culled a row once its *top* left the viewport
/// would leave a blank band here, which is the second of Iris's two
/// screenshots.
#[test]
fn the_row_across_the_top_edge_is_drawn() {
    let (mut h, screen) = opened();
    let top = list_box(&h, &screen).top_left.y;
    let mut t = PHONE_FRAME_MS * 2;

    // 40px a frame, the shape a finger pan arrives in, through a straddle
    // and out the other side of it many times over.
    for _ in 0..60 {
        t = scrolled(&mut h, &screen, 40.0, t);
        let rows = drawn_rows(&h, &screen);
        let first = *rows.first().expect("something is on screen");
        assert!(
            first.0 <= top + 0.5,
            "a band of {:.1}px under the header belongs to no row: rows start at {:.1}, the list \
             at {top:.1}",
            first.0 - top,
            first.0,
        );
        assert!(
            first.1 > top,
            "the row across the top edge was culled: it ends at {:.1}, above the list's own \
             {top:.1}",
            first.1,
        );
    }
}

/// (b): what falls outside the list's box is clipped rather than drawn
/// over whatever is there. The straddling row above is drawn *in full*,
/// so the only thing between its earlier lines and the header bar is this
/// mask -- with none, the phone drew `version = "0.1.0"` behind the "Run
/// benchmark" button.
///
/// The clip is one the screen **opted into** (`build_tree`'s `.masked()`),
/// so this reads the mask the list *inherited*. A `LazySpan` sets none of
/// its own -- masking is opt-in, like scrolling (Iris, 2026-09-08) -- so
/// this is also the test that the transcript is still asking for one.
#[test]
fn the_list_is_clipped_to_its_own_box() {
    let (h, screen) = opened();
    let active = h.render.active.get(&screen.list.id()).expect("drawn");
    assert!(
        active.mask != MaskIdx::NONE,
        "the transcript's list is drawn with nothing clipping it",
    );
    let clip = h.render.mask_region(active.mask, &h.rsc);
    let list = list_box(&h, &screen);
    assert!(
        clip.top_left.y >= list.top_left.y - 0.5 && clip.bot_right.y <= list.bot_right.y + 0.5,
        "the clip {clip:?} reaches outside the list's own box {list:?}, so a row straddling an \
         edge still draws past it",
    );

    // And the mask has to *reach* what the rows draw. The two above say a
    // mask exists and sits in the right place; neither says any primitive
    // references it, so a broken `Mask::parent` chain -- what d507ae4
    // introduced -- would leave them green while a code fence inside a row
    // drew unclipped again (review, 2026-09-07's T3).
    let rows = h
        .render
        .active
        .get(&screen.list.id())
        .expect("the list is drawn")
        .children
        .clone();
    let mut checked = 0;
    for row in rows {
        for prim in primitives_under(&h, row) {
            assert!(
                mask_chain(&h, prim).contains(&active.mask),
                "a primitive of row {row:?} clips to {:?}, a chain that never reaches the list's \
                 own mask {:?}",
                mask_chain(&h, prim),
                active.mask,
            );
            checked += 1;
        }
    }
    assert!(
        checked > 0,
        "no row primitive was checked, so this test asserted nothing",
    );
}

/// Every primitive `id` and its descendants drew, as `MaskIdx`es -- images
/// excluded, since they live in a separate instance array with their own
/// indices (`Primitives::free`).
fn primitives_under(h: &Harness, id: WidgetId) -> Vec<MaskIdx> {
    let Some(active) = h.render.active.get(&id) else {
        return Vec::new();
    };
    let mut out: Vec<MaskIdx> = active
        .primitives
        .iter()
        .filter(|p| p.binding != IMAGE_BINDING)
        .map(|p| h.render.primitives.instance(p.slot).mask_idx)
        .collect();
    for child in &active.children {
        out.extend(primitives_under(h, *child));
    }
    out
}

/// The chain the fragment stage walks from `mask`, outermost last.
fn mask_chain(h: &Harness, mask: MaskIdx) -> Vec<MaskIdx> {
    let mut chain = Vec::new();
    let mut at = mask;
    while at != MaskIdx::NONE {
        assert!(
            !chain.contains(&at),
            "the mask chain from {mask:?} loops back to {at:?}",
        );
        chain.push(at);
        at = h.rsc.ui.masks[at.idx()].parent;
    }
    chain
}

