/*

  * Copyright (c) 2008, 2013, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.  Oracle designates this

  * particular file as subject to the "Classpath" exception as provided

  * by Oracle in the LICENSE file that accompanied this code.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 package java.lang.invoke;

 import java.lang.reflect.*;

 import java.security.AccessController;

 import java.security.PrivilegedAction;

 import sun.invoke.WrapperInstance;

 import java.util.ArrayList;

 import sun.reflect.CallerSensitive;

 import sun.reflect.Reflection;

 import sun.reflect.misc.ReflectUtil;

 /**

  * This class consists exclusively of static methods that help adapt

  * method handles to other JVM types, such as interfaces.

  */

 public class MethodHandleProxies {

     private MethodHandleProxies() { }  // do not instantiate

     /**

      * Produces an instance of the given single-method interface which redirects

      * its calls to the given method handle.

      * <p>

      * A single-method interface is an interface which declares a uniquely named method.

      * When determining the uniquely named method of a single-method interface,

      * the public {@code Object} methods ({@code toString}, {@code equals}, {@code hashCode})

      * are disregarded.  For example, {@link java.util.Comparator} is a single-method interface,

      * even though it re-declares the {@code Object.equals} method.

      * <p>

      * The interface must be public.  No additional access checks are performed.

      * <p>

      * The resulting instance of the required type will respond to

      * invocation of the type's uniquely named method by calling

      * the given target on the incoming arguments,

      * and returning or throwing whatever the target

      * returns or throws.  The invocation will be as if by

      * {@code target.invoke}.

      * The target's type will be checked before the

      * instance is created, as if by a call to {@code asType},

      * which may result in a {@code WrongMethodTypeException}.

      * <p>

      * The uniquely named method is allowed to be multiply declared,

      * with distinct type descriptors.  (E.g., it can be overloaded,

      * or can possess bridge methods.)  All such declarations are

      * connected directly to the target method handle.

      * Argument and return types are adjusted by {@code asType}

      * for each individual declaration.

      * <p>

      * The wrapper instance will implement the requested interface

      * and its super-types, but no other single-method interfaces.

      * This means that the instance will not unexpectedly

      * pass an {@code instanceof} test for any unrequested type.

      * <p style="font-size:smaller;">

      * <em>Implementation Note:</em>

      * Therefore, each instance must implement a unique single-method interface.

      * Implementations may not bundle together

      * multiple single-method interfaces onto single implementation classes

      * in the style of {@link java.awt.AWTEventMulticaster}.

      * <p>

      * The method handle may throw an <em>undeclared exception</em>,

      * which means any checked exception (or other checked throwable)

      * not declared by the requested type's single abstract method.

      * If this happens, the throwable will be wrapped in an instance of

      * {@link java.lang.reflect.UndeclaredThrowableException UndeclaredThrowableException}

      * and thrown in that wrapped form.

      * <p>

      * Like {@link java.lang.Integer#valueOf Integer.valueOf},

      * {@code asInterfaceInstance} is a factory method whose results are defined

      * by their behavior.

      * It is not guaranteed to return a new instance for every call.

      * <p>

      * Because of the possibility of {@linkplain java.lang.reflect.Method#isBridge bridge methods}

      * and other corner cases, the interface may also have several abstract methods

      * with the same name but having distinct descriptors (types of returns and parameters).

      * In this case, all the methods are bound in common to the one given target.

      * The type check and effective {@code asType} conversion is applied to each

      * method type descriptor, and all abstract methods are bound to the target in common.

      * Beyond this type check, no further checks are made to determine that the

      * abstract methods are related in any way.

      * <p>

      * Future versions of this API may accept additional types,

      * such as abstract classes with single abstract methods.

      * Future versions of this API may also equip wrapper instances

      * with one or more additional public "marker" interfaces.

      * <p>

      * If a security manager is installed, this method is caller sensitive.

      * During any invocation of the target method handle via the returned wrapper,

      * the original creator of the wrapper (the caller) will be visible

      * to context checks requested by the security manager.

