stub/src/main/java/org/apache/commons/proxy2/stub/AnnotationFactory.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.commons.proxy2.stub;

import java.io.Serializable;
import java.lang.annotation.Annotation;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Map;

import org.apache.commons.lang3.AnnotationUtils;
import org.apache.commons.lang3.Validate;
import org.apache.commons.lang3.tuple.ImmutablePair;
import org.apache.commons.proxy2.Interceptor;
import org.apache.commons.proxy2.Invocation;
import org.apache.commons.proxy2.Invoker;
import org.apache.commons.proxy2.ObjectProvider;
import org.apache.commons.proxy2.ProxyFactory;
import org.apache.commons.proxy2.ProxyUtils;
import org.apache.commons.proxy2.impl.AbstractProxyFactory;
import org.apache.commons.proxy2.provider.ConstantProvider;

/**
 * {@link AnnotationFactory} provides a simplified API over {@link StubProxyFactory}
 * to stub a Java {@link Annotation}.  Like "real" runtime proxies, instances created via
 * {@link AnnotationFactory} are {@link Proxy}-based.  Non-stubbed methods including
 * {@link Annotation#annotationType()} will return methods' default values and
 * {@link Annotation#equals(Object)}/{@link Annotation#hashCode()}/{@link Annotation#toString()}
 * return values consistent with those methods' documented expectations.
 *
 * @author Matt Benson
 */
public class AnnotationFactory {
    /** Statically available instance */
    public static final AnnotationFactory INSTANCE;

    /**
     * Record the context of a call for possible use by nested annotation creations.
     */
    static final ThreadLocal<ImmutablePair<AnnotationFactory, ClassLoader>> CONTEXT =
        new ThreadLocal<ImmutablePair<AnnotationFactory, ClassLoader>>();

    private static final ProxyFactory PROXY_FACTORY;

    static {

        //underlying proxyfactory implementation based on org.apache.commons.proxy2.jdk.JdkProxyFactory
        PROXY_FACTORY = new AbstractProxyFactory() {

            public <T> T createInvokerProxy(ClassLoader classLoader, final Invoker invoker, Class<?>... proxyClasses) {
                throw new UnsupportedOperationException();
            }

            @SuppressWarnings("unchecked")
            public <T> T createInterceptorProxy(ClassLoader classLoader, Object target, Interceptor interceptor,
                Class<?>... proxyClasses) {
                return (T) Proxy.newProxyInstance(classLoader, proxyClasses, new InterceptorInvocationHandler(target,
                    interceptor));
            }

            public <T> T createDelegatorProxy(ClassLoader classLoader, ObjectProvider<?> delegateProvider,
                Class<?>... proxyClasses) {
                throw new UnsupportedOperationException();
            }
        };

        INSTANCE = new AnnotationFactory();
    }

    private static class InterceptorInvocationHandler implements InvocationHandler, Serializable {
        /** Serialization version */
        private static final long serialVersionUID = 1L;

        private final Object target;
        private final Interceptor methodInterceptor;

        public InterceptorInvocationHandler(Object target, Interceptor methodInterceptor) {
            this.target = target;
            this.methodInterceptor = methodInterceptor;
        }

        /**
         * {@inheritDoc}
         */
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            if (ProxyUtils.isHashCode(method)) {
                return AnnotationUtils.hashCode((Annotation) proxy);
            }
            if (ProxyUtils.isEqualsMethod(method)) {
                return args[0] instanceof Annotation
                    && AnnotationUtils.equals((Annotation) proxy, (Annotation) args[0]);
            }
            if ("toString".equals(method.getName()) && method.getParameterTypes().length == 0) {
                return AnnotationUtils.toString((Annotation) proxy);
            }
            final ReflectionInvocation invocation = new ReflectionInvocation(target, method, args);
            return methodInterceptor.intercept(invocation);
        }

    }

    private static class ReflectionInvocation implements Invocation, Serializable {
        /** Serialization version */
        private static final long serialVersionUID = 1L;

        private final Method method;
        private final Object[] arguments;
        private final Object target;

        public ReflectionInvocation(Object target, Method method, Object[] arguments) {
            this.method = method;
            this.arguments = (arguments == null ? ProxyUtils.EMPTY_ARGUMENTS : arguments);
            this.target = target;
        }

        public Object[] getArguments() {
            return arguments;
        }

        public Method getMethod() {
            return method;
        }

        public Object getProxy() {
            return target;
        }

        public Object proceed() throws Throwable {
            try {
                return method.invoke(target, arguments);
            } catch (InvocationTargetException e) {
                throw e.getTargetException();
            }
        }
    }

    private static class MapBasedAnnotationConfigurer<A extends Annotation> extends StubConfigurer<A> {
        private final Map<String, Object> attributes;

        /**
         * Create a new {@link MapBasedAnnotationConfigurer} instance.
         * @param stubType
         * @param attributes
         */
        public MapBasedAnnotationConfigurer(Class<A> stubType, Map<String, Object> attributes) {
            super(stubType);
            this.attributes = attributes;
        }

