package wire

import (
	"io"

	"github.com/daglabs/btcd/util/daghash"
)

// MsgGetBlockLocator implements the Message interface and represents a bitcoin
// getlocator message.  It is used to request a block locator between start and stop hash.
// The locator is returned via a locator message (MsgBlockLocator).
//
// This message has no payload.
type MsgGetBlockLocator struct {
	StartHash *daghash.Hash
	StopHash  *daghash.Hash
}

// BtcDecode decodes r using the bitcoin protocol encoding into the receiver.
// This is part of the Message interface implementation.
func (msg *MsgGetBlockLocator) BtcDecode(r io.Reader, pver uint32) error {
	msg.StartHash = &daghash.Hash{}
	err := ReadElement(r, msg.StartHash)
	if err != nil {
		return err
	}

	msg.StopHash = &daghash.Hash{}
	err = ReadElement(r, msg.StopHash)
	if err != nil {
		return err
	}
	return nil
}

// BtcEncode encodes the receiver to w using the bitcoin protocol encoding.
// This is part of the Message interface implementation.
func (msg *MsgGetBlockLocator) BtcEncode(w io.Writer, pver uint32) error {
	err := WriteElement(w, msg.StartHash)
	if err != nil {
		return err
	}

	err = WriteElement(w, msg.StopHash)
	if err != nil {
		return err
	}
	return nil
}

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

// MaxPayloadLength returns the maximum length the payload can be for the
// receiver.  This is part of the Message interface implementation.
func (msg *MsgGetBlockLocator) MaxPayloadLength(pver uint32) uint32 {
	return daghash.HashSize * 2
}

// NewMsgGetBlockLocator returns a new getlocator message that conforms to the
// Message interface using the passed parameters and defaults for the remaining
// fields.
func NewMsgGetBlockLocator(startHash, stopHash *daghash.Hash) *MsgGetBlockLocator {
	return &MsgGetBlockLocator{
		StartHash: startHash,
		StopHash:  stopHash,
	}
}