--- /dev/null
+package org.simantics.db.common.utils;
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Iterator;
+
+import org.simantics.db.ReadGraph;
+import org.simantics.db.Resource;
+import org.simantics.db.Statement;
+import org.simantics.db.exception.DatabaseException;
+import org.simantics.layer0.Layer0;
+
+import gnu.trove.map.hash.TObjectIntHashMap;
+import gnu.trove.set.hash.THashSet;
+
+/**
+ * <p>A utility to finds the nearest owner of a real or imaginary resource.</p>
+ *
+ * <p>The nearest owner
+ * is found by first finding a path (pilot path) from the input to a root resource and then
+ * trying to find other paths to the resources in the pilot path such that the other
+ * paths don't visit other resources of the pilot path. The farthest resource so found
+ * is then the nearest common owner. See the methods for the exact specification.</p>
+ *
+ * <p>The time and space complexity of the algorithm is O(m),
+ * where m is the number of resources reachable by direct-owners relation from the input.</p>
+ *
+ * @see {@link #getNearestOwner(ReadGraph, Resource)}
+ * @see {@link #getNearestOwner(ReadGraph, Collection)}</p>
+ *
+ */
+public class NearestOwnerFinder {
+ private static final int FIRST_DISTANCE = 1;
+ private static final int UNVISITED = 0;
+ private static final int NOT_INTERESTING_ANYMORE = -1;
+
+ private final ReadGraph graph;
+ private final Layer0 L0;
+
+ private final TObjectIntHashMap<Resource> resourceStatus = new TObjectIntHashMap<>();
+
+ private int nearestOwnerDistance; // = 0
+ private Resource nearestOwner; // = null
+
+ private NearestOwnerFinder(ReadGraph graph, Layer0 L0) {
+ this.graph = graph;
+ this.L0 = L0;
+ }
+
+ /**
+ * Iterates the owners of the input resource. It first
+ * tries to find the pilot path and when it has been found,
+ * it browses other owners with {@link #browseNonpilot}.
+ */
+ private void browseOwnersOfInput(Collection<Resource> owners) throws DatabaseException {
+ Iterator<Resource> it = owners.iterator();
+ while(it.hasNext()) {
+ Resource owner = it.next();
+ if(browsePilot(owner, FIRST_DISTANCE)) {
+ // Because we found a path to root, {@code owner}
+ // becomes our first candidate for nearestOwner.
+ nearestOwner = owner;
+ nearestOwnerDistance = FIRST_DISTANCE;
+
+ // Tries to find other paths to the resource in the pilot path.
+ while(it.hasNext())
+ browseNonpilot(it.next());
+ return;
+ }
+ }
+ }
+
+ /**
+ * Tries to find a first path (=pilot path) to a root with DFS.
+ */
+ private boolean browsePilot(Resource resource, int distance) throws DatabaseException {
+ if(resourceStatus.putIfAbsent(resource, distance) != UNVISITED)
+ // We recursed back to the current path or encountered previously failed path.
+ return false;
+
+ Collection<Resource> owners = getDirectOwners(graph, L0, resource);
+ if(owners.isEmpty())
+ // We found a root
+ return true;
+
+ for(Resource owner : owners)
+ if(browsePilot(owner, distance+1)) {
+ // We found a path to a root
+ return true;
+ }
+
+ // Failed to find a path to a root
+ resourceStatus.put(resource, NOT_INTERESTING_ANYMORE);
+ return false;
+ }
+
+ /**
+ * Tries to find some path to a resource on a pilot path using DFS.
+ * Marks all visited resource by {@code NOT_INTERESTING_ANYMORE}
+ * to prevent visiting the same resources more than once.
+ */
+ private void browseNonpilot(Resource resource) throws DatabaseException {
+ // In the next statement, we may overwrite also information about resource being on pilot path,
+ // but that is ok, because we don't care resources that are nearer than nearestOwnerDistance.
+ int status = resourceStatus.put(resource, NOT_INTERESTING_ANYMORE);
+ if(status == UNVISITED) {
+ Collection<Resource> owners = getDirectOwners(graph, L0, resource);
+ if(owners.isEmpty()) {
+ // This is a root that differs from the root at the end of the pilot path.
