// Copyright (c) 2017, the R8 project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
package com.android.tools.r8.classmerging;

import static com.android.tools.r8.smali.SmaliBuilder.buildCode;
import static com.android.tools.r8.utils.DexInspectorMatchers.isPresent;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertThat;
import static org.junit.Assert.assertTrue;

import com.android.tools.r8.CompilationFailedException;
import com.android.tools.r8.OutputMode;
import com.android.tools.r8.R8Command;
import com.android.tools.r8.TestBase;
import com.android.tools.r8.ToolHelper;
import com.android.tools.r8.code.Instruction;
import com.android.tools.r8.code.MoveException;
import com.android.tools.r8.graph.DexCode;
import com.android.tools.r8.origin.Origin;
import com.android.tools.r8.smali.SmaliBuilder;
import com.android.tools.r8.utils.AndroidApp;
import com.android.tools.r8.utils.DexInspector;
import com.android.tools.r8.utils.DexInspector.ClassSubject;
import com.android.tools.r8.utils.DexInspector.FoundClassSubject;
import com.android.tools.r8.utils.DexInspector.MethodSubject;
import com.android.tools.r8.utils.InternalOptions;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.List;
import java.util.Set;
import java.util.concurrent.ExecutionException;
import java.util.function.Consumer;
import java.util.function.Predicate;
import org.junit.Ignore;
import org.junit.Test;

// TODO(christofferqa): Add tests to check that statically typed invocations on method handles
// continue to work after class merging. Rewriting of method handles should be carried out by
// LensCodeRewriter.rewriteDexMethodHandle.
public class ClassMergingTest extends TestBase {

  private static final Path CF_DIR =
      Paths.get(ToolHelper.BUILD_DIR).resolve("test/examples/classes/classmerging");
  private static final Path JAVA8_CF_DIR =
      Paths.get(ToolHelper.BUILD_DIR).resolve("test/examplesAndroidO/classes/classmerging");
  private static final Path EXAMPLE_JAR = Paths.get(ToolHelper.EXAMPLES_BUILD_DIR)
      .resolve("classmerging.jar");
  private static final Path EXAMPLE_KEEP = Paths.get(ToolHelper.EXAMPLES_DIR)
      .resolve("classmerging").resolve("keep-rules.txt");
  private static final Path JAVA8_EXAMPLE_KEEP = Paths.get(ToolHelper.EXAMPLES_ANDROID_O_DIR)
      .resolve("classmerging").resolve("keep-rules.txt");
  private static final Path DONT_OPTIMIZE = Paths.get(ToolHelper.EXAMPLES_DIR)
      .resolve("classmerging").resolve("keep-rules-dontoptimize.txt");

  private void configure(InternalOptions options) {
    options.enableClassMerging = true;
    options.enableClassInlining = false;
    options.enableMinification = false;
  }

  private void runR8(Path proguardConfig, Consumer<InternalOptions> optionsConsumer)
      throws IOException, ExecutionException, CompilationFailedException {
    ToolHelper.runR8(
        R8Command.builder()
            .setOutput(Paths.get(temp.getRoot().getCanonicalPath()), OutputMode.DexIndexed)
            .addProgramFiles(EXAMPLE_JAR)
            .addProguardConfigurationFiles(proguardConfig)
            .setDisableMinification(true)
            .build(),
        optionsConsumer);
    inspector = new DexInspector(
        Paths.get(temp.getRoot().getCanonicalPath()).resolve("classes.dex"));
  }

  private DexInspector inspector;

  private final List<String> CAN_BE_MERGED = ImmutableList.of(
      "classmerging.GenericInterface",
      "classmerging.GenericAbstractClass",
      "classmerging.Outer$SuperClass",
      "classmerging.SuperClass"
  );

  @Test
  public void testClassesHaveBeenMerged() throws Exception {
    runR8(EXAMPLE_KEEP, this::configure);
    // GenericInterface should be merged into GenericInterfaceImpl.
    for (String candidate : CAN_BE_MERGED) {
      assertFalse(inspector.clazz(candidate).isPresent());
    }
    assertTrue(inspector.clazz("classmerging.GenericInterfaceImpl").isPresent());
    assertTrue(inspector.clazz("classmerging.Outer$SubClass").isPresent());
    assertTrue(inspector.clazz("classmerging.SubClass").isPresent());
  }

