/*
 * 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 org.apache.iotdb.db.queryengine.execution;

import com.google.common.collect.ImmutableSet;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.SettableFuture;

import javax.annotation.concurrent.GuardedBy;
import javax.annotation.concurrent.ThreadSafe;

import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.Executor;

import static com.google.common.util.concurrent.MoreExecutors.directExecutor;
import static java.util.Objects.requireNonNull;

@ThreadSafe
public class FutureStateChange<T> {
  // Use a separate future for each listener so canceled listeners can be removed
  @GuardedBy("listeners")
  private final Set<SettableFuture<T>> listeners = new HashSet<>();

  public ListenableFuture<T> createNewListener() {
    SettableFuture<T> listener = SettableFuture.create();
    synchronized (listeners) {
      listeners.add(listener);
    }

    // remove the listener when the future completes
    listener.addListener(
        () -> {
          synchronized (listeners) {
            listeners.remove(listener);
          }
        },
        directExecutor());

    return listener;
  }

  public void complete(T newState) {
    fireStateChange(newState, directExecutor());
  }

  public void complete(T newState, Executor executor) {
    fireStateChange(newState, executor);
  }

  private void fireStateChange(T newState, Executor executor) {
    requireNonNull(executor, "executor is null");
    Set<SettableFuture<T>> futures;
    synchronized (listeners) {
      futures = ImmutableSet.copyOf(listeners);
      listeners.clear();
    }

    for (SettableFuture<T> future : futures) {
      executor.execute(() -> future.set(newState));
    }
  }
}
