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Ordering of patches with cycles during upload (#2524)
* Ordering of patches with cyclic during upload * Ignored failing test * Refactored and added tests * Refactored * Updated code to use strongly connected resources * Review comments: Seperated the code for finding ssc. Added some tets for Bundle generation. * Refactored code and added tests. * Refactored code and added tests. * Updated StronglyConnectedPatches to compute node size * Added comments * Updated tarjan * Review comments: Updated docs
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engine/src/main/java/com/google/android/fhir/sync/upload/patch/StronglyConnectedPatches.kt
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| /* | ||
| * Copyright 2024 Google LLC | ||
| * | ||
| * Licensed under the Apache License, Version 2.0 (the "License"); | ||
| * you may not use this file except in compliance with the License. | ||
| * You may obtain a copy of the License at | ||
| * | ||
| * http://www.apache.org/licenses/LICENSE-2.0 | ||
| * | ||
| * Unless required by applicable law or agreed to in writing, software | ||
| * distributed under the License is distributed on an "AS IS" BASIS, | ||
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| * See the License for the specific language governing permissions and | ||
| * limitations under the License. | ||
| */ | ||
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| package com.google.android.fhir.sync.upload.patch | ||
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| import kotlin.math.min | ||
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| internal object StronglyConnectedPatches { | ||
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| /** | ||
| * Takes a [directedGraph] and computes all the strongly connected components in the graph. | ||
| * | ||
| * @return An ordered List of strongly connected components of the [directedGraph]. The SCCs are | ||
| * topologically ordered which may change based on the ordering algorithm and the [Node]s inside | ||
| * a SSC may be ordered randomly depending on the path taken by algorithm to discover the nodes. | ||
| */ | ||
| fun scc(directedGraph: Graph): List<List<Node>> { | ||
| return findSCCWithTarjan(directedGraph) | ||
| } | ||
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| /** | ||
| * Finds strongly connected components in topological order. See | ||
| * https://en.wikipedia.org/wiki/Tarjan%27s_strongly_connected_components_algorithm. | ||
| */ | ||
| private fun findSCCWithTarjan(diGraph: Graph): List<List<Node>> { | ||
| // Ideally the graph.keys should have all the nodes in the graph. But use values as well in case | ||
| // the input graph looks something like [ N1: [N2] ]. | ||
| val nodeToIndex = | ||
| (diGraph.keys + diGraph.values.flatten().toSet()) | ||
| .mapIndexed { index, s -> s to index } | ||
| .toMap() | ||
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| val sccs = mutableListOf<List<Node>>() | ||
| val lowLinks = IntArray(nodeToIndex.size) | ||
| var exploringCounter = 0 | ||
| val discoveryTimes = IntArray(nodeToIndex.size) | ||
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| val visitedNodes = BooleanArray(nodeToIndex.size) | ||
| val nodesCurrentlyInStack = BooleanArray(nodeToIndex.size) | ||
| val stack = ArrayDeque<Node>() | ||
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| fun Node.index() = nodeToIndex[this]!! | ||
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| fun dfs(at: Node) { | ||
| lowLinks[at.index()] = exploringCounter | ||
| discoveryTimes[at.index()] = exploringCounter | ||
| visitedNodes[at.index()] = true | ||
| exploringCounter++ | ||
| stack.addFirst(at) | ||
| nodesCurrentlyInStack[at.index()] = true | ||
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| diGraph[at]?.forEach { | ||
| if (!visitedNodes[it.index()]) { | ||
| dfs(it) | ||
| } | ||
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| if (nodesCurrentlyInStack[it.index()]) { | ||
| lowLinks[at.index()] = min(lowLinks[at.index()], lowLinks[it.index()]) | ||
| } | ||
| } | ||
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| // We have found the head node in the scc. | ||
| if (lowLinks[at.index()] == discoveryTimes[at.index()]) { | ||
| val connected = mutableListOf<Node>() | ||
| var node: Node | ||
| do { | ||
| node = stack.removeFirst() | ||
| connected.add(node) | ||
| nodesCurrentlyInStack[node.index()] = false | ||
| } while (node != at && stack.isNotEmpty()) | ||
| sccs.add(connected.reversed()) | ||
| } | ||
| } | ||
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| diGraph.keys.forEach { | ||
| if (!visitedNodes[it.index()]) { | ||
| dfs(it) | ||
| } | ||
| } | ||
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| return sccs | ||
| } | ||
| } |
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