COMMAND git -C /tmp/java-baseline-guava-3350 rev-parse HEAD
8868c096cfdabbe38170b6e395369c315cfb72a1

READ /tmp/java-baseline-guava-3350/guava/src/com/google/common/eventbus/EventBus.java
/*
 * 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 static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.util.concurrent.MoreExecutors.directExecutor;

import com.google.common.base.MoreObjects;
import java.lang.reflect.Method;
import java.util.Iterator;
import java.util.Locale;
import java.util.concurrent.Executor;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * Dispatches events to listeners, and provides ways for listeners to register themselves.

 *
 * <h2>Avoid EventBus</h2>
 *
 * <p><b>We recommend against using EventBus.</b> It was designed many years ago, and newer
 * libraries offer better ways to decouple components and react to events.
 *
 * <p>To decouple components, we recommend a dependency-injection framework. For Android code, most
 * apps use <a href="https://dagger.dev">Dagger</a>. For server code, common options include <a
 * href="https://github.com/google/guice/wiki/Motivation">Guice</a> and <a
 * href="https://docs.spring.io/spring-framework/docs/current/reference/html/core.html#beans-introduction">Spring</a>.
 * Frameworks typically offer a way to register multiple listeners independently and then request
 * them together as a set (<a href="https://dagger.dev/dev-guide/multibindings">Dagger</a>, <a
 * href="https://github.com/google/guice/wiki/Multibindings">Guice</a>, <a
 * href="https://docs.spring.io/spring-framework/docs/current/reference/html/core.html#beans-autowired-annotation">Spring</a>).
 *
 * <p>To react to events, we recommend a reactive-streams framework like <a
 * href="https://github.com/ReactiveX/RxJava/wiki">RxJava</a> (supplemented with its <a
 * href="https://github.com/ReactiveX/RxAndroid">RxAndroid</a> extension if you are building for
 * Android) or <a href="https://projectreactor.io/">Project Reactor</a>. (For the basics of
 * translating code from using an event bus to using a reactive-streams framework, see these two
 * guides: <a href="https://blog.jkl.gg/implementing-an-event-bus-with-rxjava-rxbus/">1</a>, <a
 * href="https://lorentzos.com/rxjava-as-event-bus-the-right-way-10a36bdd49ba">2</a>.) Some usages
 * of EventBus may be better written using <a
 * href="https://kotlinlang.org/docs/coroutines-guide.html">Kotlin coroutines</a>, including <a
 * href="https://kotlinlang.org/docs/flow.html">Flow</a> and <a
 * href="https://kotlinlang.org/docs/channels.html">Channels</a>. Yet other usages are better served
 * by individual libraries that provide specialized support for particular use cases.
 *
 * <p>Disadvantages of EventBus include:
 *
 * <ul>
 *   <li>It makes the cross-references between producer and subscriber harder to find. This can
 *       complicate debugging, lead to unintentional reentrant calls, and force apps to eagerly
 *       initialize all possible subscribers at startup time.
 *   <li>It uses reflection in ways that break when code is processed by optimizers/minimizers like
 *       <a href="https://developer.android.com/studio/build/shrink-code">R8 and Proguard</a>.
 *   <li>It doesn't offer a way to wait for multiple events before taking action. For example, it
 *       doesn't offer a way to wait for multiple producers to all report that they're "ready," nor
 *       does it offer a way to batch multiple events from a single producer together.
 *   <li>It doesn't support backpressure and other features needed for resilience.
 *   <li>It doesn't provide much control of threading.
 *   <li>It doesn't offer much monitoring.
 *   <li>It doesn't propagate exceptions, so apps don't have a way to react to them.
 *   <li>It doesn't interoperate well with RxJava, coroutines, and other more commonly used
 *       alternatives.
 *   <li>It imposes requirements on the lifecycle of its subscribers. For example, if an event
 *       occurs between when one subscriber is removed and the next subscriber is added, the event
 *       is dropped.
 *   <li>Its performance is suboptimal, especially under Android.
 *   <li>It <a href="https://github.com/google/guava/issues/1431">doesn't support parameterized
 *       types</a>.
 *   <li>With the introduction of lambdas in Java 8, EventBus went from less verbose than listeners
 *       to <a href="https://github.com/google/guava/issues/3311">more verbose</a>.
 * </ul>
 *

