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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) 2010-2014:
 *   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.parser;

/**
 * Parser for powers if form Power[a, b].
 *
 * @author Dmitry Bolotin
 * @author Stanislav Poslavsky
 * @since 1.0
 */
public class ParserPower implements TokenParser {
    /**
     * Singleton instance.
     */
    public static final ParserPower INSTANCE = new ParserPower();
    private static final String power = "Power";
    private static final int minLength = power.length() + 2;

    private ParserPower() {
    }

    @Override
    public int priority() {
        return 9986;
    }

    @Override
    public ParseToken parseToken(String expression, Parser parser) {
        if (expression.length() <= minLength)
            return null;
        if (!(power + '[').equals(expression.substring(0, power.length() + 1))
                || expression.charAt(expression.length() - 1) != ']')
            return null;
        int level = 0, i, comma = -1;
        char c;
        for (i = power.length(); i < expression.length(); ++i) {
            c = expression.charAt(i);
            if (c == '[')
                ++level;
            if (level < 1)
                return null;
            if (c == ']')
                --level;
            if (c == ',' && level == 1) {
                if (comma != -1)
                    throw new ParserException("Power takes only two arguments.");
                comma = i;
            }
        }
        ParseToken arg = parser.parse(expression.substring(power.length() + 1, comma));
        ParseToken power = parser.parse(expression.substring(comma + 1, expression.length() - 1));
        return new ParseToken(TokenType.Power, arg, power);
    }
}