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JMockit is a Java toolkit for developer (unit/integration) testing. It contains mocking APIs and other tools, 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) 2006-2013 Rogério Liesenfeld
 * This file is subject to the terms of the MIT license (see LICENSE.txt).
 */
package mockit.internal.expectations.mocking;

import java.lang.reflect.*;
import java.lang.reflect.Type;
import java.util.*;

import static java.util.Arrays.*;

import org.jetbrains.annotations.*;

import static mockit.external.asm4.Opcodes.*;

import mockit.external.asm4.*;
import mockit.internal.*;
import mockit.internal.util.*;

public final class SubclassGenerationModifier extends MockedTypeModifier
{
   private static final int CLASS_ACCESS_MASK = 0xFFFF - ACC_ABSTRACT;
   private static final int CONSTRUCTOR_ACCESS_MASK = ACC_PUBLIC + ACC_PROTECTED;

   // Fixed initial state:
   @Nullable private final MockingConfiguration mockingCfg;
   @NotNull private final String subclassName;
   @NotNull private final MockedTypeInfo mockedTypeInfo;
   private boolean copyConstructors;

   // Helper fields for mutable state:
   @Nullable private String superClassOfSuperClass;
   @NotNull private Set superInterfaces;
   @NotNull private final List implementedMethods;

   public SubclassGenerationModifier(
      @NotNull Type mockedType, @NotNull ClassReader classReader, @NotNull String subclassName)
   {
      this(null, mockedType, classReader, subclassName);
      copyConstructors = true;
   }

   SubclassGenerationModifier(
      @Nullable MockingConfiguration mockingConfiguration, @NotNull Type mockedType, @NotNull ClassReader classReader,
      @NotNull String subclassName)
   {
      super(classReader);
      mockingCfg = mockingConfiguration;
      this.subclassName = subclassName.replace('.', '/');
      mockedTypeInfo = new MockedTypeInfo(mockedType, "");
      implementedMethods = new ArrayList();
   }

   @Override
   public void visit(
      int version, int access, @NotNull String name, @Nullable String signature, @Nullable String superName,
      @Nullable String[] interfaces)
   {
      int subclassAccess = access & CLASS_ACCESS_MASK | ACC_FINAL;
      super.visit(version, subclassAccess, subclassName, mockedTypeInfo.implementationSignature, name, null);
      superClassOfSuperClass = superName;
      superInterfaces = new HashSet();

      if (interfaces != null && interfaces.length > 0) {
         superInterfaces.addAll(asList(interfaces));
      }
   }

   @Override
   public void visitInnerClass(String name, String outerName, String innerName, int access) {}

   @Override
   public void visitOuterClass(String owner, String name, String desc) {}

   @Override
   public void visitAttribute(Attribute attr) {}

   @Override
   public void visitSource(String file, String debug) {}

   @Override
   public FieldVisitor visitField(
      int access, @NotNull String name, @NotNull String desc, String signature, Object value) { return null; }

   @Override
   public MethodVisitor visitMethod(
      int access, @NotNull String name, @NotNull String desc, @Nullable String signature, @Nullable String[] exceptions)
   {
      if (copyConstructors && "".equals(name)) {
         if ((access & CONSTRUCTOR_ACCESS_MASK) != 0) {
            generateConstructorDelegatingToSuper(desc, signature, exceptions);
         }
      }
      else {
         // Inherits from super-class when non-abstract.
         // Otherwise, creates implementation for abstract method with call to "recordOrReplay".
         generateImplementationIfAbstractMethod(superClassName, access, name, desc, signature, exceptions);
      }

      return null;
   }

   private void generateConstructorDelegatingToSuper(
      @NotNull String desc, @Nullable String signature, @Nullable String[] exceptions)
   {
      mw = cw.visitMethod(ACC_PUBLIC, "", desc, signature, exceptions);
      mw.visitVarInsn(ALOAD, 0);
      int var = 1;

      for (mockit.external.asm4.Type paramType : mockit.external.asm4.Type.getArgumentTypes(desc)) {
         int loadOpcode = getLoadOpcodeForParameterType(paramType.getSort());
         mw.visitVarInsn(loadOpcode, var);
         var++;
      }

      mw.visitMethodInsn(INVOKESPECIAL, superClassName, "", desc);
      generateEmptyImplementation();
   }

   private int getLoadOpcodeForParameterType(int paramType)
   {
      if (paramType <= mockit.external.asm4.Type.INT) {
         return ILOAD;
      }

      switch (paramType) {
         case mockit.external.asm4.Type.FLOAT:  return FLOAD;
         case mockit.external.asm4.Type.LONG:   return LLOAD;
         case mockit.external.asm4.Type.DOUBLE: return DLOAD;
         default: return ALOAD;
      }
   }

   private void generateImplementationIfAbstractMethod(
      String className, int access, @NotNull String name, String desc, @Nullable String signature,
      @Nullable String[] exceptions)
   {
      if (!"".equals(name)) {
         String methodNameAndDesc = name + desc;

