"use client";

/**
 * Podcast episodes backed by localStorage — the same tiny observable store as
 * the homework history. An episode is the script the voice reads, the notes it
 * came from (so it can be regenerated) and the word the listener got to.
 *
 * Photos and documents were reduced to text on the client before this point;
 * originals are never stored.
 */

import { podcastSchema, type Podcast } from "./schemas";
import { markSyncDirty } from "./sync-state";

const STORAGE_KEY = "freezmo.podcasts.v1";
const EMPTY: Podcast[] = [];
/** Enough to regenerate from, while staying well under the storage quota. */
export const MAX_STORED_SOURCE = 24_000;

type Listener = () => void;

let episodes: Podcast[] | null = null;
let cached: Podcast[] = EMPTY;
const listeners = new Set<Listener>();

function read(): Podcast[] {
  if (typeof window === "undefined") return EMPTY;
  try {
    const raw = window.localStorage.getItem(STORAGE_KEY);
    if (!raw) return EMPTY;
    const parsed: unknown = JSON.parse(raw);
    if (!Array.isArray(parsed)) return EMPTY;
    const valid: Podcast[] = [];
    for (const entry of parsed) {
      const result = podcastSchema.safeParse(entry);
      if (result.success) valid.push(result.data);
      else console.warn("[freezmo] skipping invalid podcast", result.error.issues);
    }
    return valid;
  } catch (error) {
    console.warn("[freezmo] could not read the podcasts", error);
    return EMPTY;
  }
}

function ensureLoaded(): void {
  if (episodes !== null) return;
  episodes = read();
  cached = episodes;
}

function write(next: Podcast[]): void {
  episodes = next;
  cached = next;
  try {
    window.localStorage.setItem(STORAGE_KEY, JSON.stringify(next));
  } catch (error) {
    console.warn("[freezmo] could not save the podcasts (storage full?)", error);
  }
  /* An episode change with sync on pushes itself (see lib/sync-auto). */
  if (markSyncDirty()) void import("./sync-auto").then((module) => module.scheduleAutoSync());
  listeners.forEach((listener) => listener());
}

/** Used by backup import and sync: wholesale replacement of the list. */
export function replacePodcasts(next: Podcast[]): void {
  const valid: Podcast[] = [];
  for (const entry of next) {
    const result = podcastSchema.safeParse(entry);
    if (result.success) valid.push(entry);
    else console.warn("[freezmo] skipping invalid podcast in import", result.error.issues);
  }
  write(valid);
}

function onStorage(event: StorageEvent): void {
  if (event.key === STORAGE_KEY) {
    episodes = null;
    ensureLoaded();
    listeners.forEach((listener) => listener());
  }
}

export const podcastStore = {
  subscribe(listener: Listener): () => void {
    ensureLoaded();
    if (listeners.size === 0) window.addEventListener("storage", onStorage);
    listeners.add(listener);
    return () => {
      listeners.delete(listener);
      if (listeners.size === 0) window.removeEventListener("storage", onStorage);
    };
  },
  getSnapshot(): Podcast[] {
    ensureLoaded();
    return cached;
  },
  getServerSnapshot(): Podcast[] {
    return EMPTY;
  },
};

/** Newest first. */
export function sortPodcasts(list: Podcast[]): Podcast[] {
  return [...list].sort((a, b) => b.updatedAt - a.updatedAt);
}

export function getPodcast(id: string): Podcast | undefined {
  return podcastStore.getSnapshot().find((episode) => episode.id === id);
}

export function upsertPodcast(episode: Podcast): void {
  ensureLoaded();
  const current = podcastStore.getSnapshot();
  const index = current.findIndex((entry) => entry.id === episode.id);
  const next = index === -1 ? [episode, ...current] : current.map((entry) => (entry.id === episode.id ? episode : entry));
  write(next);
}

export function renamePodcast(id: string, title: string): void {
  ensureLoaded();
  write(
    podcastStore.getSnapshot().map((entry) =>
      entry.id === id ? { ...entry, title, updatedAt: Date.now() } : entry,
    ),
  );
}

export function deletePodcast(id: string): void {
  ensureLoaded();
  write(podcastStore.getSnapshot().filter((entry) => entry.id !== id));
}

/**
 * Where the listener got to. Written on pause/leave rather than per word, so
 * a long episode does not thrash localStorage.
 */
export function savePodcastProgress(id: string, progress: { section: number; word: number }): void {
  ensureLoaded();
  const current = podcastStore.getSnapshot();
  const episode = current.find((entry) => entry.id === id);
  if (!episode) return;
  const at = Date.now();
  const previous = episode.progress;
  /* First words of a section are the same place a retry would start: skip the
     write when nothing meaningfully moved. */
  if (previous && previous.section === progress.section && Math.abs(previous.word - progress.word) < 2) {
    return;
  }
  const next = current.map((entry) =>
    entry.id === id ? { ...entry, progress: { ...progress, at } } : entry,
  );
  /* updatedAt deliberately untouched: resuming must not reorder the library. */
  episodes = next;
  cached = next;
  try {
    window.localStorage.setItem(STORAGE_KEY, JSON.stringify(next));
  } catch {
    /* storage full — progress is a nicety, not worth a warning */
  }
}

/** Rough spoken length of the whole script, in minutes (150 words a minute). */
export function podcastMinutes(episode: Podcast): number {
  const words = episode.sections.reduce((total, section) => total + section.text.split(/\s+/).filter(Boolean).length, 0);
  return Math.max(1, Math.round(words / 150));
}

/** The episode's script as one string (used by tests and fallbacks). */
export function podcastScript(episode: Podcast): string {
  return episode.sections.map((section) => section.text).join("\n\n");
}