class Cassandra

  # UUID format version 1, as specified in RFC 4122, with jitter in place of the mac address and sequence counter.
  class UUID < Comparable

    class InvalidVersion < StandardError #:nodoc:
    end

    GREGORIAN_EPOCH_OFFSET = 0x01B2_1DD2_1381_4000 # Oct 15, 1582

    VARIANT = 0b1000_0000_0000_0000

    def initialize(bytes = nil)
      case bytes
      when self.class # UUID
        @bytes = bytes.to_s
      when String
        case bytes.size
        when 16 # Raw byte array
          @bytes = bytes
        when 36 # Human-readable UUID representation; inverse of #to_guid
          elements = bytes.split("-")
          raise TypeError, "Expected #{bytes.inspect} to cast to a #{self.class} (malformed UUID representation)" if elements.size != 5
          @bytes = elements.join.to_a.pack('H32')
        else
          raise TypeError, "Expected #{bytes.inspect} to cast to a #{self.class} (invalid bytecount)"
        end

      when Integer
        raise TypeError, "Expected #{bytes.inspect} to cast to a #{self.class} (integer out of range)" if bytes < 0 or bytes > 2**128
        @bytes = [
          (bytes >> 96) & 0xFFFF_FFFF,
          (bytes >> 64) & 0xFFFF_FFFF,
          (bytes >> 32) & 0xFFFF_FFFF,
          bytes & 0xFFFF_FFFF
        ].pack("NNNN")

      when NilClass, Time
        time = (bytes || Time).stamp * 10 + GREGORIAN_EPOCH_OFFSET
        # See http://github.com/spectra/ruby-uuid/
        @bytes = [
          time & 0xFFFF_FFFF,
          time >> 32,
          ((time >> 48) & 0x0FFF) | 0x1000,
          # Top 3 bytes reserved
          rand(2**13) | VARIANT,
          rand(2**16),
          rand(2**32)
        ].pack("NnnnnN")

      else
        raise TypeError, "Expected #{bytes.inspect} to cast to a #{self.class} (unknown source class)"
      end
    end

    def to_i
      ints = @bytes.unpack("NNNN")
      (ints[0] << 96) +
      (ints[1] << 64) +
      (ints[2] << 32) +
      ints[3]
    end

    def version
      time_high = @bytes.unpack("NnnQ")[2]
      version = (time_high & 0xF000).to_s(16)[0].chr.to_i
      version > 0 and version < 6 ? version : -1
    end

    def variant
      @bytes.unpack('QnnN')[1] >> 13
    end

    def to_guid
      elements = @bytes.unpack("NnnCCa6")
      node = elements[-1].unpack('C*')
      elements[-1] = '%02x%02x%02x%02x%02x%02x' % node
      "%08x-%04x-%04x-%02x%02x-%s" % elements
    end

    def seconds
      total_usecs / 1_000_000
    end

    def usecs
      total_usecs % 1_000_000
    end

    def <=>(other)
      total_usecs <=> other.send(:total_usecs)
    end

    def inspect(long = false)
      "<Cassandra::UUID##{object_id} time: #{
        Time.at(seconds).inspect
      }, usecs: #{
        usecs
      } jitter: #{
        @bytes.unpack('QQ')[1]
      }" + (long ? ", version: #{version}, variant: #{variant}, guid: #{to_guid}>" :  ">")
    end

    private

    def total_usecs
      elements = @bytes.unpack("NnnQ")
      (elements[0] + (elements[1] << 32) + ((elements[2] & 0x0FFF) << 48) - GREGORIAN_EPOCH_OFFSET) / 10
    end
  end
end