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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 2015 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.*;

import javax.annotation.Nullable;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * A compiler pass that validates values of properties.
 *
 * This pass exists to validate values that are not fully covered by the grammar definition.
 */
public class ValidatePropertyValues extends DefaultTreeVisitor implements CssCompilerPass {

    private static final String UNICODE_RANGE_ERROR = "Invalid expression for unicode range. "
            + "Expected single codepoint (U+25), range (U+0015-00FF), or wildcard range (U+3??)";
    @VisibleForTesting
    static final String UNICODE_ILLEGAL_CODEPOINT_ERROR = "Unicode code point must be within "
            + "0-10FFFF";

    private static final String CODE_POINT_PATTERN = "([\\da-zA-Z]+)";
    private static final Pattern UNICODE_RANGE_PATTERN =
            Pattern.compile(String.format("U\\+%s(?:-%s)?", CODE_POINT_PATTERN, CODE_POINT_PATTERN));
    private static final Pattern UNICODE_WILDCARD_PATTERN =
            Pattern.compile(String.format("U\\+%s(\\?+)", CODE_POINT_PATTERN));

    private final ErrorManager errorManager;

    private final VisitController visitController;

    public ValidatePropertyValues(VisitController visitController, ErrorManager errorManager) {
        this.visitController = visitController;
        this.errorManager = errorManager;
    }

    @Override
    public boolean enterValueNode(CssValueNode value) {
        if (value instanceof CssUnicodeRangeNode) {
            validateUnicodeRangeValue((CssUnicodeRangeNode) value);
        }
        return true;
    }

    /**
     * Verify that a unicode range value is legal.
     *
     * See .
     */
    private void validateUnicodeRangeValue(CssUnicodeRangeNode value) {
        Matcher rangeMatcher = UNICODE_RANGE_PATTERN.matcher(value.getValue());
        Matcher wildcardMatcher = UNICODE_WILDCARD_PATTERN.matcher(value.getValue());
        if (!rangeMatcher.matches() && !wildcardMatcher.matches()) {
            reportError(UNICODE_RANGE_ERROR, value);
            return;
        }

        if (rangeMatcher.matches()) {
            for (int i = 1; i <= rangeMatcher.groupCount(); ++i) {
                validateSingleCodePoint(rangeMatcher.group(i), value);
            }
        } else {  // wildcardMatcher.matches() == true.
            // The second group contains only question marks (?). We concatenate it as zeros to the number
            // prefix for purpose of validation.
            String codePoint = wildcardMatcher.group(1) + wildcardMatcher.group(2).replaceAll("\\?", "0");
            validateSingleCodePoint(codePoint, value);
        }
    }

    /**
     * Verifies that a code point is within the permissible range (U+0-10FFFF).
     */
    private void validateSingleCodePoint(@Nullable String codePoint, CssUnicodeRangeNode value) {
        if (codePoint == null) {
            return;
        }
        long asLong = Long.parseLong(codePoint, 16);
        if (asLong > 0x10FFFF) {
            reportError(UNICODE_ILLEGAL_CODEPOINT_ERROR, value);
        }
    }

    private void reportError(String message, CssNode node) {
        errorManager.report(new GssError(message, node.getSourceCodeLocation()));
    }

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