/**
 * ULID 生成与解析（Crockford Base32，26 字符 = 48bit 时间 + 80bit 随机）
 * 主键统一由应用侧生成 char(26) ULID（工程规范 05）。
 */
import { ULID_LENGTH } from './constants.js';

const ENCODING = '0123456789ABCDEFGHJKMNPQRSTVWXYZ';
const ENCODING_LEN = 32;

export const ULID_PATTERN = /^[0-9A-HJKMNP-TV-Z]{26}$/;

function randomBytes(length: number): Uint8Array {
  const bytes = new Uint8Array(length);
  globalThis.crypto.getRandomValues(bytes);
  return bytes;
}

/** 生成 ULID；同一毫秒内依靠 80bit 随机数避免碰撞 */
export function ulid(timestamp: number = Date.now()): string {
  if (!Number.isInteger(timestamp) || timestamp < 0 || timestamp > 0xffffffffffff) {
    throw new RangeError('ULID 时间戳必须是 48bit 非负整数');
  }
  let time = timestamp;
  const timeChars: string[] = new Array<string>(10);
  for (let i = 9; i >= 0; i -= 1) {
    timeChars[i] = ENCODING[time % ENCODING_LEN] ?? '0';
    time = Math.floor(time / ENCODING_LEN);
  }
  const randomChars = Array.from(randomBytes(16), (byte) => ENCODING[byte & 31] ?? '0');
  return `${timeChars.join('')}${randomChars.join('')}`;
}

export function isUlid(value: string): boolean {
  return value.length === ULID_LENGTH && ULID_PATTERN.test(value);
}

/** 解析 ULID 前 10 位得到毫秒时间戳 */
export function ulidToTimestamp(id: string): number {
  if (!isUlid(id)) {
    throw new TypeError(`不是合法 ULID：${id}`);
  }
  let timestamp = 0;
  for (let i = 0; i < 10; i += 1) {
    const char = id[i] ?? '';
    const value = ENCODING.indexOf(char);
    if (value < 0) {
      throw new TypeError(`ULID 含非法字符：${char}`);
    }
    timestamp = timestamp * ENCODING_LEN + value;
  }
  return timestamp;
}

export function ulidToDate(id: string): Date {
  return new Date(ulidToTimestamp(id));
}