/*
 * Copyright (C) 2016 The Guava Authors
 *
 * Licensed 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 com.google.common.graph;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.graph.GraphConstants.DEFAULT_EDGE_COUNT;
import static com.google.common.graph.GraphConstants.DEFAULT_NODE_COUNT;
import static com.google.common.graph.GraphConstants.EDGE_NOT_IN_GRAPH;
import static com.google.common.graph.GraphConstants.NODE_NOT_IN_GRAPH;

import com.google.common.collect.ImmutableSet;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
import org.checkerframework.checker.nullness.qual.Nullable;

Configurable implementation of Network that supports the options supplied by NetworkBuilder. 
This class maintains a map of nodes to NetworkConnections. This class also maintains a map of edges to reference nodes. The reference node is defined to be the edge's source node on directed graphs, and an arbitrary endpoint of the edge on undirected graphs. 
Collection-returning accessors return unmodifiable views: the view returned will reflect
changes to the graph (if the graph is mutable) but may not be modified by the user.
The time complexity of all collection-returning accessors is O(1), since views are returned.
Author:
James Sexton, Joshua O'Madadhain, Omar Darwish
Type parameters:
<N> – Node parameter type
<E> – Edge parameter type/**
 * Configurable implementation of {@link Network} that supports the options supplied by {@link
 * NetworkBuilder}.
 *
 * <p>This class maintains a map of nodes to {@link NetworkConnections}. This class also maintains a
 * map of edges to reference nodes. The reference node is defined to be the edge's source node on
 * directed graphs, and an arbitrary endpoint of the edge on undirected graphs.
 *
 * <p>Collection-returning accessors return unmodifiable views: the view returned will reflect
 * changes to the graph (if the graph is mutable) but may not be modified by the user.
 *
 * <p>The time complexity of all collection-returning accessors is O(1), since views are returned.
 *
 * @author James Sexton
 * @author Joshua O'Madadhain
 * @author Omar Darwish
 * @param <N> Node parameter type
 * @param <E> Edge parameter type
 */
class ConfigurableNetwork<N, E> extends AbstractNetwork<N, E> {
  private final boolean isDirected;
  private final boolean allowsParallelEdges;
  private final boolean allowsSelfLoops;
  private final ElementOrder<N> nodeOrder;
  private final ElementOrder<E> edgeOrder;

  protected final MapIteratorCache<N, NetworkConnections<N, E>> nodeConnections;

  // We could make this a Map<E, EndpointPair<N>>. It would make incidentNodes(edge) slightly
  // faster, but also make Networks consume 5 to 20+% (increasing with average degree) more memory.
  protected final MapIteratorCache<E, N> edgeToReferenceNode; // referenceNode == source if directed

  
Constructs a graph with the properties specified in builder. /** Constructs a graph with the properties specified in {@code builder}. */
  ConfigurableNetwork(NetworkBuilder<? super N, ? super E> builder) {
    this(
        builder,
        builder.nodeOrder.<N, NetworkConnections<N, E>>createMap(
            builder.expectedNodeCount.or(DEFAULT_NODE_COUNT)),
        builder.edgeOrder.<E, N>createMap(builder.expectedEdgeCount.or(DEFAULT_EDGE_COUNT)));
  }

  
Constructs a graph with the properties specified in builder, initialized with the given node and edge maps. /**
   * Constructs a graph with the properties specified in {@code builder}, initialized with the given
   * node and edge maps.
   */
  ConfigurableNetwork(
      NetworkBuilder<? super N, ? super E> builder,
      Map<N, NetworkConnections<N, E>> nodeConnections,
      Map<E, N> edgeToReferenceNode) {
    this.isDirected = builder.directed;
    this.allowsParallelEdges = builder.allowsParallelEdges;
    this.allowsSelfLoops = builder.allowsSelfLoops;
    this.nodeOrder = builder.nodeOrder.cast();
    this.edgeOrder = builder.edgeOrder.cast();
    // Prefer the heavier "MapRetrievalCache" for nodes if lookup is expensive. This optimizes
    // methods that access the same node(s) repeatedly, such as Graphs.removeEdgesConnecting().
    this.nodeConnections =
        (nodeConnections instanceof TreeMap)
            ? new MapRetrievalCache<N, NetworkConnections<N, E>>(nodeConnections)
            : new MapIteratorCache<N, NetworkConnections<N, E>>(nodeConnections);
    this.edgeToReferenceNode = new MapIteratorCache<>(edgeToReferenceNode);
  }

  @Override
  public Set<N> nodes() {
    return nodeConnections.unmodifiableKeySet();
  }

  @Override
  public Set<E> edges() {
    return edgeToReferenceNode.unmodifiableKeySet();
  }

  @Override
  public boolean isDirected() {
    return isDirected;
  }

  @Override
  public boolean allowsParallelEdges() {
    return allowsParallelEdges;
  }

  @Override
  public boolean allowsSelfLoops() {
    return allowsSelfLoops;
  }

  @Override
  public ElementOrder<N> nodeOrder() {
    return nodeOrder;
  }

  @Override
  public ElementOrder<E> edgeOrder() {
    return edgeOrder;
  }

  @Override
  public Set<E> incidentEdges(N node) {
    return checkedConnections(node).incidentEdges();
  }

  @Override
  public EndpointPair<N> incidentNodes(E edge) {
    N nodeU = checkedReferenceNode(edge);
    N nodeV = nodeConnections.get(nodeU).adjacentNode(edge);
    return EndpointPair.of(this, nodeU, nodeV);
  }

  @Override
  public Set<N> adjacentNodes(N node) {
    return checkedConnections(node).adjacentNodes();
  }

  @Override
  public Set<E> edgesConnecting(N nodeU, N nodeV) {
    NetworkConnections<N, E> connectionsU = checkedConnections(nodeU);
    if (!allowsSelfLoops && nodeU == nodeV) { // just an optimization, only check reference equality
      return ImmutableSet.of();
    }
    checkArgument(containsNode(nodeV), NODE_NOT_IN_GRAPH, nodeV);
    return connectionsU.edgesConnecting(nodeV);
  }

  @Override
  public Set<E> inEdges(N node) {
    return checkedConnections(node).inEdges();
  }

  @Override
  public Set<E> outEdges(N node) {
    return checkedConnections(node).outEdges();
  }

  @Override
  public Set<N> predecessors(N node) {
    return checkedConnections(node).predecessors();
  }

  @Override
  public Set<N> successors(N node) {
    return checkedConnections(node).successors();
  }

  protected final NetworkConnections<N, E> checkedConnections(N node) {
    NetworkConnections<N, E> connections = nodeConnections.get(node);
    if (connections == null) {
      checkNotNull(node);
      throw new IllegalArgumentException(String.format(NODE_NOT_IN_GRAPH, node));
    }
    return connections;
  }

  protected final N checkedReferenceNode(E edge) {
    N referenceNode = edgeToReferenceNode.get(edge);
    if (referenceNode == null) {
      checkNotNull(edge);
      throw new IllegalArgumentException(String.format(EDGE_NOT_IN_GRAPH, edge));
    }
    return referenceNode;
  }

  protected final boolean containsNode(@Nullable N node) {
    return nodeConnections.containsKey(node);
  }

  protected final boolean containsEdge(@Nullable E edge) {
    return edgeToReferenceNode.containsKey(edge);
  }
}