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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 2011 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.passes;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.collect.ImmutableList;
import com.google.common.css.compiler.ast.*;

import java.util.List;

/**
 * Utility methods that can be useful for compiler passes.
 *
 * @author [email protected] (Florian Benz)
 */
public class PassUtil {

    /**
     * Annotation to explicitly state that several consecutive declarations are
     * alternatives and it should be left up to the user agent to interpret
     * whichever is appropriate. The annotation excludes the declarations from
     * being treated as redundant.
     */
    @VisibleForTesting
    public static final String ALTERNATE = "/* @alternate */";

    private PassUtil() {
    }

    /**
     * Prints a selector including the combinators and refiners but without
     * a block behind with the compact printer.
     */
    public static String printSelector(CssSelectorNode selector) {
        CssTree t = createTreeWithSelector(selector);
        // Print the whole tree.
        String selectorString = compactPrintTree(t);
        // As the whole tree is printed, the output is the selector with an empty
        // declaration block (e.g. 'foo{}'). The two curly brackets are removed so
        // that only the selector remains.
        return selectorString.substring(0, selectorString.length() - 2);
    }

    /**
     * Prints a list of selector including the combinators and refiners but
     * without a block behind with the compact printer.
     */
    public static String printSelectorList(CssSelectorListNode selectorList) {
        CssTree t = createTreeWithSelectorList(selectorList);
        // Print the whole tree.
        String selectorListString = compactPrintTree(t);
        // As the whole tree is printed, the output is the selector with an empty
        // declaration block (e.g. 'foo{}'). The two curly brackets are removed so
        // that only the selector remains.
        return selectorListString.substring(0, selectorListString.length() - 2);
    }

    /**
     * Prints a selector including the combinators and refiners but without
     * a block behind with the pretty printer.
     */
    public static String prettyPrintSelector(CssSelectorNode selector) {
        CssTree t = createTreeWithSelector(selector);
        // Print the whole tree.
        PrettyPrinter prettyPrinter = new PrettyPrinter(t.getVisitController());
        prettyPrinter.runPass();
        String selectorString = prettyPrinter.getPrettyPrintedString();
        // As the whole tree is printed, the output is the selector with an empty
        // declaration block (e.g. 'foo {\n}\n'). The two curly brackets are removed so
        // that only the selector remains.
        int index = selectorString.indexOf('{');
        return selectorString.substring(0, index - 1);
    }

    private static CssTree createTreeWithSelector(CssSelectorNode selector) {
        // Create tree with only this selector.
        CssDeclarationBlockNode declarations = new CssDeclarationBlockNode();
        CssRulesetNode rulesetNode = new CssRulesetNode(declarations);
        rulesetNode.addSelector(selector);
        return createTreeWithRuleset(rulesetNode);
    }

    private static CssTree createTreeWithSelectorList(
            CssSelectorListNode selectorList) {
        CssDeclarationBlockNode declarations = new CssDeclarationBlockNode();
        CssRulesetNode rulesetNode = new CssRulesetNode(declarations);
        rulesetNode.setSelectors(selectorList);
        return createTreeWithRuleset(rulesetNode);
    }

    private static CssTree createTreeWithRuleset(CssRulesetNode rulesetNode) {
        List blockChildren = ImmutableList.of(rulesetNode);
        CssBlockNode block = new CssBlockNode(false, blockChildren);
        CssRootNode root = new CssRootNode(block);
        return new CssTree(null, root);
    }

    private static String compactPrintTree(CssTree tree) {
        CompactPrinter compactPrinter = new CompactPrinter(tree);
        compactPrinter.runPass();
        return compactPrinter.getCompactPrintedString();
    }

    /**
     * Returns whether the ALTERNATE comment has been found among the comments of
     * the node.
     */
    public static boolean hasAlternateAnnotation(CssNode node) {
        for (CssCommentNode comment : node.getComments()) {
            if (comment.getValue().equals(ALTERNATE)) {
                return true;
            }
        }
        return false;
    }
}