package wire

import (
	"fmt"
	"io"
)

// MsgPong implements the Message interface and represents a bitcoin pong message which is used primarily to confirm
// that a connection is still valid in response to a bitcoin ping message (MsgPing). This message was not added until
// protocol versions AFTER BIP0031Version.
type MsgPong struct {
	// Unique value associated with message that is used to identify specific ping message.
	Nonce uint64
}

// BtcDecode decodes r using the bitcoin protocol encoding into the receiver. This is part of the Message interface
// implementation.
func (msg *MsgPong) BtcDecode(r io.Reader, pver uint32, enc MessageEncoding) (e error) {
	// NOTE: <= is not a mistake here.  The BIP0031 was defined as AFTER the version unlike most others.
	if pver <= BIP0031Version {
		str := fmt.Sprintf("pong message invalid for protocol "+
			"version %d", pver,
		)
		return messageError("MsgPong.BtcDecode", str)
	}
	return readElement(r, &msg.Nonce)
}

// BtcEncode encodes the receiver to w using the bitcoin protocol encoding. This is part of the Message interface
// implementation.
func (msg *MsgPong) BtcEncode(w io.Writer, pver uint32, enc MessageEncoding) (e error) {
	// NOTE: <= is not a mistake here.  The BIP0031 was defined as AFTER the version unlike most others.
	if pver <= BIP0031Version {
		str := fmt.Sprintf("pong message invalid for protocol "+
			"version %d", pver,
		)
		return messageError("MsgPong.BtcEncode", str)
	}
	return writeElement(w, msg.Nonce)
}

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

// MaxPayloadLength returns the maximum length the payload can be for the receiver. This is part of the Message
// interface implementation.
func (msg *MsgPong) MaxPayloadLength(pver uint32) uint32 {
	plen := uint32(0)
	// The pong message did not exist for BIP0031Version and earlier. NOTE: > is not a mistake here. The BIP0031 was
	// defined as AFTER the version unlike most others.
	if pver > BIP0031Version {
		// Nonce 8 bytes.
		plen += 8
	}
	return plen
}

// NewMsgPong returns a new bitcoin pong message that conforms to the Message interface.  See MsgPong for details.
func NewMsgPong(nonce uint64) *MsgPong {
	return &MsgPong{
		Nonce: nonce,
	}
}