//! Layer 1 of docs/RUST.md's "Three test layers": a whole screen driven
//! in-process with **no window, no compositor and no GPU**, on an
//! explicit clock and a replayed touch stream.
//!
//! `layout_tests.rs` and `sense_tests.rs` already build trees over
//! `UiRenderState` with a hand-rolled `Rsc` each; this is the same idea
//! carried far enough to open a real app screen (`transcript-ui`'s, over
//! the bench fixture -- see the `transcript-fixture` crate) at the
//! phone's size and density, feed it a recorded flick, and assert on
//! where the list ended up. What it answers that the emulator cannot:
//! Android batches a 120Hz flick into one or two `MotionEvent`s
//! (`CursorState::time`), and a `ui-trace` swipe is many evenly-spaced
//! ones -- so the gesture shape a finger actually makes is only
//! reproducible from a *file* of timestamped samples.
//!
//! It is a third backend in the sense `default/` and `android/` are, and
//! deliberately the smallest one: the platform half of each of those
//! (a surface, an IME, a URL opener) becomes a recorded fact here --
//! [`HarnessState::keyboard_shown`], [`HarnessState::opened_urls`] --
//! so a test can assert the platform *was asked*, which is the only
//! thing either backend does with those calls anyway.
//!
//! ```ignore
//! let mut h = Harness::new(phone_size(), PHONE_SCALE);
//! let screen = transcript_ui::build(&mut h.rsc, &mut h.state, rows);
//! h.frame(0);
//! h.replay(&TouchScript::parse(include_str!("flick.touch"))?);
//! h.frames_until(20, 2_000, 8);
//! ```

use crate::prelude::*;
use std::marker::PhantomData;
use std::sync::Arc;
use std::sync::atomic::{AtomicUsize, Ordering};
use std::time::{Duration, Instant};

/// One replayed pointer sample: what Android's `MotionEvent` carries, cut
/// down to the part iris reads (`IrisViewPeer::on_touch_event`).
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum TouchAction {
    Down,
    Move,
    Up,
    /// The gesture taken away by the system (a parent view claiming it, a
    /// call arriving, the swipe up from the bottom edge to leave the
    /// app). It ends the press, because a release that never arrives
    /// leaves pointer capture held forever -- but it is not a release,
    /// and nothing follows from it: no tap, no selection, no fling. See
    /// `CursorState::cancelled`, which is what it sets.
    Cancel,
}

impl TouchAction {
    fn parse(word: &str) -> Option<Self> {
        match word {
            "down" => Some(Self::Down),
            "move" => Some(Self::Move),
            "up" => Some(Self::Up),
            "cancel" => Some(Self::Cancel),
            _ => None,
        }
    }

    /// The inverse of [`Self::parse`] -- what [`Harness::touch`] hands
    /// [`crate::sense::log_input_event`], so an `iris::input` line and a
    /// `.touch` file agree on one spelling of each action.
    pub fn word(self) -> &'static str {
        match self {
            Self::Down => "down",
            Self::Move => "move",
            Self::Up => "up",
            Self::Cancel => "cancel",
        }
    }
}

#[derive(Clone, Copy, Debug)]
pub struct TouchSample {
    /// Milliseconds since the start of the recording -- the sample's own
    /// time, which becomes `CursorState::time`. See that field's doc for
    /// why a replay may not date its samples by when the loop got to
    /// them.
    pub t_ms: u64,
    pub action: TouchAction,
    pub pos: Vec2,
}

