/*
 * 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.base.Preconditions.checkState;
import static com.google.common.graph.GraphConstants.SELF_LOOPS_NOT_ALLOWED;
import static com.google.common.graph.Graphs.checkNonNegative;
import static com.google.common.graph.Graphs.checkPositive;

import com.google.errorprone.annotations.CanIgnoreReturnValue;

Configurable implementation of MutableValueGraph that supports both directed and undirected graphs. Instances of this class should be constructed with ValueGraphBuilder. 
Time complexities for mutation methods are all O(1) except for removeNode(N node), which is in O(d_node) where d_node is the degree of node. 
Author:
James Sexton, Joshua O'Madadhain, Omar Darwish
Type parameters:
<N> – Node parameter type
<V> – Value parameter type/**
 * Configurable implementation of {@link MutableValueGraph} that supports both directed and
 * undirected graphs. Instances of this class should be constructed with {@link ValueGraphBuilder}.
 *
 * <p>Time complexities for mutation methods are all O(1) except for {@code removeNode(N node)},
 * which is in O(d_node) where d_node is the degree of {@code node}.
 *
 * @author James Sexton
 * @author Joshua O'Madadhain
 * @author Omar Darwish
 * @param <N> Node parameter type
 * @param <V> Value parameter type
 */
final class ConfigurableMutableValueGraph<N, V> extends ConfigurableValueGraph<N, V>
    implements MutableValueGraph<N, V> {

  
Constructs a mutable graph with the properties specified in builder. /** Constructs a mutable graph with the properties specified in {@code builder}. */
  ConfigurableMutableValueGraph(AbstractGraphBuilder<? super N> builder) {
    super(builder);
  }

  @Override
  @CanIgnoreReturnValue
  public boolean addNode(N node) {
    checkNotNull(node, "node");

    if (containsNode(node)) {
      return false;
    }

    addNodeInternal(node);
    return true;
  }

  
Adds node to the graph and returns the associated GraphConnections. 
Throws:
IllegalStateException – if node is already present/**
   * Adds {@code node} to the graph and returns the associated {@link GraphConnections}.
   *
   * @throws IllegalStateException if {@code node} is already present
   */
  @CanIgnoreReturnValue
  private GraphConnections<N, V> addNodeInternal(N node) {
    GraphConnections<N, V> connections = newConnections();
    checkState(nodeConnections.put(node, connections) == null);
    return connections;
  }

  @Override
  @CanIgnoreReturnValue
  public V putEdgeValue(N nodeU, N nodeV, V value) {
    checkNotNull(nodeU, "nodeU");
    checkNotNull(nodeV, "nodeV");
    checkNotNull(value, "value");

    if (!allowsSelfLoops()) {
      checkArgument(!nodeU.equals(nodeV), SELF_LOOPS_NOT_ALLOWED, nodeU);
    }

    GraphConnections<N, V> connectionsU = nodeConnections.get(nodeU);
    if (connectionsU == null) {
      connectionsU = addNodeInternal(nodeU);
    }
    V previousValue = connectionsU.addSuccessor(nodeV, value);
    GraphConnections<N, V> connectionsV = nodeConnections.get(nodeV);
    if (connectionsV == null) {
      connectionsV = addNodeInternal(nodeV);
    }
    connectionsV.addPredecessor(nodeU, value);
    if (previousValue == null) {
      checkPositive(++edgeCount);
    }
    return previousValue;
  }

  @Override
  @CanIgnoreReturnValue
  public boolean removeNode(N node) {
    checkNotNull(node, "node");

    GraphConnections<N, V> connections = nodeConnections.get(node);
    if (connections == null) {
      return false;
    }

    if (allowsSelfLoops()) {
      // Remove self-loop (if any) first, so we don't get CME while removing incident edges.
      if (connections.removeSuccessor(node) != null) {
        connections.removePredecessor(node);
        --edgeCount;
      }
    }

    for (N successor : connections.successors()) {
      nodeConnections.getWithoutCaching(successor).removePredecessor(node);
      --edgeCount;
    }
    if (isDirected()) { // In undirected graphs, the successor and predecessor sets are equal.
      for (N predecessor : connections.predecessors()) {
        checkState(nodeConnections.getWithoutCaching(predecessor).removeSuccessor(node) != null);
        --edgeCount;
      }
    }
    nodeConnections.remove(node);
    checkNonNegative(edgeCount);
    return true;
  }

  @Override
  @CanIgnoreReturnValue
  public V removeEdge(N nodeU, N nodeV) {
    checkNotNull(nodeU, "nodeU");
    checkNotNull(nodeV, "nodeV");

    GraphConnections<N, V> connectionsU = nodeConnections.get(nodeU);
    GraphConnections<N, V> connectionsV = nodeConnections.get(nodeV);
    if (connectionsU == null || connectionsV == null) {
      return null;
    }

    V previousValue = connectionsU.removeSuccessor(nodeV);
    if (previousValue != null) {
      connectionsV.removePredecessor(nodeU);
      checkNonNegative(--edgeCount);
    }
    return previousValue;
  }

  private GraphConnections<N, V> newConnections() {
    return isDirected()
        ? DirectedGraphConnections.<N, V>of()
        : UndirectedGraphConnections.<N, V>of();
  }
}