class ReeDatetime::HumanZoneOffset

def call(human_zone_name)
  if !ZONE_HUMAN_NAMES.has_key?(human_zone_name)
    raise ArgumentError, "invalid human zone name"
  end
  zone = ZONE_HUMAN_NAMES[human_zone_name]
  tzinfo = find_tzinfo(zone)
  offset_to_string(tzinfo.utc_offset)
end