 *
 * <h2>EventBus Summary</h2>
 *
 * <p>The EventBus allows publish-subscribe-style communication between components without requiring
 * the components to explicitly register with one another (and thus be aware of each other). It is
 * designed exclusively to replace traditional Java in-process event distribution using explicit
 * registration. It is <em>not</em> a general-purpose publish-subscribe system, nor is it intended
 * for interprocess communication.
 *
 * <h2>Receiving Events</h2>
 *
 * <p>To receive events, an object should:
 *
 * <ol>
 *   <li>Expose a public method, known as the <i>event subscriber</i>, which accepts a single
 *       argument of the type of event desired;
 *   <li>Mark it with a {@link Subscribe} annotation;
 *   <li>Pass itself to an EventBus instance's {@link #register(Object)} method.
 * </ol>
 *
 * <h2>Posting Events</h2>
 *
 * <p>To post an event, simply provide the event object to the {@link #post(Object)} method. The
 * EventBus instance will determine the type of event and route it to all registered listeners.
 *
 * <p>Events are routed based on their type &mdash; an event will be delivered to any subscriber for
 * any type to which the event is <em>assignable.</em> This includes implemented interfaces, all
 * superclasses, and all interfaces implemented by superclasses.
 *
 * <p>When {@code post} is called, all registered subscribers for an event are run in sequence, so
 * subscribers should be reasonably quick. If an event may trigger an extended process (such as a
 * database load), spawn a thread or queue it for later. (For a convenient way to do this, use an
 * {@link AsyncEventBus}.)
 *
 * <h2>Subscriber Methods</h2>
 *
 * <p>Event subscriber methods must accept only one argument: the event.
 *
 * <p>Subscribers should not, in general, throw. If they do, the EventBus will catch and log the
 * exception. This is rarely the right solution for error handling and should not be relied upon; it
 * is intended solely to help find problems during development.
 *
 * <p>The EventBus guarantees that it will not call a subscriber method from multiple threads
 * simultaneously, unless the method explicitly allows it by bearing the {@link
 * AllowConcurrentEvents} annotation. If this annotation is not present, subscriber methods need not
 * worry about being reentrant, unless also called from outside the EventBus.
 *
 * <h2>Dead Events</h2>
 *
 * <p>If an event is posted, but no registered subscribers can accept it, it is considered "dead."
 * To give the system a second chance to handle dead events, they are wrapped in an instance of
 * {@link DeadEvent} and reposted.
 *
 * <p>If a subscriber for a supertype of all events (such as Object) is registered, no event will
 * ever be considered dead, and no DeadEvents will be generated. Accordingly, while DeadEvent
 * extends {@link Object}, a subscriber registered to receive any Object will never receive a
 * DeadEvent.
 *
 * <p>This class is safe for concurrent use.
 *
 * <p>See the Guava User Guide article on <a
 * href="https://github.com/google/guava/wiki/EventBusExplained">{@code EventBus}</a>.
 *
 * @author Cliff Biffle
 * @since 10.0
 */
public class EventBus {

  private static final Logger logger = Logger.getLogger(EventBus.class.getName());

  private final String identifier;
  private final Executor executor;
  private final SubscriberExceptionHandler exceptionHandler;

  private final SubscriberRegistry subscribers = new SubscriberRegistry(this);
  private final Dispatcher dispatcher;

  /** Creates a new EventBus named "default". */
  public EventBus() {
    this("default");
  }

  /**
   * Creates a new EventBus with the given {@code identifier}.
   *
   * @param identifier a brief name for this bus, for logging purposes. Should be a valid Java
   *     identifier.
   */
  public EventBus(String identifier) {
    this(
        identifier, directExecutor(), Dispatcher.perThreadDispatchQueue(), LoggingHandler.INSTANCE);
  }

  /**
   * Creates a new EventBus with the given {@link SubscriberExceptionHandler}.
   *
   * @param exceptionHandler Handler for subscriber exceptions.
   * @since 16.0
   */
  public EventBus(SubscriberExceptionHandler exceptionHandler) {
    this("default", directExecutor(), Dispatcher.perThreadDispatchQueue(), exceptionHandler);
  }

  EventBus(
      String identifier,
      Executor executor,
      Dispatcher dispatcher,
      SubscriberExceptionHandler exceptionHandler) {
    this.identifier = checkNotNull(identifier);
    this.executor = checkNotNull(executor);
    this.dispatcher = checkNotNull(dispatcher);
    this.exceptionHandler = checkNotNull(exceptionHandler);
  }

