/*
    * Copyright (C) 2012 The Guava Authors
    *
    * 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 com.google.common.testing;
  
  import static com.google.common.base.Preconditions.checkNotNull;
  
  import com.google.common.collect.ImmutableList;
  import com.google.common.collect.Sets;
  import com.google.common.reflect.AbstractInvocationHandler;
  import com.google.common.reflect.Invokable;
  import com.google.common.reflect.Parameter;
  import com.google.common.reflect.TypeToken;
  
  import java.io.Serializable;
  import java.lang.reflect.Method;
  import java.lang.reflect.Proxy;
  import java.util.Set;
  
  import javax.annotation.Nullable;
  
  /**
   * Generates a dummy interface proxy that simply returns a dummy value for each method.
   *
   * @author Ben Yu
   */
  abstract class DummyProxy {
  
    /**
     * Returns a new proxy for {@code interfaceType}. Proxies of the same interface are equal to each
     * other if the {@link DummyProxy} instance that created the proxies are equal.
     */
    final <T> T newProxy(TypeToken<T> interfaceType) {
      Set<Class<?>> interfaceClasses = Sets.newLinkedHashSet();
      interfaceClasses.addAll(interfaceType.getTypes().interfaces().rawTypes());
      // Make the proxy serializable to work with SerializableTester
      interfaceClasses.add(Serializable.class);
      Object dummy = Proxy.newProxyInstance(
          interfaceClasses.iterator().next().getClassLoader(),
          interfaceClasses.toArray(new Class<?>[interfaceClasses.size()]),
          new DummyHandler(interfaceType));
      @SuppressWarnings("unchecked") // interfaceType is T
      T result = (T) dummy;
      return result;
    }
  
    /** Returns the dummy return value for {@code returnType}. */
    abstract <R> R dummyReturnValue(TypeToken<R> returnType);
  
    private class DummyHandler extends AbstractInvocationHandler implements Serializable {
      private final TypeToken<?> interfaceType;
  
      DummyHandler(TypeToken<?> interfaceType) {
        this.interfaceType = interfaceType;
      }
    
      @Override protected Object handleInvocation(
          Object proxy, Method method, Object[] args) {
        Invokable<?, ?> invokable = interfaceType.method(method);
        ImmutableList<Parameter> params = invokable.getParameters();
        for (int i = 0; i < args.length; i++) {
          Parameter param = params.get(i);
          if (!param.isAnnotationPresent(Nullable.class)) {
            checkNotNull(args[i]);
          }
        }
        return dummyReturnValue(interfaceType.resolveType(method.getGenericReturnType()));
      }
  
      @Override public int hashCode() {
        return identity().hashCode();
      }
  
      @Override public boolean equals(Object obj) {
        if (obj instanceof DummyHandler) {
          DummyHandler that = (DummyHandler) obj;
          return identity().equals(that.identity());
        } else {
          return false;
        }
      }
  
      private DummyProxy identity() {
        return DummyProxy.this;
      }
  
     @Override public String toString() {
       return "Dummy proxy for " + interfaceType;
     }
 
     // Since type variables aren't serializable, reduce the type down to raw type before
     // serialization.
     private Object writeReplace() {
       return new DummyHandler(TypeToken.of(interfaceType.getRawType()));
     }
   }
 }