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Redberry is an open source computer algebra system designed for tensor manipulation. It implements basic computer algebra system routines as well as complex tools for real computations in physics. This is Redberry core, which contains the implementation of the basic computer algebra routines and general-purpose transformations.

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/*
 * Redberry: symbolic tensor computations.
 *
 * Copyright (c) 2010-2015:
 *   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.core.utils;

import cc.redberry.core.indices.IndicesFactory;
import cc.redberry.core.tensor.SimpleTensor;
import cc.redberry.core.tensor.Tensor;
import cc.redberry.core.tensor.Tensors;
import gnu.trove.set.hash.TIntHashSet;

/**
 * Sequentially generates variables of the form "prefix0","prefix1","prefix2","prefix3" etc., so that each
 * symbol does not  appear in the specified tensor.
 *
 * @author Dmitry Bolotin
 * @author Stanislav Poslavsky
 * @see TensorUtils#generateReplacementsOfScalars(cc.redberry.core.tensor.Tensor, OutputPort)
 */
public class LocalSymbolsProvider implements OutputPort {
    private final String prefix;
    private final TIntHashSet forbiddenNames;
    private long counter = 0;

    /**
     * Creates provider with given prefix.
     *
     * @param forbidden forbidden content
     * @param prefix    string prefix
     */
    public LocalSymbolsProvider(Tensor forbidden, String prefix) {
        this.forbiddenNames = TensorUtils.getSimpleTensorsNames(forbidden);
        this.prefix = prefix;
    }

    @Override
    public SimpleTensor take() {
        SimpleTensor st;
        do {
            st = Tensors.simpleTensor(prefix + (counter++), IndicesFactory.EMPTY_SIMPLE_INDICES);
        } while (forbiddenNames.contains(st.getName()));
        return st;
    }
}