package wire

import (
	"io"
)

// MsgPing implements the Message interface and represents a bitcoin ping message. For versions BIP0031Version and
// earlier, it is used primarily to confirm that a connection is still valid. A transmission error is typically
// interpreted as a closed connection and that the peer should be removed. For versions AFTER BIP0031Version it contains
// an identifier which can be returned in the pong message to determine network timing. The payload for this message
// just consists of a nonce used for identifying it later.
type MsgPing 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 *MsgPing) BtcDecode(r io.Reader, pver uint32, enc MessageEncoding) (e error) {
	// There was no nonce for BIP0031Version and earlier. NOTE: > is not a mistake here. The BIP0031 was defined as
	// AFTER the version unlike most others.
	if pver > BIP0031Version {
		if e = readElement(r, &msg.Nonce); E.Chk(e) {
			return
		}
	}
	return
}

// BtcEncode encodes the receiver to w using the bitcoin protocol encoding. This is part of the Message interface
// implementation.
func (msg *MsgPing) BtcEncode(w io.Writer, pver uint32, enc MessageEncoding) (e error) {
	// There was no nonce for BIP0031Version and earlier. NOTE: > is not a mistake here. The BIP0031 was defined as
	// AFTER the version unlike most others.
	if pver > BIP0031Version {
		if e = writeElement(w, msg.Nonce); E.Chk(e) {
			return
		}
	}
	return
}

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

// MaxPayloadLength returns the maximum length the payload can be for the receiver. This is part of the Message
// interface implementation.
func (msg *MsgPing) MaxPayloadLength(pver uint32) uint32 {
	plen := uint32(0)
	// There was no nonce 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
}

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