/// A recorded gesture: one `t_ms action x y` line per sample, `#` and
/// blank lines ignored. Deliberately a plain text file rather than a
/// serialisation format -- it is written by hand as often as it is
/// recorded, and a diff of one has to be readable.
pub struct TouchScript {
    pub samples: Vec<TouchSample>,
}

impl TouchScript {
    /// Parses a script, naming the line and what was wrong with it: these
    /// are hand-written files, so a typo is the ordinary case and
    /// "expected 4 fields" without a line number is not enough to fix it.
    pub fn parse(text: &str) -> Result<Self, String> {
        let mut samples: Vec<TouchSample> = Vec::new();
        for (i, line) in text.lines().enumerate() {
            let line = line.split('#').next().unwrap_or("").trim();
            if line.is_empty() {
                continue;
            }
            let at = |what: &str| format!("touch script line {}: {what}: {line:?}", i + 1);
            let mut words = line.split_whitespace();
            let (Some(t), Some(action), Some(x), Some(y), None) = (
                words.next(),
                words.next(),
                words.next(),
                words.next(),
                words.next(),
            ) else {
                return Err(at("expected `t_ms action x y`"));
            };
            let t_ms: u64 = t.parse().map_err(|_| at("t_ms is not a whole number"))?;
            let action = TouchAction::parse(action)
                .ok_or_else(|| at("action is not down/move/up/cancel"))?;
            let x: f32 = x.parse().map_err(|_| at("x is not a number"))?;
            let y: f32 = y.parse().map_err(|_| at("y is not a number"))?;
            if let Some(last) = samples.last()
                && t_ms < last.t_ms
            {
                return Err(at("samples must be in time order"));
            }
            samples.push(TouchSample {
                t_ms,
                action,
                pos: Vec2::new(x, y),
            });
        }
        Ok(Self { samples })
    }

    /// The last sample's time, i.e. how long the recording runs.
    pub fn end_ms(&self) -> u64 {
        self.samples.last().map(|s| s.t_ms).unwrap_or(0)
    }
}

/// Counts the frames something asked for without drawing any -- the
/// harness's `RequestRedraw`. A `LazySpan` coasting through a fling asks for
/// the next frame through this (`UiData::animate` and `Widget::tick`), so a test can
/// tell "nothing moved" from "nothing was even asked to move".
#[derive(Default)]
pub struct RedrawCounter(AtomicUsize);

impl RedrawCounter {
    pub fn count(&self) -> usize {
        self.0.load(Ordering::Relaxed)
    }
}

impl RequestRedraw for RedrawCounter {
    fn request_redraw(&self) {
        self.0.fetch_add(1, Ordering::Relaxed);
    }
}

/// The harness's app state: what each real backend keeps for the platform
/// half, recorded instead of performed.
pub struct HarnessState {
    pub root: Option<StrongWidget>,
    pub focus: Option<WeakWidget<TextEdit>>,
    last_click: Instant,
    /// How many times a tap asked for the keyboard (`FocusHost::
    /// focus_gained` with a region -- `showSoftInput` on Android,
    /// `set_ime_cursor_area` on winit). The platform's own answer is not
    /// available here, so this says what was *asked*, and a test must not
    /// read it as "the IME is up".
    pub keyboard_shown: usize,
    /// Every URL a tapped link asked the platform to open, in order.
    pub opened_urls: Vec<String>,
}

impl HarnessState {
    fn new() -> Self {
        Self {
            root: None,
            focus: None,
            last_click: Instant::now(),
            keyboard_shown: 0,
            opened_urls: Vec::new(),
        }
    }
}

impl HasRoot for HarnessState {
    fn set_root(&mut self, root: StrongWidget) {
        self.root = Some(root);
    }
}

impl FocusHost for HarnessState {
    fn recent_click(&mut self) -> bool {
        crate::attr::recent_click(&mut self.last_click)
    }
    fn set_focus(&mut self, id: Option<WeakWidget<TextEdit>>) {
        self.focus = id;
    }
    fn is_focused(&self, id: WeakWidget<TextEdit>) -> bool {
        self.focus == Some(id)
    }
    fn focus_gained(&mut self, region: Option<PixelRegion>) {
        if region.is_some() {
            self.keyboard_shown += 1;
        }
    }
}

impl OpenUrl for HarnessState {
    fn open_url(&mut self, url: &str) {
        self.opened_urls.push(url.to_string());
    }
}