  /**
   * Returns the identifier for this event bus.
   *
   * @since 19.0
   */
  public final String identifier() {
    return identifier;
  }

  /** Returns the default executor this event bus uses for dispatching events to subscribers. */
  final Executor executor() {
    return executor;
  }

  /** Handles the given exception thrown by a subscriber with the given context. */
  void handleSubscriberException(Throwable e, SubscriberExceptionContext context) {
    checkNotNull(e);
    checkNotNull(context);
    try {
      exceptionHandler.handleException(e, context);
    } catch (Throwable e2) {
      // if the handler threw an exception... well, just log it
      logger.log(
          Level.SEVERE,
          String.format(Locale.ROOT, "Exception %s thrown while handling exception: %s", e2, e),
          e2);
    }
  }

  /**
   * Registers all subscriber methods on {@code object} to receive events.
   *
   * @param object object whose subscriber methods should be registered.
   */
  public void register(Object object) {
    subscribers.register(object);
  }

  /**
   * Unregisters all subscriber methods on a registered {@code object}.
   *
   * @param object object whose subscriber methods should be unregistered.
   * @throws IllegalArgumentException if the object was not previously registered.
   */
  public void unregister(Object object) {
    subscribers.unregister(object);
  }

  /**
   * Posts an event to all registered subscribers. This method will return successfully after the
   * event has been posted to all subscribers, and regardless of any exceptions thrown by
   * subscribers.
   *
   * <p>If no subscribers have been subscribed for {@code event}'s class, and {@code event} is not
   * already a {@link DeadEvent}, it will be wrapped in a DeadEvent and reposted.
   *
   * @param event event to post.
   */
  public void post(Object event) {
    Iterator<Subscriber> eventSubscribers = subscribers.getSubscribers(event);
    if (eventSubscribers.hasNext()) {
      dispatcher.dispatch(event, eventSubscribers);
    } else if (!(event instanceof DeadEvent)) {
      // the event had no subscribers and was not itself a DeadEvent
      post(new DeadEvent(this, event));
    }
  }

  @Override
  public String toString() {
    return MoreObjects.toStringHelper(this).addValue(identifier).toString();
  }

  /** Simple logging handler for subscriber exceptions. */
  static final class LoggingHandler implements SubscriberExceptionHandler {
    static final LoggingHandler INSTANCE = new LoggingHandler();

    @Override
    public void handleException(Throwable exception, SubscriberExceptionContext context) {
      Logger logger = logger(context);
      if (logger.isLoggable(Level.SEVERE)) {
        logger.log(Level.SEVERE, message(context), exception);
      }
    }

    private static Logger logger(SubscriberExceptionContext context) {
      return Logger.getLogger(EventBus.class.getName() + "." + context.getEventBus().identifier());
    }

    private static String message(SubscriberExceptionContext context) {
      Method method = context.getSubscriberMethod();
      return "Exception thrown by subscriber method "
          + method.getName()
          + '('
          + method.getParameterTypes()[0].getName()
          + ')'
          + " on subscriber "
          + context.getSubscriber()
          + " when dispatching event: "
          + context.getEvent();
    }
  }
}

READ /tmp/java-baseline-guava-3350/guava/src/com/google/common/eventbus/Dispatcher.java
/*
 * Copyright (C) 2014 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 static com.google.common.base.Preconditions.checkNotNull;
import static java.util.Objects.requireNonNull;

import java.util.ArrayDeque;
import java.util.Iterator;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;

/**
 * Handler for dispatching events to subscribers, providing different event ordering guarantees that
 * make sense for different situations.
 *
 * <p><b>Note:</b> The dispatcher is orthogonal to the subscriber's {@code Executor}. The dispatcher
 * controls the order in which events are dispatched, while the executor controls how (i.e. on which
 * thread) the subscriber is actually called when an event is dispatched to it.
 *
 * @author Colin Decker
 */
abstract class Dispatcher {

  /**
   * Returns a dispatcher that queues events that are posted reentrantly on a thread that is already
   * dispatching an event, guaranteeing that all events posted on a single thread are dispatched to
   * all subscribers in the order they are posted.
   *
   * <p>When all subscribers are dispatched to using a <i>direct</i> executor (which dispatches on
   * the same thread that posts the event), this yields a breadth-first dispatch order on each
   * thread. That is, all subscribers to a single event A will be called before any subscribers to
   * any events B and C that are posted to the event bus by the subscribers to A.
   */
  static Dispatcher perThreadDispatchQueue() {
    return new PerThreadQueuedDispatcher();
  }

