content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you 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://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.
   */
  package org.apache.beam.sdk.util.construction.graph;
  
  import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkArgument;
  import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkNotNull;
  
  import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
  import java.util.ArrayDeque;
  import java.util.ArrayList;
  import java.util.Comparator;
  import java.util.Deque;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.IdentityHashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.Map.Entry;
  import java.util.Queue;
  import java.util.Set;
  import java.util.function.Function;
  import javax.annotation.Nonnull;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.ImmutableList;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.ImmutableSet;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.Maps;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.Ordering;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.graph.ElementOrder;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.graph.EndpointPair;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.graph.Graphs;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.graph.MutableNetwork;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.graph.Network;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.graph.NetworkBuilder;
  
  /** Static utility methods for {@link Network} instances that are directed. */
  @SuppressWarnings({
    "nullness" // TODO(https://github.com/apache/beam/issues/20497)
  })
  public class Networks {
    /**
     * An abstract class that can be extended to apply a function in a type safe manner.
     *
     * <p>Applies {@link #typedApply} to all instances of {@code type}. Otherwise returns the existing
     * {@code Node} unmodified.
     */
    public abstract static class TypeSafeNodeFunction<NodeT, T extends NodeT>
        implements Function<NodeT, NodeT> {
      private final Class<T> type;
  
      public TypeSafeNodeFunction(Class<T> type) {
        checkNotNull(type);
        this.type = type;
      }
  
      @SuppressWarnings("unchecked")
      @Override
      public final NodeT apply(NodeT input) {
        if (type.isInstance(input)) {
          return typedApply((T) input);
        }
        return input;
      }
  
      public abstract NodeT typedApply(T input);
    }
  
    /**
     * Applies the {@code function} to all nodes within the {@code network}. Replaces any node which
     * is not {@link #equals(Object)} to the original node, maintaining all existing edges between
     * nodes.
     */
    public static <NodeT, EdgeT> void replaceDirectedNetworkNodes(
        MutableNetwork<NodeT, EdgeT> network, Function<NodeT, NodeT> function) {
      checkArgument(network.isDirected(), "Only directed networks are supported, given %s", network);
      checkArgument(
          !network.allowsSelfLoops(),
          "Only networks without self loops are supported, given %s",
          network);
  
      // A map from the existing node to the replacement node
      Map<NodeT, NodeT> oldNodesToNewNodes = new HashMap<>(network.nodes().size());
      for (NodeT currentNode : network.nodes()) {
        NodeT newNode = function.apply(currentNode);
        // Skip updating the network if the old node is equivalent to the new node
        if (!currentNode.equals(newNode)) {
          oldNodesToNewNodes.put(currentNode, newNode);
        }
      }
  
      // For each replacement, connect up the existing predecessors and successors to the new node
      // and then remove the old node.
      for (Map.Entry<NodeT, NodeT> entry : oldNodesToNewNodes.entrySet()) {
        NodeT oldNode = entry.getKey();
        NodeT newNode = entry.getValue();
        network.addNode(newNode);
        for (NodeT predecessor : ImmutableSet.copyOf(network.predecessors(oldNode))) {
          for (EdgeT edge : ImmutableSet.copyOf(network.edgesConnecting(predecessor, oldNode))) {
            network.removeEdge(edge);
            network.addEdge(predecessor, newNode, edge);
          }
        }
        for (NodeT successor : ImmutableSet.copyOf(network.successors(oldNode))) {
          for (EdgeT edge : ImmutableSet.copyOf(network.edgesConnecting(oldNode, successor))) {
            network.removeEdge(edge);
            network.addEdge(newNode, successor, edge);
          }
        }
        network.removeNode(oldNode);
      }
    }
  
