llink/js/desktop/src/hooks/use-stream-playback.ts

import {
  useCallback,
  useEffect,
  useEffectEvent,
  useMemo,
  useReducer,
  useRef,
} from 'react';
import { useAuthStore } from '@/stores/auth-store';
import type { Particle } from '@/api/types';
import { useLiveParticleChildren } from '@/hooks/use-particle';
import { toFirestoreDocPath, type ParticlePath } from '@/lib/particle-path';
import { updateStreamPlaybackMarker } from '@/lib/firestore-particles';

// --- Playback reducer (ID-based) ---

type PlaybackStatus = 'idle' | 'playing' | 'ended';

interface PlaybackState {
  currentParticleId: string | null;
  status: PlaybackStatus;
  initialized: boolean;
}

type PlaybackAction =
  | { type: 'INIT'; particleId: string }
  | { type: 'SET_PARTICLE'; particleId: string }
  | { type: 'END' }
  | { type: 'PARTICLE_ADDED'; particleId: string }
  | {
      type: 'PARTICLE_REMOVED';
      removedParticleId: string;
      fallbackParticleId: string | null;
    };

const initialState: PlaybackState = {
  currentParticleId: null,
  status: 'idle',
  initialized: false,
};

function playbackReducer(
  state: PlaybackState,
  action: PlaybackAction,
): PlaybackState {
  switch (action.type) {
    case 'INIT':
      return {
        currentParticleId: action.particleId,
        status: 'playing',
        initialized: true,
      };
    case 'SET_PARTICLE':
      return {
        ...state,
        currentParticleId: action.particleId,
        status: 'playing',
      };
    case 'END':
      return { ...state, status: 'ended' };
    case 'PARTICLE_ADDED':
      if (state.status === 'ended') {
        return {
          ...state,
          currentParticleId: action.particleId,
          status: 'playing',
        };
      }
      return state;
    case 'PARTICLE_REMOVED':
      if (action.removedParticleId !== state.currentParticleId) return state;
      if (action.fallbackParticleId) {
        return {
          ...state,
          currentParticleId: action.fallbackParticleId,
          status: 'playing',
        };
      }
      return { ...state, currentParticleId: null, status: 'idle' };
  }
}

// --- Init timeout ---

const INIT_FALLBACK_TIMEOUT_MS = 5000;

// --- Hook ---

interface UseStreamPlaybackResult {
  children: Particle[];
  currentParticle: Particle | null;
  currentIndex: number;
  status: PlaybackStatus;
  initialized: boolean;
  next: () => void;
  prev: () => void;
  goTo: (index: number) => void;
  goToParticle: (particleId: string) => void;
}

interface UseStreamPlaybackOptions {
  /**
   * When false, newly arriving particles don't pull playback forward after
   * it has ended (list mode browses; selection must stay put). Default true.
   */
  autoAdvanceOnNew?: boolean;
}

export function useStreamPlayback(
  streamParticle: Particle & { type: 'stream' },
  path: ParticlePath,
  { autoAdvanceOnNew = true }: UseStreamPlaybackOptions = {},
): UseStreamPlaybackResult {
  const userId = useAuthStore((s) => s.user?.id);
  const [state, dispatch] = useReducer(playbackReducer, initialState);
  // Read via ref so the onAdded subscription callback stays stable.
  const autoAdvanceOnNewRef = useRef(autoAdvanceOnNew);
  useEffect(() => {
    autoAdvanceOnNewRef.current = autoAdvanceOnNew;
  }, [autoAdvanceOnNew]);
  // Track the stream ID we've initialized for, to reset when navigating between streams
  const initializedForRef = useRef<string | null>(null);
  // Latest currentIndex for onParticleRemoved, which is passed into
  // useLiveParticleChildren. Reading it through a ref keeps the callback stable
  // (no re-subscription) and breaks the declaration cycle
  // children -> currentIndex -> callback -> children. useEffectEvent can't be
  // used here — Effect Events may not be passed to another hook.
  const currentIndexRef = useRef(0);

  // --- Firestore change callbacks ---
  const onParticleAdded = useCallback((particle: Particle) => {
    if (!autoAdvanceOnNewRef.current) return;
    dispatch({ type: 'PARTICLE_ADDED', particleId: particle.id });
  }, []);

  const onParticleRemoved = useCallback(
    (removed: Particle, updatedChildren: Particle[]) => {
      const fallbackIndex = Math.min(
        currentIndexRef.current,
        updatedChildren.length - 1,
      );
      const fallback = updatedChildren[Math.max(0, fallbackIndex)];
      dispatch({
        type: 'PARTICLE_REMOVED',
        removedParticleId: removed.id,
        fallbackParticleId: fallback?.id ?? null,
      });
    },
    [],
  );

  const { children } = useLiveParticleChildren(path, {
    orderByField: 'created_at',
    orderDirection: 'asc',
    onAdded: onParticleAdded,
    onRemoved: onParticleRemoved,
  });