  /**
   * Returns a dispatcher that queues events that are posted in a single global queue. This behavior
   * matches the original behavior of AsyncEventBus exactly, but is otherwise not especially useful.
   * For async dispatch, an {@linkplain #immediate() immediate} dispatcher should generally be
   * preferable.
   */
  static Dispatcher legacyAsync() {
    return new LegacyAsyncDispatcher();
  }

  /**
   * Returns a dispatcher that dispatches events to subscribers immediately as they're posted
   * without using an intermediate queue to change the dispatch order. This is effectively a
   * depth-first dispatch order, vs. breadth-first when using a queue.
   */
  static Dispatcher immediate() {
    return ImmediateDispatcher.INSTANCE;
  }

  /** Dispatches the given {@code event} to the given {@code subscribers}. */
  abstract void dispatch(Object event, Iterator<Subscriber> subscribers);

  /** Implementation of a {@link #perThreadDispatchQueue()} dispatcher. */
  private static final class PerThreadQueuedDispatcher extends Dispatcher {

    // This dispatcher matches the original dispatch behavior of EventBus.

    /** Per-thread queue of events to dispatch. */
    @SuppressWarnings("ThreadLocalUsage") // Each Dispatcher needs its own state.
    private final ThreadLocal<Queue<Event>> queue =
        new ThreadLocal<Queue<Event>>() {
          @Override
          protected Queue<Event> initialValue() {
            return new ArrayDeque<>();
          }
        };

    /** Per-thread dispatch state, used to avoid reentrant event dispatching. */
    @SuppressWarnings("ThreadLocalUsage") // Each Dispatcher needs its own state.
    private final ThreadLocal<Boolean> dispatching =
        new ThreadLocal<Boolean>() {
          @Override
          protected Boolean initialValue() {
            return false;
          }
        };

    @Override
    void dispatch(Object event, Iterator<Subscriber> subscribers) {
      checkNotNull(event);
      checkNotNull(subscribers);
      // requireNonNull accommodates Android's @RecentlyNullable annotation on ThreadLocal.get
      Queue<Event> queueForThread = requireNonNull(queue.get());
      queueForThread.offer(new Event(event, subscribers));

      if (!dispatching.get()) {
        dispatching.set(true);
        try {
          Event nextEvent;
          while ((nextEvent = queueForThread.poll()) != null) {
            while (nextEvent.subscribers.hasNext()) {
              nextEvent.subscribers.next().dispatchEvent(nextEvent.event);
            }
          }
        } finally {
          dispatching.remove();
          queue.remove();
        }
      }
    }

    private static final class Event {
      private final Object event;
      private final Iterator<Subscriber> subscribers;

      private Event(Object event, Iterator<Subscriber> subscribers) {
        this.event = event;
        this.subscribers = subscribers;
      }
    }
  }

  /** Implementation of a {@link #legacyAsync()} dispatcher. */
  private static final class LegacyAsyncDispatcher extends Dispatcher {

    // This dispatcher matches the original dispatch behavior of AsyncEventBus.
    //
    // We can't really make any guarantees about the overall dispatch order for this dispatcher in
    // a multithreaded environment for a couple of reasons:
    //
    // 1. Subscribers to events posted on different threads can be interleaved with each other
    //    freely. (A event on one thread, B event on another could yield any of
    //    [a1, a2, a3, b1, b2], [a1, b2, a2, a3, b2], [a1, b2, b3, a2, a3], etc.)
    // 2. It's possible for subscribers to actually be dispatched to in a different order than they
    //    were added to the queue. It's easily possible for one thread to take the head of the
    //    queue, immediately followed by another thread taking the next element in the queue. That
    //    second thread can then dispatch to the subscriber it took before the first thread does.
    //
    // All this makes me really wonder if there's any value in queueing here at all. A dispatcher
    // that simply loops through the subscribers and dispatches the event to each would actually
    // probably provide a stronger order guarantee, though that order would obviously be different
    // in some cases.