    /**
     * Returns the set of nodes that are reachable from {@code startNodes} up to and including {@code
     * endNodes}. Node B is defined as reachable from node A if there exists a path (a sequence of
     * adjacent outgoing edges) starting at node A and ending at node B which does not pass through
     * any node in {@code endNodes}. Note that a node is always reachable from itself via a
     * zero-length path.
     *
     * <p>This is a "snapshot" based on the current topology of the {@code network}, rather than a
     * live view of the set of nodes reachable from {@code node}. In other words, the returned {@link
     * Set} will not be updated after modifications to the {@code network}.
     */
    public static <NodeT, EdgeT> Set<NodeT> reachableNodes(
        Network<NodeT, EdgeT> network, Set<NodeT> startNodes, Set<NodeT> endNodes) {
      Set<NodeT> visitedNodes = new HashSet<>();
      Queue<NodeT> queuedNodes = new ArrayDeque<>();
      queuedNodes.addAll(startNodes);
      // Perform a breadth-first traversal rooted at the input node.
      while (!queuedNodes.isEmpty()) {
        NodeT currentNode = queuedNodes.remove();
        // If we have already visited this node or it is a terminal node than do not add any
        // successors.
        if (!visitedNodes.add(currentNode) || endNodes.contains(currentNode)) {
          continue;
        }
        queuedNodes.addAll(network.successors(currentNode));
      }
      return visitedNodes;
    }
  
    /**
     * Return a set of nodes in sorted topological order.
     *
     * <p>Note that back edges within directed graphs are "broken" returning a topological order for a
     * directed acyclic network which approximates the original network.
     *
     * <p>Nodes will be considered in the order specified by the {@link Network Network's} {@link
     * Network#nodeOrder()}.
     */
    public static <NodeT> Iterable<NodeT> topologicalOrder(Network<NodeT, ?> network) {
      return computeTopologicalOrder(Graphs.copyOf(network));
    }
  
    /**
     * Return a set of nodes in sorted topological order.
     *
     * <p>Note that back edges within directed graphs are "broken" returning a topological order for a
     * directed acyclic network which approximates the original network.
     *
     * <p>Nodes will be considered in the order specified by the {@link
     * ElementOrder#sorted(Comparator) sorted ElementOrder} created with the provided comparator.
     */
    public static <NodeT, EdgeT> Iterable<NodeT> topologicalOrder(
        Network<NodeT, EdgeT> network, Comparator<NodeT> nodeOrder) {
      // Copy the characteristics of the network to ensure that the result network can represent the
      // original network, just with the provided suborder
      MutableNetwork<NodeT, EdgeT> orderedNetwork =
          NetworkBuilder.from(network).nodeOrder(ElementOrder.sorted(nodeOrder)).build();
      for (NodeT node : network.nodes()) {
        orderedNetwork.addNode(node);
      }
      for (EdgeT edge : network.edges()) {
        EndpointPair<NodeT> incident = network.incidentNodes(edge);
        orderedNetwork.addEdge(incident.source(), incident.target(), edge);
      }
      return computeTopologicalOrder(orderedNetwork);
    }
  
    /**
     * Compute the topological order for a {@link Network}.
     *
     * <p>Nodes must be considered in the order specified by the {@link Network Network's} {@link
     * Network#nodeOrder()}. This ensures that any two Networks with the same nodes and node orders
     * produce the same result.
     */
    private static <NodeT> Iterable<NodeT> computeTopologicalOrder(MutableNetwork<NodeT, ?> network) {
      // TODO: (github/guava/2641) Upgrade Guava and remove this method if topological sorting becomes
      // supported externally or remove this comment if its not going to be supported externally.
  
      checkArgument(network.isDirected(), "Only directed networks are supported, given %s", network);
      checkArgument(
          !network.allowsSelfLoops(),
          "Only networks without self loops are supported, given %s",
          network);
  
      // Uses the following algorithm:
      //    A FAST & EFFECTIVE HEURISTIC FOR THE FEEDBACK ARC SET PROBLEM
      //    Peter Eades, Xuemin Lin, W. F. Smyth
      // https://pdfs.semanticscholar.org/c7ed/d9acce96ca357876540e19664eb9d976637f.pdf
      //
      // The only edges that are ignored by the algorithm are back edges.
      // The algorithm (while there are still nodes in the graph):
      //   1) Removes all sinks from the graph adding them to the beginning of "s2". Continue to do
      // this till there
      //      are no more sinks.
      //   2) Removes all source from the graph adding them to the end of "s1". Continue to do this
      // till there
      //      are no more sources.
      //   3) Remote a single node with the highest delta within the graph and add it to the end of
      // "s1".
      //
      // The topological order is then the s1 concatenated with s2.
  
