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/*
 * Redberry: symbolic tensor computations.
 *
 * Copyright (c) 2010-2012:
 *   Stanislav Poslavsky   
 *   Bolotin Dmitriy       
 *
 * This file is part of Redberry.
 *
 * Redberry is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Redberry is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Redberry. If not, see .
 */
package cc.redberry.transformation.integral;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import cc.redberry.core.tensor.Integral;
import cc.redberry.core.tensor.Product;
import cc.redberry.core.tensor.SimpleTensor;
import cc.redberry.core.tensor.Tensor;
import cc.redberry.core.tensor.TensorIterator;
import cc.redberry.transformation.Transformation;
import cc.redberry.core.utils.TensorUtils;

/**
 *
 * @author Dmitry Bolotin
 * @author Stanislav Poslavsky
 */
public class UnderIntegral implements Transformation {
    public static final UnderIntegral INSTANCE = new UnderIntegral();

    private UnderIntegral() {
    }

    @Override
    public Tensor transform(Tensor tensor) {
        if (!(tensor instanceof Product))
            return tensor;

        //remember integrals
        final List integrals = new ArrayList<>();
        TensorIterator iterator = tensor.iterator();
        Tensor current;
        while (iterator.hasNext()) {
            current = iterator.next();
            if (current instanceof Integral) {
                integrals.add((Integral) current);
                iterator.remove();
            }
        }
        //no any integrals in the expression
        if (integrals.isEmpty())
            return tensor;

        //only integrals
        if (((Product) tensor).isEmpty())
            return new Product(integrals);

        //remember integration vars for each integral
        final List> vars = new ArrayList<>();
        for (final Integral i : integrals) {
            final Map map = new HashMap<>();
            for (final SimpleTensor s : i.vars())
                map.put(s.getName(), s);
            vars.add(map);
        }

        //main routine
        iterator = tensor.iterator();
        Collection tempVars;
        while (iterator.hasNext()) {
            current = iterator.next();
            //vars in current
            tempVars = TensorUtils.getDiffSimpleTensorContent(current);

            out_for:
            for (int i = 0; i < integrals.size(); ++i) {
                final Map map = vars.get(i);

                for (SimpleTensor st : tempVars)
                    if (map.containsKey(st.getName()))
                        continue out_for;

                //current can be placed under current integral
                final Integral integral = integrals.get(i);
                integrals.set(i, new Integral(new Product(current, integral.target()), integral.vars()));
                iterator.remove();
            }
        }

        Product result = new Product();
        result.add(tensor);
        result.add(integrals);
        return result.equivalent();
    }
}