package lnwire

import (
	"bytes"
	"io"
)

// UpdateFulfillHTLC is sent by Alice to Bob when she wishes to settle a
// particular HTLC referenced by its HTLCKey within a specific active channel
// referenced by ChannelPoint.  A subsequent CommitSig message will be sent by
// Alice to "lock-in" the removal of the specified HTLC, possible containing a
// batch signature covering several settled HTLC's.
type UpdateFulfillHTLC struct {
	// ChanID references an active channel which holds the HTLC to be
	// settled.
	ChanID ChannelID

	// ID denotes the exact HTLC stage within the receiving node's
	// commitment transaction to be removed.
	ID uint64

	// PaymentPreimage is the R-value preimage required to fully settle an
	// HTLC.
	PaymentPreimage [32]byte

	// ExtraData is the set of data that was appended to this message to
	// fill out the full maximum transport message size. These fields can
	// be used to specify optional data such as custom TLV fields.
	ExtraData ExtraOpaqueData
}

// NewUpdateFulfillHTLC returns a new empty UpdateFulfillHTLC.
func NewUpdateFulfillHTLC(chanID ChannelID, id uint64,
	preimage [32]byte) *UpdateFulfillHTLC {

	return &UpdateFulfillHTLC{
		ChanID:          chanID,
		ID:              id,
		PaymentPreimage: preimage,
	}
}

// A compile time check to ensure UpdateFulfillHTLC implements the lnwire.Message
// interface.
var _ Message = (*UpdateFulfillHTLC)(nil)

// Decode deserializes a serialized UpdateFulfillHTLC message stored in the passed
// io.Reader observing the specified protocol version.
//
// This is part of the lnwire.Message interface.
func (c *UpdateFulfillHTLC) Decode(r io.Reader, pver uint32) error {
	return ReadElements(r,
		&c.ChanID,
		&c.ID,
		c.PaymentPreimage[:],
		&c.ExtraData,
	)
}

// Encode serializes the target UpdateFulfillHTLC into the passed io.Writer
// observing the protocol version specified.
//
// This is part of the lnwire.Message interface.
func (c *UpdateFulfillHTLC) Encode(w *bytes.Buffer, pver uint32) error {
	if err := WriteChannelID(w, c.ChanID); err != nil {
		return err
	}

	if err := WriteUint64(w, c.ID); err != nil {
		return err
	}

	if err := WriteBytes(w, c.PaymentPreimage[:]); err != nil {
		return err
	}

	return WriteBytes(w, c.ExtraData)
}

// MsgType returns the integer uniquely identifying this message type on the
// wire.
//
// This is part of the lnwire.Message interface.
func (c *UpdateFulfillHTLC) MsgType() MessageType {
	return MsgUpdateFulfillHTLC
}

// TargetChanID returns the channel id of the link for which this message is
// intended.
//
// NOTE: Part of peer.LinkUpdater interface.
func (c *UpdateFulfillHTLC) TargetChanID() ChannelID {
	return c.ChanID
}