/*
 * The MIT License
 * Copyright © 2014-2019 Ilkka Seppälä
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

package com.iluwatar.singleton;

import static java.time.Duration.ofMillis;
import static org.junit.jupiter.api.Assertions.assertNotNull;
import static org.junit.jupiter.api.Assertions.assertSame;
import static org.junit.jupiter.api.Assertions.assertTimeout;

import java.util.ArrayList;
import java.util.concurrent.Callable;
import java.util.concurrent.Executors;
import java.util.function.Supplier;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import org.junit.jupiter.api.Test;

/**
 * <p>This class provides several test case that test singleton construction.</p>
 *
 * <p>The first proves that multiple calls to the singleton getInstance object are the same when
 * called in the SAME thread. The second proves that multiple calls to the singleton getInstance
 * object are the same when called in the DIFFERENT thread.</p>
 *
 * <p>Date: 12/29/15 - 19:25 PM</p>
 *
 * @param <S> Supplier method generating singletons
 * @author Jeroen Meulemeester
 * @author Richard Jones
 */
public abstract class SingletonTest<S> {

  /**
   * The singleton's getInstance method.
   */
  private final Supplier<S> singletonInstanceMethod;

  /**
   * Create a new singleton test instance using the given 'getInstance' method.
   *
   * @param singletonInstanceMethod The singleton's getInstance method
   */
  public SingletonTest(final Supplier<S> singletonInstanceMethod) {
    this.singletonInstanceMethod = singletonInstanceMethod;
  }

  /**
   * Test the singleton in a non-concurrent setting.
   */
  @Test
  public void testMultipleCallsReturnTheSameObjectInSameThread() {
    // Create several instances in the same calling thread
    var instance1 = this.singletonInstanceMethod.get();
    var instance2 = this.singletonInstanceMethod.get();
    var instance3 = this.singletonInstanceMethod.get();
    // now check they are equal
    assertSame(instance1, instance2);
    assertSame(instance1, instance3);
    assertSame(instance2, instance3);
  }

  /**
   * Test singleton instance in a concurrent setting.
   */
  @Test
  public void testMultipleCallsReturnTheSameObjectInDifferentThreads() throws Exception {
    assertTimeout(ofMillis(10000), () -> {
      // Create 10000 tasks and inside each callable instantiate the singleton class
      final var tasks = IntStream.range(0, 10000)
          .<Callable<S>>mapToObj(i -> this.singletonInstanceMethod::get)
          .collect(Collectors.toCollection(ArrayList::new));

      // Use up to 8 concurrent threads to handle the tasks
      final var executorService = Executors.newFixedThreadPool(8);
      final var results = executorService.invokeAll(tasks);

      // wait for all of the threads to complete
      final var expectedInstance = this.singletonInstanceMethod.get();
      for (var res : results) {
        final var instance = res.get();
        assertNotNull(instance);
        assertSame(expectedInstance, instance);
      }

      // tidy up the executor
      executorService.shutdown();
    });

  }

}
