/**
 * 将时区偏移小时转换为 ±HHMM 格式
 * @param {number|string} offset 如 8, -4, "+8", "-04"
 * @returns {string} 如 "+0800", "-0400"
 */
const formatTimezoneOffset = (offset) => {
  const hours = Number(offset);
  if (Number.isNaN(hours)) {
    throw new Error('Invalid timezone offset');
  }

  const sign = hours >= 0 ? '+' : '-';
  const hh = String(Math.abs(hours)).padStart(2, '0');

  return `${sign}${hh}00`;
}


/**
 * 判断日期是否无效
 * @param {Date} date
 * @returns {boolean}
 */
const isInvalidDate = (date) => {
  return date instanceof Date && Number.isNaN(date.getTime());
}


/**
 * 获取指定时区当前日期或时间
 * @param {number} offset - 时区相对 UTC 的偏移（例如：-4 表示 GMT-4）
 * @param {number} timestamp - 时间戳（可选）
 * @param {boolean} [withTime=false] - 是否返回完整时间（默认只返回日期）
 * @returns {string} 格式化的日期或时间字符串
 */
const getDateInTimezone = (offset, timestamp, withTime=false) => {

  offset = Number(offset);
  if (Number.isNaN(offset)) {
    throw new Error('Invalid timezone offset');
  }

  if (typeof(timestamp) === 'undefined') {
    timestamp = Date.now();
  }
  else if (typeof(timestamp) === 'boolean') {
    withTime = timestamp;
    timestamp = Date.now();
  }
  else if (typeof(timestamp) === 'string') {
    const date = new Date(timestamp);
    if (isInvalidDate(date)) {
      throw new Error('Invalid timestamp');
    }
    timestamp = date.getTime();
  }
  else if (typeof(timestamp) !== 'number') {
    throw new Error('Invalid timestamp');
  }

  const nowUTC = new Date(timestamp);
  const targetTime = new Date(nowUTC.getTime() + offset * 60 * 60 * 1000);

  const year = targetTime.getUTCFullYear();
  const month = String(targetTime.getUTCMonth() + 1).padStart(2, '0');
  const day = String(targetTime.getUTCDate()).padStart(2, '0');

  if (!withTime) {
    return `${year}-${month}-${day}`;
  }

  const hours = String(targetTime.getUTCHours()).padStart(2, '0');
  const minutes = String(targetTime.getUTCMinutes()).padStart(2, '0');
  const seconds = String(targetTime.getUTCSeconds()).padStart(2, '0');

  return `${year}-${month}-${day}T${hours}:${minutes}:${seconds}${formatTimezoneOffset(offset)}`;
}

export default getDateInTimezone;