/*
    * Copyright (C) 2007 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.eventbus;
  
  import com.google.common.base.Objects;
  import com.google.common.base.Throwables;
  import com.google.common.cache.CacheBuilder;
  import com.google.common.cache.CacheLoader;
  import com.google.common.cache.LoadingCache;
  import com.google.common.collect.HashMultimap;
  import com.google.common.collect.ImmutableList;
  import com.google.common.collect.Maps;
  import com.google.common.collect.Multimap;
  import com.google.common.reflect.TypeToken;
  import com.google.common.util.concurrent.UncheckedExecutionException;
  
  import java.lang.reflect.Method;
  import java.util.Arrays;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  
  import javax.annotation.Nullable;
  
  /**
   * A {@link SubscriberFindingStrategy} for collecting all event subscriber methods that are marked
   * with the {@link Subscribe} annotation.
   *
   * @author Cliff Biffle
   * @author Louis Wasserman
   */
  class AnnotatedSubscriberFinder implements SubscriberFindingStrategy {
    /**
     * A thread-safe cache that contains the mapping from each class to all methods in that class and
     * all super-classes, that are annotated with {@code @Subscribe}. The cache is shared across all
     * instances of this class; this greatly improves performance if multiple EventBus instances are
     * created and objects of the same class are registered on all of them.
     */
    private static final LoadingCache<Class<?>, ImmutableList<Method>> subscriberMethodsCache =
        CacheBuilder.newBuilder()
            .weakKeys()
            .build(new CacheLoader<Class<?>, ImmutableList<Method>>() {
              @Override
              public ImmutableList<Method> load(Class<?> concreteClass) throws Exception {
                return getAnnotatedMethodsInternal(concreteClass);
              }
            });
  
    /**
     * {@inheritDoc}
     *
     * This implementation finds all methods marked with a {@link Subscribe} annotation.
     */
    @Override
    public Multimap<Class<?>, EventSubscriber> findAllSubscribers(Object listener) {
      Multimap<Class<?>, EventSubscriber> methodsInListener = HashMultimap.create();
      Class<?> clazz = listener.getClass();
      for (Method method : getAnnotatedMethods(clazz)) {
        Class<?>[] parameterTypes = method.getParameterTypes();
        Class<?> eventType = parameterTypes[0];
        EventSubscriber subscriber = makeSubscriber(listener, method);
        methodsInListener.put(eventType, subscriber);
      }
      return methodsInListener;
    }
  
    private static ImmutableList<Method> getAnnotatedMethods(Class<?> clazz) {
      try {
        return subscriberMethodsCache.getUnchecked(clazz);
      } catch (UncheckedExecutionException e) {
        throw Throwables.propagate(e.getCause());
      }
    }
  
    private static final class MethodIdentifier {
      private final String name;
      private final List<Class<?>> parameterTypes;
  
      MethodIdentifier(Method method) {
        this.name = method.getName();
        this.parameterTypes = Arrays.asList(method.getParameterTypes());
      }
  
      @Override
      public int hashCode() {
       return Objects.hashCode(name, parameterTypes);
     }
 
     @Override
     public boolean equals(@Nullable Object o) {
       if (o instanceof MethodIdentifier) {
         MethodIdentifier ident = (MethodIdentifier) o;
         return name.equals(ident.name) && parameterTypes.equals(ident.parameterTypes);
       }
       return false;
     }
   }
 
   private static ImmutableList<Method> getAnnotatedMethodsInternal(Class<?> clazz) {
     Set<? extends Class<?>> supers = TypeToken.of(clazz).getTypes().rawTypes();
     Map<MethodIdentifier, Method> identifiers = Maps.newHashMap();
     for (Class<?> superClazz : supers) {
       for (Method superClazzMethod : superClazz.getMethods()) {
         if (superClazzMethod.isAnnotationPresent(Subscribe.class)
             && !superClazzMethod.isBridge()) {
           Class<?>[] parameterTypes = superClazzMethod.getParameterTypes();
           if (parameterTypes.length != 1) {
             throw new IllegalArgumentException("Method " + superClazzMethod
                 + " has @Subscribe annotation, but requires " + parameterTypes.length
                 + " arguments.  Event subscriber methods must require a single argument.");
           }
 
           MethodIdentifier ident = new MethodIdentifier(superClazzMethod);
           if (!identifiers.containsKey(ident)) {
             identifiers.put(ident, superClazzMethod);
           }
         }
       }
     }
     return ImmutableList.copyOf(identifiers.values());
   }
 
   /**
    * Creates an {@code EventSubscriber} for subsequently calling {@code method} on
    * {@code listener}.
    * Selects an EventSubscriber implementation based on the annotations on
    * {@code method}.
    *
    * @param listener  object bearing the event subscriber method.
    * @param method  the event subscriber method to wrap in an EventSubscriber.
    * @return an EventSubscriber that will call {@code method} on {@code listener}
    *         when invoked.
    */
   private static EventSubscriber makeSubscriber(Object listener, Method method) {
     EventSubscriber wrapper;
     if (methodIsDeclaredThreadSafe(method)) {
       wrapper = new EventSubscriber(listener, method);
     } else {
       wrapper = new SynchronizedEventSubscriber(listener, method);
     }
     return wrapper;
   }
 
   /**
    * Checks whether {@code method} is thread-safe, as indicated by the
    * {@link AllowConcurrentEvents} annotation.
    *
    * @param method  subscriber method to check.
    * @return {@code true} if {@code subscriber} is marked as thread-safe,
    *         {@code false} otherwise.
    */
   private static boolean methodIsDeclaredThreadSafe(Method method) {
     return method.getAnnotation(AllowConcurrentEvents.class) != null;
   }
 }