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package org.jungrapht.visualization.layout.algorithms.sugiyama;

import java.util.*;
import java.util.function.Predicate;
import java.util.stream.Collectors;
import org.jgrapht.Graph;
import org.jgrapht.Graphs;
import org.jgrapht.graph.builder.GraphTypeBuilder;

public class DFSCycleRemoval { //implements Function, Collection> {

  private Graph graph;
  Collection edges;
  Set marked = new HashSet<>();
  Stack stack = new Stack<>();
  Set feedbackArcs = new HashSet<>();
  Predicate edgePredicate;
  Comparator comparator;

  public DFSCycleRemoval(Graph graph) {
    this(graph, (v1, v2) -> 0);
  }

  public DFSCycleRemoval(Graph graph, Comparator comparator) {
    // make a copy of the graph
    this.graph = GraphTypeBuilder.forGraph(graph).buildGraph();
    Graphs.addGraph(this.graph, graph); // dest, source
    this.edges = graph.edgeSet();
    this.comparator = comparator;
    removeCycles();
  }

  public void removeCycles() {
    List vertices = graph.vertexSet().stream().sorted(comparator).collect(Collectors.toList());
    //    Collections.reverse(vertices);
    for (V vertex : vertices) {
      this.dfsRemove(vertex);
    }
  }

  public void setEdgePredicate(Predicate edgePredicate) {
    this.edgePredicate = edgePredicate;
  }

  private void dfsRemove(V vertex) {
    if (this.marked.contains(vertex)) {
      return;
    }
    this.marked.add(vertex);
    this.stack.add(vertex);
    List outgoingEdges =
        graph
            .outgoingEdgesOf(vertex)
            .stream()
            //            .sorted(comparator)
            .collect(Collectors.toList());
    //    Collections.reverse(outgoingEdges);
    for (E edge : outgoingEdges) {
      V target = graph.getEdgeTarget(edge);
      if (this.stack.contains(target)) {
        graph.removeEdge(edge);
        feedbackArcs.add(edge);
      } else if (!this.marked.contains(target)) {
        this.dfsRemove(target);
      }
    }
    this.stack.remove(vertex);
  }

  public Collection getFeedbackArcs() {
    return this.feedbackArcs;
  }
}