module.exports = function idate(format, timestamp) {
  //  discuss at: https://locutus.io/php/idate/
  // original by: Brett Zamir (https://brett-zamir.me)
  // original by: date
  // original by: gettimeofday
  //    input by: Alex
  // bugfixed by: Brett Zamir (https://brett-zamir.me)
  // improved by: Theriault (https://github.com/Theriault)
  //   example 1: idate('y', 1255633200)
  //   returns 1: 9

  if (format === undefined) {
    throw new Error('idate() expects at least 1 parameter, 0 given')
  }
  if (!format.length || format.length > 1) {
    throw new Error('idate format is one char')
  }

  // @todo: Need to allow date_default_timezone_set() (check for $locutus.default_timezone and use)
  const _date =
    typeof timestamp === 'undefined'
      ? new Date()
      : timestamp instanceof Date
        ? new Date(timestamp)
        : new Date(timestamp * 1000)
  let a

  switch (format) {
    case 'B':
      return (
        Math.floor((_date.getUTCHours() * 36e2 + _date.getUTCMinutes() * 60 + _date.getUTCSeconds() + 36e2) / 86.4) %
        1e3
      )
    case 'd':
      return _date.getDate()
    case 'h':
      return _date.getHours() % 12 || 12
    case 'H':
      return _date.getHours()
    case 'i':
      return _date.getMinutes()
    case 'I':
      // capital 'i'
      // Logic original by getimeofday().
      // Compares Jan 1 minus Jan 1 UTC to Jul 1 minus Jul 1 UTC.
      // If they are not equal, then DST is observed.
      a = _date.getFullYear()
      return 0 + (new Date(a, 0) - Date.UTC(a, 0) !== new Date(a, 6) - Date.UTC(a, 6))
    case 'L':
      a = _date.getFullYear()
      return !(a & 3) && (a % 1e2 || !(a % 4e2)) ? 1 : 0
    case 'm':
      return _date.getMonth() + 1
    case 's':
      return _date.getSeconds()
    case 't':
      return new Date(_date.getFullYear(), _date.getMonth() + 1, 0).getDate()
    case 'U':
      return Math.round(_date.getTime() / 1000)
    case 'w':
      return _date.getDay()
    case 'W':
      a = new Date(_date.getFullYear(), _date.getMonth(), _date.getDate() - (_date.getDay() || 7) + 3)
      return 1 + Math.round((a - new Date(a.getFullYear(), 0, 4)) / 864e5 / 7)
    case 'y':
      return parseInt((_date.getFullYear() + '').slice(2), 10) // This function returns an integer, unlike _date()
    case 'Y':
      return _date.getFullYear()
    case 'z':
      return Math.floor((_date - new Date(_date.getFullYear(), 0, 1)) / 864e5)
    case 'Z':
      return -_date.getTimezoneOffset() * 60
    default:
      throw new Error('Unrecognized _date format token')
  }
}