From c21c0cf1330eea0d94e67e916c0c52f5ea56d813 Mon Sep 17 00:00:00 2001
From: Dirk Schumacher <dirk@nextmv.io>
Date: Fri, 10 May 2024 16:33:10 +0200
Subject: [PATCH] Improve multi stop plan unit generation

---
 solution_sequence_generator.go | 46 ++++++++++++++++++++++++++++++----
 solution_vehicle.go            |  6 ++---
 2 files changed, 43 insertions(+), 9 deletions(-)

diff --git a/solution_sequence_generator.go b/solution_sequence_generator.go
index 878fd5e..046b352 100644
--- a/solution_sequence_generator.go
+++ b/solution_sequence_generator.go
@@ -5,7 +5,6 @@ package nextroute
 import (
 	"math/rand"
 	"slices"
-	"sync/atomic"
 )
 
 // SequenceGeneratorChannel generates all possible sequences of solution stops
@@ -31,10 +30,10 @@ func SequenceGeneratorChannel(
 ) chan SolutionStops {
 	planUnit := pu.(*solutionPlanStopsUnitImpl)
 	solution := planUnit.solution()
-	maxSequences := int64(solution.Model().SequenceSampleSize())
 	solutionStops := planUnit.SolutionStops()
 	ch := make(chan SolutionStops)
 	go func() {
+		maxSequences := int64(solution.Model().SequenceSampleSize())
 		defer close(ch)
 		switch planUnit.ModelPlanStopsUnit().NumberOfStops() {
 		case 1:
@@ -64,7 +63,7 @@ func SequenceGeneratorChannel(
 					select {
 					case <-quit:
 						return
-					case ch <- solutionStops:
+					case ch <- slices.Clone(solutionStops):
 					}
 				},
 				-1,
@@ -85,9 +84,13 @@ func sequenceGenerator(
 	yield func(SolutionStops),
 	directSuccessor int,
 ) {
+	if *maxSequences == 0 {
+		return
+	}
 	if len(sequence) == len(stops) {
-		if atomic.AddInt64(maxSequences, -1) >= 0 {
-			yield(slices.Clone(sequence))
+		*maxSequences--
+		if *maxSequences >= 0 {
+			yield(sequence)
 		}
 		return
 	}
@@ -143,3 +146,36 @@ func sequenceGenerator(
 		}
 	}
 }
+
+func sequenceGeneratorSync(
+	pu SolutionPlanUnit,
+	yield func(SolutionStops),
+) {
+	planUnit := pu.(*solutionPlanStopsUnitImpl)
+	solutionStops := planUnit.SolutionStops()
+	if planUnit.ModelPlanStopsUnit().NumberOfStops() == 1 {
+		yield(solutionStops)
+		return
+	}
+	solution := planUnit.solution()
+	maxSequences := int64(solution.Model().SequenceSampleSize())
+	used := make([]bool, len(solutionStops))
+	inDegree := make(map[int]int, len(solutionStops))
+	modelPlanUnit := planUnit.ModelPlanUnit().(*planMultipleStopsImpl)
+	dag := modelPlanUnit.dag.(*directedAcyclicGraphImpl)
+	for _, arc := range dag.arcs {
+		inDegree[arc.Destination().Index()]++
+	}
+
+	sequenceGenerator(
+		solutionStops,
+		make([]SolutionStop, 0, len(solutionStops)),
+		used,
+		inDegree,
+		dag,
+		solution.Random(),
+		&maxSequences,
+		yield,
+		-1,
+	)
+}
diff --git a/solution_vehicle.go b/solution_vehicle.go
index 7b2f92d..9b8134c 100644
--- a/solution_vehicle.go
+++ b/solution_vehicle.go
@@ -385,12 +385,10 @@ func (v solutionVehicleImpl) bestMovePlanMultipleStops(
 	preAllocatedMoveContainer *PreAllocatedMoveContainer,
 ) SolutionMove {
 	var bestMove SolutionMove = newNotExecutableSolutionMoveStops(planUnit)
-	quitSequenceGenerator := make(chan struct{})
-	defer close(quitSequenceGenerator)
-	for sequence := range SequenceGeneratorChannel(planUnit, quitSequenceGenerator) {
+	sequenceGeneratorSync(planUnit, func(sequence SolutionStops) {
 		newMove := v.bestMoveSequence(ctx, planUnit, sequence, preAllocatedMoveContainer)
 		bestMove = takeBestInPlace(bestMove, newMove)
-	}
+	})
 	return bestMove
 }