         if (!implementedMethods.contains(methodNameAndDesc)) {
            if ((access & ACC_ABSTRACT) != 0) {
               generateMethodImplementation(className, access, name, desc, signature, exceptions);
            }

            implementedMethods.add(methodNameAndDesc);
         }
      }
   }

   @SuppressWarnings("AssignmentToMethodParameter")
   private void generateMethodImplementation(
      String className, int access, @NotNull String name, String desc,
      @Nullable String signature, @Nullable String[] exceptions)
   {
      if (signature != null) {
         signature = mockedTypeInfo.genericTypeMap.resolveReturnType(signature);
      }

      mw = super.visitMethod(ACC_PUBLIC, name, desc, signature, exceptions);

      boolean noFiltersToMatch = mockingCfg == null;

      if (
         noFiltersToMatch && !isMethodFromObject(name, desc) ||
         !noFiltersToMatch && mockingCfg.matchesFilters(name, desc)
      ) {
         generateDirectCallToHandler(className, access, name, desc, signature, exceptions, 0);
         generateReturnWithObjectAtTopOfTheStack(desc);
         mw.visitMaxs(1, 0);
      }
      else {
         generateEmptyImplementation(desc);
      }
   }

   @Override
   public void visitEnd()
   {
      generateImplementationsForInheritedAbstractMethods(superClassOfSuperClass);

      while (!superInterfaces.isEmpty()) {
         String superInterface = superInterfaces.iterator().next();
         generateImplementationsForInterfaceMethods(superInterface);
         superInterfaces.remove(superInterface);
      }
   }

   private void generateImplementationsForInheritedAbstractMethods(@Nullable String superName)
   {
      if (superName != null && !"java/lang/Object".equals(superName)) {
         new MethodModifierForSuperclass(superName);
      }
   }

   private void generateImplementationsForInterfaceMethods(String superName)
   {
      if (!"java/lang/Object".equals(superName)) {
         new MethodModifierForImplementedInterface(superName);
      }
   }

   private class BaseMethodModifier extends ClassVisitor
   {
      @NotNull final String typeName;

      BaseMethodModifier(@NotNull String typeName)
      {
         this.typeName = typeName;
         ClassFile.visitClass(typeName, this);
      }

      @Override
      public FieldVisitor visitField(
         int access, @NotNull String name, @NotNull String desc, String signature, Object value) { return null; }
   }

   private final class MethodModifierForSuperclass extends BaseMethodModifier
   {
      String superName;

      MethodModifierForSuperclass(@NotNull String className) { super(className); }

      @Override
      public void visit(
         int version, int access, @NotNull String name, @Nullable String signature, @Nullable String superName,
         @Nullable String[] interfaces)
      {
         this.superName = superName;

         if (interfaces != null) {
            superInterfaces.addAll(asList(interfaces));
         }
      }

      @Override
      public MethodVisitor visitMethod(
         int access, @NotNull String name, @NotNull String desc, String signature, String[] exceptions)
      {
         generateImplementationIfAbstractMethod(typeName, access, name, desc, signature, exceptions);
         return null;
      }

      @Override
      public void visitEnd()
      {
         generateImplementationsForInheritedAbstractMethods(superName);
      }
   }

   private final class MethodModifierForImplementedInterface extends BaseMethodModifier
   {
      MethodModifierForImplementedInterface(String interfaceName) { super(interfaceName); }

      @Override
      public void visit(
         int version, int access, @NotNull String name, @Nullable String signature, @Nullable String superName,
         @Nullable String[] interfaces)
      {
         assert interfaces != null;
         superInterfaces.addAll(asList(interfaces));
      }

      @Override
      public MethodVisitor visitMethod(
         int access, @NotNull String name, @NotNull String desc, String signature, String[] exceptions)
      {
         generateImplementationForInterfaceMethodIfMissing(access, name, desc, signature, exceptions);
         return null;
      }

      private void generateImplementationForInterfaceMethodIfMissing(
         int access, @NotNull String name, @NotNull String desc, String signature, String[] exceptions)
      {
         String methodNameAndDesc = name + desc;

         if (!implementedMethods.contains(methodNameAndDesc)) {
            if (!hasMethodImplementation(name, desc)) {
               generateMethodImplementation(typeName, access, name, desc, signature, exceptions);
            }

            implementedMethods.add(methodNameAndDesc);
         }
      }

      private boolean hasMethodImplementation(@NotNull String name, @NotNull String desc)
      {
         Class[] paramTypes = TypeDescriptor.getParameterTypes(desc);

         try {
            Method method = mockedTypeInfo.mockedClass.getMethod(name, paramTypes);
            return !method.getDeclaringClass().isInterface();
         }
         catch (NoSuchMethodException ignore) {
            return false;
         }
      }
   }
}