/*
 * 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.flink.statefun.examples.async.service;

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.TimeUnit;

/**
 * A dummy implementation that simulates a service that might take a while to compute it's result.
 */
public final class DummyTaskQueryService implements TaskQueryService {

  /**
   * used to complete the futures after an artificial random delay, that simulates network latency,
   * service busyness etc'
   */
  private final ScheduledExecutorService executor = newScheduledExecutorService();

  public CompletableFuture<TaskStatus> getTaskStatusAsync(String taskId) {
    CompletableFuture<TaskStatus> result = new CompletableFuture<>();

    final long randomCompletionDelay = ThreadLocalRandom.current().nextLong(5_000);
    executor.schedule(
        completeRandomly(taskId, result), randomCompletionDelay, TimeUnit.MILLISECONDS);

    return result;
  }

  /**
   * returns a {@link Runnable}, that when runs, it completes the supplied future {@code result}
   * with a {@link TaskStatus} that might be either done or still running. If done, then the task
   * status would have a completion time.
   */
  private static Runnable completeRandomly(String taskId, CompletableFuture<TaskStatus> result) {
    return () -> {
      boolean taskStatus = ThreadLocalRandom.current().nextBoolean();

      if (taskStatus) {
        final long now = System.currentTimeMillis();
        result.complete(new TaskStatus(taskId, true, now));
      } else {
        result.complete(new TaskStatus(taskId, false, null));
      }
    };
  }

  /** A scheduled executor service with daemon threads. */
  private static ScheduledExecutorService newScheduledExecutorService() {
    return Executors.newSingleThreadScheduledExecutor(
        r -> {
          Thread t = new Thread(r);
          t.setDaemon(true);
          return t;
        });
  }
}