class Fluent::Timezone

def self.formatter(timezone, format = nil)
  if timezone.nil?
    return nil
  end
  # [+-]HH:MM, [+-]HHMM, [+-]HH
  if NUMERIC_PATTERN === timezone
    offset = Time.zone_offset(timezone)
    if format
      return Proc.new {|time|
        Time.at(time).localtime(offset).strftime(format)
      }
    else
      return Proc.new {|time|
        Time.at(time).localtime(offset).iso8601
      }
    end
  end
  # Region/Zone, Region/Zone/Zone
  if NAME_PATTERN === timezone
    begin
      tz = TZInfo::Timezone.get(timezone)
    rescue
      return nil
    end
    if format
      return Proc.new {|time|
        Time.at(time).localtime(tz.period_for_utc(time).utc_total_offset).strftime(format)
      }
    else
      return Proc.new {|time|
        Time.at(time).localtime(tz.period_for_utc(time).utc_total_offset).iso8601
      }
    end
  end
  return nil
end

def self.validate(timezone)
  # If the specified timezone is nil.
  if timezone.nil?
    # Invalid.
    return false
  end
  # [+-]HH:MM, [+-]HHMM, [+-]HH
  if NUMERIC_PATTERN === timezone
    # Valid. It can be parsed by Time.zone_offset method.
    return true
  end
  # Region/Zone, Region/Zone/Zone
  if NAME_PATTERN === timezone
    begin
      # Get a Timezone instance for the specified timezone.
      TZInfo::Timezone.get(timezone)
    rescue
      # Invalid. The string does not exist in the timezone database.
      return false
    else
      # Valid. The string was found in the timezone database.
      return true
    end
  else
    # Invalid. Timezone abbreviations are not supported.
    return false
  end
end

def self.validate!(timezone)
  unless validate(timezone)
    raise ConfigError, "Unsupported timezone '#{timezone}'"
  end
end