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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 2016 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.gwt.client;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.gwt.core.client.EntryPoint;
import com.google.javascript.jscomp.CompilationLevel;
import com.google.javascript.jscomp.Compiler;
import com.google.javascript.jscomp.CompilerOptions;
import com.google.javascript.jscomp.CompilerOptions.LanguageMode;
import com.google.javascript.jscomp.SourceFile;
import com.google.javascript.jscomp.WarningLevel;

import jsinterop.annotations.JsPackage;
import jsinterop.annotations.JsProperty;
import jsinterop.annotations.JsType;

import java.util.Map;

/**
 * Runner for the GWT-compiled JSCompiler
 *
 * @author [email protected] (Michael Zhou)
 */
@JsType(namespace = JsPackage.GLOBAL, name = "JSCompiler")
public final class GwtRunner implements EntryPoint {

  private static final Map COMPILATION_LEVEL_MAP =
      ImmutableMap.of(
          "WHITESPACE_ONLY",
          CompilationLevel.WHITESPACE_ONLY,
          "SIMPLE",
          CompilationLevel.SIMPLE_OPTIMIZATIONS,
          "SIMPLE_OPTIMIZATIONS",
          CompilationLevel.SIMPLE_OPTIMIZATIONS,
          "ADVANCED",
          CompilationLevel.ADVANCED_OPTIMIZATIONS,
          "ADVANCED_OPTIMIZATIONS",
          CompilationLevel.ADVANCED_OPTIMIZATIONS);

  private static final Map WARNING_LEVEL_MAP =
      ImmutableMap.of(
          "QUIET",
          WarningLevel.QUIET,
          "DEFAULT",
          WarningLevel.DEFAULT,
          "VERBOSE",
          WarningLevel.VERBOSE);

  private final Compiler compiler;

  public GwtRunner() {
    compiler = new Compiler();
    compiler.disableThreads();
  }

  @JsType(namespace = JsPackage.GLOBAL, name = "Object", isNative = true)
  private interface Flags {
    @JsProperty
    String getCompilationLevel();

    @JsProperty
    String getWarningLevel();

    @JsProperty
    String getLanguageIn();

    @JsProperty
    String getLanguageOut();

    @JsProperty
    boolean getChecksOnly();

    @JsProperty
    boolean getNewTypeInf();

    @JsProperty
    boolean getPreserveTypeAnnotations();

    @JsProperty
    boolean getRewritePolyfills();
  }

  private static void applyDefaultOptions(CompilerOptions options) {
    CompilationLevel.SIMPLE_OPTIMIZATIONS.setOptionsForCompilationLevel(options);
    WarningLevel.DEFAULT.setOptionsForWarningLevel(options);
    options.setLanguageIn(LanguageMode.ECMASCRIPT5);
    options.setLanguageOut(LanguageMode.ECMASCRIPT3);
    options.setPrettyPrint(true);
  }

  // TODO(moz): Handle most compiler flags and report errors on invalid flags / values.
  private static void applyOptionsFromFlags(CompilerOptions options, Flags flags) {
    if (flags == null) {
      return;
    }

    if (flags.getCompilationLevel() != null) {
      CompilationLevel level =
          COMPILATION_LEVEL_MAP.get(flags.getCompilationLevel().toUpperCase());
      if (level != null) {
        level.setOptionsForCompilationLevel(options);
      }
    }

    if (flags.getWarningLevel() != null) {
      WarningLevel level = WARNING_LEVEL_MAP.get(flags.getWarningLevel().toUpperCase());
      if (level != null) {
        level.setOptionsForWarningLevel(options);
      }
    }

    if (flags.getLanguageIn() != null) {
      LanguageMode languageIn = LanguageMode.fromString(flags.getLanguageIn());
      if (languageIn != null) {
        options.setLanguageIn(languageIn);
      }
    }

    if (flags.getLanguageOut() != null) {
      LanguageMode languageOut = LanguageMode.fromString(flags.getLanguageOut());
      if (languageOut != null) {
        options.setLanguageOut(languageOut);
      }
    }

    options.setChecksOnly(flags.getChecksOnly());
    options.setNewTypeInference(flags.getNewTypeInf());
    options.setPreserveTypeAnnotations(flags.getPreserveTypeAnnotations());
    options.setRewritePolyfills(flags.getRewritePolyfills());
  }

  private static void disableUnsupportedOptions(CompilerOptions options) {
    options.getDependencyOptions().setDependencySorting(false);
  }

  public String compile(String js, Flags flags) {
    CompilerOptions options = new CompilerOptions();
    applyDefaultOptions(options);
    applyOptionsFromFlags(options, flags);
    disableUnsupportedOptions(options);
    SourceFile src = SourceFile.fromCode("src.js", js);
    SourceFile externs = SourceFile.fromCode("externs.js", "var window;");
    compiler.compile(ImmutableList.of(externs), ImmutableList.of(src), options);
    return compiler.toSource();
  }

  @Override
  public void onModuleLoad() {}
}