      *

      * @param <T> the desired type of the wrapper, a single-method interface

      * @param intfc a class object representing {@code T}

      * @param target the method handle to invoke from the wrapper

      * @return a correctly-typed wrapper for the given target

      * @throws NullPointerException if either argument is null

      * @throws IllegalArgumentException if the {@code intfc} is not a

      *         valid argument to this method

      * @throws WrongMethodTypeException if the target cannot

      *         be converted to the type required by the requested interface

      */

     // Other notes to implementors:

     // <p>

     // No stable mapping is promised between the single-method interface and

     // the implementation class C.  Over time, several implementation

     // classes might be used for the same type.

     // <p>

     // If the implementation is able

     // to prove that a wrapper of the required type

     // has already been created for a given

     // method handle, or for another method handle with the

     // same behavior, the implementation may return that wrapper in place of

     // a new wrapper.

     // <p>

     // This method is designed to apply to common use cases

     // where a single method handle must interoperate with

     // an interface that implements a function-like

     // API.  Additional variations, such as single-abstract-method classes with

     // private constructors, or interfaces with multiple but related

     // entry points, must be covered by hand-written or automatically

     // generated adapter classes.

     //

     @CallerSensitive

     public static

     <T> T asInterfaceInstance(final Class<T> intfc, final MethodHandle target) {

         if (!intfc.isInterface() || !Modifier.isPublic(intfc.getModifiers()))

             throw new IllegalArgumentException("not a public interface: "+intfc.getName());

         final MethodHandle mh;

         if (System.getSecurityManager() != null) {

             final Class<?> caller = Reflection.getCallerClass();

             final ClassLoader ccl = caller != null ? caller.getClassLoader() : null;

             ReflectUtil.checkProxyPackageAccess(ccl, intfc);

             mh = ccl != null ? bindCaller(target, caller) : target;

         } else {

             mh = target;

         }

         ClassLoader proxyLoader = intfc.getClassLoader();

         if (proxyLoader == null) {

             ClassLoader cl = Thread.currentThread().getContextClassLoader(); // avoid use of BCP

             proxyLoader = cl != null ? cl : ClassLoader.getSystemClassLoader();

         }

         final Method[] methods = getSingleNameMethods(intfc);

         if (methods == null)

             throw new IllegalArgumentException("not a single-method interface: "+intfc.getName());

         final MethodHandle[] vaTargets = new MethodHandle[methods.length];

         for (int i = 0; i < methods.length; i++) {

             Method sm = methods[i];

             MethodType smMT = MethodType.methodType(sm.getReturnType(), sm.getParameterTypes());

             MethodHandle checkTarget = mh.asType(smMT);  // make throw WMT

             checkTarget = checkTarget.asType(checkTarget.type().changeReturnType(Object.class));

             vaTargets[i] = checkTarget.asSpreader(Object[].class, smMT.parameterCount());

         }

         final InvocationHandler ih = new InvocationHandler() {

                 private Object getArg(String name) {

                     if ((Object)name == "getWrapperInstanceTarget")  return target;

                     if ((Object)name == "getWrapperInstanceType")    return intfc;

                     throw new AssertionError();

                 }

                 public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

                     for (int i = 0; i < methods.length; i++) {

                         if (method.equals(methods[i]))

                             return vaTargets[i].invokeExact(args);

                     }

                     if (method.getDeclaringClass() == WrapperInstance.class)

                         return getArg(method.getName());

                     if (isObjectMethod(method))

                         return callObjectMethod(proxy, method, args);

                     throw new InternalError("bad proxy method: "+method);

                 }

             };

         final Object proxy;

         if (System.getSecurityManager() != null) {

             // sun.invoke.WrapperInstance is a restricted interface not accessible

             // by any non-null class loader.

             final ClassLoader loader = proxyLoader;

             proxy = AccessController.doPrivileged(new PrivilegedAction<Object>() {

                 public Object run() {

                     return Proxy.newProxyInstance(

                             loader,

                             new Class<?>[]{ intfc, WrapperInstance.class },

                             ih);