  @Test
  public void testClassesHaveNotBeenMerged() throws Exception {
    runR8(DONT_OPTIMIZE, null);
    for (String candidate : CAN_BE_MERGED) {
      assertTrue(inspector.clazz(candidate).isPresent());
    }
  }

  @Test
  public void testConflictWasDetected() throws Exception {
    runR8(EXAMPLE_KEEP, this::configure);
    assertTrue(inspector.clazz("classmerging.ConflictingInterface").isPresent());
    assertTrue(inspector.clazz("classmerging.ConflictingInterfaceImpl").isPresent());
  }

  @Test
  public void testLambdaRewriting() throws Exception {
    String main = "classmerging.LambdaRewritingTest";
    Path[] programFiles =
        new Path[] {
          JAVA8_CF_DIR.resolve("LambdaRewritingTest.class"),
          JAVA8_CF_DIR.resolve("LambdaRewritingTest$Function.class"),
          JAVA8_CF_DIR.resolve("LambdaRewritingTest$Interface.class"),
          JAVA8_CF_DIR.resolve("LambdaRewritingTest$InterfaceImpl.class")
        };
    Set<String> preservedClassNames =
        ImmutableSet.of(
            "classmerging.LambdaRewritingTest",
            "classmerging.LambdaRewritingTest$Function",
            "classmerging.LambdaRewritingTest$InterfaceImpl");
    runTest(
        main,
        programFiles,
        name -> preservedClassNames.contains(name) || name.contains("$Lambda$"),
        getProguardConfig(JAVA8_EXAMPLE_KEEP));
  }

  @Test
  public void testSuperCallWasDetected() throws Exception {
    String main = "classmerging.SuperCallRewritingTest";
    Path[] programFiles =
        new Path[] {
          CF_DIR.resolve("SubClassThatReferencesSuperMethod.class"),
          CF_DIR.resolve("SuperClassWithReferencedMethod.class"),
          CF_DIR.resolve("SuperCallRewritingTest.class")
        };
    Set<String> preservedClassNames =
        ImmutableSet.of(
            "classmerging.SubClassThatReferencesSuperMethod",
            "classmerging.SuperCallRewritingTest");
    runTest(main, programFiles, preservedClassNames::contains);
  }

  // When a subclass A has been merged into its subclass B, we rewrite invoke-super calls that hit
  // methods in A to invoke-direct calls. However, we should be careful not to transform invoke-
  // super instructions into invoke-direct instructions simply because the static target is a method
  // in the enclosing class.
  //
  // This test hand-crafts an invoke-super instruction in SubClassThatReferencesSuperMethod that
  // targets SubClassThatReferencesSuperMethod.referencedMethod. When running without class
  // merging, R8 should not rewrite the invoke-super instruction into invoke-direct.
  @Test
  public void testSuperCallNotRewrittenToDirect() throws Exception {
    String main = "classmerging.SuperCallRewritingTest";
    Path[] programFiles =
        new Path[] {
          CF_DIR.resolve("SuperClassWithReferencedMethod.class"),
          CF_DIR.resolve("SuperCallRewritingTest.class")
        };
    Set<String> preservedClassNames =
        ImmutableSet.of(
            "classmerging.SubClassThatReferencesSuperMethod",
            "classmerging.SuperClassWithReferencedMethod",
            "classmerging.SuperCallRewritingTest");

    // Build SubClassThatReferencesMethod.
    SmaliBuilder smaliBuilder =
        new SmaliBuilder(
            "classmerging.SubClassThatReferencesSuperMethod",
            "classmerging.SuperClassWithReferencedMethod");
    smaliBuilder.addInitializer(
        0,
        "invoke-direct {p0}, Lclassmerging/SuperClassWithReferencedMethod;-><init>()V",
        "return-void");
    smaliBuilder.addInstanceMethod(
        "java.lang.String",
        "referencedMethod",
        2,
        "sget-object v0, Ljava/lang/System;->out:Ljava/io/PrintStream;",
        "const-string v1, \"In referencedMethod on SubClassThatReferencesSuperMethod\"",
        "invoke-virtual {v0, v1}, Ljava/io/PrintStream;->println(Ljava/lang/String;)V",
        "invoke-super {p0}, Lclassmerging/SubClassThatReferencesSuperMethod;->referencedMethod()Ljava/lang/String;",
        "move-result-object v1",
        "return-object v1");

