user/src/com/google/gwt/resources/gss/CreateRuntimeConditionalNodes.java

/*
 * 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.gwt.resources.gss;

import com.google.gwt.resources.gss.ast.CssJavaExpressionNode;
import com.google.gwt.resources.gss.ast.CssRuntimeConditionalRuleNode;
import com.google.gwt.thirdparty.common.css.compiler.ast.CssAtRuleNode.Type;
import com.google.gwt.thirdparty.common.css.compiler.ast.CssBooleanExpressionNode;
import com.google.gwt.thirdparty.common.css.compiler.ast.CssCompilerPass;
import com.google.gwt.thirdparty.common.css.compiler.ast.CssConditionalBlockNode;
import com.google.gwt.thirdparty.common.css.compiler.ast.CssConditionalRuleNode;
import com.google.gwt.thirdparty.common.css.compiler.ast.CssValueNode;
import com.google.gwt.thirdparty.common.css.compiler.ast.DefaultTreeVisitor;
import com.google.gwt.thirdparty.common.css.compiler.ast.MutatingVisitController;
import com.google.gwt.thirdparty.guava.common.collect.Lists;

import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Visitor that handles conditional nodes with conditions that need to be evaluated at runtime.
 *
 * <p>The corresponding GSS handled by this pass looks like:
 *
 * <pre>
 *   @if(eval("com.foo.BAR")) {
 *   }
 *   @elseif(eval("com.foo.bar()")) {
 *   }
 * }
 * </pre>
 */
public class CreateRuntimeConditionalNodes extends DefaultTreeVisitor implements CssCompilerPass {
  // TODO(jdr): valid input like eval('foo(")\')")') will break this regex
  private static final Pattern EVAL_FUNCTION = Pattern.compile("^eval\\(([\"'])(((?!\\1).)*)\\1\\)$");

  private final MutatingVisitController visitController;

  public CreateRuntimeConditionalNodes(MutatingVisitController visitController) {
    this.visitController = visitController;
  }

  @Override
  public boolean enterConditionalBlock(CssConditionalBlockNode block) {
    // We have to visit all the CssConditionalRuleNode when we visit the CssConditionalBlockNode
    // parent node because we are going to replace CssConditionalRuleNode by another node and
    // unfortunately the visitController doesn't support to replace a CssConditionalRuleNode and
    // we have to do it manually. That implies that the new nodes won't be visited by the
    // visitor if we do that during the visit of the CssConditionalRuleNodes and they can contain
    // other CssConditionalBlockNodes that won't be visited.
    // Once MutatingVisitController supports replacement of CssConditionalRuleNode,
    // we will be able to visit CssConditionalRuleNode directly.

    // Make a copy in order to avoid ConcurrentModificationException
    List<CssConditionalRuleNode> children = Lists.newArrayList(block.getChildren());
    for (CssConditionalRuleNode ruleNode : children) {
      visitConditionalRule(ruleNode, block);
    }
    return true;
  }

  private void visitConditionalRule(CssConditionalRuleNode node,
      CssConditionalBlockNode parent) {

    if (node.getType() != Type.ELSE) {
      CssBooleanExpressionNode nodeCondition = node.getCondition();
      String condition = extractRuntimeCondition(nodeCondition);

      if (condition != null) {
        CssJavaExpressionNode newNode = new CssJavaExpressionNode(condition,
            nodeCondition.getSourceCodeLocation());

        CssRuntimeConditionalRuleNode newRuleNode = new CssRuntimeConditionalRuleNode(node,
            newNode);

        // Unfortunately visitController.replaceCurrentBlockChildWith doesn't work with
        // CssConditionnalRuleNode
        int index = parent.getChildren().indexOf(node);
        parent.replaceChildAt(index, Lists.newArrayList(newRuleNode));
      }
    }
  }

  private String extractRuntimeCondition(CssValueNode node) {
    Matcher m = EVAL_FUNCTION.matcher(node.getValue());
    return m.matches() ? m.group(2) : null;
  }

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