class ReeDatetime::OffsetToString

def call(offset)
  return OFFSET_CACHE[offset] if OFFSET_CACHE.has_key?(offset)
  if !(-MAX_OFFSET..MAX_OFFSET).include?(offset)
    raise ArgumentError, "offset should be in (-#{MAX_OFFSET}..#{MAX_OFFSET})"
  end
  val = offset.abs
  hours = val / 3600
  minutes = (val % 3600) / 60
  str = "#{offset < 0 ? '-' : '+'}#{hours < 10 ? '0' : ''}#{hours}:#{minutes < 10 ? '0' : ''}#{minutes}"
  OFFSET_CACHE[offset] = str
end