import { localDateKey, normalizeTimezone } from '../../schedule-time.mjs';

export function hashString(input) {
  let hash = 2166136261;
  for (let i = 0; i < input.length; i += 1) {
    hash ^= input.charCodeAt(i);
    hash = Math.imul(hash, 16777619);
  }
  return Math.abs(hash);
}

/** 按用户 + 本地日期 + salt 从话术库稳定选取一条。 */
export function pickDailyLibraryEntry({
  userId = '',
  timezone = 'Asia/Shanghai',
  now = Date.now(),
  library = [],
  salt = 'daily',
} = {}) {
  const pool = Array.isArray(library) && library.length ? library : [];
  if (!pool.length) return '';
  const tz = normalizeTimezone(timezone);
  const dateKey = localDateKey(now, tz);
  const seed = hashString(`${String(userId)}:${dateKey}:${salt}`);
  return pool[seed % pool.length];
}