import { computed, markRaw, nextTick, onMounted, onUnmounted, shallowRef, watch, type Component, type Ref } from 'vue';
import { setDashcamOpen } from '@/journey/dashcam-feed';
import { isEditableTarget } from '@/composables/useKeyboardNavigation';

const LIVE_STAGE = ".reading-stage[data-reading-stage='live']";
const RISE_MS = 400;
/** Phones: no shutter in the gantry bay (dashcam.css), and no `c` key either. */
const NARROW = '(max-width: 767px)';
/** One retry for a failed frame chunk, then the open is abandoned. */
export const DASHCAM_RETRY_MS = 350;
/** A frame that has not mounted in this long is abandoned (nothing changed). */
export const DASHCAM_LOAD_TIMEOUT_MS = 4_000;

type FrameModule = { default: Component };
const importFrame = (): Promise<FrameModule> => import('@/components/DashcamFrame.vue');

/**
 * DASHCAM, DOM side (initial chunk, kept minimal): availability, the `c` key,
 * html[data-dashcam] and the lazy frame. The frame itself (telemetry, focus
 * trap, capture, the shutter) loads on first open or button hover. Starts
 * after mount, so the server HTML carries none of it.
 *
 * Opening is two-phase so the page can never fold away without a frame on
 * top of it: show() asks for the frame (rendered once the chunk is in), and
 * only the frame's `ready` (its mount) folds the page, closes the lens and
 * hands it the title. A chunk that fails twice or never mounts abandons the
 * open with nothing changed. Anything that would leave the frame stranded
 * (motion withdrawn, the scene dropping out of `running`, a resize to phone
 * width) closes it.
 */
export function useDashcam(sources: {
  /** Motion allowed in full and the scene not withheld: closes the dashcam when it drops. */
  allowed: Readonly<Ref<boolean>>;
  sceneRunning: Readonly<Ref<boolean>>;
  /** Fine pointer on high/medium: the lens drifts and the bars ease. */
  drift: () => boolean;
  /** Test seam: the frame chunk loader. */
  load?: () => Promise<FrameModule>;
}) {
  const load = sources.load ?? importFrame;
  /** The page is folded and the frame is mounted. */
  const open = shallowRef(false);
  /** The frame should render (requested and loaded); `open` follows on its mount. */
  const engaged = shallowRef(false);
  const frame = shallowRef<Component | null>(null);
  const available = computed(() => sources.allowed.value && sources.sceneRunning.value);
  let loading: Promise<boolean> | null = null;
  let requested = false;
  let riseTimer = 0;
  let loadTimer = 0;
  const root = (): HTMLElement => document.documentElement;
  const narrow = (): boolean => window.matchMedia?.(NARROW).matches ?? false;

  const attempt = (): Promise<boolean> => load().then(
    (module) => { frame.value = markRaw(module.default); return true; },
    () => false,
  );
  const prefetch = (): Promise<boolean> => {
    if (frame.value) return Promise.resolve(true);
    return (loading ??= attempt()
      .then((ok) => ok || new Promise<boolean>((resolve) => { window.setTimeout(() => { void attempt().then(resolve); }, DASHCAM_RETRY_MS); }))
      .then((ok) => { if (!ok) loading = null; return ok; }));
  };

  /** Drops a pending or mounting open; nothing on the page has changed yet. */
  const abandon = (): void => {
    requested = false;
    engaged.value = false;
    window.clearTimeout(loadTimer);
  };

  const show = (): void => {
    if (requested || open.value || !available.value || document.querySelector(LIVE_STAGE) === null) return;
    if (narrow()) return;
    requested = true;
    window.clearTimeout(loadTimer);
    loadTimer = window.setTimeout(() => { if (!open.value) abandon(); }, DASHCAM_LOAD_TIMEOUT_MS);
    void prefetch().then((ok) => {
      if (!requested) return;
      if (!ok || !available.value || narrow()) abandon();
      else engaged.value = true;
    });
  };

  /** The frame has mounted: fold the page and close the lens. */
  const ready = (): void => {
    if (!requested || open.value) return;
    window.clearTimeout(loadTimer);
    window.clearTimeout(riseTimer);
    open.value = true;
    setDashcamOpen(true, sources.drift());
    root().dataset.dashcam = 'on';
  };

  const close = (): void => {
    if (!open.value) {
      if (requested) abandon();
      return;
    }
    abandon();
    open.value = false;
    setDashcamOpen(false, false);
    root().dataset.dashcam = 'rise';
    riseTimer = window.setTimeout(() => { delete root().dataset.dashcam; }, RISE_MS);
    void nextTick(() => document.querySelector<HTMLElement>('.drive-controls__dashcam')?.focus());
  };

  const onKeydown = (event: KeyboardEvent): void => {
    if (event.defaultPrevented || event.altKey || event.ctrlKey || event.metaKey || isEditableTarget(event.target)) return;
    const active = open.value || requested;
    if (active && event.key === 'Escape') {
      event.preventDefault();
      close();
    } else if (!event.shiftKey && !event.repeat && event.key.toLowerCase() === 'c') {
      if (active) close();
      else show();
      if (active || requested) event.preventDefault();
    }
  };
  const onResize = (): void => { if ((open.value || requested) && narrow()) close(); };

  watch(available, (ok) => { if (!ok) close(); });
  onMounted(() => {
    window.addEventListener('keydown', onKeydown);
    window.addEventListener('resize', onResize, { passive: true });
  });
  onUnmounted(() => {
    window.removeEventListener('keydown', onKeydown);
    window.removeEventListener('resize', onResize);
    window.clearTimeout(riseTimer);
    window.clearTimeout(loadTimer);
    if (open.value) setDashcamOpen(false, false);
    delete root().dataset.dashcam;
  });

  return { open, engaged, frame, available, show, ready, close, prefetch };
}