    // Build app.
    AndroidApp.Builder builder = AndroidApp.builder();
    builder.addProgramFiles(programFiles);
    builder.addDexProgramData(smaliBuilder.compile(), Origin.unknown());

    // Run test.
    runTestOnInput(
        main,
        builder.build(),
        preservedClassNames::contains,
        // Prevent class merging, such that the generated code would be invalid if we rewrite the
        // invoke-super instruction into an invoke-direct instruction.
        getProguardConfig(EXAMPLE_KEEP, "-keep class *"));
  }

  // The following test checks that our rewriting of invoke-super instructions in a class F works
  // if a super type of F has previously been merged into its sub class.
  //
  //   class A {}                                               <- A is kept to preserve the error
  //   class B extends A {                                         in F.invokeMethodOnA().
  //     public void m() {}
  //   }
  //   class C extends B {                                      <- C will be merged into D.
  //     @Override
  //     public void m() { "invoke-super B.m()" }
  //   }
  //   class D extends C {
  //     @Override
  //     public void m() { "invoke-super C.m()" }
  //   }
  //   class E extends D {                                      <- E will be merged into F.
  //     @Override
  //     public void m() { "invoke-super D.m()" }
  //   }
  //   class F extends E {
  //     @Override
  //     public void m() { throw new Exception() }              <- Should be dead code.
  //
  //     public void invokeMethodOnA() { "invoke-super A.m()" } <- Should yield NoSuchMethodError.
  //     public void invokeMethodOnB() { "invoke-super B.m()" }
  //     public void invokeMethodOnC() { "invoke-super C.m()" }
  //     public void invokeMethodOnD() { "invoke-super D.m()" }
  //     public void invokeMethodOnE() { "invoke-super E.m()" }
  //     public void invokeMethodOnF() { "invoke-super F.m()" }
  //   }
  @Ignore
  @Test
  public void testSuperCallToMergedClassIsRewritten() throws Exception {
    String main = "classmerging.SuperCallToMergedClassIsRewrittenTest";
    Set<String> preservedClassNames =
        ImmutableSet.of(
            "classmerging.SuperCallToMergedClassIsRewrittenTest",
            "classmerging.A",
            "classmerging.B",
            "classmerging.D",
            "classmerging.F");

    SmaliBuilder smaliBuilder = new SmaliBuilder();

    smaliBuilder.addClass(main);
    smaliBuilder.addMainMethod(
        2,
        // Instantiate B so that it is not merged into C.
        "new-instance v1, Lclassmerging/B;",
        "invoke-direct {v1}, Lclassmerging/B;-><init>()V",
        "invoke-virtual {v1}, Lclassmerging/B;->m()V",
        // Instantiate D so that it is not merged into E.
        "new-instance v1, Lclassmerging/D;",
        "invoke-direct {v1}, Lclassmerging/D;-><init>()V",
        "invoke-virtual {v1}, Lclassmerging/D;->m()V",
        // Start the actual testing.
        "new-instance v1, Lclassmerging/F;",
        "invoke-direct {v1}, Lclassmerging/F;-><init>()V",
        "invoke-virtual {v1}, Lclassmerging/F;->invokeMethodOnB()V",
        "invoke-virtual {v1}, Lclassmerging/F;->invokeMethodOnC()V",
        "invoke-virtual {v1}, Lclassmerging/F;->invokeMethodOnD()V",
        "invoke-virtual {v1}, Lclassmerging/F;->invokeMethodOnE()V",
        "invoke-virtual {v1}, Lclassmerging/F;->invokeMethodOnF()V",
        // The method invokeMethodOnA() should yield a NoSuchMethodError.
        ":try_start",
        "invoke-virtual {v1}, Lclassmerging/F;->invokeMethodOnA()V",
        ":try_end",
        "return-void",
        ".catch Ljava/lang/NoSuchMethodError; {:try_start .. :try_end} :catch",
        ":catch",
        smaliCodeForPrinting("NoSuchMethodError", 0, 1),
        "return-void");