    /** Global event queue. */
    private final ConcurrentLinkedQueue<EventWithSubscriber> queue = new ConcurrentLinkedQueue<>();

    @Override
    void dispatch(Object event, Iterator<Subscriber> subscribers) {
      checkNotNull(event);
      while (subscribers.hasNext()) {
        queue.add(new EventWithSubscriber(event, subscribers.next()));
      }

      EventWithSubscriber e;
      while ((e = queue.poll()) != null) {
        e.subscriber.dispatchEvent(e.event);
      }
    }

    private static final class EventWithSubscriber {
      private final Object event;
      private final Subscriber subscriber;

      private EventWithSubscriber(Object event, Subscriber subscriber) {
        this.event = event;
        this.subscriber = subscriber;
      }
    }
  }

  /** Implementation of {@link #immediate()}. */
  private static final class ImmediateDispatcher extends Dispatcher {
    private static final ImmediateDispatcher INSTANCE = new ImmediateDispatcher();

    @Override
    void dispatch(Object event, Iterator<Subscriber> subscribers) {
      checkNotNull(event);
      while (subscribers.hasNext()) {
        subscribers.next().dispatchEvent(event);
      }
    }
  }
}

READ /tmp/java-baseline-guava-3350/guava/src/com/google/common/eventbus/Subscriber.java
/*
 * Copyright (C) 2014 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 static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.VisibleForTesting;
import com.google.j2objc.annotations.Weak;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.concurrent.Executor;
import org.jspecify.annotations.Nullable;

/**
 * A subscriber method on a specific object, plus the executor that should be used for dispatching
 * events to it.
 *
 * <p>Two subscribers are equivalent when they refer to the same method on the same object (not
 * class). This property is used to ensure that no subscriber method is registered more than once.
 *
 * @author Colin Decker
 */
class Subscriber {

  /** Creates a {@code Subscriber} for {@code method} on {@code listener}. */
  static Subscriber create(EventBus bus, Object listener, Method method) {
    return isDeclaredThreadSafe(method)
        ? new Subscriber(bus, listener, method)
        : new SynchronizedSubscriber(bus, listener, method);
  }

  /** The event bus this subscriber belongs to. */
  @Weak private final EventBus bus;

  /** The object with the subscriber method. */
  @VisibleForTesting final Object target;

  /** Subscriber method. */
  private final Method method;

  /** Executor to use for dispatching events to this subscriber. */
  private final Executor executor;

  private Subscriber(EventBus bus, Object target, Method method) {
    this.bus = bus;
    this.target = checkNotNull(target);
    this.method = method;
    method.setAccessible(true);

    this.executor = bus.executor();
  }

  /** Dispatches {@code event} to this subscriber using the proper executor. */
  final void dispatchEvent(Object event) {
    executor.execute(
        () -> {
          try {
            invokeSubscriberMethod(event);
          } catch (InvocationTargetException e) {
            bus.handleSubscriberException(e.getCause(), context(event));
          }
        });
  }

  /**
   * Invokes the subscriber method. This method can be overridden to make the invocation
   * synchronized.
   */
  @VisibleForTesting
  void invokeSubscriberMethod(Object event) throws InvocationTargetException {
    try {
      method.invoke(target, checkNotNull(event));
    } catch (IllegalArgumentException e) {
      throw new Error("Method rejected target/argument: " + event, e);
    } catch (IllegalAccessException e) {
      throw new Error("Method became inaccessible: " + event, e);
    } catch (InvocationTargetException e) {
      if (e.getCause() instanceof Error) {
        throw (Error) e.getCause();
      }
      throw e;
    }
  }

  /** Gets the context for the given event. */
  private SubscriberExceptionContext context(Object event) {
    return new SubscriberExceptionContext(bus, event, target, method);
  }

  @Override
  public final int hashCode() {
    return (31 + method.hashCode()) * 31 + System.identityHashCode(target);
  }

  @Override
  public final boolean equals(@Nullable Object obj) {
    if (obj instanceof Subscriber) {
      Subscriber that = (Subscriber) obj;
      // Use == so that different equal instances will still receive events.
      // We only guard against the case that the same object is registered
      // multiple times
      return target == that.target && method.equals(that.method);
    }
    return false;
  }

  /**
   * Checks whether {@code method} is thread-safe, as indicated by the presence of the {@link
   * AllowConcurrentEvents} annotation.
   */
  private static boolean isDeclaredThreadSafe(Method method) {
    return method.getAnnotation(AllowConcurrentEvents.class) != null;
  }

  /**
   * Subscriber that synchronizes invocations of a method to ensure that only one thread may enter
   * the method at a time.
   */
  @VisibleForTesting
  static final class SynchronizedSubscriber extends Subscriber {

    private SynchronizedSubscriber(EventBus bus, Object target, Method method) {
      super(bus, target, method);
    }

