import { format } from 'date-fns';
import { toZonedTime } from 'date-fns-tz';

export const TAIPEI_TIME_ZONE = 'Asia/Taipei';

const defaultFormatter = 'yyyy/MM/dd HH:mm:ss';

function assertIsoDate(utcDateString: string): Date {
  const sourceDate = new Date(utcDateString);
  if (Number.isNaN(sourceDate.getTime())) {
    throw new Error(`非法的 UTC 時間戳：${utcDateString}`);
  }
  return sourceDate;
}

export function toTaipeiDate(utcDateString: string): Date {
  const source = assertIsoDate(utcDateString);
  return toZonedTime(source, TAIPEI_TIME_ZONE);
}

export function formatToTaipeiTime(utcDateString: string, formatString = defaultFormatter): string {
  const taipeiDate = toTaipeiDate(utcDateString);
  return format(taipeiDate, formatString);
}

export function isTodayTaipei(utcDateString: string, now = new Date()): boolean {
  const target = toTaipeiDate(utcDateString);
  const local = toZonedTime(now, TAIPEI_TIME_ZONE);
  return (
    target.getFullYear() === local.getFullYear()
    && target.getMonth() === local.getMonth()
    && target.getDate() === local.getDate()
  );
}