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

import { useCallback, useEffect, 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";
import { logError } from "@/lib/errors";
import { useEvent } from "@/hooks/use-event";

// --- 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" };
  }
}

const INIT_FALLBACK_TIMEOUT_MS = 5000;

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;
}

export function useStreamPlayback(
  streamParticle: Particle & { type: "stream" },
  path: ParticlePath,
): UseStreamPlaybackResult {
  const userId = useAuthStore((s) => s.user?.id);
  const [state, dispatch] = useReducer(playbackReducer, initialState);
  // Track which stream we initialized for, so navigating to a sibling resets cleanly.
  const initializedForRef = useRef<string | null>(null);

  const onParticleAdded = useCallback((particle: Particle) => {
    dispatch({ type: "PARTICLE_ADDED", particleId: particle.id });
  }, []);

  const onParticleRemoved = useEvent(
    (removed: Particle, updatedChildren: Particle[]) => {
      const fallbackIndex = Math.min(currentIndex, 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;

  const initFallback = useEvent(() => {
    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(() => {
    if (
      initializedForRef.current !== null &&
      initializedForRef.current !== streamParticle.id
    ) {
      initializedForRef.current = null;
    }

    if (state.initialized && initializedForRef.current === streamParticle.id)
      return;

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

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

    if (!playbackPosition) {
      initializedForRef.current = streamParticle.id;
      dispatch({ type: "INIT", particleId: children[0].id });
      return;
    }

    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,
      });
    }

    const timeout = setTimeout(initFallback, INIT_FALLBACK_TIMEOUT_MS);
    return () => clearTimeout(timeout);
  }, [
    children,
    streamParticle.id,
    streamParticle.playback_markers,
    userId,
    state.initialized,
    initFallback,
  ]);

  // --- 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];

    if (existingMarker && currentTime.getTime() <= existingMarker.getTime())
      return;

    lastPersistedMarkerRef.current = currentTime;
    const streamDocPath = toFirestoreDocPath(path);
    updateStreamPlaybackMarker(streamDocPath, userId, currentTime).catch(
      (err) => logError(err, { scope: "playback.marker", path }),
    );
    // streamParticle.playback_markers is read at effect time; not in deps to
    // avoid double-writes when the snapshot we just persisted echoes back.
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [currentParticle?.id, 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],
  );

  // If the particle isn't in `children` yet (e.g. just-created), the live
  // query will resolve it shortly and the derived index/particle will catch up.
  const goToParticle = useCallback((particleId: string) => {
    dispatch({ type: "SET_PARTICLE", particleId });
  }, []);

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