// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package fidl

import (
	"sync"

	"syscall/zx"
)

// messageBytesPool is a pool of buffers that can fit the data part of any
// FIDL message.
var messageBytesPool = sync.Pool{
	New: func() interface{} {
		return make([]byte, zx.ChannelMaxMessageBytes)
	},
}

// messageHandleInfosPool is a pool of buffers that can fit the handle infos
// for a FIDL message.
var messageHandleInfosPool = sync.Pool{
	New: func() interface{} {
		return make([]zx.HandleInfo, zx.ChannelMaxMessageHandles)
	},
}

// messageHandlesPool is a pool of buffers that can fit the handle dispositions
// for a FIDL message.
var messageHandleDispositionsPool = sync.Pool{
	New: func() interface{} {
		return make([]zx.HandleDisposition, zx.ChannelMaxMessageHandles)
	},
}

// MarshalHeaderThenMessage marshals a transactional message
// (see https://fuchsia.googlesource.com/fuchsia/+/master/docs/development/languages/fidl/reference/wire-format/README.md#messages-for-transactions).
// It marshals a `MessageHeader`, optionally followed by a `Message` (body).
func MarshalHeaderThenMessage(header *MessageHeader, body Message, data []byte, handleDispositions []zx.HandleDisposition) (int, int, error) {
	ctx := header.NewCtx()
	hnb, _, err := Marshal(ctx, header, data, nil)
	if err != nil {
		return 0, 0, err
	}
	if body == nil {
		return hnb, 0, nil
	}
	nb, nh, err := Marshal(ctx, body, data[hnb:], handleDispositions)
	if err != nil {
		return 0, 0, err
	}
	return hnb + nb, nh, nil
}

// UnmarshalHeaderThenMessage unmarshals a transactional message
// (see https://fuchsia.googlesource.com/fuchsia/+/master/docs/development/languages/fidl/reference/wire-format/README.md#messages-for-transactions).
// It unmarshals a `MessageHeader`, optionally followed by a `Message` (body).
func UnmarshalHeaderThenMessage(data []byte, handleInfos []zx.HandleInfo, header *MessageHeader, body Message) error {
	ctx := header.NewCtx()
	if err := Unmarshal(ctx, data[:MessageHeaderSize], nil, header); err != nil {
		return err
	}
	if body == nil {
		return nil
	}
	return Unmarshal(ctx, data[MessageHeaderSize:], handleInfos, body)
}