  // Derive current index and particle from ID
  const currentIndex = useMemo(() => {
    if (!state.currentParticleId) return -1;
    return children.findIndex((c) => c.id === state.currentParticleId);
  }, [children, state.currentParticleId]);

  const currentParticle = currentIndex !== -1 ? children[currentIndex] : null;

  // Keep the ref read by onParticleRemoved in sync with the derived index.
  useEffect(() => {
    currentIndexRef.current = currentIndex;
  }, [currentIndex]);

  // Fallback init — always sees latest children/state via useEffectEvent
  const initFallback = useEffectEvent(() => {
    if (state.initialized || children.length === 0) return;
    initializedForRef.current = streamParticle.id;
    dispatch({ type: 'INIT', particleId: children[0].id });
  });

  // --- Init logic: runs on every children change until initialized ---
  useEffect(() => {
    // Reset if we navigated to a different stream
    if (
      initializedForRef.current !== null &&
      initializedForRef.current !== streamParticle.id
    ) {
      initializedForRef.current = null;
    }

    // Already initialized for this stream
    if (state.initialized && initializedForRef.current === streamParticle.id)
      return;

    if (children.length === 0) return;

    const playbackPosition = streamParticle.playback_markers?.[userId ?? ''];

    if (!playbackPosition) {
      // No marker — start from the beginning
      initializedForRef.current = streamParticle.id;
      dispatch({ type: 'INIT', particleId: children[0].id });
      return;
    }

    // Try to find the marker's target particle
    const found = children.find(
      (c) => c.created_at.getTime() > playbackPosition.getTime(),
    );

    if (found) {
      initializedForRef.current = streamParticle.id;
      dispatch({ type: 'INIT', particleId: found.id });
      return;
    } else {
      initializedForRef.current = streamParticle.id;
      dispatch({ type: 'INIT', particleId: children[children.length - 1].id });
    }

    // Marker target not found yet — fall back after timeout
    const timeout = setTimeout(initFallback, INIT_FALLBACK_TIMEOUT_MS);
    return () => clearTimeout(timeout);
  }, [
    children,
    streamParticle.id,
    streamParticle.playback_markers,
    userId,
    state.initialized,
  ]);

  // --- Persist playback marker (only advance forward, never backwards) ---
  const lastPersistedMarkerRef = useRef<Date | null>(null);

  useEffect(() => {
    if (!userId || !state.initialized || !currentParticle) return;

    const currentTime = currentParticle.created_at;
    const existingMarker =
      lastPersistedMarkerRef.current ??
      streamParticle.playback_markers?.[userId];

    // Only update if advancing beyond the current marker
    if (existingMarker && currentTime.getTime() <= existingMarker.getTime())
      return;

    lastPersistedMarkerRef.current = currentTime;
    const streamDocPath = toFirestoreDocPath(path);
    updateStreamPlaybackMarker(streamDocPath, userId, currentTime);
  }, [
    currentParticle,
    streamParticle.playback_markers,
    state.initialized,
    userId,
    path,
  ]);

  // --- Navigation callbacks ---
  const next = useCallback(() => {
    if (currentIndex === -1) return;
    if (currentIndex < children.length - 1) {
      dispatch({
        type: 'SET_PARTICLE',
        particleId: children[currentIndex + 1].id,
      });
    } else {
      dispatch({ type: 'END' });
    }
  }, [children, currentIndex]);

  const prev = useCallback(() => {
    if (currentIndex <= 0) return;
    dispatch({
      type: 'SET_PARTICLE',
      particleId: children[currentIndex - 1].id,
    });
  }, [children, currentIndex]);

  const goTo = useCallback(
    (index: number) => {
      if (index >= 0 && index < children.length) {
        dispatch({ type: 'SET_PARTICLE', particleId: children[index].id });
      }
    },
    [children],
  );

  // NOTE: if particle doesn't exist in children, this will lead to a brief moment where currentParticle is null
  const goToParticle = useCallback((particleId: string) => {
    // Dispatch directly by ID — if the particle isn't in children yet
    // (e.g. just created), it will resolve once the live query delivers it.
    dispatch({ type: 'SET_PARTICLE', particleId });
  }, []);

  return {
    children,
    currentParticle,
    currentIndex,
    status: state.status,
    initialized: state.initialized,
    next,
    prev,
    goTo,
    goToParticle,
  };
}