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/**
 * EdgeProbabilityBuilder.java
 * Created Aug 18, 2012
 */

package com.googlecode.blaisemath.graph.modules.suppliers;

/*
 * #%L
 * BlaiseGraphTheory
 * --
 * Copyright (C) 2009 - 2016 Elisha Peterson
 * --
 * 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.
 * #L%
 */

import static com.google.common.base.Preconditions.checkArgument;
import com.googlecode.blaisemath.graph.Graph;
import com.googlecode.blaisemath.graph.SparseGraph;
import com.googlecode.blaisemath.graph.modules.suppliers.GraphSuppliers.GraphSupplierSupport;
import java.util.Comparator;
import java.util.Set;
import java.util.TreeSet;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * Generate random graph with specified edge count.
 */
public class EdgeCountGraphSupplier extends GraphSupplierSupport {

    //
    // COMPARATOR CONSTANTS
    //
    
    /**
     * Used to sort pairs of integers when order of the two matters.
     */
    static final Comparator PAIR_COMPARE = new Comparator() {
        public int compare(Integer[] o1, Integer[] o2) {
            if (o1.length != 2 || o2.length != 2) {
                throw new IllegalStateException("This object only compares integer pairs.");
            }
            return o1[0] == o2[0] ? o1[1] - o2[1] : o1[0] - o2[0];
        }
    };

    /**
     * Used to sort pairs of integers when order of the two does not matter.
     */
    static final Comparator PAIR_COMPARE_UNDIRECTED = new Comparator() {
        public int compare(Integer[] o1, Integer[] o2) {
            if (o1.length != 2 || o2.length != 2) {
                throw new IllegalStateException("This object only compares integer pairs.");
            }
            int min1 = Math.min(o1[0], o1[1]);
            int min2 = Math.min(o2[0], o2[1]);
            return min1 == min2 ? Math.max(o1[0], o1[1]) - Math.max(o2[0], o2[1]) : min1 - min2;
        }
    };
    
    //
    //
    //

    private int edges;

    public EdgeCountGraphSupplier() {
    }

    public EdgeCountGraphSupplier(boolean directed, int nodes, int edges) {
        super(directed, nodes);
        setEdges(edges);
    }

    @Override
    public String toString() {
        return "EdgeCountGraphSupplier{" + "edges=" + edges + '}';
    }

    @Override
    public void setDirected(boolean directed) {
        super.setDirected(directed);
        checkEdgeCount();
    }

    @Override
    public void setNodes(int nodes) {
        super.setNodes(nodes);
        checkEdgeCount();
    }

    public int getEdges() {
        return edges;
    }

    public void setEdges(int edges) {
        checkArgument(edges >= 0);
        this.edges = edges;
        checkEdgeCount();
    }
    
    private void checkEdgeCount() {
        if (!directed && edges > (nodes * (nodes - 1)) / 2) {
            Logger.getLogger(EdgeCountGraphSupplier.class.getName()).log(Level.WARNING, 
                    "Too many edges! (n,e)=({0},{1})", new Object[]{nodes, edges});
            edges = (nodes*(nodes-1))/2;
        }
        if (directed && edges > nodes * nodes) {
            Logger.getLogger(EdgeCountGraphSupplier.class.getName()).log(Level.WARNING, 
                    "Too many edges! (n,e)=({0},{1})", new Object[]{nodes, edges});
            edges = nodes*nodes;
        }
    }

    public Graph get() {
        Set edgeSet = new TreeSet(directed ? PAIR_COMPARE : PAIR_COMPARE_UNDIRECTED);
        Integer[] potential;
        for (int i = 0; i < edges; i++) {
            do {
                potential = new Integer[]{(int) (nodes * Math.random()), (int) (nodes * Math.random())};
            } while ((!directed && potential[0] == potential[1]) || edgeSet.contains(potential));
            edgeSet.add(potential);
        }
        return SparseGraph.createFromArrayEdges(directed, GraphSuppliers.intList(nodes), edgeSet);
    }
}