import { createHash } from "node:crypto";

/** "1,204" / "532 / 3" → 1204 / 532;非数字返回 null(未知 ≠ 0)。 */
export function parseCount(text: string | null | undefined): number | null {
  if (text == null) return null;
  const head = String(text).split("/")[0]!.replace(/[,\s]/g, "");
  return /^\d+$/.test(head) ? Number(head) : null;
}

/** 站点本地时间 "YYYY-MM-DD HH:mm:ss" + 站点时区偏移("+08:00")→ UTC ISO。 */
export function parseSiteTime(text: string | null | undefined, tzOffset: string): string | null {
  if (!text) return null;
  const m = /(\d{4})-(\d{2})-(\d{2})[ T](\d{2}):(\d{2})(?::(\d{2}))?/.exec(text);
  if (!m) return null;
  const iso = `${m[1]}-${m[2]}-${m[3]}T${m[4]}:${m[5]}:${m[6] ?? "00"}${tzOffset}`;
  const t = Date.parse(iso);
  return Number.isNaN(t) ? null : new Date(t).toISOString();
}

export function extractImdbId(text: string | null | undefined): string | undefined {
  return text ? (/\b(tt\d{6,10})\b/.exec(text)?.[1] ?? undefined) : undefined;
}

export function extractDoubanId(text: string | null | undefined): string | undefined {
  return text ? (/douban\.com\/subject\/(\d+)/.exec(text)?.[1] ?? undefined) : undefined;
}

// ---- .torrent 校验与 infohash(最小 bencode 扫描,只为定位 info 字典字节范围) ----

function skipValue(buf: Uint8Array, pos: number, depth = 0): number {
  if (depth > 64) throw new Error("bencode 嵌套过深");
  const c = buf[pos];
  if (c === undefined) throw new Error("bencode 意外结束");
  if (c === 0x69 /* i */) {
    const end = buf.indexOf(0x65, pos);
    if (end < 0) throw new Error("bencode 整数未结束");
    return end + 1;
  }
  if (c === 0x6c /* l */ || c === 0x64 /* d */) {
    let p = pos + 1;
    while (buf[p] !== 0x65) {
      if (p >= buf.length) throw new Error("bencode 容器未结束");
      p = skipValue(buf, p, depth + 1);
    }
    return p + 1;
  }
  if (c >= 0x30 && c <= 0x39) {
    const colon = buf.indexOf(0x3a, pos);
    if (colon < 0) throw new Error("bencode 字符串缺少冒号");
    const len = Number(new TextDecoder().decode(buf.subarray(pos, colon)));
    if (!Number.isInteger(len) || len < 0 || colon + 1 + len > buf.length) throw new Error("bencode 字符串越界");
    return colon + 1 + len;
  }
  throw new Error("bencode 非法前缀");
}

function readString(buf: Uint8Array, pos: number): { value: Uint8Array; next: number } {
  const colon = buf.indexOf(0x3a, pos);
  const len = Number(new TextDecoder().decode(buf.subarray(pos, colon)));
  return { value: buf.subarray(colon + 1, colon + 1 + len), next: colon + 1 + len };
}

export interface TorrentInspection {
  infoHash: string;
  name: string | null;
}

/** 校验字节是 .torrent(顶层字典且含 info),返回 v1 infohash(info 字典原始字节的 sha1)。非 torrent 返回 null。 */
export function inspectTorrent(bytes: Uint8Array): TorrentInspection | null {
  try {
    if (bytes[0] !== 0x64) return null;
    let p = 1;
    while (bytes[p] !== 0x65) {
      const key = readString(bytes, p);
      const keyText = new TextDecoder().decode(key.value);
      const end = skipValue(bytes, key.next);
      if (keyText === "info") {
        const info = bytes.subarray(key.next, end);
        const infoHash = createHash("sha1").update(info).digest("hex");
        let name: string | null = null;
        // info 字典内找 name
        let q = 1;
        while (info[q] !== 0x65 && q < info.length) {
          const k = readString(info, q);
          const vEnd = skipValue(info, k.next);
          if (new TextDecoder().decode(k.value) === "name" && info[k.next]! >= 0x30 && info[k.next]! <= 0x39) {
            name = new TextDecoder().decode(readString(info, k.next).value);
          }
          q = vEnd;
        }
        return { infoHash, name };
      }
      p = end;
      if (p >= bytes.length) return null;
    }
    return null;
  } catch {
    return null;
  }
}