// 曲库索引：扫描音乐目录，按「歌名 + 歌手文件夹 / 专辑文件夹」判断某首歌是否已在曲库中，
// 用于给不是通过本服务下载的文件也打上标记。
import fs from 'node:fs';
import path from 'node:path';
import { config } from './config.ts';
import { sanitize, sanitizePathSegment } from './core/util.ts';

const AUDIO_EXTS = new Set(['.mp3', '.flac', '.m4a', '.ogg', '.wav', '.aac', '.ape', '.opus']);
const REBUILD_INTERVAL = 30 * 60 * 1000;

interface Entry {
  artists: Set<string>;
  album: string;
  file: string; // 相对音乐目录
}

/** 比较用的规范化：全角转半角、小写、去掉空白与引号类符号 */
export function norm(s: string): string {
  return s
    .normalize('NFKC')
    .toLowerCase()
    .replace(/[\s'"’‘“”`·・]/g, '');
}

let index = new Map<string, Entry[]>();
let building: Promise<void> | null = null;
let builtAt = 0;
let fileCount = 0;

function addFile(map: Map<string, Entry[]>, rel: string) {
  const parts = rel.split('/');
  const fileName = parts.at(-1)!;
  const base = fileName.slice(0, fileName.length - path.extname(fileName).length);
  const artists = new Set<string>();
  let title = base.replace(/^\d+[.\s_-]+\s*/, '');

  // 「歌手 - 歌名」（旧版扁平格式）
  const dash = base.match(/^(.+?)\s+-\s+(.+)$/);
  if (dash && !/^\d+[.\s]/.test(base)) {
    title = dash[2]!;
    for (const a of dash[1]!.split(/\s*[/_&,，、]\s*/)) if (a) artists.add(norm(a));
  }
  // 「歌手/专辑/NN. 歌名」：第一层目录是歌手（专辑艺人）
  if (parts.length >= 2) artists.add(norm(parts[0]!));
  const album = parts.length >= 3 ? norm(parts.at(-2)!) : '';

  const key = norm(title);
  if (!key) return;
  const list = map.get(key) ?? [];
  list.push({ artists, album, file: rel });
  map.set(key, list);
}

async function walk(dir: string, rel: string, map: Map<string, Entry[]>) {
  const entries = await fs.promises.readdir(dir, { withFileTypes: true }).catch(() => []);
  for (const e of entries) {
    if (e.name.startsWith('.') || e.name.startsWith('@')) continue;
    const childRel = rel ? `${rel}/${e.name}` : e.name;
    if (e.isDirectory()) await walk(path.join(dir, e.name), childRel, map);
    else if (AUDIO_EXTS.has(path.extname(e.name).toLowerCase())) {
      addFile(map, childRel);
      fileCount++;
    }
  }
}

export function rebuildLibraryIndex(): Promise<void> {
  building ??= (async () => {
    const started = Date.now();
    const map = new Map<string, Entry[]>();
    fileCount = 0;
    await walk(config.musicDir, '', map);
    index = map;
    builtAt = Date.now();
    console.log(`📚 曲库索引：${fileCount} 个音频文件，用时 ${Date.now() - started} ms`);
  })().finally(() => (building = null));
  return building;
}

/** 下载完成后增量加入，不必等下次重建 */
export function addToLibraryIndex(relFile: string) {
  addFile(index, relFile.split(path.sep).join('/'));
}

export function startLibraryIndex() {
  void rebuildLibraryIndex();
  setInterval(() => void rebuildLibraryIndex(), REBUILD_INTERVAL).unref();
}

export function libraryIndexInfo() {
  return { files: fileCount, builtAt: builtAt ? new Date(builtAt).toISOString() : null, building: !!building };
}

/**
 * 在曲库中查找同名歌曲：歌名一致，且歌手文件夹与任一歌手一致或专辑文件夹与专辑一致。
 * 返回匹配到的文件（相对路径），找不到返回 undefined。
 */
export function findInLibrary(track: { name: string; artists: string; album?: string }): string | undefined {
  // 下载时文件名经过 sanitize，这里同样处理，"A/B" 才能对上 "A_B"
  const candidates = index.get(norm(sanitize(track.name)));
  if (!candidates) return undefined;
  const artists = track.artists
    .split(/\s*\/\s*/)
    .filter(Boolean)
    .map((a) => norm(sanitizePathSegment(a, a)));
  const album = track.album ? norm(sanitizePathSegment(track.album, track.album)) : '';
  return candidates.find((c) => artists.some((a) => c.artists.has(a)) || (album && c.album === album))?.file;
}