/// A row that has left the viewport entirely is not drawn at all. Before
/// the fix the walk ran from the anchor -- which `scroll` leaves wherever
/// it was, however far outside the viewport that ends up -- and drew
/// every row on the way: 8 scrolls of 3000px left **64 rows** placed for
/// a 2012px viewport, ~59 of them off screen and painting over the
/// header.
///
/// The box is asserted on every leg *except the first*, because a row
/// whose height has never been measured has to be drawn to be measured
/// (`LazySpan::place`'s doc), which on the first walk back is every row
/// entering from the top. Every later leg crosses the same rows with
/// every height already known -- including the second walk *back*, which
/// is there because a regression that draws rows in the wrong place while
/// travelling backwards would otherwise be checked only by the row count
/// (review, 2026-09-07's T2). That is also the ordinary state of a
/// transcript being panned around in. The bound on how many rows are
/// placed at once holds on all three.
#[test]
fn rows_that_have_left_the_viewport_are_not_drawn() {
    let (mut h, screen) = opened();
    let list = list_box(&h, &screen);
    let mut t = PHONE_FRAME_MS * 2;
    let bounded = |rows: &[(f32, f32)], leg: &str, step: usize| {
        // A handful of rows whatever distance has been travelled -- the
        // module doc's own claim about this widget.
        assert!(
            rows.len() <= 24,
            "{leg} {step}: {} rows drawn for one 2012px viewport",
            rows.len(),
        );
    };
    let inside = |rows: &[(f32, f32)], leg: &str, step: usize| {
        for &(top, bottom) in rows {
            assert!(
                bottom > list.top_left.y - 0.5 && top < list.bot_right.y + 0.5,
                "{leg} {step}: a row at ({top:.1}, {bottom:.1}) is outside the list's box \
                 {list:?} and was drawn anyway",
            );
        }
    };

    for step in 0..40 {
        t = scrolled(&mut h, &screen, 400.0, t);
        bounded(&drawn_rows(&h, &screen), "measuring", step);
    }
    for step in 0..40 {
        t = scrolled(&mut h, &screen, -400.0, t);
        let rows = drawn_rows(&h, &screen);
        bounded(&rows, "forward", step);
        inside(&rows, "forward", step);
    }
    for step in 0..40 {
        t = scrolled(&mut h, &screen, 400.0, t);
        let rows = drawn_rows(&h, &screen);
        bounded(&rows, "back", step);
        inside(&rows, "back", step);
    }
}

/// The end the fix had no reason to touch: the row across the *bottom*
/// edge, where the composer starts. Same rule, other direction -- and the
/// list opens pinned there, so this is the ordinary state of the screen
/// rather than a scrolled-to one.
#[test]
fn the_row_across_the_bottom_edge_is_drawn() {
    let (mut h, screen) = opened();
    let list = list_box(&h, &screen);
    let mut t = PHONE_FRAME_MS * 2;

    for _ in 0..40 {
        t = scrolled(&mut h, &screen, 37.0, t);
        let rows = drawn_rows(&h, &screen);
        let last = *rows.last().expect("something is on screen");
        assert!(
            last.1 >= list.bot_right.y - 0.5,
            "a band of {:.1}px above the composer belongs to no row",
            list.bot_right.y - last.1,
        );
        assert!(
            last.0 < list.bot_right.y,
            "the row across the bottom edge was culled: it starts at {:.1}, below the list's own \
             {:.1}",
            last.0,
            list.bot_right.y,
        );
    }
}

/// Panning past the first row settles *on* it rather than beyond it. The
/// list is scrolled far further back than the fixture is long, which is
/// what a hard fling toward the top does; before the clamp existed it
/// stayed wherever that left it -- the phone's "black from the header
/// down", and a whole blank screen in `iris`'s own
/// `fling_toward_the_start_stops_at_the_first_row`.
#[test]
fn scrolling_past_the_first_row_settles_on_it() {
    let (mut h, screen) = opened();
    let list = list_box(&h, &screen);
    let mut t = PHONE_FRAME_MS * 2;

    for _ in 0..60 {
        t = scrolled(&mut h, &screen, 100_000.0, t);
    }
    // No settling frame on purpose: the draw that discovers the gap gives
    // it back inside that same frame (`LazySpan::overscroll_gap`), so the last
    // frame `scrolled` drew is already flush with the first row. Adding
    // one here would hide a regression to the old next-frame correction.
    let rows = drawn_rows(&h, &screen);
    let first = *rows.first().expect("the first row is on screen");
    assert!(
        (first.0 - list.top_left.y).abs() < 0.5,
        "the transcript is parked {:.1}px past its own first row, so the top of the list is blank",
        first.0 - list.top_left.y,
    );
}

/// The same clamp at the other end, which is where Iris met it second
/// ("you shouldn't be able to scroll below the bottom (or above top)").
/// The list opens flush with its newest row, so this drags *forward* off
/// the end of the content and back.
#[test]
fn scrolling_past_the_last_row_settles_on_it() {
    let (mut h, screen) = opened();
    let list = list_box(&h, &screen);
    let mut t = PHONE_FRAME_MS * 2;

    for _ in 0..20 {
        t = scrolled(&mut h, &screen, -100_000.0, t);
    }

    let rows = drawn_rows(&h, &screen);
    let last = *rows.last().expect("the last row is on screen");
    assert!(
        (last.1 - list.bot_right.y).abs() < 0.5,
        "the transcript is parked {:.1}px past its own last row, so the bottom of the list is \
         blank",
        list.bot_right.y - last.1,
    );
}