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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.refactoring.testing;

import static com.google.common.truth.Truth.assertThat;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.io.Files;
import com.google.common.truth.Correspondence;
import com.google.javascript.jscomp.CommandLineRunner;
import com.google.javascript.jscomp.CompilerOptions;
import com.google.javascript.refactoring.ApplySuggestedFixes;
import com.google.javascript.refactoring.RefactoringDriver;
import com.google.javascript.refactoring.RefasterJsScanner;
import com.google.javascript.refactoring.SuggestedFix;
import java.io.File;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.util.List;

/** Utilities for testing RefasterJs templates. */
public final class RefasterJsTestUtils {

  /**
   * Performs refactoring using a RefasterJs template and asserts that result is as expected.
   *
   * @param refasterJsTemplate path of the file or resource containing the RefasterJs template to
   *     apply
   * @param testDataPathPrefix path prefix of the directory from which input and expected-output
   *     file will be read
   * @param originalFile file name of the JavaScript source file to apply the refaster template to
   * @param additionalSourceFiles list of additional source files to provide to the compiler (e.g.
   *     dependencies)
   * @param expectedFileChoices the expected result options of applying the specified template to
   *     {@code originalFile}
   * @throws IOException
   */
  public static void assertFileRefactoring(
      String refasterJsTemplate,
      String testDataPathPrefix,
      String originalFile,
      List additionalSourceFiles,
      String... expectedFileChoices)
      throws IOException {
    RefasterJsScanner scanner = new RefasterJsScanner();
    scanner.loadRefasterJsTemplate(refasterJsTemplate);

    final String originalFilePath = testDataPathPrefix + File.separator + originalFile;

    ImmutableList.Builder expectedCodeBuilder = ImmutableList.builder();
    for (String expectedFile : expectedFileChoices) {
      expectedCodeBuilder.add(slurpFile(testDataPathPrefix + File.separator + expectedFile));
    }
    final ImmutableList expectedCode = expectedCodeBuilder.build();

    RefactoringDriver.Builder driverBuilder =
        new RefactoringDriver.Builder()
            .addExterns(CommandLineRunner.getBuiltinExterns(CompilerOptions.Environment.BROWSER));

    for (String additionalSource : additionalSourceFiles) {
      driverBuilder.addInputsFromFile(testDataPathPrefix + File.separator + additionalSource);
    }
    RefactoringDriver driver = driverBuilder.addInputsFromFile(originalFilePath).build();

    List fixes = driver.drive(scanner);
    assertThat(driver.getCompiler().getErrors()).isEmpty();
    assertThat(driver.getCompiler().getWarnings()).isEmpty();

    ImmutableList newCode =
        ApplySuggestedFixes.applyAllSuggestedFixChoicesToCode(
                fixes, ImmutableMap.of(originalFilePath, slurpFile(originalFilePath)))
            .stream()
            .map(m -> m.get(originalFilePath))
            .collect(ImmutableList.toImmutableList());
    assertThat(newCode)
        .comparingElementsUsing(IGNORING_WHITESPACE_CORRESPONDENCE)
        .containsExactlyElementsIn(expectedCode);
  }

  private static String slurpFile(String originalFile) throws IOException {
    return Files.asCharSource(new File(originalFile), StandardCharsets.UTF_8).read();
  }

  private RefasterJsTestUtils() {}

  private static final Correspondence IGNORING_WHITESPACE_CORRESPONDENCE =
      Correspondence.transforming(
          RefasterJsTestUtils::replaceTrailingWhitespace,
          RefasterJsTestUtils::replaceTrailingWhitespace,
          "equals (except for whitespace)");

  private static String replaceTrailingWhitespace(String contents) {
    return contents.replaceAll("[ \t]*\n", "\n");
  }
}