import { onMounted, onUnmounted, readonly, shallowRef, type Ref } from 'vue';
import { createScrollDriveController } from '@/journey/scroll-drive-controller';
import type { ScrollDriveSample, ScrollDriveSnapshot } from '@/journey/types';

const PASSIVE_LISTENER: AddEventListenerOptions = { passive: true };

const initialSnapshot = (): ScrollDriveSnapshot => ({
  scrollY: 0,
  routeProgress: 0,
  direction: 0,
  acceleration: 0,
  driveSpeed: 0.18,
});

export interface ScrollDriveBinding {
  snapshot: Readonly<Ref<ScrollDriveSnapshot>>;
  requestFrame(): void;
  subscribeFrame(
    listener: (now: number, snapshot: ScrollDriveSnapshot) => boolean,
  ): () => void;
}

export function useScrollDrive(): ScrollDriveBinding {
  const controller = createScrollDriveController();
  const snapshot = shallowRef<ScrollDriveSnapshot>(initialSnapshot());
  const subscribers = new Set<(
    now: number,
    snapshot: ScrollDriveSnapshot,
  ) => boolean>();
  let requestFrame = (): void => {};
  let disposed = false;
  let teardown = (): void => {};

  onMounted(() => {
    let frameId: number | undefined;
    let resetOnNextFrame = false;
    const visualViewport = window.visualViewport;

    const readSample = (now: number): ScrollDriveSample => {
      const scrollingElement = document.scrollingElement ?? document.documentElement;
      const viewportHeight = visualViewport?.height ?? document.documentElement.clientHeight;
      return {
        scrollY: scrollingElement.scrollTop,
        now,
        maxScrollY: Math.max(0, scrollingElement.scrollHeight - viewportHeight),
        viewportHeight,
      };
    };

    let scheduleFrame = (): void => {};

    const runFrame = (now: number): void => {
      frameId = undefined;
      const input = readSample(now);
      const nextSnapshot = resetOnNextFrame
        ? controller.reset(input)
        : controller.sample(input);
      snapshot.value = nextSnapshot;
      resetOnNextFrame = false;
      let keepRunning = false;
      for (const subscriber of [...subscribers]) {
        keepRunning = subscriber(now, nextSnapshot) || keepRunning;
      }
      if (nextSnapshot.acceleration > 0 || keepRunning) scheduleFrame();
    };

    scheduleFrame = (): void => {
      if (frameId === undefined && document.visibilityState !== 'hidden') {
        frameId = requestAnimationFrame(runFrame);
      }
    };
    requestFrame = scheduleFrame;

    const handleVisibilityChange = (): void => {
      if (document.visibilityState === 'hidden') {
        resetOnNextFrame = true;
        if (frameId !== undefined) {
          cancelAnimationFrame(frameId);
          frameId = undefined;
        }
        snapshot.value = controller.reset();
        return;
      }
      resetOnNextFrame = true;
      scheduleFrame();
    };

    snapshot.value = controller.reset(readSample(performance.now()));
    window.addEventListener('scroll', scheduleFrame, PASSIVE_LISTENER);
    window.addEventListener('resize', scheduleFrame, PASSIVE_LISTENER);
    visualViewport?.addEventListener('resize', scheduleFrame, PASSIVE_LISTENER);
    visualViewport?.addEventListener('scroll', scheduleFrame, PASSIVE_LISTENER);
    document.addEventListener('visibilitychange', handleVisibilityChange, PASSIVE_LISTENER);

    teardown = (): void => {
      disposed = true;
      requestFrame = (): void => {};
      window.removeEventListener('scroll', scheduleFrame, PASSIVE_LISTENER);
      window.removeEventListener('resize', scheduleFrame, PASSIVE_LISTENER);
      visualViewport?.removeEventListener('resize', scheduleFrame, PASSIVE_LISTENER);
      visualViewport?.removeEventListener('scroll', scheduleFrame, PASSIVE_LISTENER);
      document.removeEventListener('visibilitychange', handleVisibilityChange, PASSIVE_LISTENER);
      if (frameId !== undefined) {
        cancelAnimationFrame(frameId);
        frameId = undefined;
      }
      subscribers.clear();
    };
  });

  onUnmounted(() => teardown());

  return {
    snapshot: readonly(snapshot),
    requestFrame: () => requestFrame(),
    subscribeFrame(listener) {
      if (disposed) return () => {};
      subscribers.add(listener);
      return () => subscribers.delete(listener);
    },
  };
}