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JMockit is a Java toolkit for automated developer testing. It contains mocking/faking APIs and a code coverage tool, supporting both JUnit and TestNG. The mocking APIs allow all kinds of Java code, without testability restrictions, to be tested in isolation from selected dependencies.

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/*
 * Copyright (c) 2006 JMockit developers
 * This file is subject to the terms of the MIT license (see LICENSE.txt).
 */
package mockit.internal.faking;

import java.lang.instrument.*;
import java.lang.reflect.*;
import javax.annotation.*;

import mockit.*;
import mockit.asm.classes.*;
import mockit.internal.*;
import mockit.internal.startup.*;
import mockit.internal.state.*;
import static mockit.internal.util.Utilities.getClassType;

public final class FakeClassSetup
{
   @Nonnull final Class realClass;
   @Nullable private ClassReader rcReader;
   @Nonnull private final FakeMethods fakeMethods;
   @Nonnull private final MockUp fake;
   private final boolean forStartupFake;

   FakeClassSetup(@Nonnull Type fakedType, @Nonnull MockUp fake) {
      this(getClassType(fakedType), fake, fakedType);
   }

   public FakeClassSetup(@Nonnull Class classToFake, @Nonnull MockUp fake, @Nonnull Type fakedType) {
      realClass = classToFake;
      this.fake = fake;
      forStartupFake = Startup.initializing;
      fakeMethods = new FakeMethods(classToFake, fakedType);
      collectFakeMethods();
      registerFakeClassAndItsStates();
   }

   private void collectFakeMethods() {
      Class fakeClass = fake.getClass();
      new FakeMethodCollector(fakeMethods).collectFakeMethods(fakeClass);
   }

   private void registerFakeClassAndItsStates() {
      fakeMethods.registerFakeStates(fake, forStartupFake);

      FakeClasses fakeClasses = TestRun.getFakeClasses();

      if (forStartupFake) {
         fakeClasses.addFake(fakeMethods.getFakeClassInternalName(), fake);
      }
      else {
         fakeClasses.addFake(fake);
      }
   }

   public void redefineMethods() {
      @Nullable Class classToModify = realClass;

      while (classToModify != null && fakeMethods.hasUnusedFakes()) {
         byte[] modifiedClassFile = modifyRealClass(classToModify);

         if (modifiedClassFile != null) {
            applyClassModifications(classToModify, modifiedClassFile);
         }

         Class superClass = classToModify.getSuperclass();
         classToModify = superClass == Object.class || superClass == Proxy.class ? null : superClass;
         rcReader = null;
      }
   }

   @Nullable
   private byte[] modifyRealClass(@Nonnull Class classToModify) {
      if (rcReader == null) {
         rcReader = ClassFile.createReaderFromLastRedefinitionIfAny(classToModify);
      }

      FakedClassModifier modifier = new FakedClassModifier(rcReader, classToModify, fake, fakeMethods);
      rcReader.accept(modifier);

      return modifier.wasModified() ? modifier.toByteArray() : null;
   }

   @Nonnull
   BaseClassModifier createClassModifier(@Nonnull ClassReader cr) {
      return new FakedClassModifier(cr, realClass, fake, fakeMethods);
   }

   void applyClassModifications(@Nonnull Class classToModify, @Nonnull byte[] modifiedClassFile) {
      ClassDefinition classDef = new ClassDefinition(classToModify, modifiedClassFile);
      Startup.redefineMethods(classDef);

      if (forStartupFake) {
         CachedClassfiles.addClassfile(classToModify, modifiedClassFile);
      }
      else {
         String fakeClassDesc = fakeMethods.getFakeClassInternalName();
         TestRun.mockFixture().addRedefinedClass(fakeClassDesc, classDef);
      }
   }
}