        @Override
        protected void configure(A stub) {
            if (attributes == null) {
                return;
            }
            When<Object> bud;
            StubConfiguration dy = this;
            for (Map.Entry<String, Object> attr : attributes.entrySet()) {
                Method m;
                try {
                    m = getStubType().getDeclaredMethod(attr.getKey());
                } catch (Exception e1) {
                    throw new IllegalArgumentException(String.format("Could not detect annotation attribute %1$s",
                        attr.getKey()));
                }
                try {
                    bud = dy.when(m.invoke(stub));
                } catch (Exception e) {
                    //it must have happened on the invoke, so we didn't call when... it shouldn't happen, but we'll simply skip:
                    continue;
                }
                dy = bud.thenReturn(attr.getValue());
            }
        }
    }

    private static final Invoker ANNOTATION_INVOKER = new Invoker() {

        /** Serialization version */
        private static final long serialVersionUID = 1L;

        public Object invoke(Object proxy, Method method, Object[] arguments) throws Throwable {
            Object result = method.getDefaultValue();
            if (result == null) {
                if (method.getReturnType().isPrimitive()) {
                    return ProxyUtils.nullValue(method.getReturnType());
                }
            }
            return result;
        }
    };

    private static final ThreadLocal<Object> CONFIGURER = new ThreadLocal<Object>();

    private ProxyFactory proxyFactory;

    /**
     * Create a new AnnotationFactory instance.
     */
    public AnnotationFactory() {
        this.proxyFactory = new AnnotationStubProxyFactory(AnnotationFactory.PROXY_FACTORY, new SharedConfigurer());
    }

    /**
     * Create an annotation of the type supported by <code>configurer</code>.
     * @param <A>
     * @param configurer
     * @return stubbed annotation proxy
     */
    public <A extends Annotation> A create(StubConfigurer<A> configurer) {
        return create(Thread.currentThread().getContextClassLoader(), Validate.notNull(configurer, "null configurer"));
    }

    /**
     * Create a delegating annotation of the type supported by <code>configurer</code>.
     * @param <A>
     * @param target not {@code null}
     * @param configurer not {@code null}
     * @return stubbed annotation proxy
     */
    public <A extends Annotation> A createDelegator(A target, StubConfigurer<A> configurer) {
        return createInternal(Thread.currentThread().getContextClassLoader(),
            Validate.notNull(target, "null target"), Validate.notNull(configurer, "null configurer"));
    }

    /**
     * Create an annotation of the type supported by <code>configurer</code> in the specified classpath.
     * @param <A>
     * @param classLoader not {@code null}
     * @param configurer not {@code null}
     * @return stubbed annotation proxy
     */
    public <A extends Annotation> A create(ClassLoader classLoader, StubConfigurer<A> configurer) {
        return createInternal(Validate.notNull(classLoader, "null classLoader"),
            null, Validate.notNull(configurer, "null configurer"));
    }

    /**
     * Create a delegating annotation of the type supported by <code>configurer</code> in the specified classpath.
     * @param <A>
     * @param classLoader not {@code null}
     * @param target not {@code null}
     * @param configurer not {@code null}
     * @return stubbed annotation proxy
     */
    public <A extends Annotation> A createDelegator(ClassLoader classLoader, A target, StubConfigurer<A> configurer) {
        return createInternal(Validate.notNull(classLoader, "null classLoader"),
            Validate.notNull(target, "null target"), Validate.notNull(configurer, "null configurer"));
    }

    /**
     * Create an annotation of <code>annotationType</code> with fully default behavior.
     * @param <A>
     * @param annotationType not {@code null}
     * @return stubbed annotation proxy
     */
    public <A extends Annotation> A create(Class<A> annotationType) {
        @SuppressWarnings("unchecked")
        final A result =
            (A) createInternal(Thread.currentThread().getContextClassLoader(),
                Validate.notNull(annotationType, "null annotationType"));
        return result;
    }

    /**
     * Create an annotation of <code>annotationType</code> with fully default behavior.
     * @param <A>
     * @param classLoader not {@code null}
     * @param annotationType not {@code null}
     * @return stubbed annotation proxy
     */
    public <A extends Annotation> A create(ClassLoader classLoader, Class<A> annotationType) {
        @SuppressWarnings("unchecked")
        final A result =
            (A) createInternal(Validate.notNull(classLoader, "null classLoader"),
                Validate.notNull(annotationType, "null annotationType"));
        return result;
    }

    /**
     * Create an annotation of <code>annotationType</code> with behavior specified by a {@link String}-keyed {@link Map}.
     * @param <A>
     * @param annotationType not {@code null}
     * @param attributes
     * @return stubbed annotation proxy
     */
    public <A extends Annotation> A create(Class<A> annotationType, Map<String, Object> attributes) {
        if (attributes == null || attributes.isEmpty()) {
            return create(annotationType);
        }
        return create(new MapBasedAnnotationConfigurer<A>(annotationType, attributes));
    }

