package lnwire

import (
	"io"

	"github.com/roasbeef/btcd/wire"
)

// UpdateFufillHTLC 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 UpdateFufillHTLC struct {
	// ChannelPoint references an active channel which holds the HTLC to be
	// settled.
	ChannelPoint wire.OutPoint

	// 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
}

// NewUpdateFufillHTLC returns a new empty UpdateFufillHTLC.
func NewUpdateFufillHTLC(chanPoint wire.OutPoint, id uint64,
	preimage [32]byte) *UpdateFufillHTLC {

	return &UpdateFufillHTLC{
		ChannelPoint:    chanPoint,
		ID:              id,
		PaymentPreimage: preimage,
	}
}

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

// Decode deserializes a serialized UpdateFufillHTLC message stored in the passed
// io.Reader observing the specified protocol version.
//
// This is part of the lnwire.Message interface.
func (c *UpdateFufillHTLC) Decode(r io.Reader, pver uint32) error {
	// ChannelPoint(8)
	// ID(8)
	// PaymentPreimage(32)
	err := readElements(r,
		&c.ChannelPoint,
		&c.ID,
		c.PaymentPreimage[:],
	)
	if err != nil {
		return err
	}

	return nil
}

// Encode serializes the target UpdateFufillHTLC into the passed io.Writer
// observing the protocol version specified.
//
// This is part of the lnwire.Message interface.
func (c *UpdateFufillHTLC) Encode(w io.Writer, pver uint32) error {
	err := writeElements(w,
		c.ChannelPoint,
		c.ID,
		c.PaymentPreimage[:],
	)
	if err != nil {
		return err
	}

	return nil
}

// Command returns the integer uniquely identifying this message type on the
// wire.
//
// This is part of the lnwire.Message interface.
func (c *UpdateFufillHTLC) Command() uint32 {
	return CmdUpdateFufillHTLC
}

// MaxPayloadLength returns the maximum allowed payload size for a UpdateFufillHTLC
// complete message observing the specified protocol version.
//
// This is part of the lnwire.Message interface.
func (c *UpdateFufillHTLC) MaxPayloadLength(uint32) uint32 {
	// 36 + 8 + (32 * 15)
	return 524
}

// Validate performs any necessary sanity checks to ensure all fields present
// on the UpdateFufillHTLC are valid.
//
// This is part of the lnwire.Message interface.
func (c *UpdateFufillHTLC) Validate() error {
	// We're good!
	return nil
}