If multiple paths exist to target, and they differ in throughput, now cables will combine their throughput

src/main/kotlin/ru/dbotthepony/mc/otm/block/entity/cable/EnergyCableGraph.kt

@@ -31,11 +31,31 @@ class EnergyCableGraph : GraphNodeList<EnergyCableBlockEntity.Node, EnergyCableG
 		}
 	}
 
-	// TODO: LRU cache?
-	private val pathCache = HashMap<Pair<EnergyCableBlockEntity.Node, EnergyCableBlockEntity.Node>, ArrayList<SegmentPath?>>()
+	private class CacheEntry {
+		val paths = ArrayList<SegmentPath>(1)
+		var saturated = false
+	}
 
-	private class SearchNode(val node: EnergyCableBlockEntity.Node, target: EnergyCableBlockEntity.Node, var parent: SearchNode? = null) : Comparable<SearchNode> {
-		val heuristics: Double = node.position.distSqr(target.position) * 0.0001 - ln(node.segment.availableThroughput.coerceAtMost(Decimal.LONG_MAX_VALUE).toDouble())
+	// TODO: LRU cache?
+	private val pathCache = HashMap<Pair<EnergyCableBlockEntity.Node, EnergyCableBlockEntity.Node>, CacheEntry>()
+
+	private class SearchNode(
+		val node: EnergyCableBlockEntity.Node,
+		target: EnergyCableBlockEntity.Node,
+		var parent: SearchNode? = null,
+		previouslySeen: Boolean
+	) : Comparable<SearchNode> {
+		val heuristics: Double
+
+		init {
+			var heuristics = node.position.distSqr(target.position) * 0.0001
+
+			if (!previouslySeen) {
+				heuristics -= ln(node.segment.availableThroughput.coerceAtMost(Decimal.LONG_MAX_VALUE).toDouble())
+			}
+
+			this.heuristics = heuristics
+		}
 
 		override fun compareTo(other: SearchNode): Int {
 			return heuristics.compareTo(other.heuristics)
@@ -51,6 +71,18 @@ class EnergyCableGraph : GraphNodeList<EnergyCableBlockEntity.Node, EnergyCableG
 		val availableThroughput: Decimal
 			get() = segments.minOfOrNull { it.availableThroughput } ?: Decimal.ZERO
 
+		operator fun contains(node: EnergyCableBlockEntity.Node): Boolean {
+			return segments.any { node in it }
+		}
+
+		override fun equals(other: Any?): Boolean {
+			return this === other || other is SegmentPath && segments == other.segments
+		}
+
+		override fun hashCode(): Int {
+			return segments.hashCode()
+		}
+
 		fun transfer(amount: Decimal, simulate: Boolean, instantSnapshot: MutableMap<Segment, Decimal>): Decimal {
 			if (!amount.isPositive || shortCircuit) {
 				return Decimal.ZERO
@@ -66,19 +98,22 @@ class EnergyCableGraph : GraphNodeList<EnergyCableBlockEntity.Node, EnergyCableG
 				}
 			}
 
-			var min = amount
+			val min = if (simulate) segments.minOf { it.throughput(instantSnapshot) } else segments.minOf { it.availableThroughput }
 
-			for (segment in segments) {
-				min = minOf(segment.transfer(amount, instantSnapshot), min)
-				if (!min.isPositive) return Decimal.ZERO
+			if (min.isPositive) {
+				if (simulate)
+					segments.forEach { it.transfer(min, instantSnapshot) }
+				else
+					segments.forEach { it.transfer(min) }
 			}
 
-			if (!simulate)
-				segments.forEach { it.transfer(min) }
-
 			return min
 		}
 
+		fun refund(amount: Decimal, simulate: Boolean, instantSnapshot: MutableMap<Segment, Decimal>) {
+			segments.forEach { it.refund(amount, simulate, instantSnapshot) }
+		}
+
 		fun remove() {
 			segments.toTypedArray().forEach { it.remove(this) }
 		}
@@ -93,18 +128,25 @@ class EnergyCableGraph : GraphNodeList<EnergyCableBlockEntity.Node, EnergyCableG
 		private val nodes = HashSet<EnergyCableBlockEntity.Node>()
 		private val paths = HashSet<SegmentPath>()
 
+		operator fun contains(node: EnergyCableBlockEntity.Node): Boolean {
+			return node in nodes
+		}
+
 		var throughput = Decimal.ZERO
 			private set
 
+		private fun checkThroughput() {
+			if (!throughputKnown) {
+				throughput = nodes.maxOf { it.energyThroughput }
+				throughputKnown = true
+			}
+		}
+
 		var transferredLastTick = Decimal.ZERO
 			private set
 
 		val availableThroughput: Decimal get() {
-			if (!throughputKnown) {
-				throughput = nodes.maxOf { it.energyThroughput }
-				throughputKnown = true
-			}
-
+			checkThroughput()
 			return throughput - transferredLastTick
 		}
 