    /**
     * Create a delegating annotation of <code>annotationType</code> with behavior specified by a {@link String}-keyed {@link Map}.
     * @param <A>
     * @param target not {@code null}
     * @param attributes
     * @return stubbed annotation proxy
     */
    public <A extends Annotation> A createDelegator(A target, Map<String, Object> attributes) {
        @SuppressWarnings("unchecked")
        final Class<A> annotationType = (Class<A>) Validate.notNull(target, "null target").annotationType();
        return createDelegator(target, new MapBasedAnnotationConfigurer<A>(annotationType, attributes));
    }

    /**
     * Create an annotation of <code>annotationType</code> with behavior specified by a {@link String}-keyed {@link Map}.
     * @param <A>
     * @param classLoader
     * @param annotationType
     * @param attributes
     * @return stubbed annotation proxy
     */
    public <A extends Annotation> A create(ClassLoader classLoader, Class<A> annotationType,
        Map<String, Object> attributes) {
        return create(classLoader, new MapBasedAnnotationConfigurer<A>(annotationType, attributes));
    }

    /**
     * Create a delegating annotation of <code>annotationType</code> with behavior specified by a {@link String}-keyed {@link Map}.
     * @param <A>
     * @param classLoader
     * @param target
     * @param attributes
     * @return stubbed annotation proxy
     */
    public <A extends Annotation> A createDelegator(ClassLoader classLoader, A target, Map<String, Object> attributes) {
        @SuppressWarnings("unchecked")
        final Class<A> annotationType = (Class<A>) Validate.notNull(target, "null target").annotationType();
        return createDelegator(classLoader, target, new MapBasedAnnotationConfigurer<A>(annotationType, attributes));
    }

    private <A extends Annotation> A createInternal(ClassLoader classLoader, Object configurer) {
        return createInternal(classLoader, null, configurer);
    }

    private <A extends Annotation> A createInternal(ClassLoader classLoader, A target, Object configurer) {
        final Object existingConfigurer = CONFIGURER.get();
        final boolean outerContext = CONTEXT.get() == null;
        try {
            CONFIGURER.set(configurer);
            if (outerContext) {
                CONTEXT.set(ImmutablePair.of(this, classLoader));
            }
            final A result;
            if (target == null) {
                @SuppressWarnings("unchecked")
                A invoker = (A) proxyFactory.createInvokerProxy(classLoader, ANNOTATION_INVOKER, getStubType());
                result = invoker;
            } else {
                @SuppressWarnings("unchecked")
                A delegator =
                    (A) proxyFactory.createDelegatorProxy(classLoader, new ConstantProvider<A>(target), getStubType());
                result = delegator;
            }
            return validate(result);
        } finally {
            if (existingConfigurer == null) {
                CONFIGURER.remove();
            } else {
                CONFIGURER.set(existingConfigurer);
            }
            if (outerContext) {
                CONTEXT.remove();
            }
        }
    }

    private <A extends Annotation> A validate(A annotation) {
        Class<?> annotationType = annotation.annotationType();
        for (Method m : annotationType.getDeclaredMethods()) {
            Object value = null;
            Exception caught = null;
            try {
                value = m.invoke(annotation);
            } catch (Exception e) {
                caught = e;
            }
            if (value == null) {
                throw new IllegalStateException(String.format("annotation %s is missing %s", annotationType,
                    m.getName()), caught);
            }
        }
        return annotation;
    }

    private static <A extends Annotation> Class<? extends A> getStubType() {
        Object o = CONFIGURER.get();
        if (o instanceof Class<?>) {
            @SuppressWarnings("unchecked")
            final Class<? extends A> result = (Class<? extends A>) o;
            return result;
        }
        @SuppressWarnings("unchecked")
        final StubConfigurer<A> configurer = (StubConfigurer<A>) o;
        return configurer.getStubType();
    }

    private static class SharedConfigurer extends StubConfigurer<Annotation> {

        /**
         * {@inheritDoc}
         */
        @Override
        public Class<Annotation> getStubType() {
            /*
             * Suppress the warning because we are using this shared object in
             * a very special, albeit peculiar, way, and effectively
             * hijacking the only place where the generic type of the
             * instance matters:  namely, providing the type of
             * Annotation to be stubbed at any given time.
             */
            @SuppressWarnings("unchecked")
            Class<Annotation> result = (Class<Annotation>) AnnotationFactory.getStubType();
            return result;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        protected void configure(Annotation stub) {
            when(stub.annotationType()).thenReturn(getStubType());
            Object o = CONFIGURER.get();
            if (o instanceof StubConfigurer<?>) {
                @SuppressWarnings("unchecked")
                final StubConfigurer<Annotation> configurer = (StubConfigurer<Annotation>) o;
                configurer.configure(requireStubInterceptor(), stub);
            }
        }
    }

    private static class AnnotationStubProxyFactory extends StubProxyFactory {

        private AnnotationStubProxyFactory(ProxyFactory proxyFactory, StubConfigurer<Annotation> sharedConfigurer) {
            super(proxyFactory, sharedConfigurer);
        }

        /**
         * {@inheritDoc}
         */
        protected boolean acceptsValue(Method m, Object o) {
            return !(m.getDeclaringClass().isAnnotation() && o == null);
        }
    }
}