kozan-platform 0.1.0

//! View context — the user-facing API inside a view thread.
//!
//! Like Chrome's `LocalFrame` + `LocalDOMWindow` — the entry point for
//! accessing the document, spawning async work, and communicating
//! back to the main thread.
//!
//! Zero windowing-backend knowledge. Communicates through `PlatformHost` trait.

use std::cell::RefCell;
use std::future::Future;
use std::pin::Pin;
use std::rc::Rc;
use std::sync::Arc;
use std::sync::mpsc;

use kozan_core::Document;
use kozan_core::compositor::layer_tree::LayerTree;
use kozan_core::paint::DisplayList;
use kozan_core::scroll::ScrollOffsets;
use kozan_core::scroll::ScrollTree;
use kozan_core::widget::FrameWidget;
use kozan_scheduler::WakeSender;

use crate::host::PlatformHost;
use crate::id::WindowId;
use crate::pipeline::render_loop::RenderEvent;

/// Pinned boxed future that can live on the view thread.
///
/// `!Send` is fine — these are spawned into the `LocalExecutor` which
/// only runs on the view thread. `'static` so captured DOM handles
/// (which are `'static` index types) can cross `.await` points.
pub(crate) type StagedFuture = Pin<Box<dyn Future<Output = ()> + 'static>>;

/// A frame callback — like `requestAnimationFrame(callback)`.
/// Returns `true` to keep for next frame (loop), `false` for one-shot.
pub(crate) type FrameCallback = Box<dyn FnMut(kozan_scheduler::FrameInfo) -> bool + 'static>;

/// Everything the view thread produces per frame — posted to the render thread.
///
/// Chrome: `LayerTreeHost::FinishCommit()` posts this to the compositor's
/// task queue. Ownership transfers — no shared state, no mutex.
pub struct FrameOutput {
    pub display_list: Arc<DisplayList>,
    pub layer_tree: LayerTree,
    pub scroll_tree: ScrollTree,
}

/// The user-facing API inside a view.
///
/// Passed to the view's init closure. Provides access to:
/// - The document (DOM tree, via `FrameWidget`)
/// - The cross-thread sender (for giving to background tasks)
/// - The platform host (for requesting redraws, setting title, etc.)
/// - The window identity (which window this view belongs to)
///
/// # Example
///
/// ```ignore
/// app.window(WindowConfig::default(), |ctx| {
///     let doc = ctx.document();
///     let btn = doc.create::<HtmlButtonElement>();
///     btn.set_text("Hello!");
///     doc.root().append(btn);
/// });
/// ```
pub struct ViewContext {
    /// The engine entry point — DOM, layout, paint.
    /// Chrome equivalent: `LocalFrameView`.
    frame: FrameWidget,

    wake_sender: WakeSender,
    host: Arc<dyn PlatformHost>,
    window_id: WindowId,

    /// Channel to post frames to the render thread.
    /// Chrome: `ProxyMain` posts commits to compositor's task queue.
    render_sender: mpsc::Sender<RenderEvent>,

    /// Futures queued via `spawn()` during the init closure.
    ///
    /// After init returns, `run_view_thread` drains these into the
    /// `LocalExecutor`. Using `Rc<RefCell<...>>` (not Arc/Mutex) because
    /// `ViewContext` is `!Send` and lives entirely on the view thread.
    staged_futures: Rc<RefCell<Vec<StagedFuture>>>,

    /// Frame callbacks queued via `request_frame()`.
    /// Drained into the scheduler each tick — like `requestAnimationFrame`.
    staged_frame_callbacks: Rc<RefCell<Vec<FrameCallback>>>,

    /// Last computed FPS — updated each frame by the scheduler.
    /// Shared via `Rc<Cell>` so async tasks can read it.
    last_fps: Rc<std::cell::Cell<f64>>,
}

impl ViewContext {
    /// Create a new view context. Called internally by the view thread.
    pub(crate) fn new(
        frame: FrameWidget,
        wake_sender: WakeSender,
        host: Arc<dyn PlatformHost>,
        window_id: WindowId,
        render_sender: mpsc::Sender<RenderEvent>,
    ) -> Self {
        Self {
            frame,
            wake_sender,
            host,
            window_id,
            render_sender,
            staged_futures: Rc::new(RefCell::new(Vec::new())),
            staged_frame_callbacks: Rc::new(RefCell::new(Vec::new())),
            last_fps: Rc::new(std::cell::Cell::new(0.0)),
        }
    }