@@ -141,6 +183,17 @@ class EnergyCableGraph : GraphNodeList<EnergyCableBlockEntity.Node, EnergyCableG
 			}
 		}
 
+		fun throughput(instantSnapshot: Map<Segment, Decimal>): Decimal {
+			if (lastTick != UNIVERSE_TICKS) {
+				transferredLastTick = Decimal.ZERO
+				lastTick = UNIVERSE_TICKS
+			}
+
+			checkThroughput()
+			val currentTransferred = instantSnapshot[this] ?: transferredLastTick
+			return throughput - currentTransferred
+		}
+
 		fun transfer(amount: Decimal, instantSnapshot: MutableMap<Segment, Decimal>): Decimal {
 			if (lastTick != UNIVERSE_TICKS) {
 				transferredLastTick = Decimal.ZERO
@@ -180,6 +233,16 @@ class EnergyCableGraph : GraphNodeList<EnergyCableBlockEntity.Node, EnergyCableG
 			return diff
 		}
 
+		fun refund(amount: Decimal, simulate: Boolean, instantSnapshot: MutableMap<Segment, Decimal>) {
+			if (simulate) {
+				if (this in instantSnapshot) {
+					instantSnapshot[this] = maxOf(instantSnapshot[this]!! - amount, Decimal.ZERO)
+				}
+			} else {
+				transferredLastTick = maxOf(transferredLastTick, Decimal.ZERO)
+			}
+		}
+
 		fun remove(node: EnergyCableBlockEntity.Node) {
 			check(nodes.remove(node)) { "Tried to remove node $node from segment $this, but that node does not belong to this segment" }
 
@@ -198,10 +261,7 @@ class EnergyCableGraph : GraphNodeList<EnergyCableBlockEntity.Node, EnergyCableG
 			check(paths.add(path)) { "Path $path should already contain $this" }
 			check(path.segments.add(this)) { "Path set and Segment disagree whenever $this is absent from $path" }
 
-			if (!throughputKnown) {
-				throughput = nodes.maxOf { it.energyThroughput }
-				throughputKnown = true
-			}
+			checkThroughput()
 		}
 
 		fun remove(path: SegmentPath) {
@@ -241,23 +301,18 @@ class EnergyCableGraph : GraphNodeList<EnergyCableBlockEntity.Node, EnergyCableG
 		nodes.forEach { it.onInvalidate() }
 	}
 
-	// TODO: Multiple paths, so energy can be delivered to receiver through different paths if previously found path is congested
-	private fun getPath(a: EnergyCableBlockEntity.Node, b: EnergyCableBlockEntity.Node, energyToTransfer: Decimal): SegmentPath? {
-		if (!a.canTraverse || !b.canTraverse)
+	// isn't exactly A*, but greedy algorithm, which searched for locally optimal solutions because they lead to globally optimal ones
+	private fun findPath(a: EnergyCableBlockEntity.Node, b: EnergyCableBlockEntity.Node, existing: Collection<SegmentPath>, threshold: Decimal): SegmentPath? {
+		val seenTop = existing.any { a in it }
+
+		if (seenTop && a.energyThroughput <= threshold) {
 			return null
+		}
 
-		val list = pathCache.computeIfAbsent(a to b) { ArrayList(1) }
-
-		if (list.isNotEmpty())
-			return list.first
-
-		// no free paths available, try to find extra one
-		// while this use A* algorithm, this is done purely for biasing search towards end point (to speed up search),
-		// on small cable networks simple flooding will do just fine, if we consider overloaded cables as closed flood gates
 		val openNodes = PriorityQueue<SearchNode>()
 		val seenNodes = HashSet<EnergyCableBlockEntity.Node>()
 
-		openNodes.add(SearchNode(a, b))
+		openNodes.add(SearchNode(a, b, null, seenTop))
 
 		while (openNodes.isNotEmpty()) {
 			val first = openNodes.remove()
@@ -280,21 +335,45 @@ class EnergyCableGraph : GraphNodeList<EnergyCableBlockEntity.Node, EnergyCableG
 				val path = SegmentPath(a.blockEntity.blockPos, b.blockEntity.blockPos)
 				touchedSegments.forEach { it.add(path) }
 
-				list.add(path)
 				return path
 			} else {
 				for (neighbour in first.node.neighboursView.values) {
 					if (!seenNodes.add(neighbour) || !neighbour.canTraverse) continue
-					openNodes.add(SearchNode(neighbour, b, first))
+					val seen = existing.any { neighbour in it }
+					if (seen && neighbour.energyThroughput <= threshold) continue
+					openNodes.add(SearchNode(neighbour, b, first, seen))
 				}
 			}
 		}
 