                 }

             });

         } else {

             proxy = Proxy.newProxyInstance(proxyLoader,

                                            new Class<?>[]{ intfc, WrapperInstance.class },

                                            ih);

         }

         return intfc.cast(proxy);

     }

     private static MethodHandle bindCaller(MethodHandle target, Class<?> hostClass) {

         MethodHandle cbmh = MethodHandleImpl.bindCaller(target, hostClass);

         if (target.isVarargsCollector()) {

             MethodType type = cbmh.type();

             int arity = type.parameterCount();

             return cbmh.asVarargsCollector(type.parameterType(arity-1));

         }

         return cbmh;

     }

     /**

      * Determines if the given object was produced by a call to {@link #asInterfaceInstance asInterfaceInstance}.

      * @param x any reference

      * @return true if the reference is not null and points to an object produced by {@code asInterfaceInstance}

      */

     public static

     boolean isWrapperInstance(Object x) {

         return x instanceof WrapperInstance;

     }

     private static WrapperInstance asWrapperInstance(Object x) {

         try {

             if (x != null)

                 return (WrapperInstance) x;

         } catch (ClassCastException ex) {

         }

         throw new IllegalArgumentException("not a wrapper instance");

     }

     /**

      * Produces or recovers a target method handle which is behaviorally

      * equivalent to the unique method of this wrapper instance.

      * The object {@code x} must have been produced by a call to {@link #asInterfaceInstance asInterfaceInstance}.

      * This requirement may be tested via {@link #isWrapperInstance isWrapperInstance}.

      * @param x any reference

      * @return a method handle implementing the unique method

      * @throws IllegalArgumentException if the reference x is not to a wrapper instance

      */

     public static

     MethodHandle wrapperInstanceTarget(Object x) {

         return asWrapperInstance(x).getWrapperInstanceTarget();

     }

     /**

      * Recovers the unique single-method interface type for which this wrapper instance was created.

      * The object {@code x} must have been produced by a call to {@link #asInterfaceInstance asInterfaceInstance}.

      * This requirement may be tested via {@link #isWrapperInstance isWrapperInstance}.

      * @param x any reference

      * @return the single-method interface type for which the wrapper was created

      * @throws IllegalArgumentException if the reference x is not to a wrapper instance

      */

     public static

     Class<?> wrapperInstanceType(Object x) {

         return asWrapperInstance(x).getWrapperInstanceType();

     }

     private static

     boolean isObjectMethod(Method m) {

         switch (m.getName()) {

         case "toString":

             return (m.getReturnType() == String.class

                     && m.getParameterTypes().length == 0);

         case "hashCode":

             return (m.getReturnType() == int.class

                     && m.getParameterTypes().length == 0);

         case "equals":

             return (m.getReturnType() == boolean.class

                     && m.getParameterTypes().length == 1

                     && m.getParameterTypes()[0] == Object.class);

         }

         return false;

     }

     private static

     Object callObjectMethod(Object self, Method m, Object[] args) {

         assert(isObjectMethod(m)) : m;

         switch (m.getName()) {

         case "toString":

             return self.getClass().getName() + "@" + Integer.toHexString(self.hashCode());

         case "hashCode":

             return System.identityHashCode(self);

         case "equals":

             return (self == args[0]);

         }

         return null;

     }

     private static

     Method[] getSingleNameMethods(Class<?> intfc) {

         ArrayList<Method> methods = new ArrayList<Method>();

         String uniqueName = null;

         for (Method m : intfc.getMethods()) {

             if (isObjectMethod(m))  continue;

             if (!Modifier.isAbstract(m.getModifiers()))  continue;

             String mname = m.getName();

             if (uniqueName == null)

                 uniqueName = mname;

             else if (!uniqueName.equals(mname))

                 return null;  // too many abstract methods

             methods.add(m);

         }

         if (uniqueName == null)  return null;

         return methods.toArray(new Method[methods.size()]);

     }

 }