import NetInfo, { type NetInfoState } from '@react-native-community/netinfo';
import { unwrap, type AuthSession, type Track } from '@pipu/core';
import * as FileSystem from 'expo-file-system';
import * as SecureStore from 'expo-secure-store';

import { qualityPrefs } from '../lib/prefs';
import { shortHash } from '../lib/storage';
import { getDb } from './db';

export type DownloadStatus = 'queued' | 'downloading' | 'done' | 'error';

export interface DownloadItem {
  track: Track;
  status: DownloadStatus;
  progress: number;
  bytes: number;
  addedAt: number;
}

export interface DownloadsState {
  items: ReadonlyMap<string, DownloadItem>;
  wifiOnly: boolean;
  autoLikes: boolean;
  /** Сеть разрешает загрузку прямо сейчас (с учётом «только Wi-Fi»). */
  allowed: boolean;
}

const PARALLEL = 2;
const WIFI_KEY = 'pipu.dl.wifi';
const AUTO_LIKES_KEY = 'pipu.dl.autolikes';

/**
 * Загрузки для офлайна: файлы — в documentDirectory/offline/<owner>/, метаданные (DTO трека) — в SQLite.
 * Не более двух загрузок параллельно; по умолчанию только по Wi-Fi; прерванные продолжаются при запуске.
 */
class Downloads {
  private session: AuthSession | null = null;
  private server = '';
  private owner = '';
  private active = new Map<string, FileSystem.DownloadResumable | null>();
  private net: NetInfoState | null = null;
  private unsubscribeNet: (() => void) | null = null;
  private listeners = new Set<() => void>();
  private current: DownloadsState = { items: new Map(), wifiOnly: true, autoLikes: false, allowed: false };

  get state(): DownloadsState {
    return this.current;
  }

  subscribe = (fn: () => void) => {
    this.listeners.add(fn);
    return () => this.listeners.delete(fn);
  };

  private set(patch: Partial<DownloadsState>) {
    this.current = { ...this.current, ...patch };
    for (const fn of this.listeners) fn();
  }

  private setItem(id: string, patch: Partial<DownloadItem> | null) {
    const items = new Map(this.current.items);
    if (patch === null) items.delete(id);
    else {
      const prev = items.get(id);
      if (!prev && !patch.track) return;
      items.set(id, { ...(prev as DownloadItem), ...patch });
    }
    this.set({ items });
  }

  private get dir() {
    return `${FileSystem.documentDirectory}offline/${this.owner}/`;
  }

  private file(trackId: string) {
    return `${this.dir}${trackId}.opus`;
  }

  private cover(albumId: string) {
    return `${this.dir}covers/${albumId}.webp`;
  }

  /** Привязка к пользователю: загружает список скачанного и продолжает незавершённые загрузки. */
  async attach(session: AuthSession | null, server: string, userId: string | null) {
    const owner = session && userId ? shortHash(`${server}|${userId}`) : '';
    if (owner === this.owner && session === this.session) return;
    for (const d of this.active.values()) void d?.pauseAsync().catch(() => undefined);
    this.active.clear();
    this.session = session;
    this.server = server;
    this.owner = owner;
    if (!owner) {
      this.set({ items: new Map() });
      return;
    }
    const [wifi, autoLikes] = await Promise.all([SecureStore.getItemAsync(WIFI_KEY), SecureStore.getItemAsync(AUTO_LIKES_KEY)]);
    await FileSystem.makeDirectoryAsync(`${this.dir}covers/`, { intermediates: true }).catch(() => undefined);
    const db = await getDb();
    await db.runAsync(`UPDATE downloads SET status = 'queued' WHERE owner = ? AND status = 'downloading'`, owner);
    const rows = await db.getAllAsync<{ track_id: string; track: string; status: DownloadStatus; bytes: number; added_at: number }>(
      'SELECT track_id, track, status, bytes, added_at FROM downloads WHERE owner = ? ORDER BY added_at',
      owner,
    );
    const items = new Map<string, DownloadItem>();
    for (const r of rows) {
      items.set(r.track_id, { track: JSON.parse(r.track) as Track, status: r.status, progress: r.status === 'done' ? 1 : 0, bytes: r.bytes, addedAt: r.added_at });
    }
    this.set({ items, wifiOnly: wifi !== '0', autoLikes: autoLikes === '1' });

    this.unsubscribeNet ??= NetInfo.addEventListener((st) => {
      this.net = st;
      this.set({ allowed: this.networkAllowed() });
      this.pump();
    });
    this.net = await NetInfo.fetch();
    this.set({ allowed: this.networkAllowed() });
    this.pump();
  }

  private networkAllowed(): boolean {
    if (!this.net?.isConnected) return false;
    return !this.current.wifiOnly || this.net.type === 'wifi' || this.net.type === 'ethernet';
  }

  async setWifiOnly(v: boolean) {
    await SecureStore.setItemAsync(WIFI_KEY, v ? '1' : '0');
    this.set({ wifiOnly: v });
    this.set({ allowed: this.networkAllowed() });
    this.pump();
  }

  async setAutoLikes(v: boolean) {
    await SecureStore.setItemAsync(AUTO_LIKES_KEY, v ? '1' : '0');
    this.set({ autoLikes: v });
  }

  isDownloaded(trackId: string): boolean {
    return this.current.items.get(trackId)?.status === 'done';
  }

  /** Локальный файл трека, если он скачан. */
  localTrack(trackId: string): string | undefined {
    return this.isDownloaded(trackId) ? this.file(trackId) : undefined;
  }

  localCover(track: Track): string | undefined {
    return this.isDownloaded(track.id) && track.album.cover_url ? this.cover(track.album.id) : undefined;
  }

