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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:https://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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