    @Override
    void invokeSubscriberMethod(Object event) throws InvocationTargetException {
      synchronized (this) {
        super.invokeSubscriberMethod(event);
      }
    }
  }
}

READ /tmp/java-baseline-guava-3350/guava/src/com/google/common/eventbus/SubscriberRegistry.java
/*
 * Copyright (C) 2014 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 static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.MoreObjects;
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.ImmutableSet;
import com.google.common.collect.Iterators;
import com.google.common.collect.Lists;
import com.google.common.collect.Maps;
import com.google.common.collect.Multimap;
import com.google.common.primitives.Primitives;
import com.google.common.reflect.TypeToken;
import com.google.common.util.concurrent.UncheckedExecutionException;
import com.google.j2objc.annotations.Weak;
import java.lang.reflect.Method;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Objects;
import java.util.Set;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.CopyOnWriteArraySet;
import org.jspecify.annotations.Nullable;

/**
 * Registry of subscribers to a single event bus.
 *
 * @author Colin Decker
 */
final class SubscriberRegistry {

  /**
   * All registered subscribers, indexed by event type.
   *
   * <p>The {@link CopyOnWriteArraySet} values make it easy and relatively lightweight to get an
   * immutable snapshot of all current subscribers to an event without any locking.
   */
  private final ConcurrentMap<Class<?>, CopyOnWriteArraySet<Subscriber>> subscribers =
      Maps.newConcurrentMap();

  /** The event bus this registry belongs to. */
  @Weak private final EventBus bus;

  SubscriberRegistry(EventBus bus) {
    this.bus = checkNotNull(bus);
  }

  /** Registers all subscriber methods on the given listener object. */
  void register(Object listener) {
    Multimap<Class<?>, Subscriber> listenerMethods = findAllSubscribers(listener);

    for (Entry<Class<?>, Collection<Subscriber>> entry : listenerMethods.asMap().entrySet()) {
      Class<?> eventType = entry.getKey();
      Collection<Subscriber> eventMethodsInListener = entry.getValue();

      CopyOnWriteArraySet<Subscriber> eventSubscribers = subscribers.get(eventType);

      if (eventSubscribers == null) {
        CopyOnWriteArraySet<Subscriber> newSet = new CopyOnWriteArraySet<>();
        eventSubscribers =
            MoreObjects.firstNonNull(subscribers.putIfAbsent(eventType, newSet), newSet);
      }

      eventSubscribers.addAll(eventMethodsInListener);
    }
  }

  /** Unregisters all subscribers on the given listener object. */
  void unregister(Object listener) {
    Multimap<Class<?>, Subscriber> listenerMethods = findAllSubscribers(listener);

    for (Entry<Class<?>, Collection<Subscriber>> entry : listenerMethods.asMap().entrySet()) {
      Class<?> eventType = entry.getKey();
      Collection<Subscriber> listenerMethodsForType = entry.getValue();

      CopyOnWriteArraySet<Subscriber> currentSubscribers = subscribers.get(eventType);
      if (currentSubscribers == null || !currentSubscribers.removeAll(listenerMethodsForType)) {
        // if removeAll returns true, all we really know is that at least one subscriber was
        // removed... however, barring something very strange we can assume that if at least one
        // subscriber was removed, all subscribers on listener for that event type were... after
        // all, the definition of subscribers on a particular class is totally static
        throw new IllegalArgumentException(
            "missing event subscriber for an annotated method. Is " + listener + " registered?");
      }

      // don't try to remove the set if it's empty; that can't be done safely without a lock
      // anyway, if the set is empty it'll just be wrapping an array of length 0
    }
  }

  @VisibleForTesting
  Set<Subscriber> getSubscribersForTesting(Class<?> eventType) {
    return MoreObjects.firstNonNull(subscribers.get(eventType), ImmutableSet.<Subscriber>of());
  }

  /**
   * Gets an iterator representing an immutable snapshot of all subscribers to the given event at
   * the time this method is called.
   */
  Iterator<Subscriber> getSubscribers(Object event) {
    ImmutableSet<Class<?>> eventTypes = flattenHierarchy(event.getClass());

