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Merge pull request #354 from modelix/fix/LinearHistory
fix(model-datastructure): fix LinearHistory
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model-datastructure/src/commonMain/kotlin/org/modelix/model/LinearHistory.kt
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| Original file line number | Diff line number | Diff line change |
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| @@ -1,99 +1,138 @@ | ||
| package org.modelix.model | ||
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| import org.modelix.model.lazy.CLVersion | ||
| import org.modelix.model.lazy.IDeserializingKeyValueStore | ||
| import org.modelix.model.lazy.KVEntryReference | ||
| import org.modelix.model.persistent.CPVersion | ||
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| /** | ||
| * Was introduced in https://github.com/modelix/modelix/commit/19c74bed5921028af3ac3ee9d997fc1c4203ad44 | ||
| * together with the UndoOp. The idea is that an undo should only revert changes if there is no other change that relies | ||
| * on it. In that case the undo should do nothing, to not indirectly undo newer changes. | ||
| * For example, if you added a node and someone else started changing properties on the that node, your undo should not | ||
| * remove the node to not lose the property changes. | ||
| * This requires the versions to be ordered in a way that the undo appears later. | ||
| */ | ||
| class LinearHistory(val baseVersionHash: String?) { | ||
| class LinearHistory(private val baseVersionHash: String?) { | ||
| /** | ||
| * Children indexed by their parent versions. | ||
| * A version is a parent of a child, | ||
| * if the [CLVersion.baseVersion], the [CLVersion.getMergedVersion1] or [CLVersion.getMergedVersion2] | ||
| */ | ||
| private val byVersionChildren = mutableMapOf<CLVersion, MutableSet<CLVersion>>() | ||
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| val version2directDescendants: MutableMap<Long, Set<Long>> = HashMap() | ||
| val versions: MutableMap<Long, CLVersion> = LinkedHashMap() | ||
| /** | ||
| * Global roots are versions without parents. | ||
| * It may be only the version denoted [baseVersionHash] | ||
| * or many versions, if no base version was specified and versions without a common global root are ordered. | ||
| */ | ||
| private val globalRoot = mutableSetOf<CLVersion>() | ||
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| /** | ||
| * @param fromVersions it is assumed that the versions are sorted by the oldest version first. When merging a new | ||
| * version into an existing one the new version should appear after the existing one. The resulting order | ||
| * will prefer existing versions to new ones, meaning during the conflict resolution the existing changes | ||
| * have a higher probability of surviving. | ||
| * @returns oldest version first | ||
| * The distance of a version from its root. | ||
| * Aka how many children a between the root and a version. | ||
| */ | ||
| private val byVersionDistanceFromGlobalRoot = mutableMapOf<CLVersion, Int>() | ||
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| /** | ||
| * Returns all versions between the [fromVersions] and a common version. | ||
| * The common version may be identified by [baseVersionHash]. | ||
| * If no [baseVersionHash] is given, the common version wile be the first version | ||
| * aka the version without a [CLVersion.baseVersion]. | ||
| * | ||
| * The order also ensures three properties: | ||
| * 1. The versions are ordered topologically starting with the versions without parents. | ||
| * 2. The order is also "monotonic". | ||
| * This means adding a version to the set of all versions will never change | ||
| * the order of versions that were previously in the history. | ||
| * For example, given versions 1, 2 and 3: | ||
| * If 1 and 2 are ordered as (1, 2), ordering 1, 2 and 3 will never produce (2, 3, 1). | ||
| * 3 can come anywhere (respecting the topological ordering), but 2 has to come after 1. | ||
| * 3. "Close versions are kept together" | ||
| * Formally: A version that has only one child (ignoring) should always come before the child. | ||
| * Example: 1 <- 2 <- 3 and 1 <- x, then [1, 2, 4, 3] is not allowed, | ||
| * because 3 is the only child of 2. | ||
| * Valid orders would be (1, x, 3, 4) and (1, x, 2, 3) | ||
| * This is relevant for UnduOp and RedoOp. | ||
| * See UndoTest. | ||
| */ | ||
| fun load(vararg fromVersions: CLVersion): List<CLVersion> { | ||
| for (fromVersion in fromVersions) { | ||
| collect(fromVersion) | ||
| } | ||
| // Traverse the versions once to index need data: | ||
| // * Collect all relevant versions. | ||
| // * Collect the distance to the base for each version. | ||
| // * Collect the roots of relevant versions. | ||
| // * Collect the children of each version. | ||
| indexData(*fromVersions) | ||
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| var result: List<Long> = emptyList() | ||
| // The following algorithm orders the version by | ||
| // 1. Finding out the roots of so-called subtrees. | ||
| // A subtree is a tree of all versions that have the same version as root ancestor. | ||
| // A root ancestor of a version is the first ancestor in the chain of ancestors | ||
| // that is either a merge or a global root. | ||
| // Each version belongs to exactly one root ancestor, and it will be the same (especially future merges). | ||
| // 2. Sort the roots of subtrees according to their distance (primary) and id (secondary) | ||
| // 3. Order topologically inside each subtree. | ||
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| for (version in versions.values.filter { !it.isMerge() }.sortedBy { it.id }) { | ||
| val descendantIds = collectAllDescendants(version.id).filter { !versions[it]!!.isMerge() }.sorted().toSet() | ||
