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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.Sets;
import com.google.common.css.compiler.ast.*;

import java.util.HashMap;
import java.util.Map;
import java.util.Set;

/**
 * Compiler pass that collects all mixin definitions and afterwards provides a
 * mapping of mixin definition names to {@link CssMixinDefinitionNode} instances.
 *
 * In addition, this pass checks that no two definitions with the same name
 * exist and that no definition exits that has arguments with the same name
 * exist.
 *
 * {@link CreateConstantReferences} has to run before.
 *
 * @author [email protected] (Florian Benz)
 */
public class CollectMixinDefinitions extends DefaultTreeVisitor
        implements CssCompilerPass {
    @VisibleForTesting
    static final String DUPLICATE_MIXIN_DEFINITION_NAME_ERROR_MESSAGE =
            "A mixin definition name occured more than once";
    @VisibleForTesting
    static final String DUPLICATE_ARGUMENT_NAME_ERROR_MESSAGE =
            "The mixin definition has arguments with the same name";
    @VisibleForTesting
    static final String INVALID_ARGUMENT_ERROR_MESSAGE =
            "The mixin definition has invalid arguments";
    @VisibleForTesting
    static final String INVALID_BLOCK_ERROR_MESSAGE =
            "The mixin definition is not placed on the top level";

    private final MutatingVisitController visitController;
    private final ErrorManager errorManager;
    private final Map definitions;

    public CollectMixinDefinitions(MutatingVisitController visitController,
                                   ErrorManager errorManager) {
        this.visitController = visitController;
        this.errorManager = errorManager;
        this.definitions = new HashMap<>();
    }

    @Override
    public boolean enterMixinDefinition(CssMixinDefinitionNode node) {
        if (!node.getParent().getParent().getClass().equals(CssRootNode.class)) {
            errorManager.report(new GssError(INVALID_BLOCK_ERROR_MESSAGE,
                    node.getSourceCodeLocation()));
            return false;
        }
        if (definitions.containsKey(node.getDefinitionName())) {
            errorManager.report(new GssError(
                    DUPLICATE_MIXIN_DEFINITION_NAME_ERROR_MESSAGE,
                    node.getSourceCodeLocation()));
            return false;
        }
        if (!checkArguments(node)) {
            return false;
        }
        definitions.put(node.getDefinitionName(), node);
        return true;
    }

    @Override
    public void leaveMixinDefinition(CssMixinDefinitionNode node) {
        visitController.removeCurrentNode();
    }

    /**
     * Checks that every argument has a unique name and that the argument only
     * consists of capital letters and digits.
     */
    private boolean checkArguments(CssMixinDefinitionNode node) {
        Set arguments = Sets.newHashSetWithExpectedSize(
                node.getArguments().numChildren());
        for (CssValueNode arg : node.getArguments().getChildren()) {
            boolean isSeparator = ",".equals(arg.getValue());
            if (!isSeparator
                    && !CssConstantReferenceNode.isDefinitionReference(arg.getValue())) {
                errorManager.report(new GssError(INVALID_ARGUMENT_ERROR_MESSAGE,
                        node.getSourceCodeLocation()));
                return false;
            }
            if (arguments.contains(arg.getValue())) {
                errorManager.report(new GssError(DUPLICATE_ARGUMENT_NAME_ERROR_MESSAGE,
                        node.getSourceCodeLocation()));
                return false;
            }
            if (!isSeparator) {
                arguments.add(arg.getValue());
            }
        }
        return true;
    }

    public Map getDefinitions() {
        return definitions;
    }

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