package kafka

import (
	"bytes"
	"compress/gzip"
	"io/ioutil"
)

type compressionCodec int

const (
	COMPRESSION_NONE   compressionCodec = 0
	COMPRESSION_GZIP   compressionCodec = 1
	COMPRESSION_SNAPPY compressionCodec = 2
)

// The spec just says: "This is a version id used to allow backwards compatible evolution of the message
// binary format." but it doesn't say what the current value is, so presumably 0...
const message_format int8 = 0

type message struct {
	codec compressionCodec
	key   *[]byte
	value *[]byte
}

func (m *message) encode(pe packetEncoder) {
	pe.pushCRC32()

	pe.putInt8(message_format)

	var attributes int8 = 0
	attributes |= int8(m.codec & 0x07)
	pe.putInt8(attributes)

	pe.putBytes(m.key)

	var body *[]byte
	switch m.codec {
	case COMPRESSION_NONE:
		body = m.value
	case COMPRESSION_GZIP:
		if m.value != nil {
			var buf bytes.Buffer
			writer := gzip.NewWriter(&buf)
			writer.Write(*m.value)
			writer.Close()
			tmp := buf.Bytes()
			body = &tmp
		}
	case COMPRESSION_SNAPPY:
		// TODO
	}
	pe.putBytes(body)

	pe.pop()
}

func (m *message) decode(pd packetDecoder) (err error) {
	err = pd.pushCRC32()
	if err != nil {
		return err
	}

	format, err := pd.getInt8()
	if err != nil {
		return err
	}
	if format != message_format {
		return DecodingError{}
	}

	attribute, err := pd.getInt8()
	if err != nil {
		return err
	}
	m.codec = compressionCodec(attribute & 0x07)

	m.key, err = pd.getBytes()
	if err != nil {
		return err
	}

	m.value, err = pd.getBytes()
	if err != nil {
		return err
	}

	switch m.codec {
	case COMPRESSION_NONE:
		// nothing to do
	case COMPRESSION_GZIP:
		if m.value == nil {
			return DecodingError{"Nil contents cannot be compressed."}
		}
		reader, err := gzip.NewReader(bytes.NewReader(*m.value))
		if err != nil {
			return err
		}
		tmp, err := ioutil.ReadAll(reader)
		if err != nil {
			return err
		}
		m.value = &tmp
	case COMPRESSION_SNAPPY:
		// TODO
	default:
		return DecodingError{"Unknown compression codec."}
	}

	err = pd.pop()
	if err != nil {
		return err
	}

	return nil
}

func newMessage(key, value encoder) (msg *message, err error) {
	msg = new(message)

	msg.key, err = buildBytes(key)
	if err != nil {
		return nil, err
	}

	msg.value, err = buildBytes(value)
	if err != nil {
		return nil, err
	}

	return msg, nil
}