'use strict';

var Chinese = require('./Chinese.cjs');

/**
 * @copyright 2016 commenthol
 * @license MIT
 */

/**
 * @see http://law.e-gov.go.jp/htmldata/M19/M19CO051.html
 */
const UTC_DATES = [
  {
    date: new Date('1888-02-11T15:00:00.000Z'), // 1888-02-12T00:00:00+0900
    shift: 9 / 24
  } // +9:00:00h (135° East) Japanese standard meridian
];

/**
 * Note: I could not find details about the epoch(s) for the year zero of the
 * Japanese calendar dating before 1873. Therefore this calendar uses (wrongly)
 * the Chinese epoch.
 *
 * According to <https://en.wikipedia.org/wiki/History_of_Japan> the eras are:
 *
 * Yayoi  300 BC – 250 AD
 * Kofun  250 – 538
 * Asuka  538 – 710
 * Nara   710 – 794
 * Heian  794 – 1185
 * Kamakura   1185 – 1333
 * Kenmu Restoration  1333 – 1336
 * Muromachi 1336 – 1573
 * Azuchi–Momoyama 1568 – 1603
 * Edo  1603 – 1868
 * Meiji  1868 – 1912
 * Taishō 1912 – 1926
 * Shōwa  1926 – 1989
 * Heisei 1989 – present
 *
 * Unfortunately the linking from era to calendar era (especially to the Chinese
 * pre 1873 one) is unknown to me.
 */

class CalendarJapanese extends Chinese {
  /**
   * timeshift to UTC
   *
   * @param {CalendarGregorian} gcal - gregorian calendar date
   * @return {Number} timeshift in fraction of day
   */
  timeshiftUTC (gcal) {
    const date = gcal.toDate();
    for (const i in UTC_DATES) {
      if (date >= UTC_DATES[i].date) {
        return UTC_DATES[i].shift
      }
    }
    return 4193 / 450 / 24 // +9:19:04h (139°46'E)
  }
}

module.exports = CalendarJapanese;