    // Class A deliberately has no method m. We need to make sure that the "invoke-super A.m()"
    // instruction in class F is not rewritten into something that does not throw.
    smaliBuilder.addClass("classmerging.A");
    smaliBuilder.addDefaultConstructor();

    // Class B declares a virtual method m() that prints "In B.m()".
    smaliBuilder.addClass("classmerging.B", "classmerging.A");
    smaliBuilder.addDefaultConstructor();
    smaliBuilder.addInstanceMethod(
        "void", "m", 2, smaliCodeForPrinting("In B.m()", 0, 1), "return-void");

    // Class C, D, and E declare a virtual method m() that prints "In C.m()", "In D.m()", and
    // "In E.m()", respectively.
    String[][] pairs =
        new String[][] {new String[] {"C", "B"}, new String[] {"D", "C"}, new String[] {"E", "D"}};
    for (String[] pair : pairs) {
      String name = pair[0], superName = pair[1];
      smaliBuilder.addClass("classmerging." + name, "classmerging." + superName);
      smaliBuilder.addDefaultConstructor();
      smaliBuilder.addInstanceMethod(
          "void",
          "m",
          2,
          smaliCodeForPrinting("In " + name + ".m()", 0, 1),
          buildCode("invoke-super {p0}, Lclassmerging/" + superName + ";->m()V", "return-void"));
    }

    // Class F declares a virtual method m that throws an exception (it is expected to be dead).
    smaliBuilder.addClass("classmerging.F", "classmerging.E");
    smaliBuilder.addDefaultConstructor();
    smaliBuilder.addInstanceMethod(
        "void",
        "m",
        1,
        "new-instance v1, Ljava/lang/Exception;",
        "invoke-direct {v1}, Ljava/lang/Exception;-><init>()V",
        "throw v1");

    // Add methods to F with an "invoke-super X.m()" instruction for X in {A, B, C, D, E, F}.
    for (String type : ImmutableList.of("A", "B", "C", "D", "E", "F")) {
      String code =
          buildCode("invoke-super {p0}, Lclassmerging/" + type + ";->m()V", "return-void");
      smaliBuilder.addInstanceMethod("void", "invokeMethodOn" + type, 0, code);
    }

    // Build app.
    AndroidApp.Builder builder = AndroidApp.builder();
    builder.addDexProgramData(smaliBuilder.compile(), Origin.unknown());

    // Run test.
    runTestOnInput(
        main,
        builder.build(),
        preservedClassNames::contains,
        String.format("-keep class %s { public static void main(...); }", main));
  }

  private static String smaliCodeForPrinting(String message, int reg0, int reg1) {
    return buildCode(
        String.format("sget-object v%d, Ljava/lang/System;->out:Ljava/io/PrintStream;", reg0),
        String.format("const-string v1, \"%s\"", message),
        String.format(
            "invoke-virtual {v%d, v%d}, Ljava/io/PrintStream;->println(Ljava/lang/String;)V",
            reg0, reg1));
  }

  @Test
  public void testConflictingInterfaceSignatures() throws Exception {
    String main = "classmerging.ConflictingInterfaceSignaturesTest";
    Path[] programFiles =
        new Path[] {
          CF_DIR.resolve("ConflictingInterfaceSignaturesTest.class"),
          CF_DIR.resolve("ConflictingInterfaceSignaturesTest$A.class"),
          CF_DIR.resolve("ConflictingInterfaceSignaturesTest$B.class"),
          CF_DIR.resolve("ConflictingInterfaceSignaturesTest$InterfaceImpl.class")
        };
    Set<String> preservedClassNames =
        ImmutableSet.of(
            "classmerging.ConflictingInterfaceSignaturesTest",
            "classmerging.ConflictingInterfaceSignaturesTest$InterfaceImpl");
    runTest(main, programFiles, preservedClassNames::contains);
  }