      Deque<NodeT> s1 = new ArrayDeque<>();
      Deque<NodeT> s2 = new ArrayDeque<>();
  
      Ordering<NodeT> maximumOrdering =
          new Ordering<NodeT>() {
            @SuppressFBWarnings(
                value = "NP_METHOD_PARAMETER_TIGHTENS_ANNOTATION",
                justification = "https://github.com/google/guava/issues/920")
            @Override
            public int compare(@Nonnull NodeT t0, @Nonnull NodeT t1) {
              return (network.outDegree(t0) - network.inDegree(t0))
                  - (network.outDegree(t1) - network.inDegree(t1));
            }
          };
  
      while (!network.nodes().isEmpty()) {
        boolean nodeRemoved;
        do {
          nodeRemoved = false;
          for (NodeT possibleSink : ImmutableList.copyOf(network.nodes())) {
            if (network.outDegree(possibleSink) == 0) {
              network.removeNode(possibleSink);
              s2.addFirst(possibleSink);
              nodeRemoved = true;
            }
          }
        } while (nodeRemoved);
  
        do {
          nodeRemoved = false;
          for (NodeT possibleSource : ImmutableList.copyOf(network.nodes())) {
            if (network.inDegree(possibleSource) == 0) {
              network.removeNode(possibleSource);
              s1.addLast(possibleSource);
              nodeRemoved = true;
            }
          }
        } while (nodeRemoved);
  
        if (!network.nodes().isEmpty()) {
          NodeT maximum = maximumOrdering.max(network.nodes());
          network.removeNode(maximum);
          s1.addLast(maximum);
        }
      }
  
      return ImmutableList.<NodeT>builder().addAll(s1).addAll(s2).build();
    }
  
    public static <NodeT, EdgeT> String toDot(Network<NodeT, EdgeT> network) {
      StringBuilder builder = new StringBuilder();
      builder.append(String.format("digraph network {%n"));
      IdentityHashMap<NodeT, String> nodeName = Maps.newIdentityHashMap();
      network.nodes().forEach(node -> nodeName.put(node, "n" + nodeName.size()));
      for (Entry<NodeT, String> nodeEntry : nodeName.entrySet()) {
        builder.append(
            String.format(
                "  %s [fontname=\"Courier New\" label=\"%s\"];%n",
                nodeEntry.getValue(), escapeDot(nodeEntry.getKey().toString())));
      }
      for (EdgeT edge : network.edges()) {
        EndpointPair<NodeT> endpoints = network.incidentNodes(edge);
        builder.append(
            String.format(
                "  %s -> %s [fontname=\"Courier New\" label=\"%s\"];%n",
                nodeName.get(endpoints.source()),
                nodeName.get(endpoints.target()),
                escapeDot(edge.toString())));
      }
      builder.append("}");
      return builder.toString();
    }
  
    private static String escapeDot(String s) {
      return s.replace("\\", "\\\\")
          .replace("\"", "\\\"")
          // http://www.graphviz.org/doc/info/attrs.html#k:escString
          // The escape sequences "\n", "\l" and "\r" divide the label into lines, centered,
          // left-justified, and right-justified, respectively.
          .replace("\n", "\\l");
    }
  
    /**
     * Returns a list of all distinct paths from roots of the network to leaves. The list can be in
     * arbitrary orders and can contain duplicate paths if there are multiple edges from two nodes.
     */
    public static <NodeT, EdgeT> List<List<NodeT>> allPathsFromRootsToLeaves(
        Network<NodeT, EdgeT> network) {
      ArrayDeque<List<NodeT>> paths = new ArrayDeque<>();
      // Populate the list with all roots
      for (NodeT node : network.nodes()) {
        if (network.inDegree(node) == 0) {
          paths.add(ImmutableList.of(node));
        }
      }
  
      List<List<NodeT>> distinctPathsFromRootsToLeaves = new ArrayList<>();
      while (!paths.isEmpty()) {
        List<NodeT> path = paths.removeFirst();
        NodeT lastNode = path.get(path.size() - 1);
        if (network.outDegree(lastNode) == 0) {
          distinctPathsFromRootsToLeaves.add(new ArrayList<>(path));
        } else {
          for (EdgeT edge : network.outEdges(lastNode)) {
            paths.addFirst(
                ImmutableList.<NodeT>builder()
                    .addAll(path)
                    .add(network.incidentNodes(edge).target())
                    .build());
          }
        }
      }
      return distinctPathsFromRootsToLeaves;
    }
  
    // Hide visibility to prevent instantiation
    private Networks() {}
  }
  