    List<Iterator<Subscriber>> subscriberIterators =
        Lists.newArrayListWithCapacity(eventTypes.size());

    for (Class<?> eventType : eventTypes) {
      CopyOnWriteArraySet<Subscriber> eventSubscribers = subscribers.get(eventType);
      if (eventSubscribers != null) {
        // eager no-copy snapshot
        subscriberIterators.add(eventSubscribers.iterator());
      }
    }

    return Iterators.concat(subscriberIterators.iterator());
  }

  /**
   * 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(CacheLoader.from(SubscriberRegistry::getAnnotatedMethodsNotCached));

  /**
   * Returns all subscribers for the given listener grouped by the type of event they subscribe to.
   */
  private Multimap<Class<?>, Subscriber> findAllSubscribers(Object listener) {
    Multimap<Class<?>, Subscriber> methodsInListener = HashMultimap.create();
    Class<?> clazz = listener.getClass();
    for (Method method : getAnnotatedMethods(clazz)) {
      Class<?>[] parameterTypes = method.getParameterTypes();
      Class<?> eventType = parameterTypes[0];
      methodsInListener.put(eventType, Subscriber.create(bus, listener, method));
    }
    return methodsInListener;
  }

  private static ImmutableList<Method> getAnnotatedMethods(Class<?> clazz) {
    try {
      return subscriberMethodsCache.getUnchecked(clazz);
    } catch (UncheckedExecutionException e) {
      if (e.getCause() instanceof IllegalArgumentException) {
        /*
         * IllegalArgumentException is the one unchecked exception that we know is likely to happen
         * (thanks to the checkArgument calls in getAnnotatedMethodsNotCached). If it happens, we'd
         * prefer to propagate an IllegalArgumentException to the caller. However, we don't want to
         * simply rethrow an exception (e.getCause()) that may in rare cases have come from another
         * thread. To accomplish both goals, we wrap that IllegalArgumentException in a new
         * instance.
         */
        throw new IllegalArgumentException(e.getCause().getMessage(), e.getCause());
      }
      /*
       * If some other exception happened, we just propagate the wrapper
       * UncheckedExecutionException, which has the stack trace from this thread and which has its
       * cause set to the underlying exception (which may be from another thread). If we someday
       * learn that some other exception besides IllegalArgumentException is common, then we could
       * add another special case to throw an instance of it, too.
       */
      throw e;
    }
  }

  private static ImmutableList<Method> getAnnotatedMethodsNotCached(Class<?> clazz) {
    Set<? extends Class<?>> supertypes = TypeToken.of(clazz).getTypes().rawTypes();
    Map<MethodIdentifier, Method> identifiers = new HashMap<>();
    for (Class<?> supertype : supertypes) {
      for (Method method : supertype.getDeclaredMethods()) {
        if (method.isAnnotationPresent(Subscribe.class) && !method.isSynthetic()) {
          // TODO(cgdecker): Should check for a generic parameter type and error out
          Class<?>[] parameterTypes = method.getParameterTypes();
          checkArgument(
              parameterTypes.length == 1,
              "Method %s has @Subscribe annotation but has %s parameters. "
                  + "Subscriber methods must have exactly 1 parameter.",
              method,
              parameterTypes.length);

          checkArgument(
              !parameterTypes[0].isPrimitive(),
              "@Subscribe method %s's parameter is %s. "
                  + "Subscriber methods cannot accept primitives. "
                  + "Consider changing the parameter to %s.",
              method,
              parameterTypes[0].getName(),
              Primitives.wrap(parameterTypes[0]).getSimpleName());

          MethodIdentifier ident = new MethodIdentifier(method);
          if (!identifiers.containsKey(ident)) {
            identifiers.put(ident, method);
          }
        }
      }
    }
    return ImmutableList.copyOf(identifiers.values());
  }

  /** Global cache of classes to their flattened hierarchy of supertypes. */
  private static final LoadingCache<Class<?>, ImmutableSet<Class<?>>> flattenHierarchyCache =
      CacheBuilder.newBuilder()
          .weakKeys()
          .build(
              CacheLoader.from(
                  concreteClass ->
                      ImmutableSet.copyOf(TypeToken.of(concreteClass).getTypes().rawTypes())));

  /**
   * Flattens a class's type hierarchy into a set of {@code Class} objects including all
   * superclasses (transitively) and all interfaces implemented by these superclasses.
   */
  @VisibleForTesting
  static ImmutableSet<Class<?>> flattenHierarchy(Class<?> concreteClass) {
    return flattenHierarchyCache.getUnchecked(concreteClass);
  }

  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.hash(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;
    }
  }
}
