sweep: add new interface Cluster to manage grouping inputs

This commit adds a new interface `Cluster` to manage cluster-level
inputs grouping. This new interface replaces the `inputCluster` and will
be futher refactored so the sweeper can use a much smaller coin
selection lock.

sweep/txgenerator.go

@@ -37,112 +37,6 @@ type txInput interface {
 	parameters() Params
 }
 
-// inputSet is a set of inputs that can be used as the basis to generate a tx
-// on.
-type inputSet []input.Input
-
-// generateInputPartitionings goes through all given inputs and constructs sets
-// of inputs that can be used to generate a sensible transaction. Each set
-// contains up to the configured maximum number of inputs. Negative yield
-// inputs are skipped. No input sets with a total value after fees below the
-// dust limit are returned.
-func generateInputPartitionings(sweepableInputs []txInput,
-	feePerKW, maxFeeRate chainfee.SatPerKWeight, maxInputsPerTx int,
-	wallet Wallet) ([]inputSet, error) {
-
-	// Sort input by yield. We will start constructing input sets starting
-	// with the highest yield inputs. This is to prevent the construction
-	// of a set with an output below the dust limit, causing the sweep
-	// process to stop, while there are still higher value inputs
-	// available. It also allows us to stop evaluating more inputs when the
-	// first input in this ordering is encountered with a negative yield.
-	//
-	// Yield is calculated as the difference between value and added fee
-	// for this input. The fee calculation excludes fee components that are
-	// common to all inputs, as those wouldn't influence the order. The
-	// single component that is differentiating is witness size.
-	//
-	// For witness size, the upper limit is taken. The actual size depends
-	// on the signature length, which is not known yet at this point.
-	yields := make(map[wire.OutPoint]int64)
-	for _, input := range sweepableInputs {
-		size, _, err := input.WitnessType().SizeUpperBound()
-		if err != nil {
-			return nil, fmt.Errorf(
-				"failed adding input weight: %v", err)
-		}
-
-		yields[*input.OutPoint()] = input.SignDesc().Output.Value -
-			int64(feePerKW.FeeForWeight(int64(size)))
-	}
-
-	sort.Slice(sweepableInputs, func(i, j int) bool {
-		// Because of the specific ordering and termination condition
-		// that is described above, we place force sweeps at the start
-		// of the list. Otherwise we can't be sure that they will be
-		// included in an input set.
-		if sweepableInputs[i].parameters().Force {
-			return true
-		}
-
-		return yields[*sweepableInputs[i].OutPoint()] >
-			yields[*sweepableInputs[j].OutPoint()]
-	})
-
-	// Select blocks of inputs up to the configured maximum number.
-	var sets []inputSet
-	for len(sweepableInputs) > 0 {
-		// Start building a set of positive-yield tx inputs under the
-		// condition that the tx will be published with the specified
-		// fee rate.
-		txInputs := newTxInputSet(
-			wallet, feePerKW, maxFeeRate, maxInputsPerTx,
-		)
-
-		// From the set of sweepable inputs, keep adding inputs to the
-		// input set until the tx output value no longer goes up or the
-		// maximum number of inputs is reached.
-		txInputs.addPositiveYieldInputs(sweepableInputs)
-
-		// If there are no positive yield inputs, we can stop here.
-		inputCount := len(txInputs.inputs)
-		if inputCount == 0 {
-			return sets, nil
-		}
-
-		// Check the current output value and add wallet utxos if
-		// needed to push the output value to the lower limit.
-		if err := txInputs.tryAddWalletInputsIfNeeded(); err != nil {
-			return nil, err
-		}
-
-		// If the output value of this block of inputs does not reach
-		// the dust limit, stop sweeping. Because of the sorting,
-		// continuing with the remaining inputs will only lead to sets
-		// with an even lower output value.
-		if !txInputs.enoughInput() {
-			// The change output is always a p2tr here.
-			dl := lnwallet.DustLimitForSize(input.P2TRSize)
-			log.Debugf("Input set value %v (required=%v, "+
-				"change=%v) below dust limit of %v",
-				txInputs.totalOutput(), txInputs.requiredOutput,
-				txInputs.changeOutput, dl)
-			return sets, nil
-		}
-
-		log.Infof("Candidate sweep set of size=%v (+%v wallet inputs), "+
-			"has yield=%v, weight=%v",
-			inputCount, len(txInputs.inputs)-inputCount,
-			txInputs.totalOutput()-txInputs.walletInputTotal,
-			txInputs.weightEstimate(true).weight())
-
-		sets = append(sets, txInputs.inputs)
-		sweepableInputs = sweepableInputs[inputCount:]
-	}
-
-	return sets, nil
-}
-
 // createSweepTx builds a signed tx spending the inputs to the given outputs,
 // sending any leftover change to the change script.
 func createSweepTx(inputs []input.Input, outputs []*wire.TxOut,