// Copyright 2019 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.

// +build fuchsia

package fidl

const FidlWireFormatMagicNumberInitial = 1

type MarshalerContext struct {
	DecodeUnionsFromXUnionBytes bool
	EncodeUnionsAsXUnionBytes   bool
}

// MessageHeader represents a transactional message header.
type MessageHeader struct {
	_       struct{} `fidl:"s,16,8" fidl_size_v1:"16" fidl_alignment_v1:"8"`
	Txid    uint32   `fidl:"0" fidl_offset_v1:"0"`
	Flags   [3]uint8 `fidl:"4" fidl_offset_v1:"4"`
	Magic   uint8    `fidl:"7" fidl_offset_v1:"7"`
	Ordinal uint64   `fidl:"8" fidl_offset_v1:"8"`
}

func (msg *MessageHeader) IsSupportedVersion() bool {
	return msg.Magic == FidlWireFormatMagicNumberInitial
}

func (msg *MessageHeader) HasUnionFromXunionBytes() bool {
	return msg.Flags[0]&0x01 != 0
}

func (msg *MessageHeader) SetUnionFromXunionBytes() {
	msg.Flags[0] |= 0x01
}

func (msg *MessageHeader) UnsetUnionFromXunionBytes() {
	msg.Flags[0] &= ^(uint8(0x01))
}

// NewCtx creates a new MarshalerContext for unmarshaling based on the flags in
// the MessageHeader
func (msg *MessageHeader) NewCtx() MarshalerContext {
	ctx := newCtx()
	ctx.DecodeUnionsFromXUnionBytes = msg.HasUnionFromXunionBytes()
	return ctx
}

var mMessageHeader = MustCreateMarshaler(MessageHeader{})

var MessageHeaderSize = 16

func (msg *MessageHeader) Marshaler() Marshaler {
	return mMessageHeader
}

// NewHeader create a new MessageHeader for marshaling with the correct flags
// set based on the MarshalerContext. It is the caller's responsibilty to set
// the transaction ID and method ordinal
func (ctx MarshalerContext) NewHeader() MessageHeader {
	header := MessageHeader{
		Flags: [3]uint8{0, 0, 0},
		Magic: FidlWireFormatMagicNumberInitial,
	}
	if ctx.EncodeUnionsAsXUnionBytes {
		header.SetUnionFromXunionBytes()
	} else {
		header.UnsetUnionFromXunionBytes()
	}
	return header
}