    /// Read-only access to the document.
    #[inline]
    pub fn document(&self) -> &Document {
        self.frame.document()
    }

    /// Register custom font data (TTF/OTF/TTC bytes) into the font system.
    ///
    /// Chrome equivalent: `document.fonts.add(new FontFace(...))`.
    /// After registration, the font's family name is available for CSS
    /// `font-family` matching. The family name is auto-detected from
    /// the font file's `name` table.
    ///
    /// Accepts `&'static [u8]` (zero-copy for `include_bytes!()`),
    /// `Vec<u8>` (runtime-loaded), or `Arc<[u8]>` (pre-shared).
    ///
    /// Returns the registered family names.
    ///
    /// # Example
    ///
    /// ```ignore
    /// // Static — zero copy:
    /// ctx.register_font(include_bytes!("../assets/Cairo.ttf") as &[u8]);
    ///
    /// // Runtime — from a file:
    /// ctx.register_font(std::fs::read("font.ttf").unwrap());
    /// ```
    pub fn register_font(
        &self,
        data: impl Into<kozan_core::layout::inline::font_system::FontBlob>,
    ) -> Vec<String> {
        self.frame.font_system().register_font(data)
    }

    /// Spawn a `!Send` async task on the view thread's executor.
    ///
    /// The future runs on the view thread — it can safely capture and
    /// mutate DOM handles across `.await` points. No `Arc`, no `Mutex`,
    /// no `WakeSender` needed.
    ///
    /// ```ignore
    /// ctx.spawn(async move {
    ///     kozan_platform::time::sleep(Duration::from_millis(500)).await;
    ///     card.set_style(activated_style());
    /// });
    /// ```
    ///
    /// If called during the init closure the future is queued and started
    /// on the first scheduler tick. If called later (e.g. from an event
    /// handler posted via `WakeSender`) it is spawned into the executor
    /// immediately — use `WakeSender::post` for that case.
    pub fn spawn(&self, future: impl Future<Output = ()> + 'static) {
        self.staged_futures.borrow_mut().push(Box::pin(future));
    }

    /// Drain futures queued by `spawn()` during init.
    ///
    /// Called by `run_view_thread` after the init closure returns.
    pub(crate) fn take_staged_futures(&self) -> Vec<StagedFuture> {
        self.staged_futures.borrow_mut().drain(..).collect()
    }

    /// Take frame callbacks queued via `request_frame()`.
    ///
    /// Called by the event loop each tick to register them with the scheduler.
    /// Uses `mem::take` — zero allocation, swaps with empty Vec.
    pub(crate) fn take_staged_frame_callbacks(&self) -> Vec<FrameCallback> {
        std::mem::take(&mut *self.staged_frame_callbacks.borrow_mut())
    }

    /// Get a clone of the cross-thread sender.
    ///
    /// Give this to background threads so they can send results
    /// back to this view's scheduler.
    #[inline]
    pub fn wake_sender(&self) -> WakeSender {
        self.wake_sender.clone()
    }

    /// Request a redraw for this view's window.
    pub fn request_redraw(&self) {
        self.host.request_redraw(self.window_id);
    }

    /// Set the window title.
    pub fn set_title(&self, title: &str) {
        self.host.set_title(self.window_id, title);
    }

    /// Close this view's window.
    pub fn close_window(&self) {
        self.host.close_window(self.window_id);
    }

    /// The `WindowId` this view belongs to.
    #[inline]
    pub fn window_id(&self) -> WindowId {
        self.window_id
    }

    /// Current FPS — updated each frame by the scheduler.
    ///
    /// Returns 0.0 on the first frame. Use this to build FPS overlays.
    ///
    /// ```ignore
    /// let fps_rc = ctx.fps_cell();
    /// ctx.spawn(async move {
    ///     loop {
    ///         sleep(Duration::from_millis(200)).await;
    ///         label.set_text(&format!("{:.0} FPS", fps_rc.get()));
    ///     }
    /// });
    /// ```
    #[inline]
    pub fn fps(&self) -> f64 {
        self.last_fps.get()
    }

