import { createHash, randomBytes } from 'node:crypto';

const BOT_USERNAME_PATTERN = /^[a-z][a-z0-9_]{4,31}$/;

export function normalizeBotUsername(username: string) {
  return username.trim().toLowerCase().replace(/[^a-z0-9_]/g, '');
}

export function assertValidBotUsername(username: string) {
  const normalized = normalizeBotUsername(username);
  if (!BOT_USERNAME_PATTERN.test(normalized)) {
    throw new Error('INVALID_BOT_USERNAME');
  }
  if (normalized.endsWith('_bot')) {
    throw new Error('INVALID_BOT_USERNAME');
  }
  return `${normalized}_bot`;
}

export function generateTelegramStyleBotToken() {
  const botId = randomBytes(4).readUInt32BE(0) % 900_000_000 + 100_000_000;
  const secret = randomBytes(32)
    .toString('base64')
    .replace(/\+/g, '-')
    .replace(/\//g, '_')
    .replace(/=+$/g, '');
  const token = `${botId}:${secret}`;
  return { token, tokenPrefix: `${botId}:${secret.slice(0, 6)}…` };
}

export function hashBotToken(token: string) {
  return createHash('sha256').update(token.trim()).digest('hex');
}

export function deriveTelegramChatId(source: string) {
  const hash = createHash('sha256').update(source).digest();
  const value = hash.readBigInt64BE(0);
  const positive = value < 0n ? -value : value;
  return positive % 9_000_000_000_000n + 1_000_000_000_000n;
}

export function deriveTelegramUserId(userId: string) {
  return Number(deriveTelegramChatId(`user:${userId}`));
}