ai-app/app-rust/tests/catch_a_fling.rs

//! Layer 1 of docs/RUST.md's "Three test layers", for catching a fling:
//! the real transcript screen over the real bench fixture, at the phone's
//! size and density, with no window, no compositor and no GPU.
//!
//! docs/IRIS_TODO.md's 2026-09-07 night report -- "sometimes when I try to
//! catch it while it's still moving (particularly if I drag) then it fails
//! to stop & snap to where finger is". The finger goes down on content
//! that is still travelling and the content does not follow it until
//! `DRAG_SLOP` has been crossed, which at a fling's speed is several
//! frames of the content sliding *away* from a finger that is already
//! down. Compose does not do that: a down while `isScrollInProgress`
//! starts the drag immediately (`scrollable`'s `startDragImmediately`).

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

/// The screen open on the fixture, framed twice -- once to draw, once for
/// `LazySpan::repair_anchor` to resolve the opening `snap_end` into a real
/// anchor, which is what every assertion about scroll position reads.
fn opened() -> (Harness, ai_app::ui::TranscriptScreen) {
    let mut h = Harness::new(phone_size(), PHONE_SCALE);
    let opened = ai_app::ui::fixture::open(&mut h.rsc, &mut h.state).expect("the fixture folds");
    h.frame(0);
    h.frame(PHONE_FRAME_MS);
    (h, opened.screen)
}

/// Where the content is, in window pixels: the top of whichever row is
/// under the middle of the viewport. `LazySpan` has no travel accessor and
/// this needs none -- a row's own extent moves exactly as far as the
/// content does, and the row is picked once so the two readings compare.
fn tracked_row(h: &mut Harness, screen: &ai_app::ui::TranscriptScreen) -> (RowKey, f32) {
    let middle = phone_size().y / 2.0;
    let list = (screen.list)(&mut h.rsc);
    let key = list.key_at(middle).expect("a row under the viewport");
    let (top, _) = list.extent(key).expect("that row has an extent");
    (key, top)
}

fn row_top(h: &mut Harness, screen: &ai_app::ui::TranscriptScreen, key: RowKey) -> f32 {
    (screen.list)(&mut h.rsc)
        .extent(key)
        .expect("the tracked row is still loaded")
        .0
}

/// Three finger samples 8ms apart, each moving `STEP` further down the
/// screen. `STEP * 3` is deliberately **under** `DRAG_SLOP`: a gesture
/// this small moves nothing at all on a settled list (the control below),
/// so anything it moves here is the catch and not the slop being crossed.
const STEP: f32 = 2.0;
const SAMPLES: usize = 3;
const CATCH_X: f32 = 540.0;

/// Feeds the down and its `SAMPLES` moves from `y0` at `t0`, asserting
/// after each one that the content moved by exactly the finger's own
/// delta. Returns the release time.
fn drag_from(
    h: &mut Harness,
    screen: &ai_app::ui::TranscriptScreen,
    key: RowKey,
    y0: f32,
    t0: u64,
    expect_tracking: bool,
) -> u64 {
    let before = row_top(h, screen, key);
    h.touch(TouchAction::Down, Vec2::new(CATCH_X, y0), t0);
    assert_eq!(
        row_top(h, screen, key),
        before,
        "the down itself must not move the content, only stop it"
    );
    let mut t = t0;
    for i in 1..=SAMPLES {
        let moved = STEP * i as f32;
        t = t0 + 8 * i as u64;
        h.touch(TouchAction::Move, Vec2::new(CATCH_X, y0 + moved), t);
        let travelled = row_top(h, screen, key) - before;
        if expect_tracking {
            assert!(
                (travelled - moved).abs() < 0.5,
                "sample {i}: the finger has moved {moved}px since the down and the content \
                 {travelled:.1}px -- it is not pinned to the finger"
            );
        } else {
            assert!(
                travelled.abs() < 0.5,
                "sample {i}: a {moved}px drag is inside DRAG_SLOP ({DRAG_SLOP}px) and must move \
                 nothing, but the content moved {travelled:.1}px"
            );
        }
    }
    t += 8;
    h.touch(
        TouchAction::Up,
        Vec2::new(CATCH_X, y0 + STEP * SAMPLES as f32),
        t,
    );
    t
}

