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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 2013 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.fuzzing;

import com.google.common.base.Preconditions;
import com.google.common.collect.Lists;
import com.google.common.collect.Sets;
import com.google.javascript.rhino.Node;

import org.json.JSONException;
import org.json.JSONObject;

import java.util.ArrayList;
import java.util.EnumSet;
import java.util.Set;

/**
 * UNDER DEVELOPMENT. DO NOT USE!
 */
abstract class Dispatcher extends AbstractFuzzer {
  private Set supportedTypes;
  Dispatcher(FuzzingContext context) {
    super(context);
  }
  protected AbstractFuzzer[] candidates;

  @Override
  protected boolean isEnough(int budget) {
    if (budget < 1) {
      return false;
    }
    Preconditions.checkNotNull(
        getCandidates(),
        "Candidate fuzzers need to be initialized before being used.");

    for (AbstractFuzzer fuzzer : getCandidates()) {
      if (fuzzer.isEnough(budget)) {
        return true;
      }
    }
    return false;
  }

  /* (non-Javadoc)
   * @see com.google.javascript.jscomp.fuzzing.AbstractFuzzer#generate(int, Set)
   */
  @Override
  protected Node generate(int budget, Set types) {
    AbstractFuzzer fuzzer = selectFuzzer(budget, types);
    return fuzzer.generate(budget, types);
  }

  @Override
  protected Set supportedTypes() {
    if (supportedTypes == null) {
      supportedTypes = EnumSet.noneOf(Type.class);
      for (AbstractFuzzer fuzzer : getCandidates()) {
        supportedTypes.addAll(fuzzer.supportedTypes());
      }
    }
    return Sets.immutableEnumSet(supportedTypes);
  }

  protected AbstractFuzzer selectFuzzer(int budget, Set types) {
    Preconditions.checkNotNull(
        getCandidates(),
        "Candidate fuzzers need to be initialized before being used.");
    ArrayList typeCorrectCandidates;
    typeCorrectCandidates = Lists.newArrayList();
    for (AbstractFuzzer fuzzer : getCandidates()) {
      if (!Sets.intersection(fuzzer.supportedTypes(), types).
          isEmpty()) {
        typeCorrectCandidates.add(fuzzer);
      }
    }
    JSONObject weightConfig = getOwnConfig().optJSONObject("weights");
    ArrayList validFuzzers = Lists.newArrayList();
    ArrayList weights = Lists.newArrayList();
    int stepSize = 2;
    budget -= stepSize;
    do {
      // increase the budget until it is enough for some fuzzers
      budget += stepSize;
      for (AbstractFuzzer fuzzer : typeCorrectCandidates) {
        if (fuzzer.isEnough(budget)) {
          validFuzzers.add(fuzzer);
          try {
            weights.add(weightConfig.getDouble(fuzzer.getConfigName()));
          } catch (JSONException e) {
            e.printStackTrace();
          }
        }
      }
    } while (validFuzzers.isEmpty());
    DiscreteDistribution dd =
        new DiscreteDistribution<>(context.random, validFuzzers, weights);
    return dd.nextItem();
  }

  protected abstract void initCandidates();

  private AbstractFuzzer[] getCandidates() {
    if (candidates == null) {
      initCandidates();
    }
    return candidates;
  }
}