//! A ui with no window: build a tree, run frames, move a pointer, and read
//! back where widgets landed.
//!
//! It does not draw. A claim about pixels still needs a real surface.

use crate::prelude::*;
use std::{
    sync::{
        Arc,
        mpsc::{Receiver, SyncSender, sync_channel},
    },
    time::Duration,
};

/// There is no loop here to post to, so updates queue until the test asks
/// for them.
struct Queue(SyncSender<Box<dyn TaskUpdate<DefaultRsc<HarnessState>>>>);

impl TaskQueue<DefaultRsc<HarnessState>> for Queue {
    fn send(&self, update: Box<dyn TaskUpdate<DefaultRsc<HarnessState>>>) {
        let _ = self.0.send(update);
    }
}

/// `assert_eq!` for where a frame put a widget, written as its two corners.
#[macro_export]
macro_rules! assert_corners {
    ($harness:expr, $id:expr, ($x0:expr, $y0:expr), ($x1:expr, $y1:expr)) => {
        assert_eq!(
            $harness.region(&$id).expect("widget drew nothing"),
            $crate::core::PixelRegion {
                top_left: $crate::core::PxVec2::new(
                    $crate::core::Px::from_f32($x0 as f32),
                    $crate::core::Px::from_f32($y0 as f32),
                ),
                bot_right: $crate::core::PxVec2::new(
                    $crate::core::Px::from_f32($x1 as f32),
                    $crate::core::Px::from_f32($y1 as f32),
                ),
            }
        );
    };
}
pub use crate::assert_corners;

/// One replayed pointer sample, cut down to what a window delivers: where the
/// pointer is, and whether the button changed.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum TouchAction {
    Down,
    Move,
    Up,
}

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

#[derive(Clone, Copy, Debug)]
pub struct TouchSample {
    pub t_ms: u64,
    pub action: TouchAction,
    pub pos: Vec2,
}

/// A recorded gesture, in the output's own pixels: `<ms> down|move|up <x> <y>`
/// a line, `#` to end of line ignored.
///
/// One parser for both ways of replaying a recording -- into a harness, and
/// into a real window -- so the two cannot read the same file differently.
pub struct TouchScript {
    pub samples: Vec<TouchSample>,
}

impl TouchScript {
    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"))?;
            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 })
    }
}

#[derive(Default)]
pub struct HarnessState {
    pub root: Option<StrongWidget>,
}

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

pub struct Harness {
    pub rsc: DefaultRsc<HarnessState>,
    pub render: UiRenderState,
    pub state: HarnessState,
    updates: Receiver<Box<dyn TaskUpdate<DefaultRsc<HarnessState>>>>,
    cursor: CursorState,
}

impl Harness {
    /// `size` is the output in physical pixels.
    pub fn new(size: impl Into<Vec2>) -> Self {
        // A `TaskQueue` must be `Sync`, which `mpsc::Sender` is not; the
        // bound that comes with `SyncSender` is far past anything a test
        // leaves unread.
        let (send, updates) = sync_channel(1024);
        let rsc = DefaultRsc::init(Arc::new(Queue(send)));
        let mut render = UiRenderState::new();
        render.resize(size);
        Self {
            rsc,
            render,
            state: HarnessState::default(),
            updates,
            cursor: CursorState::default(),
        }
    }

    pub fn size(&self) -> Vec2 {
        self.render.output_size().to_f32()
    }

    pub fn resize(&mut self, size: impl Into<Vec2>) {
        self.render.resize(size);
    }

    /// Changes a length rule after the fact, the way `.width()` sets one.
    pub fn set_len(&mut self, id: impl IdLike, axis: Axis, len: impl Into<LayoutLen>) {
        self.rsc
            .widgets_mut()
            .set_size_rule(id, axis, SizeRule::Exact(len.into()));
    }

    /// Sets the root and lays it out, so a pointer event has something to hit.
    pub fn set_root<T>(&mut self, widget: impl WidgetLike<DefaultRsc<HarnessState>, T>) {
        widget.set_root(&mut self.rsc, &mut self.state);
        self.frame();
    }

    pub fn needs_redraw(&self) -> bool {
        self.render
            .needs_redraw(&self.state.root, self.rsc.widgets())
    }

    pub fn apply_updates(&mut self) -> usize {
        let mut applied = 0;
        while let Ok(update) = self.updates.try_recv() {
            update(&mut self.state, &mut self.rsc);
            applied += 1;
        }
        applied
    }

