famous strftime (linux+python) format implementation in js (intl)

intl-strftime.js

export function IranLocale () {
  const weekdays = 'یک\u200Cشنبه_دوشنبه_سه\u200Cشنبه_چهارشنبه_پنج\u200Cشنبه_جمعه_شنبه'.split('_')
  const weekdaysAbbr = 'ی_د_س_چ_پ_ج_ش'.split('_')
  const monthNames = ('فروردین_اردیبهشت_خرداد_تیر_مرداد_شهریور_مهر_آبان_آذر_دی_بهمن_اسفند').split('_')
  const monthNamesAbbr = 'فرو_ارد_خرد_تیر_مرد_شهر_مهر_آبا_آذر_دی_بهم_اسف'.split('_')
  const intlDate = new Intl.DateTimeFormat('en-US', {
    hour12: false,
    calendar: 'persian',
    numberingSystem: 'arabext',
    year: 'numeric',
    month: 'numeric',
    day: 'numeric',
    hour: 'numeric',
    minute: 'numeric'
  })
  const intlNum = new Intl.NumberFormat('fa-IR', { useGrouping: false })
  const self = this

  function zeroPad (nNum, nPad) {
    return ('' + (Math.pow(10, nPad) + nNum)).slice(1)
  }

  this.formatToParts = function (date) {
    const parts = {}
    intlDate.formatToParts(date).forEach((v) => {
      parts[v.type] = isNaN(v.value) ? v.value : parseInt(v.value)
    })
    return parts
  }

  this.formatNumber = function (v) {
    return intlNum.format(v)
  }

  this.strftime = function (date, format) {
    // partial strftime
    const parts = self.formatToParts()
    const nYear = parts.year
    const nMonth = parts.month
    const nDate = parts.day
    const nDay = date.getDay()
    const isLeapYear = (nYear % 4 === 0 && nYear % 100 !== 0) || nYear % 400 === 0
    const aDayCount = [0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334]
    const xI = (parts.hour + 11) % 12 + 1
    const xJ = aDayCount[nMonth] + nDate + ((nMonth > 1 && isLeapYear()) ? 1 : 0)
    const matches = {
      // Weekday as locale’s abbreviated name.
      '%a': weekdaysAbbr[nDay],
      // Weekday as locale’s full name.
      '%A': weekdays[nDay],
      // Weekday as a decimal number, where 0 is Sunday and 6 is Saturday.
      '%w': '' + nDay,
      // Day of the month as a zero-padded decimal number.
      '%d': zeroPad(nDate, 2),
      // Day of the month as a decimal number. (Platform specific)
      '%-d': '' + nDate,
      // Month as locale’s abbreviated name.
      '%b': monthNamesAbbr[nMonth],
      // Month as locale’s full name.
      '%B': monthNames[nMonth],
      // Month as a zero-padded decimal number.
      '%m': zeroPad(nMonth, 2),
      // Month as a decimal number. (Platform specific)
      '%-m': '' + nMonth,
      // Year without century as a zero-padded decimal number.
      '%y': ('' + parts.year).slice(2),
      // Year with century as a decimal number.
      '%Y': parts.year,
      // Hour (24-hour clock) as a zero-padded decimal number.
      '%H': zeroPad(parts.hour, 2),
      // Hour (24-hour clock) as a decimal number. (Platform specific)
      '%-H': '' + parts.hour,
      // Hour (12-hour clock) as a zero-padded decimal number.
      '%I': zeroPad(xI, 2),
      // Hour (12-hour clock) as a decimal number. (Platform specific)
      '%-I': '' + xI,
      // Locale’s equivalent of either AM or PM.
      '%p': (parts.hour < 12) ? 'AM' : 'PM',
      '%P': (parts.hour < 12) ? 'am' : 'pm',
      // Minute as a zero-padded decimal number.
      '%M': zeroPad(date.getMinutes(), 2),
      // Minute as a decimal number. (Platform specific)
      '%-M': '' + date.getMinutes(),
      // Second as a zero-padded decimal number.
      '%S': zeroPad(date.getSeconds(), 2),
      // Second as a decimal number. (Platform specific)
      '%-S': '' + date.getSeconds(),