| val idsInResult = result.toHashSet() | ||
| if (idsInResult.contains(version.id)) { | ||
| result = | ||
| result + | ||
| descendantIds.filter { !idsInResult.contains(it) } | ||
| } else { | ||
| result = | ||
| result.filter { !descendantIds.contains(it) } + | ||
| version.id + | ||
| result.filter { descendantIds.contains(it) } + | ||
| descendantIds.filter { !idsInResult.contains(it) } | ||
| } | ||
| } | ||
| return result.map { versions[it]!! } | ||
| } | ||
| // Ordering the subtree root first, ensures the order is also "monotonic". | ||
| // Then ordering the inside subtree ensures "close versions are kept together" without breaking "monotonicity". | ||
| // Ordering inside a subtree ensures "monotonicity", because a subtree has no merges. | ||
| // Only a subtrees root can be a merge. | ||
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| private fun collectAllDescendants(root: Long): Set<Long> { | ||
| val result = LinkedHashSet<Long>() | ||
| var previousSize = 0 | ||
| result += root | ||
| // Sorting the subtree roots by distance from base ensures topological order. | ||
| val comparator = compareBy(byVersionDistanceFromGlobalRoot::getValue) | ||
| // Sorting the subtree roots by distance from base and then by id ensures "monotonic" order. | ||
| .thenBy(CLVersion::id) | ||
| val rootsOfSubtreesToVisit = globalRoot + byVersionDistanceFromGlobalRoot.keys.filter(CLVersion::isMerge) | ||
| val orderedRootsOfSubtree = rootsOfSubtreesToVisit.distinct().sortedWith(comparator) | ||
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| while (previousSize != result.size) { | ||
| val nextElements = result.asSequence().drop(previousSize).toList() | ||
| previousSize = result.size | ||
| for (ancestor in nextElements) { | ||
| version2directDescendants[ancestor]?.let { result += it } | ||
| val history = orderedRootsOfSubtree.flatMap { rootOfSubtree -> | ||
| val historyOfSubtree = mutableListOf<CLVersion>() | ||
| val stack = ArrayDeque<CLVersion>() | ||
| stack.add(rootOfSubtree) | ||
| while (stack.isNotEmpty()) { | ||
| val version = stack.removeLast() | ||
| historyOfSubtree.add(version) | ||
| val children = byVersionChildren.getOrElse(version, ::emptyList) | ||
| val childrenWithoutMerges = children.filterNot(CLVersion::isMerge) | ||
| // Order so that child with the lowest id is processed first | ||
| // and comes first in the history. | ||
| stack.addAll(childrenWithoutMerges.sortedByDescending(CLVersion::id)) | ||
| } | ||
| historyOfSubtree | ||
| } | ||
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| return result.drop(1).toSet() | ||
| return history.filterNot(CLVersion::isMerge) | ||
| } | ||
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| private fun collect(root: CLVersion) { | ||
| if (root.getContentHash() == baseVersionHash) return | ||
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| var previousSize = versions.size | ||
| versions[root.id] = root | ||
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| while (previousSize != versions.size) { | ||
| val nextElements = versions.asSequence().drop(previousSize).map { it.value }.toList() | ||
| previousSize = versions.size | ||
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| for (descendant in nextElements) { | ||
| val ancestors = if (descendant.isMerge()) { | ||
| sequenceOf( | ||
| getVersion(descendant.data!!.mergedVersion1!!, descendant.store), | ||
| getVersion(descendant.data!!.mergedVersion2!!, descendant.store), | ||
| ) | ||
| private fun indexData(vararg fromVersions: CLVersion): MutableMap<CLVersion, Int> { | ||
| val stack = ArrayDeque<CLVersion>() | ||
| fromVersions.forEach { fromVersion -> | ||
| if (byVersionDistanceFromGlobalRoot.contains(fromVersion)) { | ||
| return@forEach | ||
| } | ||
| stack.addLast(fromVersion) | ||
| while (stack.isNotEmpty()) { | ||
| val version = stack.last() | ||
| val parents = version.getParents() | ||
| // Version is the base version or the first version and therfore a root. | ||
| if (parents.isEmpty()) { | ||
| stack.removeLast() | ||
| globalRoot.add(version) | ||
| byVersionDistanceFromGlobalRoot[version] = 0 | ||
| } else { | ||
| sequenceOf(descendant.baseVersion) | ||
| }.filterNotNull().filter { it.getContentHash() != baseVersionHash }.toList() | ||
| for (ancestor in ancestors) { | ||
| versions[ancestor.id] = ancestor | ||
| version2directDescendants[ancestor.id] = (version2directDescendants[ancestor.id] ?: emptySet()) + setOf(descendant.id) | ||
| parents.forEach { parent -> | ||
| byVersionChildren.getOrPut(parent, ::mutableSetOf).add(version) | ||
| } | ||
| val (visitedParents, notVisitedParents) = parents.partition(byVersionDistanceFromGlobalRoot::contains) | ||
| // All children where already visited and have their distance known. | ||
| if (notVisitedParents.isEmpty()) { | ||
| stack.removeLast() | ||
| val depth = visitedParents.maxOf { byVersionDistanceFromGlobalRoot[it]!! } + 1 | ||
| byVersionDistanceFromGlobalRoot[version] = depth | ||
| // Children need to be visited | ||
| } else { | ||
| stack.addAll(notVisitedParents) | ||
| } | ||
| } | ||
| } | ||
| } | ||
| return byVersionDistanceFromGlobalRoot | ||
| } | ||
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| private fun getVersion(hash: KVEntryReference<CPVersion>, store: IDeserializingKeyValueStore): CLVersion { | ||
| return CLVersion(hash.getValue(store), store) | ||
| private fun CLVersion.getParents(): List<CLVersion> { | ||
| val ancestors = if (isMerge()) { | ||
| listOf(getMergedVersion1()!!, getMergedVersion2()!!) | ||
| } else { | ||
| listOfNotNull(baseVersion) | ||
| } | ||
| return ancestors.filter { it.getContentHash() != baseVersionHash } | ||
| } | ||
| } |
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