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.runners.dataflow.worker.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 java.util.ArrayDeque;
  import java.util.ArrayList;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.IdentityHashMap;
  import java.util.LinkedHashSet;
  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 org.apache.beam.runners.dataflow.worker.graph.Nodes.Node;
  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.graph.EndpointPair;
  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;
  
  /** 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
     * {@link Node} unmodified.
     */
    public abstract static class TypeSafeNodeFunction<T extends Node>
        implements Function<Node, Node> {
      private final Class<T> type;
  
      public TypeSafeNodeFunction(Class<T> type) {
        checkNotNull(type);
        this.type = type;
      }
  
      @SuppressWarnings("unchecked")
      @Override
      public final Node apply(Node input) {
        if (type.isInstance(input)) {
          return typedApply((T) input);
        }
        return input;
      }
  
      public abstract Node 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 <N, E> void replaceDirectedNetworkNodes(
        MutableNetwork<N, E> network, Function<N, N> 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<N, N> oldNodesToNewNodes = new HashMap<>(network.nodes().size());
      for (N currentNode : network.nodes()) {
        N 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<N, N> entry : oldNodesToNewNodes.entrySet()) {
        N oldNode = entry.getKey();
        N newNode = entry.getValue();
        network.addNode(newNode);
        for (N predecessor : ImmutableSet.copyOf(network.predecessors(oldNode))) {
          for (E edge : ImmutableSet.copyOf(network.edgesConnecting(predecessor, oldNode))) {
            network.removeEdge(edge);
            network.addEdge(predecessor, newNode, edge);
          }
        }
        for (N successor : ImmutableSet.copyOf(network.successors(oldNode))) {
          for (E 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 <N, E> Set<N> reachableNodes(
        Network<N, E> network, Set<N> startNodes, Set<N> endNodes) {
      Set<N> visitedNodes = new HashSet<>();
      Queue<N> queuedNodes = new ArrayDeque<>();
      queuedNodes.addAll(startNodes);
      // Perform a breadth-first traversal rooted at the input node.
      while (!queuedNodes.isEmpty()) {
        N 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;
    }
  
    /** Returns a set of nodes sorted in topological order. */
    public static <N, E> Set<N> topologicalOrder(Network<N, E> network) {
      // TODO: 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);
  
      // Linked hashset will prevent duplicates from appearing and will maintain insertion order.
      LinkedHashSet<N> nodes = new LinkedHashSet<>(network.nodes().size());
      Queue<N> processingOrder = new ArrayDeque<>();
      // Add all the roots
      for (N node : network.nodes()) {
        if (network.inDegree(node) == 0) {
          processingOrder.add(node);
        }
      }
  
      while (!processingOrder.isEmpty()) {
        N current = processingOrder.remove();
        // If all predecessors have already been added, then we can add this node, otherwise
        // we need to add the node to the back of the processing queue.
        if (nodes.containsAll(network.predecessors(current))) {
          nodes.add(current);
          processingOrder.addAll(network.successors(current));
        } else {
          processingOrder.add(current);
        }
      }
  
      return nodes;
    }
  
    public static <N, E> String toDot(Network<N, E> network) {
      StringBuilder builder = new StringBuilder();
      builder.append("digraph network {\n");
      IdentityHashMap<N, String> nodeName = Maps.newIdentityHashMap();
      network.nodes().forEach(node -> nodeName.put(node, "n" + nodeName.size()));
      for (Entry<N, String> nodeEntry : nodeName.entrySet()) {
        builder.append(
            String.format(
                "  %s [fontname=\"Courier New\" label=\"%s\"];%n",
                nodeEntry.getValue(), escapeDot(nodeEntry.getKey().toString())));
      }
      for (E edge : network.edges()) {
        EndpointPair<N> 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() {}
  }
  