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//               The Next Generation Logic Library                       //
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//  Copyright 2015-20xx Christoph Zengler                                //
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//  Licensed under the Apache License, Version 2.0 (the "License");      //
//  you may not use this file except in compliance with the License.     //
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//  http://www.apache.org/licenses/LICENSE-2.0                           //
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package org.logicng.graphs.generators;

import org.logicng.formulas.Formula;
import org.logicng.formulas.Variable;
import org.logicng.graphs.datastructures.Graph;

import java.util.Collection;

/**
 * A graph generator which generates a constraint graph for a
 * given list of formulas.
 * @version 2.4.0
 * @since 2.0.0
 */
public final class ConstraintGraphGenerator {

    /**
     * Private constructor.
     */
    private ConstraintGraphGenerator() {
        // Intentionally left empty.
    }

    /**
     * Constructs the constraint graph.
     * @param formula the formula in extended CNF
     * @return the constraint graph for the given formula
     * @deprecated the constraint graph generation is not CNF specific. Use general method {@link #generateFromFormulas(Collection)} instead.
     */
    @Deprecated
    public static Graph generateFromCnf(final Formula formula) {
        final Graph constraintGraph = new Graph<>();
        addToGraph(formula, constraintGraph);
        return constraintGraph;
    }

    /**
     * Constructs the constraint graph.
     * @param formulas the formulas in extended CNF as set of CNFs
     * @return the constraint graph for the given formula
     * @deprecated the constraint graph generation is not CNF specific. Use general method {@link #generateFromFormulas(Collection)} instead.
     */
    @Deprecated
    public static Graph generateFromCnf(final Collection formulas) {
        final Graph constraintGraph = new Graph<>();
        for (final Formula clause : formulas) {
            addToGraph(clause, constraintGraph);
        }
        return constraintGraph;
    }

    /**
     * Constructs the constraint graph.
     * @param formulas the formulas
     * @return the constraint graph for the given formula
     */
    public static Graph generateFromFormulas(final Collection formulas) {
        final Graph constraintGraph = new Graph<>();
        for (final Formula formula : formulas) {
            addClause(formula, constraintGraph);
        }
        return constraintGraph;
    }

    private static void addToGraph(final Formula formula, final Graph constraintGraph) {
        switch (formula.type()) {
            case FALSE:
            case TRUE:
                break;
            case LITERAL:
            case OR:
            case PBC:
                addClause(formula, constraintGraph);
                break;
            case AND:
                for (final Formula clause : formula) {
                    addClause(clause, constraintGraph);
                }
                break;
            default:
                throw new IllegalArgumentException("Can only generate a constraint graph from a CNF");
        }
    }

    private static void addClause(final Formula clause, final Graph graph) {
        final Variable[] variables = clause.variables().toArray(new Variable[0]);
        if (variables.length == 1) {
            graph.node(variables[0]);
        }
        for (int i = 0; i < variables.length; i++) {
            for (int j = i + 1; j < variables.length; j++) {
                graph.connect(graph.node(variables[i]), graph.node(variables[j]));
            }
        }
    }
}