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Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs.

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/*
 * Copyright 2008 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 com.google.javascript.rhino.Node;

/**
 * For use with CodeGenerator to determine the cost of generated code.
 *
 * @see CodeGenerator
 * @see CodePrinter
 */
class InlineCostEstimator {
  // For now simply assume identifiers are 2 characters.
  private static final String ESTIMATED_IDENTIFIER = "ab";
  static final int ESTIMATED_IDENTIFIER_COST = ESTIMATED_IDENTIFIER.length();

  private InlineCostEstimator() {
  }

  /**
   * Determines the size of the JS code.
   */
  static int getCost(Node root) {
    return getCost(root, Integer.MAX_VALUE);
  }

  /**
   * Determines the estimated size of the JS snippet represented by the node.
   */
  static int getCost(Node root, int costThreshold) {
    CompiledSizeEstimator estimator = new CompiledSizeEstimator(costThreshold);
    estimator.add(root);
    return estimator.getCost();
  }

  /**
   * Code consumer that estimates compiled size by assuming names are
   * shortened and all whitespace is stripped.
   */
  private static class CompiledSizeEstimator extends CodeConsumer {
    private final int maxCost;
    private int cost = 0;
    private char last = '\0';
    private boolean continueProcessing = true;

    CompiledSizeEstimator(int costThreshold) {
      this.maxCost = costThreshold;
    }

    void add(Node root) {
      CodeGenerator cg = CodeGenerator.forCostEstimation(this);
      cg.add(root);
    }

    int getCost() {
      return cost;
    }

    @Override
    boolean continueProcessing() {
      return continueProcessing;
    }

    @Override
    char getLastChar() {
      return last;
    }

    @Override
    void append(String str){
      last = str.charAt(str.length() - 1);
      cost += str.length();
      if (maxCost <= cost) {
        continueProcessing = false;
      }
    }

    @Override
    void addIdentifier(String identifier) {
      add(ESTIMATED_IDENTIFIER);
    }

    /**
     * Constants (true, false, null) are considered basically free,
     * because it's likely that they will get folded when we're done.
     */
    @Override
    void addConstant(String newcode) {
      add("0");
    }
  }
}