MutableDirectedGraph.java

/*
Copyright 2011-2016 Google Inc. All Rights Reserved.

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.security.zynamics.zylib.types.graphs;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import com.google.common.base.Preconditions;

/**
 * Simple mutable directed graph class that contains nodes and directed edges.
 * 
 * @param <NodeType> Type of the nodes in the graph.
 * @param <EdgeType> Type of the edges in the graph.
 */
public class MutableDirectedGraph<NodeType, EdgeType extends IGraphEdge<NodeType>> implements
    IDirectedGraph<NodeType, EdgeType>, Iterable<NodeType> {

  /**
   * Nodes of the graph.
   */
  private final List<NodeType> m_nodes;

  /**
   * Edges of the graph.
   */
  private final List<EdgeType> m_edges;

  /**
   * Map that keeps track what edges belong to a node.
   */
  private final Map<NodeType, List<EdgeType>> m_nodeToEdges =
      new HashMap<NodeType, List<EdgeType>>();

  /**
   * Creates a new mutable directed graph.
   * 
   * @param nodes The nodes of the graph.
   * @param edges The edges of the graph.
   */
  public MutableDirectedGraph(final List<NodeType> nodes, final List<EdgeType> edges) {
    m_nodes = Preconditions.checkNotNull(nodes, "Nodes argument can not be null");
    m_edges = Preconditions.checkNotNull(edges, "Edges argument can not be null");

    for (final NodeType node : nodes) {
      Preconditions.checkNotNull(node, "Node list contains null-nodes");
      m_nodeToEdges.put(node, new ArrayList<EdgeType>());
    }

    for (final EdgeType edge : edges) {
      updateNodeToEdgeMapping(edge);
    }
  }

  private void updateNodeToEdgeMapping(final EdgeType edge) {
    Preconditions.checkNotNull(edge, "Error: edge argument can not be null");

    if (m_nodeToEdges.get(edge.getSource()) != null) {
      m_nodeToEdges.get(edge.getSource()).add(edge);
    } else {
      throw new IllegalStateException(
          "Error: The given edge has a source node which is not known to the graph.");
    }
    if (m_nodeToEdges.get(edge.getTarget()) != null) {
      m_nodeToEdges.get(edge.getTarget()).add(edge);
    } else {
      throw new IllegalStateException(
          "Error: the given edge has a target node which is not known to the graph.");
    }
  }

  /**
   * Adds an edge to the graph.
   * 
   * @param edge The edge to add.
   */
  public void addEdge(final EdgeType edge) {
    Preconditions.checkNotNull(edge, "Edge argument can not be null");

    m_edges.add(edge);
    updateNodeToEdgeMapping(edge);
  }

  /**
   * Adds a node to the graph.
   * 
   * @param node The node to add to the graph.
   */
  public void addNode(final NodeType node) {
    Preconditions.checkNotNull(node, "Node argument can not be null");

    m_nodes.add(node);
    m_nodeToEdges.put(node, new ArrayList<EdgeType>());
  }

  @Override
  public int edgeCount() {
    return m_edges.size();
  }

  /**
   * Returns an unmodifiable list of edges in the graph.
   * 
   * @return Unmodifiable collection of edges.
   */
  @Override
  public List<EdgeType> getEdges() {
    return Collections.unmodifiableList(m_edges);
  }

  /**
   * Returns an unmodifiable list of nodes in the graph.
   * 
   * @return Unmodifiable collection of nodes.
   */
  @Override
  public List<NodeType> getNodes() {
    return Collections.unmodifiableList(m_nodes);
  }

  @Override
  public Iterator<NodeType> iterator() {
    return m_nodes.iterator();
  }

  @Override
  public int nodeCount() {
    return m_nodes.size();
  }

  /**
   * Removes an edge from the graph.
   * 
   * @param edge The edge to remove.
   */
  public void removeEdge(final EdgeType edge) {
    Preconditions.checkArgument(m_edges.remove(edge), "Error: Edge was not part of the graph");
    m_nodeToEdges.get(edge.getSource()).remove(edge);
    m_nodeToEdges.get(edge.getTarget()).remove(edge);
  }

  /**
   * Removes a node from the graph.
   * 
   * @param node The node to remove.
   */
  public void removeNode(final NodeType node) {
    Preconditions.checkArgument(m_nodes.remove(node),
        String.format("Error: Node '%s' was not part of the graph", node));
    m_edges.removeAll(m_nodeToEdges.get(node));
    m_nodeToEdges.remove(node);
  }
}