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/**
 * Copyright (C) 2011 Google Inc.
 *
 * 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 xyz.truenight.latte;

import java.io.ObjectInputStream;
import java.io.ObjectStreamClass;
import java.lang.reflect.Field;
import java.lang.reflect.Method;

/**
 * Do sneaky things to allocate objects without invoking their constructors.
 *
 * @author Joel Leitch
 * @author Jesse Wilson
 */
public abstract class UnsafeAllocator {
    public abstract  T newInstance(Class c) throws Exception;

    public static UnsafeAllocator create() {
        // try JVM
        // public class Unsafe {
        //   public Object allocateInstance(Class type);
        // }
        try {
            Class unsafeClass = Class.forName("sun.misc.Unsafe");
            Field f = unsafeClass.getDeclaredField("theUnsafe");
            f.setAccessible(true);
            final Object unsafe = f.get(null);
            final Method allocateInstance = unsafeClass.getMethod("allocateInstance", Class.class);
            return new UnsafeAllocator() {
                @Override
                @SuppressWarnings("unchecked")
                public  T newInstance(Class c) throws Exception {
                    return (T) allocateInstance.invoke(unsafe, c);
                }
            };
        } catch (Exception ignored) {
        }

        // try dalvikvm, post-gingerbread
        // public class ObjectStreamClass {
        //   private static native int getConstructorId(Class c);
        //   private static native Object newInstance(Class instantiationClass, int methodId);
        // }
        try {
            Method getConstructorId = ObjectStreamClass.class
                    .getDeclaredMethod("getConstructorId", Class.class);
            getConstructorId.setAccessible(true);
            final int constructorId = (Integer) getConstructorId.invoke(null, Object.class);
            final Method newInstance = ObjectStreamClass.class
                    .getDeclaredMethod("newInstance", Class.class, int.class);
            newInstance.setAccessible(true);
            return new UnsafeAllocator() {
                @Override
                @SuppressWarnings("unchecked")
                public  T newInstance(Class c) throws Exception {
                    return (T) newInstance.invoke(null, c, constructorId);
                }
            };
        } catch (Exception ignored) {
        }

        // try dalvikvm, pre-gingerbread
        // public class ObjectInputStream {
        //   private static native Object newInstance(
        //     Class instantiationClass, Class constructorClass);
        // }
        try {
            final Method newInstance = ObjectInputStream.class
                    .getDeclaredMethod("newInstance", Class.class, Class.class);
            newInstance.setAccessible(true);
            return new UnsafeAllocator() {
                @Override
                @SuppressWarnings("unchecked")
                public  T newInstance(Class c) throws Exception {
                    return (T) newInstance.invoke(null, c, Object.class);
                }
            };
        } catch (Exception ignored) {
        }

        // give up
        return new UnsafeAllocator() {
            @Override
            public  T newInstance(Class c) {
                throw new UnsupportedOperationException("Cannot allocate " + c);
            }
        };
    }
}