    /// Returns the shared FPS counter — callers may read or write.
    #[inline]
    pub fn fps_cell(&self) -> Rc<std::cell::Cell<f64>> {
        Rc::clone(&self.last_fps)
    }

    /// Register a frame callback — like `requestAnimationFrame`.
    ///
    /// Returns `bool`: `true` = keep for next frame, `false` = one-shot.
    ///
    /// ```ignore
    /// // One-shot:
    /// ctx.request_frame(|_info| { do_something(); false });
    ///
    /// // Render loop (like requestAnimationFrame in a loop):
    /// ctx.request_frame(move |info| {
    ///     fps_label.set_content(format!("{:.0} FPS", info.fps));
    ///     true // keep running
    /// });
    /// ```
    pub fn request_frame(
        &self,
        callback: impl FnMut(kozan_scheduler::FrameInfo) -> bool + 'static,
    ) {
        self.staged_frame_callbacks
            .borrow_mut()
            .push(Box::new(callback));
    }

    // ── Internal (view thread only) ───────────────────────────────────────

    /// Update FPS from the scheduler's frame info.
    pub(crate) fn set_last_fps(&self, fps: f64) {
        self.last_fps.set(fps);
    }

    /// Previous frame's pipeline timing.
    pub(crate) fn last_frame_timing(&self) -> kozan_primitives::timing::FrameTiming {
        self.frame.last_timing()
    }

    /// Check if the document has pending changes that need a frame.
    ///
    /// Called after `scheduler.tick()` — spawned tasks may have mutated the DOM
    /// (e.g. `style().w(pct(...))`) without requesting a frame.
    /// Chrome equivalent: checking `Document::NeedsStyleRecalc()` after microtask checkpoint.
    pub(crate) fn document_needs_frame(&self) -> bool {
        self.frame.document().needs_visual_update()
    }

    /// Apply scroll offsets received from the compositor.
    /// Chrome: main thread applies scroll deltas posted from compositor thread.
    pub(crate) fn apply_scroll_sync(&mut self, offsets: ScrollOffsets) {
        self.frame.apply_compositor_scroll(&offsets);
    }

    /// Run style → layout → paint, then post the result to the render thread.
    /// Chrome: `LocalFrameView::UpdateLifecyclePhases()` then `FinishCommit()`.
    pub(crate) fn update_lifecycle_and_commit(&mut self) {
        self.frame.update_lifecycle();

        let dl = self.frame.last_display_list();
        let layer_tree = self.frame.take_layer_tree();

        if let (Some(dl), Some(tree)) = (dl, layer_tree) {
            let (scroll_tree, _scroll_offsets) = self.frame.scroll_state_snapshot();
            let _ = self.render_sender.send(RenderEvent::Commit(FrameOutput {
                display_list: dl,
                layer_tree: tree,
                scroll_tree,
            }));
        }
    }

    /// Process an input event — hit test + DOM dispatch.
    ///
    /// Returns `true` if DOM state changed (hover/focus/active changed,
    /// or event listeners were dispatched that may have mutated the DOM).
    pub(crate) fn on_input(&mut self, input: kozan_core::InputEvent) -> bool {
        self.frame.handle_input(input)
    }

    /// Mark that styles need recalculation.
    ///
    /// Called when `ElementState` changes (hover, focus, active) or when
    /// event listeners may have mutated the DOM. Chrome equivalent:
    /// `Document::SetNeedsStyleRecalc()`.
    pub(crate) fn invalidate_style(&mut self) {
        self.frame.mark_needs_update();
    }

    /// Notify the frame of a resize event.
    pub(crate) fn on_resize(&mut self, width: u32, height: u32) {
        self.frame.resize(width, height);
    }

    /// Notify the frame of a scale factor change.
    pub(crate) fn on_scale_factor_changed(&mut self, factor: f64) {
        self.frame.set_scale_factor(factor);
    }
}