/// The harness's `Rsc` -- identical in substance to `DefaultRsc`/
/// `AndroidRsc` minus the windowing, for the same reason those two are
/// separate types (`AndroidRsc`'s own doc).
pub struct HarnessRsc {
    pub ui: UiData,
    pub events: EventManager<Self>,
    pub tasks: Tasks<Self>,
    pub state: WidgetState,
    _state: PhantomData<HarnessState>,
}

impl UiRsc for HarnessRsc {
    fn ui(&self) -> &UiData {
        &self.ui
    }
    fn ui_mut(&mut self) -> &mut UiData {
        &mut self.ui
    }
    fn on_draw(&mut self, active: &ActiveData) {
        self.events.draw(active);
    }
    fn on_undraw(&mut self, active: &ActiveData) {
        self.events.undraw(active);
    }
    fn on_remove(&mut self, id: WidgetId) {
        self.events.remove(id);
        self.state.remove(id);
    }
}

impl HasState for HarnessRsc {
    type State = HarnessState;
}

impl HasEvents for HarnessRsc {
    fn events(&self) -> &EventManager<Self> {
        &self.events
    }
    fn events_mut(&mut self) -> &mut EventManager<Self> {
        &mut self.events
    }
}

impl HasTasks for HarnessRsc {
    fn tasks_mut(&mut self) -> &mut Tasks<Self> {
        &mut self.tasks
    }
}

impl HasWidgetState for HarnessRsc {
    fn widget_state(&self) -> &WidgetState {
        &self.state
    }
    fn widget_state_mut(&mut self) -> &mut WidgetState {
        &mut self.state
    }
}

impl<I: RscIdx<HarnessRsc>> std::ops::Index<I> for HarnessRsc {
    type Output = I::Output;
    fn index(&self, index: I) -> &Self::Output {
        index.get(self)
    }
}

impl<I: RscIdx<HarnessRsc>> std::ops::IndexMut<I> for HarnessRsc {
    fn index_mut(&mut self, index: I) -> &mut Self::Output {
        index.get_mut(self)
    }
}

/// A screen running with no window: the widget tree, the frame loop and
/// the pointer, all advanced by the caller. See the module doc.
pub struct Harness {
    pub rsc: HarnessRsc,
    pub render: UiRenderState,
    pub state: HarnessState,
    task_recv: TaskMsgReceiver<HarnessRsc>,
    redraws: Arc<RedrawCounter>,
    cursor: CursorState,
    /// Time zero. Every `t_ms` in this harness is an offset from here, so
    /// nothing reads the wall clock -- see [`Self::at`].
    base: Instant,
    size: Vec2,
}

impl Harness {
    /// `size` is in physical pixels and `density` is physical pixels per
    /// dp, the pair Android reads from the surface and
    /// `DisplayMetrics.density` (`AndroidUiState::content_scale`). The
    /// phone's own numbers are `transcript_fixture::PHONE_SIZE`/
    /// `PHONE_SCALE`.
    pub fn new(size: Vec2, density: f32) -> Self {
        let redraws = Arc::new(RedrawCounter::default());
        let (tasks, task_recv) = Tasks::init(redraws.clone());
        let mut rsc = HarnessRsc {
            ui: UiData::default(),
            events: EventManager::default(),
            tasks,
            state: WidgetState::default(),
            _state: PhantomData,
        };
        rsc.ui.text.density = density;
        let mut render = UiRenderState::new();
        render.set_density(density);
        render.resize(size);
        Self {
            rsc,
            render,
            state: HarnessState::new(),
            task_recv,
            redraws,
            cursor: CursorState::default(),
            base: Instant::now(),
            size,
        }
    }

