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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.parser;

import cc.redberry.core.context.OutputFormat;
import cc.redberry.core.indices.Indices;
import cc.redberry.core.indices.IndicesBuilder;
import cc.redberry.core.indices.IndicesFactory;
import cc.redberry.core.tensor.Tensor;
import cc.redberry.core.tensor.Tensors;

import java.util.Arrays;

/**
 * Abstract syntax tree. The implementation is a simple linked tree.
 *
 * @author Dmitry Bolotin
 * @author Stanislav Poslavsky
 * @since 1.0
 */
public class ParseToken {

    /**
     * Node type.
     */
    public final TokenType tokenType;
    /**
     * Child nodes.
     */
    public final ParseToken[] content;
    /**
     * Parent node.
     */
    public ParseToken parent;

    /**
     * @param tokenType node type
     * @param content   child nodes
     */
    public ParseToken(TokenType tokenType, ParseToken... content) {
        this.tokenType = tokenType;
        this.content = content;
        for (ParseToken node : content)
            node.setParent(this);
    }

    private void setParent(ParseToken parent) {
        this.parent = parent;
    }

    /**
     * Returns {@link Indices} of the corresponding mathematical expression.
     *
     * @return {@link Indices} of the corresponding mathematical expression
     */
    public Indices getIndices() {
        switch (tokenType) {
            case Product:
            case Trace:
                IndicesBuilder builder = new IndicesBuilder();
                for (ParseToken node : content)
                    builder.append(node.getIndices());
                return builder.getIndices();
            case Sum:
                return IndicesFactory.create(content[0].getIndices());
            case Power:
                return IndicesFactory.EMPTY_INDICES;
        }
        throw new ParserException("Unknown tensor type: " + tokenType);
    }

    @Override
    public String toString() {
        StringBuilder builder = new StringBuilder();
        builder.append(tokenType).append("[");
        for (ParseToken node : content)
            builder.append(node).append(", ");
        builder.deleteCharAt(builder.length() - 1).deleteCharAt(builder.length() - 1).append("]");
        return builder.toString();
    }

    public String toString(OutputFormat mode) {
        StringBuilder sb = new StringBuilder();
        switch (tokenType) {
            case Trace:
                sb.append("Tr[");
            case Product:
                char operatorChar = mode.is(OutputFormat.LaTeX) ? ' ' : '*';

                for (int i = 0; ; ++i) {
                    sb.append(content[i].toString(mode));
                    if (i == content.length - 1)
                        return tokenType == TokenType.Trace ? sb.append("]").toString() : sb.toString();
                    sb.append(operatorChar);
                }
                //throw new RuntimeException();
            case Sum:
                sb.append("(");
                String temp;
                for (int i = 0; ; ++i) {
                    temp = content[i].toString(mode);
                    if ((temp.charAt(0) == '-' || temp.charAt(0) == '+') && sb.length() != 0)
                        sb.deleteCharAt(sb.length() - 1);
                    sb.append(content[i].toString(mode));
                    if (i == content.length - 1)
                        return sb.append(")").toString();
                    sb.append('+');
                }
                //throw new RuntimeException();
        }
        throw new RuntimeException("Unsupported token type.");
    }

    protected Tensor[] contentToTensors() {
        Tensor[] tensors = new Tensor[content.length];
        for (int i = 0; i < content.length; ++i)
            tensors[i] = content[i].toTensor();
        return tensors;
    }

    /**
     * Converts this AST to tensor.
     *
     * @return resulting tensor
     */
    public Tensor toTensor() {
        switch (tokenType) {
            case Sum:
                return Tensors.sum(contentToTensors());
            case Power:
                assert content.length == 2;
                return Tensors.pow(content[0].toTensor(), content[1].toTensor());
            case Trace:
            case Product:
                return Tensors.multiplyAndRenameConflictingDummies(contentToTensors());
        }
        throw new ParserException("Unknown tensor type: " + tokenType);
    }

    @Override
    public boolean equals(Object obj) {
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        final ParseToken other = (ParseToken) obj;
        if (this.tokenType != other.tokenType)
            return false;
        return Arrays.deepEquals(this.content, other.content);
    }
}