    /// Waits for a task's first update, then applies everything waiting.
    /// False if none arrived in time.
    #[must_use]
    pub fn await_update(&mut self, timeout: Duration) -> bool {
        let Ok(update) = self.updates.recv_timeout(timeout) else {
            return false;
        };
        update(&mut self.state, &mut self.rsc);
        self.apply_updates();
        true
    }

    /// Lays the tree out and builds its primitives.
    pub fn frame(&mut self) {
        self.apply_updates();
        self.render.update(&self.state.root, &mut self.rsc);
    }

    /// Where the last frame put a widget, or `None` if it drew nothing.
    pub fn region(&self, id: &impl IdLike) -> Option<PixelRegion> {
        self.render.window_region(id)
    }

    pub fn move_to(&mut self, pos: impl Into<Vec2>) {
        self.cursor.pos = pos.into();
        self.cursor.exists = true;
        self.sense();
    }

    pub fn leave(&mut self) {
        self.cursor.exists = false;
        self.sense();
    }

    pub fn press(&mut self, button: CursorButton) {
        self.button(button).update(true);
        self.sense();
    }

    pub fn release(&mut self, button: CursorButton) {
        self.button(button).update(false);
        self.sense();
    }

    /// A wheel carries no position, so this goes wherever the cursor was last
    /// moved to -- nowhere, until it has been moved.
    pub fn scroll(&mut self, delta: impl Into<Vec2>) {
        self.cursor.scroll_delta = delta.into();
        self.sense();
    }

    pub fn click(&mut self, pos: impl Into<Vec2>) {
        self.move_to(pos);
        self.press(CursorButton::Left);
        self.release(CursorButton::Left);
    }

    /// Drives a recorded gesture through the harness.
    pub fn replay(&mut self, script: &TouchScript) {
        for sample in &script.samples {
            match sample.action {
                TouchAction::Down => {
                    self.move_to(sample.pos);
                    self.press(CursorButton::Left);
                }
                TouchAction::Move => self.move_to(sample.pos),
                TouchAction::Up => {
                    self.move_to(sample.pos);
                    self.release(CursorButton::Left);
                }
            }
        }
    }

    fn button(&mut self, button: CursorButton) -> &mut ActivationState {
        let buttons = &mut self.cursor.buttons;
        match button {
            CursorButton::Left => &mut buttons.left,
            CursorButton::Middle => &mut buttons.middle,
            CursorButton::Right => &mut buttons.right,
        }
    }

    /// Dispatches against the layout of the last frame, which is what a
    /// window delivers input against too.
    fn sense(&mut self) {
        let cursor = self.cursor.clone();
        self.render
            .run_sensors(&mut self.rsc, &mut self.state, cursor);
        self.cursor.end_frame();
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn parse(text: &str) -> Result<Vec<(u64, TouchAction, f32, f32)>, String> {
        Ok(TouchScript::parse(text)?
            .samples
            .iter()
            .map(|s| (s.t_ms, s.action, s.pos.x, s.pos.y))
            .collect())
    }

    #[test]
    fn a_recording_is_time_action_and_a_point() {
        assert_eq!(
            parse("0 down 10 20\n16 move 10.5 24\n32 up 10.5 24").unwrap(),
            [
                (0, TouchAction::Down, 10.0, 20.0),
                (16, TouchAction::Move, 10.5, 24.0),
                (32, TouchAction::Up, 10.5, 24.0),
            ]
        );
    }

    #[test]
    fn blank_lines_and_comments_are_not_samples() {
        assert_eq!(
            parse("# a flick\n\n 0 down 1 2   # the finger lands\n\n").unwrap(),
            [(0, TouchAction::Down, 1.0, 2.0)]
        );
    }

    #[test]
    fn a_recording_that_goes_backwards_is_rejected() {
        // Replay waits out the gap between samples, so time running backwards
        // would silently become no wait at all.
        let err = parse("16 down 1 2\n0 up 1 2").unwrap_err();
        assert!(err.contains("time order"), "{err}");
    }

    #[test]
    fn a_line_that_is_not_a_sample_says_which_line() {
        let err = parse("0 down 1 2\n16 wiggle 1 2").unwrap_err();
        assert!(err.contains("line 2"), "{err}");
        assert!(err.contains("down/move/up"), "{err}");
    }
}