package wire

import (
	"fmt"
	"io"
)

// MsgSendHeaders implements the Message interface and represents a bitcoin sendheaders message. It is used to request
// the peer send block headers rather than inventory vectors. This message has no payload and was not added until
// protocol versions starting with SendHeadersVersion.
type MsgSendHeaders struct{}

// BtcDecode decodes r using the bitcoin protocol encoding into the receiver. This is part of the Message interface
// implementation.
func (msg *MsgSendHeaders) BtcDecode(r io.Reader, pver uint32, enc MessageEncoding) (e error) {
	if pver < SendHeadersVersion {
		str := fmt.Sprintf("sendheaders message invalid for protocol "+
			"version %d", pver,
		)
		return messageError("MsgSendHeaders.BtcDecode", str)
	}
	return nil
}

// BtcEncode encodes the receiver to w using the bitcoin protocol encoding. This is part of the Message interface
// implementation.
func (msg *MsgSendHeaders) BtcEncode(w io.Writer, pver uint32, enc MessageEncoding) (e error) {
	if pver < SendHeadersVersion {
		str := fmt.Sprintf("sendheaders message invalid for protocol "+
			"version %d", pver,
		)
		return messageError("MsgSendHeaders.BtcEncode", str)
	}
	return nil
}

// Command returns the protocol command string for the message. This is part of the Message interface implementation.
func (msg *MsgSendHeaders) Command() string {
	return CmdSendHeaders
}

// MaxPayloadLength returns the maximum length the payload can be for the receiver. This is part of the Message
// interface implementation.
func (msg *MsgSendHeaders) MaxPayloadLength(pver uint32) uint32 {
	return 0
}

// NewMsgSendHeaders returns a new bitcoin sendheaders message that conforms to the Message interface. See
// MsgSendHeaders for details.
func NewMsgSendHeaders() *MsgSendHeaders {
	return &MsgSendHeaders{}
}