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

import { useCallback, useEffect, useEffectEvent, useMemo, useReducer, useRef, useState } from "react";
import { useAuthStore } from "@/stores/auth-store";
import type { Particle } from "@/api/types";
import { useLiveParticleChildren } from "@/hooks/use-particle";
import { parseParticlePath, 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;
  paused: boolean;
  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 }
  | { type: "PAUSE" }
  | { type: "RESUME" };

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

function playbackReducer(state: PlaybackState, action: PlaybackAction): PlaybackState {
  switch (action.type) {
    case "INIT":
      return {
        currentParticleId: action.particleId,
        status: "playing",
        paused: false,
        initialized: true,
      };
    case "SET_PARTICLE":
      return {
        ...state,
        currentParticleId: action.particleId,
        status: "playing",
        paused: false,
      };
    case "END":
      return { ...state, status: "ended", paused: false };
    case "PARTICLE_ADDED":
      if (state.status === "ended") {
        return { ...state, currentParticleId: action.particleId, status: "playing", paused: false };
      }
      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" };
    case "PAUSE":
      return { ...state, paused: true };
    case "RESUME":
      return { ...state, paused: false };
  }
}

// --- Init timeout ---

const INIT_FALLBACK_TIMEOUT_MS = 5000;

// --- Hook ---

interface UseStreamPlaybackResult {
  children: Particle[];
  currentParticle: Particle | null;
  currentIndex: number;
  status: PlaybackStatus;
  paused: boolean;
  initialized: boolean;
  next: () => void;
  prev: () => void;
  goTo: (index: number) => void;
  goToParticle: (particleId: string) => void;
  pause: () => void;
  resume: () => 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 the stream ID we've initialized for, to reset when navigating between streams
  const initializedForRef = useRef<string | null>(null);

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

  const onParticleRemoved = useEffectEvent((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;

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

    const streamDocPath = toFirestoreDocPath(path);
    updateStreamPlaybackMarker(streamDocPath, userId, currentParticle.created_at);
  }, [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],
  );

  // 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 });
    }, []);

  const pause = useCallback(() => dispatch({ type: "PAUSE" }), []);
  const resume = useCallback(() => dispatch({ type: "RESUME" }), []);

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