  // If an exception class A is merged into another exception class B, then all exception tables
  // should be updated, and class A should be removed entirely.
  @Test
  public void testExceptionTables() throws Exception {
    String main = "classmerging.ExceptionTest";
    Path[] programFiles =
        new Path[] {
          CF_DIR.resolve("ExceptionTest.class"),
          CF_DIR.resolve("ExceptionTest$ExceptionA.class"),
          CF_DIR.resolve("ExceptionTest$ExceptionB.class"),
          CF_DIR.resolve("ExceptionTest$Exception1.class"),
          CF_DIR.resolve("ExceptionTest$Exception2.class")
        };
    Set<String> preservedClassNames =
        ImmutableSet.of(
            "classmerging.ExceptionTest",
            "classmerging.ExceptionTest$ExceptionB",
            "classmerging.ExceptionTest$Exception2");
    DexInspector inspector = runTest(main, programFiles, preservedClassNames::contains);

    ClassSubject mainClass = inspector.clazz(main);
    assertThat(mainClass, isPresent());

    MethodSubject mainMethod =
        mainClass.method("void", "main", ImmutableList.of("java.lang.String[]"));
    assertThat(mainMethod, isPresent());

    // Check that the second catch handler has been removed.
    DexCode code = mainMethod.getMethod().getCode().asDexCode();
    int numberOfMoveExceptionInstructions = 0;
    for (Instruction instruction : code.instructions) {
      if (instruction instanceof MoveException) {
        numberOfMoveExceptionInstructions++;
      }
    }
    assertEquals(2, numberOfMoveExceptionInstructions);
  }

  @Test
  public void testNoIllegalClassAccess() throws Exception {
    String main = "classmerging.SimpleInterfaceAccessTest";
    Path[] programFiles =
        new Path[] {
          CF_DIR.resolve("SimpleInterfaceAccessTest.class"),
          CF_DIR.resolve("SimpleInterfaceAccessTest$SimpleInterface.class"),
          CF_DIR.resolve("SimpleInterfaceAccessTest$OtherSimpleInterface.class"),
          CF_DIR.resolve("SimpleInterfaceAccessTest$OtherSimpleInterfaceImpl.class"),
          CF_DIR.resolve("pkg/SimpleInterfaceImplRetriever.class"),
          CF_DIR.resolve("pkg/SimpleInterfaceImplRetriever$SimpleInterfaceImpl.class")
        };
    // SimpleInterface cannot be merged into SimpleInterfaceImpl because SimpleInterfaceImpl
    // is in a different package and is not public.
    ImmutableSet<String> preservedClassNames =
        ImmutableSet.of(
            "classmerging.SimpleInterfaceAccessTest",
            "classmerging.SimpleInterfaceAccessTest$SimpleInterface",
            "classmerging.SimpleInterfaceAccessTest$OtherSimpleInterface",
            "classmerging.SimpleInterfaceAccessTest$OtherSimpleInterfaceImpl",
            "classmerging.pkg.SimpleInterfaceImplRetriever",
            "classmerging.pkg.SimpleInterfaceImplRetriever$SimpleInterfaceImpl");
    runTest(main, programFiles, preservedClassNames::contains);
  }

  @Test
  public void testNoIllegalClassAccessWithAccessModifications() throws Exception {
    // If access modifications are allowed then SimpleInterface should be merged into
    // SimpleInterfaceImpl.
    String main = "classmerging.SimpleInterfaceAccessTest";
    Path[] programFiles =
        new Path[] {
          CF_DIR.resolve("SimpleInterfaceAccessTest.class"),
          CF_DIR.resolve("SimpleInterfaceAccessTest$SimpleInterface.class"),
          CF_DIR.resolve("SimpleInterfaceAccessTest$OtherSimpleInterface.class"),
          CF_DIR.resolve("SimpleInterfaceAccessTest$OtherSimpleInterfaceImpl.class"),
          CF_DIR.resolve("pkg/SimpleInterfaceImplRetriever.class"),
          CF_DIR.resolve("pkg/SimpleInterfaceImplRetriever$SimpleInterfaceImpl.class")
        };
    ImmutableSet<String> preservedClassNames =
        ImmutableSet.of(
            "classmerging.SimpleInterfaceAccessTest",
            // TODO(christofferqa): Should be able to merge SimpleInterface into SimpleInterfaceImpl
            // when access modifications are allowed.
            "classmerging.SimpleInterfaceAccessTest$SimpleInterface",
            "classmerging.SimpleInterfaceAccessTest$OtherSimpleInterfaceImpl",
            "classmerging.pkg.SimpleInterfaceImplRetriever",
            "classmerging.pkg.SimpleInterfaceImplRetriever$SimpleInterfaceImpl");
    // Allow access modifications (and prevent SimpleInterfaceImplRetriever from being removed as
    // a result of inlining).
    runTest(
        main,
        programFiles,
        preservedClassNames::contains,
        getProguardConfig(
            EXAMPLE_KEEP,
            "-allowaccessmodification",
            "-keep public class classmerging.pkg.SimpleInterfaceImplRetriever"));
  }

