contractcourt: unify the lease specific HTLC sweeping logic

In this commit, we consolidate the _lease specific_ logic for the
success and timeout HTLC resolvers. We do this with the addition of a
new struct which is then composed via struct embedding with the two
existing structs. This fixes a flake in the integration tests by
ensuring the height is set up front, rather than eventually once the
height matches the lock time.

contractcourt/htlc_lease_resolver.go

@@ -0,0 +1,84 @@
+package contractcourt
+
+import (
+	"math"
+
+	"github.com/btcsuite/btcd/wire"
+	"github.com/lightningnetwork/lnd/chainntnfs"
+	"github.com/lightningnetwork/lnd/channeldb"
+	"github.com/lightningnetwork/lnd/input"
+)
+
+// htlcLeaseResolver is a struct that houses the lease specific HTLC resolution
+// logic. This includes deriving the _true_ waiting height, as well as the
+// input to offer to the sweeper.
+type htlcLeaseResolver struct {
+	// channelInitiator denotes whether the party responsible for resolving
+	// the contract initiated the channel.
+	channelInitiator bool
+
+	// leaseExpiry denotes the additional waiting period the contract must
+	// hold until it can be resolved. This waiting period is known as the
+	// expiration of a script-enforced leased channel and only applies to
+	// the channel initiator.
+	//
+	// NOTE: This value should only be set when the contract belongs to a
+	// leased channel.
+	leaseExpiry uint32
+}
+
+// hasCLTV denotes whether the resolver must wait for an additional CLTV to
+// expire before resolving the contract.
+func (h *htlcLeaseResolver) hasCLTV() bool {
+	return h.channelInitiator && h.leaseExpiry > 0
+}
+
+// deriveWaitHeight computes the height the resolver needs to wait until it can
+// sweep the input.
+func (h *htlcLeaseResolver) deriveWaitHeight(csvDelay uint32,
+	commitSpend *chainntnfs.SpendDetail) uint32 {
+
+	waitHeight := uint32(commitSpend.SpendingHeight) + csvDelay - 1
+	if h.hasCLTV() {
+		waitHeight = uint32(math.Max(
+			float64(waitHeight), float64(h.leaseExpiry),
+		))
+	}
+
+	return waitHeight
+}
+
+// makeSweepInput constructs the type of input (either just csv or csv+ctlv) to
+// send to the sweeper so the output can ultimately be swept.
+func (h *htlcLeaseResolver) makeSweepInput(op *wire.OutPoint,
+	wType, cltvWtype input.StandardWitnessType,
+	signDesc *input.SignDescriptor,
+	csvDelay, broadcastHeight uint32, payHash [32]byte) *input.BaseInput {
+
+	if h.hasCLTV() {
+		log.Infof("%T(%x): CSV and CLTV locks expired, offering "+
+			"second-layer output to sweeper: %v", h, payHash, op)
+
+		return input.NewCsvInputWithCltv(
+			op, cltvWtype, signDesc,
+			broadcastHeight, csvDelay,
+			h.leaseExpiry,
+		)
+	}
+
+	log.Infof("%T(%x): CSV lock expired, offering second-layer output to "+
+		"sweeper: %v", h, payHash, op)
+
+	return input.NewCsvInput(op, wType, signDesc, broadcastHeight, csvDelay)
+}
+
+// SupplementState allows the user of a ContractResolver to supplement it with
+// state required for the proper resolution of a contract.
+//
+// NOTE: Part of the ContractResolver interface.
+func (h *htlcLeaseResolver) SupplementState(state *channeldb.OpenChannel) {
+	if state.ChanType.HasLeaseExpiration() {
+		h.leaseExpiry = state.ThawHeight
+	}
+	h.channelInitiator = state.IsInitiator
+}