    /// The `Instant` this harness means by `t_ms`. Public because a
    /// caller driving `ScrollController::tick` or `DragGesture` by hand needs
    /// to date those calls on the same clock the touch samples use.
    pub fn at(&self, t_ms: u64) -> Instant {
        self.base + Duration::from_millis(t_ms)
    }

    pub fn size(&self) -> Vec2 {
        self.size
    }

    /// How many frames were asked for so far -- see [`RedrawCounter`].
    pub fn redraws(&self) -> usize {
        self.redraws.count()
    }

    /// One frame at `t_ms`: drain finished tasks, advance anything
    /// animating, lay out and "draw". The same three steps
    /// `DefaultApp::window_event`'s `RedrawRequested` arm and
    /// `IrisViewPeer::render` take, minus handing primitives to a GPU.
    pub fn frame(&mut self, t_ms: u64) {
        while let Ok(update) = self.task_recv.try_recv() {
            update(&mut self.state, &mut self.rsc);
        }
        let now = self.at(t_ms);
        let at = Instant::now();
        let animating = self.rsc.ui.tick_animations(now);
        self.render.update(&self.state.root, &mut self.rsc);
        // No GPU here, so there is nothing to acquire and nothing to
        // submit: the frame is all `build`, which is honest rather than
        // zero-filled (`FrameParts::whole`). `layout`/`redraw`/
        // `primitives` are still real, because `render.update` just ran;
        // see `iris::diagnostics::log_frame`'s own doc for why this reads
        // those back rather than timing anything itself.
        crate::diagnostics::log_frame(
            &self.render,
            now,
            FrameParts::whole(at.elapsed()),
            animating,
        );
    }

    /// Frames every `step_ms` up to and including `end_ms` -- what a
    /// fling needs, since it moves only while something ticks it
    /// (`ScrollController::fling`'s doc). Returns the time of the last frame run.
    pub fn frames_until(&mut self, from_ms: u64, end_ms: u64, step_ms: u64) -> u64 {
        debug_assert!(step_ms > 0, "a frame loop with no step never ends");
        let mut t = from_ms;
        while t <= end_ms {
            self.frame(t);
            t += step_ms;
        }
        t - step_ms
    }

    /// One pointer sample through the sensors, then the frame it belongs
    /// to -- `IrisViewPeer::on_touch_event` and `after_input`, in one
    /// call. Each sample is its own input frame, dated by the sample
    /// rather than by when this ran.
    pub fn touch(&mut self, action: TouchAction, pos: Vec2, t_ms: u64) {
        self.cursor.time = self.at(t_ms);
        self.cursor.pos = pos;
        match action {
            TouchAction::Down => {
                self.cursor.exists = true;
                self.cursor.buttons.left.update(true);
            }
            TouchAction::Move => {}
            TouchAction::Up => self.cursor.buttons.left.update(false),
            // The platform taking the gesture away, not the finger
            // lifting -- see `CursorState::cancelled`.
            TouchAction::Cancel => {
                self.cursor.buttons.left.update(false);
                self.cursor.cancelled = true;
            }
        }
        // Layer 1's half of `iris::input` (`sense::log_input_event`'s own
        // doc): no batching happens here, so `historical` is always empty
        // and `t_ms` is the script's own column, which is what makes this
        // round-trip through `report_to_touch.py` back into an identical
        // `TouchScript`.
        crate::sense::log_input_event(action.word(), pos.x, pos.y, t_ms, &[]);
        let cursor = self.cursor.clone();
        self.render
            .run_sensors(&mut self.rsc, &mut self.state, cursor, self.size);
        self.frame(t_ms);
        self.cursor.end_frame();
    }

    /// Replays a whole recorded gesture. Nothing is inserted between the
    /// samples: a file with three lines produces three input frames, so
    /// the batched shape a real flick arrives in is preserved exactly as
    /// recorded rather than smoothed into evenly-spaced motion.
    pub fn replay(&mut self, script: &TouchScript) {
        for sample in &script.samples {
            self.touch(sample.action, sample.pos, sample.t_ms);
        }
    }
}