package raft

import (
	"bytes"
	"code.google.com/p/goprotobuf/proto"
	"encoding/json"
	"fmt"
	"github.com/goraft/raft/protobuf"
	"io"
)

// A log entry stores a single item in the log.
type LogEntry struct {
	log         *Log
	Index       uint64
	Term        uint64
	CommandName string
	Command     []byte
	Position    int64 // position in the log file
	event       *ev
}

// Creates a new log entry associated with a log.
func newLogEntry(log *Log, event *ev, index uint64, term uint64, command Command) (*LogEntry, error) {
	var buf bytes.Buffer
	var commandName string
	if command != nil {
		commandName = command.CommandName()
		if encoder, ok := command.(CommandEncoder); ok {
			if err := encoder.Encode(&buf); err != nil {
				return nil, err
			}
		} else {
			json.NewEncoder(&buf).Encode(command)
		}
	}

	e := &LogEntry{
		log:         log,
		Index:       index,
		Term:        term,
		CommandName: commandName,
		Command:     buf.Bytes(),
		event:       event,
	}

	return e, nil
}

// Encodes the log entry to a buffer. Returns the number of bytes
// written and any error that may have occurred.
func (e *LogEntry) encode(w io.Writer) (int, error) {
	defer e.log.pBuffer.Reset()
	e.log.pLogEntry.Index = proto.Uint64(e.Index)
	e.log.pLogEntry.Term = proto.Uint64(e.Term)
	e.log.pLogEntry.CommandName = proto.String(e.CommandName)
	e.log.pLogEntry.Command = e.Command

	err := e.log.pBuffer.Marshal(e.log.pLogEntry)
	if err != nil {
		return -1, err
	}

	if _, err = fmt.Fprintf(w, "%8x\n", len(e.log.pBuffer.Bytes())); err != nil {
		return -1, err
	}

	return w.Write(e.log.pBuffer.Bytes())
}

// Decodes the log entry from a buffer. Returns the number of bytes read and
// any error that occurs.
func (e *LogEntry) decode(r io.Reader) (int, error) {

	var length int
	_, err := fmt.Fscanf(r, "%8x\n", &length)
	if err != nil {
		return -1, err
	}

	data := make([]byte, length)
	_, err = r.Read(data)

	if err != nil {
		return -1, err
	}

	pb := &protobuf.ProtoLogEntry{}
	if err = proto.Unmarshal(data, pb); err != nil {
		return -1, err
	}

	e.Term = pb.GetTerm()
	e.Index = pb.GetIndex()
	e.CommandName = pb.GetCommandName()
	e.Command = pb.Command

	return length, nil
}