-		// solution does not exist
-		list.add(null)
 		return null
 	}
 
+	private fun getPath(a: EnergyCableBlockEntity.Node, b: EnergyCableBlockEntity.Node, energyToTransfer: Decimal): List<SegmentPath> {
+		if (!a.canTraverse || !b.canTraverse)
+			return listOf()
+
+		val list = pathCache.computeIfAbsent(a to b) { CacheEntry() }
+
+		if (!list.saturated) {
+			var maxThroughput = list.paths.maxOfOrNull { it.availableThroughput } ?: Decimal.ZERO
+
+			while (maxThroughput < energyToTransfer && !list.saturated) {
+				val find = findPath(a, b, list.paths, maxThroughput)
+
+				if (find == null || find in list.paths) {
+					list.saturated = true
+				} else {
+					list.paths.add(find)
+					maxThroughput = maxOf(maxThroughput, find.availableThroughput)
+				}
+			}
+		}
+
+		list.paths.sortByDescending { it.availableThroughput }
+		return list.paths
+	}
+
 	override fun onNodeRemoved(node: EnergyCableBlockEntity.Node) {
 		if (livelyNodes.remove(node)) {
 			check(livelyNodesList.remove(node))
@@ -321,31 +400,79 @@ class EnergyCableGraph : GraphNodeList<EnergyCableBlockEntity.Node, EnergyCableG
 			var hit = false
 
 			for (side in node.sides.values) {
-				if (side.isEnabled) {
-					if (fromNode === node && side.side === fromSide) {
-						hit = true
+				if (!side.isEnabled)
+					continue
+				else if (fromNode === node && side.side === fromSide) {
+					hit = true
+					continue
+				}
+
+				val it = side.neighbour.get() ?: continue
+				if (it is EnergyCableBlockEntity.CableSide) continue
+
+				val paths = getPath(fromNode, node, residue)
+				hit = true
+
+				if (paths.size == 1) {
+					// Single path, fast scenario
+					val path = paths[0]
+					val pathTransferred = path.transfer(residue, simulate, snapshot)
+					val thisReceived = it.receiveEnergy(pathTransferred, simulate)
+
+					// If cable transferred more than machine accepted, then "refund" energy
+					// so cables record actual value transferred through them
+					if (thisReceived != pathTransferred) {
+						path.refund(pathTransferred - thisReceived, simulate, snapshot)
+					}
+
+					received += thisReceived
+					residue -= thisReceived
+					if (!residue.isPositive) return received
+				} else if (paths.size >= 2) {
+					// Multiple paths, a bit more complicated
+					// Determine how much machine is likely to accept
+					val potentiallyAccepted = it.receiveEnergy(residue, true)
+
+					// Won't accept anything
+					if (potentiallyAccepted <= Decimal.ZERO)
+						continue
+
+					// Now determine combined available throughput
+					// Make a copy of snapshot, so we can freely write into it
+					val copy = snapshot.clone()
+					var calcResidue = potentiallyAccepted
+
+					// TODO: Currently, all transfers cause Braess's paradox, because of greedy selection of "fastest" cable
+					//  Need to implement heuristics to better distribute load across different paths/segments
+					for (path in paths) {
+						val passed = path.transfer(calcResidue, true, copy)
+						calcResidue -= passed
+						if (calcResidue <= Decimal.ZERO) break
+					}
+
+					if (calcResidue == potentiallyAccepted) {
+						// мда
 						continue
 					}
 
-					side.neighbour.get()?.let {
-						if (it !is EnergyCableBlockEntity.CableSide) {
-							val path = getPath(fromNode, node, residue)
-							hit = true
+					var thisReceived = it.receiveEnergy(potentiallyAccepted - calcResidue, simulate)
+					received += thisReceived
+					residue -= thisReceived
 
-							if (path != null) {
-								val thisReceived = it.receiveEnergy(path.transfer(residue, simulate, snapshot), simulate)
-								received += thisReceived
-								residue -= thisReceived
-								if (!residue.isPositive) return received
-							}
-						}
+					for (path in paths) {
+						val passed = path.transfer(thisReceived, simulate, snapshot)
+						thisReceived -= passed
+						if (thisReceived <= Decimal.ZERO) break
 					}
+
+					if (!residue.isPositive) return received
+					check(thisReceived <= Decimal.ZERO) { "Путом, алло, Путом, какого чёрта Путом? Путом почему ты заблокировал логику, а Путом?" }
 				}
 			}
 
 			if (!hit) {
 				itr.remove()
-				check(livelyNodes.remove(node))
+				check(livelyNodes.remove(node)) { "Lively nodes Set does not contain $node" }
 			}
 		}