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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.css.compiler.ast.*;

/**
 * Compiler pass which ensures that @keyframes rules are only allowed if
 * they are enabled. In addition this pass checks if the keys are between
 * 0% and 100%. If CSS simplification is enabled, "from" is replaced by "0%"
 * and "100%" is replaced by "to".
 *
 * @author [email protected] (Florian Benz)
 */
public class ProcessKeyframes extends DefaultTreeVisitor
        implements CssCompilerPass {
    @VisibleForTesting
    static final String KEYFRAMES_NOT_ALLOWED_ERROR_MESSAGE =
            "a @keyframes rule occured but the option for it is disabled";
    @VisibleForTesting
    static final String WRONG_KEY_VALUE_ERROR_MESSAGE =
            "the value of the key is not between 0% and 100%";
    static final String INVALID_NUMBER_ERROR_MESSAGE =
            "the value of the key is invalid (not 'from', 'to', or 'XXX.XXX%')";

    private final VisitController visitController;
    private final ErrorManager errorManager;
    private final boolean keyframesAllowed;
    private final boolean simplifyCss;

    public ProcessKeyframes(VisitController visitController,
                            ErrorManager errorManager,
                            boolean keyframesAllowed,
                            boolean simplifyCss) {
        this.visitController = visitController;
        this.errorManager = errorManager;
        this.keyframesAllowed = keyframesAllowed;
        this.simplifyCss = simplifyCss;
    }

    @Override
    public boolean enterKeyframesRule(CssKeyframesNode node) {
        if (!keyframesAllowed) {
            errorManager.report(new GssError(KEYFRAMES_NOT_ALLOWED_ERROR_MESSAGE,
                    node.getSourceCodeLocation()));
        }
        return keyframesAllowed;
    }

    @Override
    public boolean enterKey(CssKeyNode node) {
        if (!keyframesAllowed) {
            return false;
        }
        String value = node.getKeyValue();
        float percentage = -1;
        if (value.contains("%")) {
            try {
                // parse to a float by excluding '%'
                percentage = Float.parseFloat(value.substring(0, value.length() - 1));
            } catch (NumberFormatException e) {
                // should not happen if the generated parser works correctly
                errorManager.report(new GssError(INVALID_NUMBER_ERROR_MESSAGE,
                        node.getSourceCodeLocation()));
                return false;
            }
            if (!checkRangeOfPercentage(node, percentage)) {
                return false;
            }
        } else {
            if (!value.equals("from") && !value.equals("to")) {
                errorManager.report(new GssError(INVALID_NUMBER_ERROR_MESSAGE,
                        node.getSourceCodeLocation()));
                return false;
            }
        }
        if (simplifyCss) {
            compactRepresentation(node, percentage);
        }
        return true;
    }

    /**
     * Checks if the percentage is between 0% and 100% inclusive.
     *
     * @param node       The {@link CssKeyNode} to get the location in case of an error
     * @param percentage The value represented as a float
     * @return Returns true if there is no error
     */
    private boolean checkRangeOfPercentage(CssKeyNode node, float percentage) {
        // check whether the percentage is between 0% and 100%
        if (percentage < 0 || percentage > 100) {
            errorManager.report(new GssError(WRONG_KEY_VALUE_ERROR_MESSAGE,
                    node.getSourceCodeLocation()));
            return false;
        }
        return true;
    }

    /**
     * Shortens the representation of the key.
     *
     * @param node       The {@link CssKeyNode} where the percentage belongs to.
     * @param percentage The value represented as a float
     */
    @VisibleForTesting
    void compactRepresentation(CssKeyNode node, float percentage) {
        if (node.getKeyValue().equals("from")) {
            node.setKeyValue("0%");
        } else if (percentage == 100) {
            node.setKeyValue("to");
        } else if (percentage != -1) {
            String percentageStr = Float.toString(percentage);
            if (0 < percentage && percentage < 1) {
                // eliminate an unnecessary leading 0
                percentageStr = percentageStr.substring(1);
            }
            // eliminate a trailing zero like in 0.0
            percentageStr = percentageStr.replaceAll("0+$", "");
            if (percentageStr.endsWith(".")) {
                // if the number ends with '.' then eliminate that too
                percentageStr = percentageStr.substring(0, percentageStr.length() - 1);
            }
            node.setKeyValue(percentageStr + "%");
        }
    }

    @Override
    public void runPass() {
        visitController.startVisit(this);
    }
}