module EtOrbi

  def self.unalias(name)

    return name unless (name.match(/./) rescue nil)

    ZONE_ALIASES[name.sub(/ Daylight /, ' Standard ')] ||
    unzz(name) ||
    name
  end

  def self.unzz(name)

    m = name.match(/\A([A-Z]{3,4})([+-])(\d{1,2}):?(\d{2})?\z/)
    return nil unless m

    abbs = [ m[1] ]; a = m[1]
    abbs << "#{a}T" if a.size < 4

    off = (m[2] == '+' ? 1 : -1) * (m[3].to_i * 3600 + (m[4] || '0').to_i * 60)

    t = Time.now
    twin = Time.utc(t.year, 1, 1) # winter
    tsum = Time.utc(t.year, 7, 1) # summer

    (@tz_all ||= ::TZInfo::Timezone.all)
      .each { |tz|
        abbs.each { |abb|
          per = tz.period_for_utc(twin)
          return tz.name \
            if per.abbreviation.to_s == abb && per.utc_total_offset == off
          per = tz.period_for_utc(tsum)
          return tz.name \
            if per.abbreviation.to_s == abb && per.utc_total_offset == off } }

    nil
  end

  ZONE_ALIASES = {
    'Coordinated Universal Time' => 'UTC',
    'Afghanistan Standard Time' => 'Asia/Kabul',
    'FLE Standard Time' => 'Europe/Helsinki',
    'Central Europe Standard Time' => 'Europe/Prague',
    'UTC-11' => 'Etc/GMT+11',
    'W. Europe Standard Time' => 'Europe/Rome',
    'W. Central Africa Standard Time' => 'Africa/Lagos',
    'SA Western Standard Time' => 'America/La_Paz',
    'Pacific SA Standard Time' => 'America/Santiago',
    'Argentina Standard Time' => 'America/Argentina/Buenos_Aires',
    'Caucasus Standard Time' => 'Asia/Yerevan',
    'AUS Eastern Standard Time' => 'Australia/Sydney',
    'Azerbaijan Standard Time' => 'Asia/Baku',
    'Eastern Standard Time' => 'America/New_York',
    'Arab Standard Time' => 'Asia/Riyadh',
    'Bangladesh Standard Time' => 'Asia/Dhaka',
    'Belarus Standard Time' => 'Europe/Minsk',
    'Romance Standard Time' => 'Europe/Paris',
    'Central America Standard Time' => 'America/Belize',
    'Atlantic Standard Time' => 'Atlantic/Bermuda',
    'Venezuela Standard Time' => 'America/Caracas',
    'Central European Standard Time' => 'Europe/Warsaw',
    'South Africa Standard Time' => 'Africa/Johannesburg',
    #'UTC' => 'Etc/UTC', # 'UTC' is good as is
    'E. South America Standard Time' => 'America/Sao_Paulo',
    'Central Asia Standard Time' => 'Asia/Almaty',
    'Singapore Standard Time' => 'Asia/Singapore',
    'Greenwich Standard Time' => 'Africa/Monrovia',
    'Cape Verde Standard Time' => 'Atlantic/Cape_Verde',
    'SE Asia Standard Time' => 'Asia/Bangkok',
    'SA Pacific Standard Time' => 'America/Bogota',
    'China Standard Time' => 'Asia/Shanghai',
    'Myanmar Standard Time' => 'Asia/Yangon',
    'E. Africa Standard Time' => 'Africa/Nairobi',
    'Hawaiian Standard Time' => 'Pacific/Honololu',
    'E. Europe Standard Time' => 'Europe/Nicosia',
    'Tokyo Standard Time' => 'Asia/Tokyo',
    'Egypt Standard Time' => 'Africa/Cairo',
    'SA Eastern Standard Time' => 'America/Cayenne',
    'GMT Standard Time' => 'Europe/London',
    'Fiji Standard Time' => 'Pacific/Fiji',
    'West Asia Standard Time' => 'Asia/Tashkent',
    'Georgian Standard Time' => 'Asia/Tbilisi',
    'GTB Standard Time' => 'Europe/Athens',
    'Greenland Standard Time' => 'America/Godthab',
    'West Pacific Standard Time' => 'Pacific/Guam',
    'Mauritius Standard Time' => 'Indian/Mauritius',
    'India Standard Time' => 'Asia/Kolkata',
    'Iran Standard Time' => 'Asia/Tehran',
    'Arabic Standard Time' => 'Asia/Baghdad',
    'Israel Standard Time' => 'Asia/Jerusalem',
    'Jordan Standard Time' => 'Asia/Amman',
    'UTC+12' => 'Etc/GMT-12',
    'Korea Standard Time' => 'Asia/Seoul',
    'Middle East Standard Time' => 'Asia/Beirut',
    'Central Standard Time (Mexico)' => 'America/Mexico_City',
    'Ulaanbaatar Standard Time' => 'Asia/Ulaanbaatar',
    'Morocco Standard Time' => 'Africa/Casablanca',
    'Namibia Standard Time' => 'Africa/Windhoek',
    'Nepal Standard Time' => 'Asia/Kathmandu',
    'Central Pacific Standard Time' => 'Etc/GMT-11',
    'New Zealand Standard Time' => 'Pacific/Auckland',
    'Arabian Standard Time' => 'Asia/Dubai',
    'Pakistan Standard Time' => 'Asia/Karachi',
    'Paraguay Standard Time' => 'America/Asuncion',
    'Pacific Standard Time' => 'America/Los_Angeles',
    'Russian Standard Time' => 'Europe/Moscow',
    'Samoa Standard Time' => 'Pacific/Pago_Pago',
    'UTC-02' => 'Etc/GMT+2',
    'Sri Lanka Standard Time' => 'Asia/Kolkata',
    'Syria Standard Time' => 'Asia/Damascus',
    'Taipei Standard Time' => 'Asia/Taipei',
    'Tonga Standard Time' => 'Pacific/Tongatapu',
    'Turkey Standard Time' => 'Asia/Istanbul',
    'Montevideo Standard Time' => 'America/Montevideo' }
end