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/*
 * Copyright 2015 The Closure Compiler Authors.
 *
 * 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.javascript.jscomp;

import static com.google.common.base.Preconditions.checkArgument;

import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.jscomp.parsing.parser.FeatureSet.Feature;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;

/** An optimization that does peephole optimizations of ES6 code. */
class SubstituteEs6Syntax extends AbstractPostOrderCallback implements CompilerPass {

  private final AbstractCompiler compiler;
  private boolean objectLiteralShorthandWasAdded = false;

  public SubstituteEs6Syntax(AbstractCompiler compiler) {
    this.compiler = compiler;
  }

  @Override
  public void process(Node externs, Node root) {
    NodeTraversal.traverse(compiler, root, this);
  }

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    switch (n.getToken()) {
      case FUNCTION:
        if (n.isArrowFunction()) {
          maybeSimplifyArrowFunctionBody(n, n.getLastChild());
        }
        break;
      case STRING_KEY:
        if (n.getFirstChild().isName() && n.getFirstChild().getString().equals(n.getString())) {
          n.setShorthandProperty(true);
          objectLiteralShorthandWasAdded = true;
        }
        break;
      case SCRIPT:
        if (objectLiteralShorthandWasAdded) {
          NodeUtil.addFeatureToScript(n, Feature.EXTENDED_OBJECT_LITERALS, compiler);
          objectLiteralShorthandWasAdded = false; // false for the next script
        }
        break;
      default:
        break;
    }
  }

  /**
   * If possible, replace functions of the form ()=>{ return x; } with ()=>x
   */
  private void maybeSimplifyArrowFunctionBody(Node arrowFunction, Node body) {
    checkArgument(arrowFunction.isArrowFunction());
    if (!body.isBlock() || !body.hasOneChild() || !body.getFirstChild().isReturn()) {
      return;
    }
    Node returnValue = body.getFirstChild().removeFirstChild();
    Node replacement = returnValue != null ? returnValue : IR.name("undefined");
    body.replaceWith(replacement);
    compiler.reportChangeToEnclosingScope(replacement);
  }
}