/*
 * 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.core.construction.graph;

import static org.apache.beam.vendor.guava.v20_0.com.google.common.base.Preconditions.checkArgument;
import static org.hamcrest.Matchers.containsInAnyOrder;
import static org.hamcrest.Matchers.emptyIterable;
import static org.hamcrest.Matchers.equalTo;
import static org.hamcrest.Matchers.greaterThan;
import static org.hamcrest.collection.IsEmptyCollection.empty;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertThat;

import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;
import org.apache.beam.vendor.guava.v20_0.com.google.common.collect.ImmutableList;
import org.apache.beam.vendor.guava.v20_0.com.google.common.collect.ImmutableSet;
import org.apache.beam.vendor.guava.v20_0.com.google.common.collect.Iterables;
import org.apache.beam.vendor.guava.v20_0.com.google.common.collect.Ordering;
import org.apache.beam.vendor.guava.v20_0.com.google.common.collect.Sets;
import org.apache.beam.vendor.guava.v20_0.com.google.common.graph.ElementOrder;
import org.apache.beam.vendor.guava.v20_0.com.google.common.graph.EndpointPair;
import org.apache.beam.vendor.guava.v20_0.com.google.common.graph.MutableNetwork;
import org.apache.beam.vendor.guava.v20_0.com.google.common.graph.NetworkBuilder;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.JUnit4;

/** Tests for {@link Networks}. */
@RunWith(JUnit4.class)
public class NetworksTest {
  @Test
  public void testTopologicalSortWithEmptyNetwork() {
    assertThat(Networks.topologicalOrder(createEmptyNetwork()), emptyIterable());
  }

  @Test
  public void testTopologicalSort() {
    MutableNetwork<String, String> network = createNetwork();
    Iterable<String> sortedNodes = Networks.topologicalOrder(network);
    Map<String, Integer> nodeToPosition = new HashMap<>(Iterables.size(sortedNodes));
    int i = 0;
    for (String node : sortedNodes) {
      nodeToPosition.put(node, i);
      i += 1;
    }

    for (String node : network.nodes()) {
      for (String descendant :
          Sets.difference(
              Networks.reachableNodes(network, ImmutableSet.of(node), Collections.emptySet()),
              Sets.newHashSet(node))) {
        assertThat(
            String.format(
                "Expected position of node %s to be before descendant %s,"
                    + " order returned %s for network %s",
                node, descendant, sortedNodes, network),
            nodeToPosition.get(descendant),
            greaterThan(nodeToPosition.get(node)));
      }
    }
  }

  @Test
  public void testTopologicalSortWithSuborder() {
    // This cast is required to narrow the type accepted by the comparator
    Comparator<String> subOrder = (Comparator<String>) (Comparator) Ordering.arbitrary();
    MutableNetwork<String, String> network = createNetwork();

    Iterable<String> sortedNodes = Networks.topologicalOrder(network, subOrder);

    MutableNetwork<String, String> naturalOrderedNetwork =
        NetworkBuilder.from(network)
            .nodeOrder(ElementOrder.<String>natural())
            .edgeOrder(ElementOrder.<String>natural())
            .build();
    MutableNetwork<String, String> arbitraryOrderNetwork =
        NetworkBuilder.from(network)
            .nodeOrder(ElementOrder.unordered())
            .edgeOrder(ElementOrder.unordered())
            .build();
    MutableNetwork<String, String> reverseNaturalOrderNetwork =
        NetworkBuilder.from(network)
            .nodeOrder(ElementOrder.sorted(Ordering.natural().reverse()))
            .edgeOrder(ElementOrder.sorted(Ordering.natural().reverse()))
            .build();

    for (String node : network.nodes()) {
      naturalOrderedNetwork.addNode(node);
      arbitraryOrderNetwork.addNode(node);
      reverseNaturalOrderNetwork.addNode(node);
    }

    for (String edge : network.edges()) {
      EndpointPair<String> incident = network.incidentNodes(edge);
      naturalOrderedNetwork.addEdge(incident.source(), incident.target(), edge);
      arbitraryOrderNetwork.addEdge(incident.source(), incident.target(), edge);
      reverseNaturalOrderNetwork.addEdge(incident.source(), incident.target(), edge);
    }

    Iterable<String> naturalSortedNodes =
        Networks.topologicalOrder(naturalOrderedNetwork, subOrder);
    Iterable<String> arbitrarySortedNodes =
        Networks.topologicalOrder(arbitraryOrderNetwork, subOrder);
    Iterable<String> reverseNaturalSortedNodes =
        Networks.topologicalOrder(reverseNaturalOrderNetwork, subOrder);

    assertThat(sortedNodes, equalTo(naturalSortedNodes));
    assertThat(sortedNodes, equalTo(arbitrarySortedNodes));
    assertThat(sortedNodes, equalTo(reverseNaturalSortedNodes));
  }

  @Test
  public void testTopologicalOrderWithFeedbackArcs() throws Exception {
    MutableNetwork<String, String> network = createNetwork();
    network.addEdge("F", "B", "FB");
    Iterable<String> sortedNodes = Networks.topologicalOrder(network);
    Map<String, Integer> nodeToPosition = new HashMap<>(Iterables.size(sortedNodes));
    int i = 0;
    for (String node : sortedNodes) {
      nodeToPosition.put(node, i);
      i += 1;
    }

    for (String node : network.nodes()) {
      for (String descendant :
          Sets.difference(
              Networks.reachableNodes(network, ImmutableSet.of(node), Collections.emptySet()),
              Sets.newHashSet(node))) {
        if (!Networks.reachableNodes(network, ImmutableSet.of(descendant), Collections.emptySet())
            .contains(node)) {
          // We only reliably compare nodes outside of a loop.
          assertThat(
              String.format(
                  "Expected position of node %s to be before descendant %s,"
                      + " order returned %s for network %s",
                  node, descendant, sortedNodes, network),
              nodeToPosition.get(descendant),
              greaterThan(nodeToPosition.get(node)));
        }
      }
    }
  }

