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Closure Stylesheets is an extension to CSS that adds variables, functions, conditionals, and mixins to standard CSS. The tool also supports minification, linting, RTL flipping, and CSS class renaming.

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/*
 * Copyright 2014 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.google.common.css.compiler.ast;

import com.google.common.collect.ImmutableList;
import com.google.common.css.SourceCode;

import java.util.List;

/**
 * Base parser implementation that delegates management of the underlying
 * JavaCC parser to the subclass. This class does not expose any public
 * methods; subclasses should expose an appropriate interface.
 *
 * @see GssParser
 */
public abstract class AbstractGssParser {

    protected static final StringCharStream EMPTY_CHAR_STREAM =
            new StringCharStream("");

    /**
     * Parses a list of GSS sources. Subclasses should use this method to do
     * the actual parsing of {@code SourceCode} objects. It will in turn call
     * the subclass's implementation of {@link #getParser()} as necessary.
     *
     * @param sources       a list of GSS {@link SourceCode} objects to parse
     * @param errorHandling if error handling should be enabled. If this is
     *                      {@code false}, no {@code GssParserException}s will be returned in
     *                      the result.
     * @return ParseResult the result containing the {@link CssTree} and
     * parsing errors
     */
    protected final ParseResult parseInternal(List sources,
                                              boolean errorHandling) throws GssParserException {
        SourceCode globalSourceCode = new SourceCode("global", null);
        CssBlockNode globalBlock =
                new CssBlockNode(false /* isEnclosedWithBraces */);
        CssTree tree = new CssTree(globalSourceCode, new CssRootNode(globalBlock));
        ImmutableList.Builder builder =
                ImmutableList.builder();
        for (SourceCode source : sources) {
            getParser().parse(globalBlock, source, errorHandling, builder);
        }
        return new ParseResult(tree, builder.build());
    }

    /**
     * Implementations must return an empty {@code GssParserCC} object. Whether
     * this object is actually new or not isn't important which allows pooling.
     */
    protected abstract GssParserCC getParser();

    protected static class ParseResult {
        private final CssTree cssTree;
        private final ImmutableList handledErrors;

        private ParseResult(CssTree cssTree,
                            ImmutableList handledErrors) {
            this.cssTree = cssTree;
            this.handledErrors = handledErrors;
        }

        protected CssTree getCssTree() {
            return cssTree;
        }

        protected ImmutableList getHandledErrors() {
            return handledErrors;
        }
    }
}