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/*
 * 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.giraph.examples;

import org.apache.giraph.graph.BasicComputation;
import org.apache.giraph.edge.Edge;
import org.apache.giraph.utils.ArrayListWritable;
import org.apache.giraph.graph.Vertex;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.NullWritable;

import com.google.common.base.Objects;
import com.google.common.collect.Maps;
import com.google.common.collect.Sets;

import java.io.IOException;
import java.util.Map;
import java.util.Set;

/**
 * Demonstrates triangle closing in simple,
 * unweighted graphs for Giraph.
 *
 * Triangle Closing: Vertex A and B maintain out-edges to C and D
 * The algorithm, when finished, populates all vertices' value with an
 * array of Writables representing all the vertices that each
 * should form an out-edge to (connect with, if this is a social
 * graph.)
 * In this example, vertices A and B would hold empty arrays
 * since they are already connected with C and D. Results:
 * If the graph is undirected, C would hold value, D and D would
 * hold value C, since both are neighbors of A and B and yet both
 * were not previously connected to each other.
 *
 * In a social graph, the result values for vertex X would represent people
 * that are likely a part of a person X's social circle (they know one or more
 * people X is connected to already) but X had not previously met them yet.
 * Given this new information, X can decide to connect to vertices (peoople) in
 * the result array or not.
 *
 * Results at each vertex are ordered in terms of the # of neighbors
 * who are connected to each vertex listed in the final vertex value.
 * The more of a vertex's neighbors who "know" someone, the stronger
 * your social relationship is presumed to be to that vertex (assuming
 * a social graph) and the more likely you should connect with them.
 *
 * In this implementation, Edge Values are not used, but could be
 * adapted to represent additional qualities that could affect the
 * ordering of the final result array.
 */
public class SimpleTriangleClosingComputation extends BasicComputation<
  IntWritable, SimpleTriangleClosingComputation.IntArrayListWritable,
  NullWritable, IntWritable> {
  /** Vertices to close the triangle, ranked by frequency of in-msgs */
  private Map closeMap =
    Maps.newHashMap();

  @Override
  public void compute(
      Vertex vertex,
      Iterable messages) throws IOException {
    if (getSuperstep() == 0) {
      // send list of this vertex's neighbors to all neighbors
      for (Edge edge : vertex.getEdges()) {
        sendMessageToAllEdges(vertex, edge.getTargetVertexId());
      }
    } else {
      for (IntWritable message : messages) {
        final int current = (closeMap.get(message) == null) ?
          0 : closeMap.get(message) + 1;
        closeMap.put(message, current);
      }
      // make sure the result values are sorted and
      // packaged in an IntArrayListWritable for output
      Set sortedResults = Sets.newTreeSet();
      for (Map.Entry entry : closeMap.entrySet()) {
        sortedResults.add(new Pair(entry.getKey(), entry.getValue()));
      }
      IntArrayListWritable
        outputList = new IntArrayListWritable();
      for (Pair pair : sortedResults) {
        if (pair.value > 0) {
          outputList.add(pair.key);
        } else {
          break;
        }
      }
      vertex.setValue(outputList);
    }
    vertex.voteToHalt();
  }

  /** Quick, immutable K,V storage for sorting in tree set */
  public static class Pair implements Comparable {
    /** key
     * @param key the IntWritable key */
    private final IntWritable key;
    /** value
     * @param value the Integer value */
    private final Integer value;
    /** Constructor
     * @param k the key
     * @param v the value
     */
    public Pair(IntWritable k, Integer v) {
      key = k;
      value = v;
    }
    /** key getter
     * @return the key */
    public IntWritable getKey() { return key; }
    /** value getter
     * @return the value */
    public Integer getValue() { return value; }
    /** Comparator to quickly sort by values
     * @param other the Pair to compare with THIS
     * @return the comparison value as an integer */
    @Override
    public int compareTo(Pair other) {
      return other.value - this.value;
    }

    @Override
    public boolean equals(Object obj) {
      if (this == obj) {
        return true;
      }
      if (obj instanceof Pair) {
        Pair other = (Pair) obj;
        return Objects.equal(value, other.value);
      }
      return false;
    }

    @Override
    public int hashCode() {
      return Objects.hashCode(value);
    }
  }

  /** Utility class for delivering the array of vertices THIS vertex
    * should connect with to close triangles with neighbors */
  public static class IntArrayListWritable
    extends ArrayListWritable {
    /** Default constructor for reflection */
    public IntArrayListWritable() {
      super();
    }
    /** Set storage type for this ArrayListWritable */
    @Override
    @SuppressWarnings("unchecked")
    public void setClass() {
      setClass(IntWritable.class);
    }
  }
}