  @Test
  public void testReachableNodesWithEmptyNetwork() {
    assertThat(
        Networks.reachableNodes(
            createEmptyNetwork(), Collections.emptySet(), Collections.emptySet()),
        empty());
  }

  @Test
  public void testReachableNodesFromAllRoots() {
    assertEquals(
        createNetwork().nodes(),
        Networks.reachableNodes(
            createNetwork(), ImmutableSet.of("A", "D", "I", "M", "O"), Collections.emptySet()));
  }

  @Test
  public void testReachableNodesFromAllRootsToAllRoots() {
    assertEquals(
        ImmutableSet.of("A", "D", "I", "M", "O"),
        Networks.reachableNodes(
            createNetwork(),
            ImmutableSet.of("A", "D", "I", "M", "O"),
            ImmutableSet.of("A", "D", "I", "M", "O")));
  }

  @Test
  public void testReachableNodesWithPathAroundBoundaryNode() {
    // Since there is a path around J, we will include E, G, and H
    assertEquals(
        ImmutableSet.of("I", "J", "E", "G", "H", "K", "L"),
        Networks.reachableNodes(createNetwork(), ImmutableSet.of("I"), ImmutableSet.of("J")));
  }

  @Test
  public void testNodeReplacementInEmptyNetwork() {
    MutableNetwork<String, String> network = createEmptyNetwork();
    Networks.replaceDirectedNetworkNodes(network, String::toLowerCase);
    assertThat(network.nodes(), empty());
  }

  @Test
  public void testNodeReplacement() {
    Function<String, String> function =
        input -> {
          if ("E".equals(input) || "J".equals(input) || "M".equals(input) || "O".equals(input)) {
            return input.toLowerCase();
          }
          checkArgument(
              !input.toLowerCase().equals(input),
              "All inputs should be in upper case, got %s. "
                  + "This may indicate calling the function on multiple inputs",
              input);
          return input;
        };

    MutableNetwork<String, String> network = createNetwork();
    Networks.replaceDirectedNetworkNodes(network, function);
    MutableNetwork<String, String> originalNetwork = createNetwork();
    for (String node : originalNetwork.nodes()) {
      assertEquals(
          originalNetwork.successors(node).stream()
              .map(function)
              .collect(Collectors.toCollection(HashSet::new)),
          network.successors(function.apply(node)));
    }
    assertEquals(
        network.nodes(),
        originalNetwork.nodes().stream()
            .map(function)
            .collect(Collectors.toCollection(HashSet::new)));
  }

  @Test
  public void testAllPathsFromRootsToLeaves() {
    // Expected paths:
    // D
    // A, B, C, F
    // A, B, E, G
    // A, B, E, G (again)
    // A, B, E, H
    // I, J, E, G
    // I, J, E, G (again)
    // I, J, E, H
    // I, E, G
    // I, E, G (again)
    // I, E, H
    // I, K, L
    // M, N, L
    // M, N, L (again)
    // O
    List<List<String>> expectedPaths =
        ImmutableList.of(
            ImmutableList.of("D"),
            ImmutableList.of("A", "B", "C", "F"),
            ImmutableList.of("A", "B", "E", "G"),
            ImmutableList.of("A", "B", "E", "G"),
            ImmutableList.of("A", "B", "E", "H"),
            ImmutableList.of("I", "J", "E", "G"),
            ImmutableList.of("I", "J", "E", "G"),
            ImmutableList.of("I", "J", "E", "H"),
            ImmutableList.of("I", "E", "G"),
            ImmutableList.of("I", "E", "G"),
            ImmutableList.of("I", "E", "H"),
            ImmutableList.of("I", "K", "L"),
            ImmutableList.of("M", "N", "L"),
            ImmutableList.of("M", "N", "L"),
            ImmutableList.of("O"));

    MutableNetwork<String, String> network = createNetwork();
    List<List<String>> actualPaths = Networks.allPathsFromRootsToLeaves(network);

    assertThat(actualPaths, containsInAnyOrder(expectedPaths.toArray()));
    assertEquals(actualPaths.size(), expectedPaths.size());
  }

  private static MutableNetwork<String, String> createNetwork() {
    // D
    //        /--> C --> F
    // A --> B      /--\
    //        |--> E --> G
    //  /--> J    / \--> H
    // I --------/
    //  \--> K
    //  /---\ |--> L
    // M --> N
    // O
    List<String> nodesInNetwork =
        ImmutableList.of("A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O");
    MutableNetwork<String, String> network = createEmptyNetwork();
    for (String node : nodesInNetwork) {
      network.addNode(node);
    }
    network.addEdge("A", "B", "AB");
    network.addEdge("B", "C", "BC");
    network.addEdge("B", "E", "BE");
    network.addEdge("C", "F", "CF");
    network.addEdge("E", "G", "EG1");
    network.addEdge("E", "G", "EG2");
    network.addEdge("E", "H", "EH");
    network.addEdge("I", "J", "IJ");
    network.addEdge("I", "E", "IE");
    network.addEdge("I", "K", "IK");
    network.addEdge("J", "E", "JE");
    network.addEdge("K", "L", "KL");
    network.addEdge("M", "N", "MN1");
    network.addEdge("M", "N", "MN2");
    network.addEdge("N", "L", "NL");
    return network;
  }

  private static MutableNetwork<String, String> createEmptyNetwork() {
    return NetworkBuilder.directed().allowsSelfLoops(false).allowsParallelEdges(true).build();
  }
}