+ // Therefore there cannot be a nearest owner.
+ nearestOwnerDistance = Integer.MAX_VALUE;
+ nearestOwner = null;
+ return;
+ }
+ for(Resource owner : owners)
+ browseNonpilot(owner);
+ }
+ else if(status > nearestOwnerDistance) {
+ nearestOwnerDistance = status;
+ nearestOwner = resource;
+ }
+ }
+
+ private static Collection<Resource> getDirectOwners(ReadGraph graph, Layer0 L0, Resource resource) throws DatabaseException {
+ Collection<Resource> owners = graph.getObjects(resource, L0.IsOwnedBy);
+ if(owners.isEmpty()) {
+ if(resource.equals(graph.getRootLibrary()))
+ return Collections.emptyList();
+
+ owners = new THashSet<Resource>();
+
+ // If there are no owners, collect resources referring to this resource by IsRelatedTo
+ for(Statement statement : graph.getStatements(resource, L0.IsWeaklyRelatedTo)) {
+ Resource inverse = graph.getPossibleInverse(statement.getPredicate());
+ if(inverse != null) {
+ if(graph.isSubrelationOf(inverse, L0.IsRelatedTo)) {
+ // Filter away tags
+ if(resource.equals(statement.getObject()))
+ continue;
+ owners.add(statement.getObject());
+ }
+ }
+ }
+ }
+ else if(owners.size() > 1) {
+ // TODO: getObjects returns duplicate entries (https://www.simantics.org/redmine/issues/4885) and therefore direct is Set<Resource>.
+ // Fix getObjects to not return duplicate entries
+ owners = new HashSet<Resource>(owners);
+ }
+
+ return owners;
+ }
+
+ /**
+ * <p>Finds the nearest owner of a resource. Nearest owner is the
+ * <a href="https://en.wikipedia.org/wiki/Dominator_(graph_theory)">immediate dominator</a>
+ * of the resource in a graph defined in the following way:
+ * Each IsComposedOf statement is an edge of the graph.
+ * Additionally an IsRelatedTo statement in an edge of graph if
+ * no IsComposedOf statement points to its object.</p>
+ *
+ * <p>The root of the graph is any resource without owners or the root resource
+ * of the database. If the search encounters two distinct roots, there
+ * cannot be a nearest owner.</p>
+ *
+ * @return The nearest owner or {@code null} if no roots or more than one roots are found.
+ */
+ public static Resource getNearestOwner(ReadGraph graph, Resource resource) throws DatabaseException {
+ // Handle cases of one or zero direct owners
+ Layer0 L0 = Layer0.getInstance(graph);
+ Collection<Resource> owners = getDirectOwners(graph, L0, resource);
+ if(owners.size() == 1)
+ return owners.iterator().next();
+ if(owners.isEmpty())
+ return null;
+
+ // There are two or more direct owners
+ NearestOwnerFinder finder = new NearestOwnerFinder(graph, L0);
+ finder.resourceStatus.put(resource, NOT_INTERESTING_ANYMORE);
+ finder.browseOwnersOfInput(owners);
+ return finder.nearestOwner;
+ }
+
+ /**
+ * <p>Finds the nearest owner of a real or imaginary resource whose direct owners are known. This works in the same
+ * way as the method for one resource {@link #getNearestOwner(ReadGraph, Resource)}
+ * but we add one extra node to the graph that has the input resources as direct owners and
+ * find the immediate dominator of that extra node.</p>
+ *
+ * <p>Note that this method may return one of the input resources if it is dominator of all other
+ * resources in the collection. Returns {@code null} if the input collection is empty.</p>
+ */
+ public static Resource getNearestOwnerFromDirectOwners(ReadGraph graph, Collection<Resource> owners) throws DatabaseException {
+ // Handle the cases of one or zero direct owners
+ if(owners.size() == 1)
+ return owners.iterator().next();
+ if(owners.isEmpty())
+ return null;
+
+ // There are two or more direct owners
+ Layer0 L0 = Layer0.getInstance(graph);
+ NearestOwnerFinder finder = new NearestOwnerFinder(graph, L0);
+ finder.browseOwnersOfInput(owners);
+ return finder.nearestOwner;
+ }
+}
Code Review / simantics / platform.git / blobdiff