package htlcswitch

import (
	"encoding/binary"
	"io"

	"github.com/lightningnetwork/lnd/channeldb"
	"github.com/lightningnetwork/lnd/htlcswitch/hop"
	"github.com/lightningnetwork/lnd/lnwire"
)

// EmptyCircuitKey is a default value for an outgoing circuit key returned when
// a circuit's keystone has not been set. Note that this value is invalid for
// use as a keystone, since the outgoing channel id can never be equal to
// sourceHop.
var EmptyCircuitKey CircuitKey

// CircuitKey is a tuple of channel ID and HTLC ID, used to uniquely identify
// HTLCs in a circuit. Circuits are identified primarily by the circuit key of
// the incoming HTLC. However, a circuit may also be referenced by its outgoing
// circuit key after the HTLC has been forwarded via the outgoing link.
type CircuitKey = channeldb.CircuitKey

// PaymentCircuit is used by the switch as placeholder between when the
// switch makes a forwarding decision and the outgoing link determines the
// proper HTLC ID for the local log. After the outgoing HTLC ID has been
// determined, the half circuit will be converted into a full PaymentCircuit.
type PaymentCircuit struct {
	// AddRef is the forward reference of the Add update in the incoming
	// link's forwarding package. This value is set on the htlcPacket of the
	// returned settle/fail so that it can be removed from disk.
	AddRef channeldb.AddRef

	// Incoming is the circuit key identifying the incoming channel and htlc
	// index from which this ADD originates.
	Incoming CircuitKey

	// Outgoing is the circuit key identifying the outgoing channel, and the
	// HTLC index that was used to forward the ADD. It will be nil if this
	// circuit's keystone has not been set.
	Outgoing *CircuitKey

	// PaymentHash used as unique identifier of payment.
	PaymentHash [32]byte

	// IncomingAmount is the value of the HTLC from the incoming link.
	IncomingAmount lnwire.MilliSatoshi

	// OutgoingAmount specifies the value of the HTLC leaving the switch,
	// either as a payment or forwarded amount.
	OutgoingAmount lnwire.MilliSatoshi

	// ErrorEncrypter is used to re-encrypt the onion failure before
	// sending it back to the originator of the payment.
	ErrorEncrypter hop.ErrorEncrypter

	// LoadedFromDisk is set true for any circuits loaded after the circuit
	// map is reloaded from disk.
	//
	// NOTE: This value is determined implicitly during a restart. It is not
	// persisted, and should never be set outside the circuit map.
	LoadedFromDisk bool
}

// HasKeystone returns true if an outgoing link has assigned this circuit's
// outgoing circuit key.
func (c *PaymentCircuit) HasKeystone() bool {
	return c.Outgoing != nil
}

// newPaymentCircuit initializes a payment circuit on the heap using the payment
// hash and an in-memory htlc packet.
func newPaymentCircuit(hash *[32]byte, pkt *htlcPacket) *PaymentCircuit {
	var addRef channeldb.AddRef
	if pkt.sourceRef != nil {
		addRef = *pkt.sourceRef
	}

	return &PaymentCircuit{
		AddRef: addRef,
		Incoming: CircuitKey{
			ChanID: pkt.incomingChanID,
			HtlcID: pkt.incomingHTLCID,
		},
		PaymentHash:    *hash,
		IncomingAmount: pkt.incomingAmount,
		OutgoingAmount: pkt.amount,
		ErrorEncrypter: pkt.obfuscator,
	}
}

// makePaymentCircuit initializes a payment circuit on the stack using the
// payment hash and an in-memory htlc packet.
func makePaymentCircuit(hash *[32]byte, pkt *htlcPacket) PaymentCircuit {
	var addRef channeldb.AddRef
	if pkt.sourceRef != nil {
		addRef = *pkt.sourceRef
	}

	return PaymentCircuit{
		AddRef: addRef,
		Incoming: CircuitKey{
			ChanID: pkt.incomingChanID,
			HtlcID: pkt.incomingHTLCID,
		},
		PaymentHash:    *hash,
		IncomingAmount: pkt.incomingAmount,
		OutgoingAmount: pkt.amount,
		ErrorEncrypter: pkt.obfuscator,
	}
}

// Encode writes a PaymentCircuit to the provided io.Writer.
func (c *PaymentCircuit) Encode(w io.Writer) error {
	if err := c.AddRef.Encode(w); err != nil {
		return err
	}

	if err := c.Incoming.Encode(w); err != nil {
		return err
	}

	if _, err := w.Write(c.PaymentHash[:]); err != nil {
		return err
	}

	var scratch [8]byte

	binary.BigEndian.PutUint64(scratch[:], uint64(c.IncomingAmount))
	if _, err := w.Write(scratch[:]); err != nil {
		return err
	}

	binary.BigEndian.PutUint64(scratch[:], uint64(c.OutgoingAmount))
	if _, err := w.Write(scratch[:]); err != nil {
		return err
	}

	// Defaults to EncrypterTypeNone.
	var encrypterType hop.EncrypterType
	if c.ErrorEncrypter != nil {
		encrypterType = c.ErrorEncrypter.Type()
	}

	err := binary.Write(w, binary.BigEndian, encrypterType)
	if err != nil {
		return err
	}

	// Skip encoding of error encrypter if this half add does not have one.
	if encrypterType == hop.EncrypterTypeNone {
		return nil
	}

	return c.ErrorEncrypter.Encode(w)
}

// Decode reads a PaymentCircuit from the provided io.Reader.
func (c *PaymentCircuit) Decode(r io.Reader) error {
	if err := c.AddRef.Decode(r); err != nil {
		return err
	}

	if err := c.Incoming.Decode(r); err != nil {
		return err
	}

	if _, err := io.ReadFull(r, c.PaymentHash[:]); err != nil {
		return err
	}

	var scratch [8]byte

	if _, err := io.ReadFull(r, scratch[:]); err != nil {
		return err
	}
	c.IncomingAmount = lnwire.MilliSatoshi(
		binary.BigEndian.Uint64(scratch[:]))

	if _, err := io.ReadFull(r, scratch[:]); err != nil {
		return err
	}
	c.OutgoingAmount = lnwire.MilliSatoshi(
		binary.BigEndian.Uint64(scratch[:]))

	// Read the encrypter type used for this circuit.
	var encrypterType hop.EncrypterType
	err := binary.Read(r, binary.BigEndian, &encrypterType)
	if err != nil {
		return err
	}

	switch encrypterType {
	case hop.EncrypterTypeNone:
		// No encrypter was provided, such as when the payment is
		// locally initiated.
		return nil

	case hop.EncrypterTypeSphinx:
		// Sphinx encrypter was used as this is a forwarded HTLC.
		c.ErrorEncrypter = hop.NewSphinxErrorEncrypter()

	case hop.EncrypterTypeMock:
		// Test encrypter.
		c.ErrorEncrypter = NewMockObfuscator()

	default:
		return UnknownEncrypterType(encrypterType)
	}

	return c.ErrorEncrypter.Decode(r)
}

// InKey returns the primary identifier for the circuit corresponding to the
// incoming HTLC.
func (c *PaymentCircuit) InKey() CircuitKey {
	return c.Incoming
}

// OutKey returns the keystone identifying the outgoing link and HTLC ID. If the
// circuit hasn't been completed, this method returns an EmptyKeystone, which is
// an invalid outgoing circuit key. Only call this method if HasKeystone returns
// true.
func (c *PaymentCircuit) OutKey() CircuitKey {
	if c.Outgoing != nil {
		return *c.Outgoing
	}

	return EmptyCircuitKey
}