  // TODO(christofferqa): This test checks that the invoke-super instruction in B is not rewritten
  // into an invoke-direct instruction after it gets merged into class C. We should add a test that
  // checks that this works with and without inlining of the method B.m().
  @Test
  public void testRewritePinnedMethod() throws Exception {
    String main = "classmerging.RewritePinnedMethodTest";
    Path[] programFiles =
        new Path[] {
          CF_DIR.resolve("RewritePinnedMethodTest.class"),
          CF_DIR.resolve("RewritePinnedMethodTest$A.class"),
          CF_DIR.resolve("RewritePinnedMethodTest$B.class"),
          CF_DIR.resolve("RewritePinnedMethodTest$C.class")
        };
    Set<String> preservedClassNames =
        ImmutableSet.of(
            "classmerging.RewritePinnedMethodTest",
            "classmerging.RewritePinnedMethodTest$A",
            "classmerging.RewritePinnedMethodTest$C");
    runTest(
        main,
        programFiles,
        preservedClassNames::contains,
        getProguardConfig(
            EXAMPLE_KEEP, "-keep class classmerging.RewritePinnedMethodTest$A { *; }"));
  }

  @Test
  public void testTemplateMethodPattern() throws Exception {
    String main = "classmerging.TemplateMethodTest";
    Path[] programFiles =
        new Path[] {
          CF_DIR.resolve("TemplateMethodTest.class"),
          CF_DIR.resolve("TemplateMethodTest$AbstractClass.class"),
          CF_DIR.resolve("TemplateMethodTest$AbstractClassImpl.class")
        };
    Set<String> preservedClassNames =
        ImmutableSet.of(
            "classmerging.TemplateMethodTest", "classmerging.TemplateMethodTest$AbstractClassImpl");
    runTest(main, programFiles, preservedClassNames::contains);
  }

  private DexInspector runTest(
      String main, Path[] programFiles, Predicate<String> preservedClassNames) throws Exception {
    return runTest(main, programFiles, preservedClassNames, getProguardConfig(EXAMPLE_KEEP));
  }

  private DexInspector runTest(
      String main,
      Path[] programFiles,
      Predicate<String> preservedClassNames,
      String proguardConfig)
      throws Exception {
    return runTestOnInput(
        main, readProgramFiles(programFiles), preservedClassNames, proguardConfig);
  }

  private DexInspector runTestOnInput(
      String main, AndroidApp input, Predicate<String> preservedClassNames, String proguardConfig)
      throws Exception {
    AndroidApp output = compileWithR8(input, proguardConfig, this::configure);
    DexInspector inputInspector = new DexInspector(input);
    DexInspector outputInspector = new DexInspector(output);
    // Check that all classes in [preservedClassNames] are in fact preserved.
    for (FoundClassSubject classSubject : inputInspector.allClasses()) {
      String className = classSubject.getOriginalName();
      boolean shouldBePresent = preservedClassNames.test(className);
      assertEquals(
          "Class " + className + " should be " + (shouldBePresent ? "present" : "absent"),
          shouldBePresent,
          outputInspector.clazz(className).isPresent());
    }
    // Check that the R8-generated code produces the same result as D8-generated code.
    assertEquals(runOnArt(compileWithD8(input), main), runOnArt(output, main));
    return outputInspector;
  }

  private String getProguardConfig(Path path, String... additionalRules) throws IOException {
    StringBuilder builder = new StringBuilder();
    for (String line : Files.readAllLines(path)) {
      builder.append(line);
      builder.append(System.lineSeparator());
    }
    for (String rule : additionalRules) {
      builder.append(rule);
      builder.append(System.lineSeparator());
    }
    return builder.toString();
  }
}