  /** Обложка альбома на устройстве, если из него что-то скачано. */
  localAlbumCover(albumId: string): string | undefined {
    for (const it of this.current.items.values()) {
      if (it.status === 'done' && it.track.album.id === albumId && it.track.album.cover_url) return this.cover(albumId);
    }
    return undefined;
  }

  /** Скачанные треки в порядке добавления. */
  downloaded(): Track[] {
    return [...this.current.items.values()].filter((i) => i.status === 'done').map((i) => i.track);
  }

  async enqueue(tracks: Track[]) {
    if (!this.owner) return;
    const db = await getDb();
    const now = Date.now();
    for (const [n, t] of tracks.entries()) {
      if (!t.available || this.current.items.has(t.id)) continue;
      const addedAt = now + n;
      await db.runAsync(
        `INSERT OR IGNORE INTO downloads (owner, track_id, track, status, added_at) VALUES (?, ?, ?, 'queued', ?)`,
        this.owner,
        t.id,
        JSON.stringify(t),
        addedAt,
      );
      this.setItem(t.id, { track: t, status: 'queued', progress: 0, bytes: 0, addedAt });
    }
    this.pump();
  }

  async remove(trackIds: string[]) {
    const db = await getDb();
    for (const id of trackIds) {
      const d = this.active.get(id);
      this.active.delete(id);
      await d?.pauseAsync().catch(() => undefined);
      await FileSystem.deleteAsync(this.file(id), { idempotent: true });
      await FileSystem.deleteAsync(`${this.file(id)}.part`, { idempotent: true });
      await db.runAsync('DELETE FROM downloads WHERE owner = ? AND track_id = ?', this.owner, id);
      this.setItem(id, null);
    }
    this.pump();
  }

  /** Реакция в сохранённом DTO: офлайн-волна и списки скачанного видят её без сети. */
  async setReaction(trackId: string, reaction: Track['reaction']) {
    const it = this.current.items.get(trackId);
    if (!it || it.track.reaction === reaction) return;
    const track = { ...it.track, reaction };
    this.setItem(trackId, { track });
    const db = await getDb();
    await db.runAsync('UPDATE downloads SET track = ? WHERE owner = ? AND track_id = ?', JSON.stringify(track), this.owner, trackId);
  }

  /** Повторить загрузки с ошибкой. */
  async retry() {
    const db = await getDb();
    await db.runAsync(`UPDATE downloads SET status = 'queued' WHERE owner = ? AND status = 'error'`, this.owner);
    for (const [id, it] of this.current.items) if (it.status === 'error') this.setItem(id, { status: 'queued', progress: 0 });
    this.pump();
  }

  /** Занято на устройстве и свободно в телефоне (байты). */
  async usage(): Promise<{ used: number; free: number }> {
    let used = 0;
    for (const it of this.current.items.values()) used += it.bytes;
    const free = await FileSystem.getFreeDiskStorageAsync().catch(() => 0);
    return { used, free };
  }

  private pump() {
    if (!this.owner || !this.current.allowed) return;
    for (const [id, it] of this.current.items) {
      if (this.active.size >= PARALLEL) return;
      if (it.status !== 'queued' || this.active.has(id)) continue;
      this.active.set(id, null);
      void this.run(id).finally(() => {
        this.active.delete(id);
        this.pump();
      });
    }
  }

  private async run(id: string) {
    const session = this.session;
    const owner = this.owner;
    if (!session) return;
    const db = await getDb();
    const status = async (s: DownloadStatus, patch: Partial<DownloadItem> = {}, track?: Track) => {
      if (this.owner !== owner) return;
      await db.runAsync(
        'UPDATE downloads SET status = ?, bytes = ?, track = COALESCE(?, track) WHERE owner = ? AND track_id = ?',
        s,
        patch.bytes ?? 0,
        track ? JSON.stringify(track) : null,
        owner,
        id,
      );
      this.setItem(id, { status: s, ...patch, ...(track ? { track } : {}) });
    };
    try {
      await status('downloading', { progress: 0 });
      // Подписанные ссылки живут 12 ч — перед загрузкой берём свежий DTO.
      const res = unwrap(await session.client.POST('/api/v1/tracks/batch', { body: { ids: [id] } }));
      const track = res.items[0];
      if (!track?.available || !track.stream_url) {
        await status('error');
        return;
      }
      const part = `${this.file(id)}.part`;
      const q = (await qualityPrefs.load()).download;
      const dl = FileSystem.createDownloadResumable(`${this.abs(track.stream_url)}&q=${q}`, part, {}, (p) => {
        if (p.totalBytesExpectedToWrite > 0) this.setItem(id, { progress: p.totalBytesWritten / p.totalBytesExpectedToWrite });
      });
      this.active.set(id, dl);
      const out = await dl.downloadAsync();
      if (this.active.get(id) !== dl) return; // отменено (удалили или сменился пользователь)
      if (!out || out.status !== 200) throw new Error(`status ${out?.status}`);
      await FileSystem.moveAsync({ from: part, to: this.file(id) });

      if (track.album.cover_url) {
        const cover = this.cover(track.album.id);
        const info = await FileSystem.getInfoAsync(cover);
        if (!info.exists) await FileSystem.downloadAsync(`${this.abs(track.album.cover_url)}&size=300`, cover).catch(() => undefined);
      }
      const info = await FileSystem.getInfoAsync(this.file(id));
      await status('done', { progress: 1, bytes: info.exists ? info.size : 0 }, track);
    } catch {
      await status('error', { progress: 0 });
    }
  }

  private abs(path: string) {
    return /^https?:/.test(path) ? path : this.server + path;
  }
}

export const downloads = new Downloads();