      // UTC offset in the form ±HHMM[SS[.ffffff]]
      // (empty string if the object is naive).
      '%z': date.toTimeString().replace(/.+GMT([+-]\d+).+/, '$1'),
      // Time zone name (empty string if the object is naive).
      '%Z': date.toTimeString().replace(/.+\((.+?)\)$/, '$1'),
      // Day of the year as a zero-padded decimal number.
      '%j': zeroPad(xJ, 3),
      // Day of the year as a decimal number. (Platform specific)
      '%-j': '' + xJ,
      // Week number of the year (Sunday as the first day of the week) as a
      // zero padded decimal number. All days in a new year preceding the
      // first Sunday are considered to be in week 0.
      '%U': zeroPad('' + (nDay || 7), 2),
      '%u': '' + (nDay || 7),
      // Locale’s appropriate date and time representation.
      '%c': date.toUTCString(),
      // Locale’s appropriate date representation.
      '%x': date.toLocaleDateString(),
      // Locale’s appropriate time representation.
      '%X': date.toLocaleTimeString(),
      // The number of seconds since the Epoch, 1970-01-01 00:00:00
      // +0000 (UTC). (TZ) (Calculated from mktime(tm).)
      '%s': Math.round(date.getTime() / 1000)

      // // The preferred date and time representation for the current
      // // locale.  (The specific format used in the current locale
      // //   can be obtained by calling nl_langinfo(3) with D_T_FMT as
      // //   an argument for the %c conversion specification, and with
      // //   ERA_D_T_FMT for the %Ec conversion specification.)  (In
      // //   the POSIX locale this is equivalent to %a %b %e %H:%M:%S
      // //   %Y.)
      // '%C': Math.floor(nYear / 100),
      // // Microsecond as a decimal number, zero-padded on the left.
      // '%f': '',
      // // Week number of the year (Monday as the first day of the week) as a
      // // decimal number. All days in a new year preceding the first Monday are
      // // considered to be in week 0.
      // '%W': '',
      // // Like %d, the day of the month as a decimal number, but a
      // // leading zero is replaced by a space. (SU) (Calculated from
      // //   tm_mday.)
      // '%e': nDate,
      // // Equivalent to %Y-%m-%d (the ISO 8601 date format). (C99)
      // '%F': date.toISOString().slice(0,10),
      // // The ISO 8601 week-based year (see NOTES) with century as a
      // // decimal number.  The 4-digit year corresponding to the ISO
      // // week number (see %V).  This has the same format and value
      // // as %Y, except that if the ISO week number belongs to the
      // // previous or next year, that year is used instead. (TZ)
      // // (Calculated from tm_year, tm_yday, and tm_wday.)
      // '%G': getThursday().getFullYear(),
      // // Like %G, but without century, that is, with a 2-digit year
      // // (00–99). (TZ) (Calculated from tm_year, tm_yday, and
      // //   tm_wday.)
      // '%g': ('' + getThursday().getFullYear()).slice(2),
      // // The hour as a decimal number using a 12-hour clock (range
      // // 01 to 12).  (Calculated from tm_hour.)
      // '%I': zeroPad((nHour+11)%12 + 1, 2),
      // // The hour (24-hour clock) as a decimal number (range 0 to
      // // 23); single digits are preceded by a blank.  (See also
      // // %H.)  (Calculated from tm_hour.)  (TZ)
      // '%k': '' + nHour,
      // // The hour (12-hour clock) as a decimal number (range 1 to
      // // 12); single digits are preceded by a blank.  (See also
      // //   %I.)  (Calculated from tm_hour.)  (TZ)
      // '%l': (nHour+11)%12 + 1,
      // // The ISO 8601 week number (see NOTES) of the current year
      // // as a decimal number, range 01 to 53, where week 1 is the
      // // first week that has at least 4 days in the new year.  See
      // // also %U and %W.  (Calculated from tm_year, tm_yday, and
      // // tm_wday.)  (SU)
      // '%V': (function() {
      //   var target = getThursday(),
      //     n1stThu = target.valueOf();
      //   target.setMonth(0, 1);
      //   var nJan1 = target.getDay();
      //   if (nJan1!==4) target.setMonth(0, 1 + ((4-nJan1)+7)%7);
      //   return zeroPad(1 + Math.ceil((n1stThu-target)/604800000), 2);
      // })(),
    }
    return format.replace(/%[a-z-]/gi, v => matches[v] || v)
  }
}