// Copyright 2015 CoreOS, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package wal

import (
	"bufio"
	"encoding/binary"
	"hash"
	"io"
	"sync"

	"github.com/coreos/etcd/pkg/crc"
	"github.com/coreos/etcd/wal/walpb"
)

type encoder struct {
	mu sync.Mutex
	bw *bufio.Writer

	crc hash.Hash32
}

func newEncoder(w io.Writer, prevCrc uint32) *encoder {
	return &encoder{
		bw:  bufio.NewWriter(w),
		crc: crc.New(prevCrc, crcTable),
	}
}

func (e *encoder) encode(rec *walpb.Record) error {
	e.mu.Lock()
	defer e.mu.Unlock()

	e.crc.Write(rec.Data)
	rec.Crc = e.crc.Sum32()
	data, err := rec.Marshal()
	if err != nil {
		return err
	}
	if err := writeInt64(e.bw, int64(len(data))); err != nil {
		return err
	}
	_, err = e.bw.Write(data)
	return err
}

func (e *encoder) flush() error {
	e.mu.Lock()
	defer e.mu.Unlock()
	return e.bw.Flush()
}

func writeInt64(w io.Writer, n int64) error {
	return binary.Write(w, binary.LittleEndian, n)
}