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use std::{convert::Infallible, time::Instant};

use rxrust::prelude::{Observer, Subject};

/// Frame ticker emit message when new frame need to draw.
#[derive(Default, Clone)]
pub struct FrameTicker {
  subject: Subject<'static, FrameMsg, Infallible>,
}

/// Message emitted at different status of a frame.

#[derive(Clone)]
pub enum FrameMsg {
  /// This msg emit when all event has processed and framework ready to do
  /// layout & paint.
  NewFrame(Instant),
  /// This Msg emit when performed layout finished, and widget tree ready to
  /// draw. Notice, this message may emit more than once, if someone listen
  /// this message and do some stuff to lead to some widget need relayout, be
  /// careful to modify widget in the listener of this message.
  LayoutReady(Instant),
  /// This msg emit after render data has submitted that mean all stuffs of
  /// current frame need to processed by framework done.
  Finish(Instant),
}

impl FrameTicker {
  #[inline]
  pub(crate) fn emit(&mut self, msg: FrameMsg) { self.subject.next(msg) }

  #[inline]
  pub fn frame_tick_stream(&self) -> Subject<'static, FrameMsg, Infallible> { self.subject.clone() }
}