//! 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);
    }
}

#[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()
    }

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

    /// 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
    /// [`move_to`](Self::move_to) last put the cursor -- nowhere, until it has
    /// been called.
    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);
    }

    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 last [`frame`](Self::frame)'s layout, which is
    /// what a window delivers input against too.
    fn sense(&mut self) {
        let cursor = self.cursor.clone();
        let size = self.render.output_size();
        self.render
            .run_sensors(&mut self.rsc, &mut self.state, cursor, size);
        self.cursor.end_frame();
    }
}