/// The report itself: flick, let the fling run for 150ms, then put a
/// finger down and drag it a little. From the down onwards the content is
/// pinned to the finger, sample for sample -- no slop, and no coasting
/// past the place the finger stopped it.
#[test]
fn a_press_on_a_flinging_list_pins_the_content_to_the_finger() {
    let (mut h, screen) = opened();

    let flick = TouchScript::parse(include_str!("../touch/flick-120hz.touch"))
        .unwrap_or_else(|e| panic!("flick-120hz.touch: {e}"));
    h.replay(&flick);

    // Frames, not a file: the second half of this gesture has to arrive
    // *while* the fling is ticking, and a `.touch` replay inserts no
    // frames between its samples, so a fling recorded that way would be
    // running on paper and stationary in fact.
    let catch_at = flick.end_ms() + 150;
    h.frames_until(
        flick.end_ms() + PHONE_FRAME_MS,
        catch_at - PHONE_FRAME_MS,
        PHONE_FRAME_MS,
    );
    assert!(
        (screen.list)(&mut h.rsc).is_scrolling(),
        "the fling must still be running 150ms in, or this test catches nothing"
    );

    let (key, _) = tracked_row(&mut h, &screen);
    drag_from(&mut h, &screen, key, 1200.0, catch_at, true);
}

/// The other half of the same rule: a catch that never moved at all is a
/// `Released(None)`, not a tap. Compose's scrollable consumes that DOWN,
/// so no click detector under it ever sees the gesture -- stopping a
/// fling with a finger must not also follow the link it landed on, and
/// must not hand the list a velocity to start again with.
#[test]
fn a_catch_that_never_moved_is_not_a_tap_and_does_not_fling() {
    let (mut h, screen) = opened();

    let flick = TouchScript::parse(include_str!("../touch/flick-120hz.touch"))
        .unwrap_or_else(|e| panic!("flick-120hz.touch: {e}"));
    h.replay(&flick);
    let catch_at = flick.end_ms() + 150;
    h.frames_until(
        flick.end_ms() + PHONE_FRAME_MS,
        catch_at - PHONE_FRAME_MS,
        PHONE_FRAME_MS,
    );
    assert!(
        (screen.list)(&mut h.rsc).is_scrolling(),
        "the fling must still be running 150ms in, or this test catches nothing"
    );

    let (key, _) = tracked_row(&mut h, &screen);
    h.touch(TouchAction::Down, Vec2::new(CATCH_X, 1200.0), catch_at);
    let stopped_at = row_top(&mut h, &screen, key);
    h.touch(TouchAction::Up, Vec2::new(CATCH_X, 1200.0), catch_at + 8);

    assert_eq!(
        (screen.list)(&mut h.rsc).fling_velocity(),
        None,
        "a press that stopped a fling and moved nothing must not start another"
    );
    h.frames_until(catch_at + 16, catch_at + 500, PHONE_FRAME_MS);
    assert!(
        (row_top(&mut h, &screen, key) - stopped_at).abs() < 0.5,
        "the content moved after a catch was released without moving"
    );
    assert_eq!(
        h.state.opened_urls,
        Vec::<String>::new(),
        "a catch is not a tap: nothing under it may be followed"
    );
}

/// The half this change had no reason to touch: on a list that is *not*
/// moving, the same tiny drag is still inside `DRAG_SLOP` and still moves
/// nothing. Without this, making every press pin the content would pass
/// the test above and take the slop away from every ordinary press.
#[test]
fn the_same_small_drag_on_a_settled_list_moves_nothing() {
    let (mut h, screen) = opened();

    let flick = TouchScript::parse(include_str!("../touch/flick-120hz.touch"))
        .unwrap_or_else(|e| panic!("flick-120hz.touch: {e}"));
    h.replay(&flick);
    // Long past the spline's own 2071ms for this recording.
    let settled = h.frames_until(
        flick.end_ms() + PHONE_FRAME_MS,
        flick.end_ms() + 4000,
        PHONE_FRAME_MS,
    );
    assert!(
        !(screen.list)(&mut h.rsc).is_scrolling(),
        "the fling must have stopped, or this is the same case as the test above"
    );

    let (key, _) = tracked_row(&mut h, &screen);
    drag_from(
        &mut h,
        &screen,
        key,
        1200.0,
        settled + PHONE_FRAME_MS,
        false,
    );
}