/*
 *
 * Copyright 2014 gRPC authors.
 *
 * 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 grpc

import (
	"math"
	"sync"

	"github.com/golang/protobuf/proto"
)

// Codec defines the interface gRPC uses to encode and decode messages.
// Note that implementations of this interface must be thread safe;
// a Codec's methods can be called from concurrent goroutines.
type Codec interface {
	// Marshal returns the wire format of v.
	Marshal(v interface{}) ([]byte, error)
	// Unmarshal parses the wire format into v.
	Unmarshal(data []byte, v interface{}) error
	// String returns the name of the Codec implementation. The returned
	// string will be used as part of content type in transmission.
	String() string
}

// protoCodec is a Codec implementation with protobuf. It is the default codec for gRPC.
type protoCodec struct {
}

type cachedProtoBuffer struct {
	lastMarshaledSize uint32
	proto.Buffer
}

func capToMaxInt32(val int) uint32 {
	if val > math.MaxInt32 {
		return uint32(math.MaxInt32)
	}
	return uint32(val)
}

func (p protoCodec) marshal(v interface{}, cb *cachedProtoBuffer) ([]byte, error) {
	protoMsg := v.(proto.Message)
	newSlice := make([]byte, 0, cb.lastMarshaledSize)

	cb.SetBuf(newSlice)
	cb.Reset()
	if err := cb.Marshal(protoMsg); err != nil {
		return nil, err
	}
	out := cb.Bytes()
	cb.lastMarshaledSize = capToMaxInt32(len(out))
	return out, nil
}

func (p protoCodec) Marshal(v interface{}) ([]byte, error) {
	if pm, ok := v.(proto.Marshaler); ok {
		// object can marshal itself, no need for buffer
		return pm.Marshal()
	}

	cb := protoBufferPool.Get().(*cachedProtoBuffer)
	out, err := p.marshal(v, cb)

	// put back buffer and lose the ref to the slice
	cb.SetBuf(nil)
	protoBufferPool.Put(cb)
	return out, err
}

func (p protoCodec) Unmarshal(data []byte, v interface{}) error {
	protoMsg := v.(proto.Message)
	protoMsg.Reset()

	if pu, ok := protoMsg.(proto.Unmarshaler); ok {
		// object can unmarshal itself, no need for buffer
		return pu.Unmarshal(data)
	}

	cb := protoBufferPool.Get().(*cachedProtoBuffer)
	cb.SetBuf(data)
	err := cb.Unmarshal(protoMsg)
	cb.SetBuf(nil)
	protoBufferPool.Put(cb)
	return err
}

func (protoCodec) String() string {
	return "proto"
}

var protoBufferPool = &sync.Pool{
	New: func() interface{} {
		return &cachedProtoBuffer{
			Buffer:            proto.Buffer{},
			lastMarshaledSize: 16,
		}
	},
}
