server/protocols/jmap-draft/src/main/java/org/apache/james/jmap/draft/utils/DependencyGraph.java

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package org.apache.james.jmap.draft.utils;

import java.util.Optional;
import java.util.function.Function;
import java.util.stream.Stream;

import org.apache.james.util.streams.Iterators;
import org.jgrapht.alg.cycle.CycleDetector;
import org.jgrapht.graph.DefaultDirectedGraph;
import org.jgrapht.graph.DefaultEdge;
import org.jgrapht.graph.builder.GraphBuilder;
import org.jgrapht.traverse.TopologicalOrderIterator;

public class DependencyGraph<T> {

    private final GraphBuilder<T, DefaultEdge, DefaultDirectedGraph<T, DefaultEdge>> builder;
    private final Function<T, Optional<T>> getParent;

    public DependencyGraph(Function<T, Optional<T>> getParent) {
        this.getParent = getParent;
        this.builder = new GraphBuilder<>(new DefaultDirectedGraph<>(DefaultEdge.class));
    }

    public void registerItem(T item) {
        builder.addVertex(item);
        getParent.apply(item)
                .map(parentNode -> builder.addEdge(parentNode, item));
    }

    public Stream<T> getBuildChain() throws CycleDetectedException {
        DefaultDirectedGraph<T, DefaultEdge> graph = builder.build();
        ensureNoCycle(graph);
        return Iterators.toStream(new TopologicalOrderIterator<>(graph));
    }

    private void ensureNoCycle(DefaultDirectedGraph<T, DefaultEdge> graph) throws CycleDetectedException {
        CycleDetector<T, DefaultEdge> cycleDetector = new CycleDetector<>(graph);
        if (cycleDetector.detectCycles()) {
            throw new CycleDetectedException();
        }
    }

    public String toString() {
        return builder.build().toString();
    }
    
    public static class CycleDetectedException extends RuntimeException {
        
    }
}