/*
    * 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.commons.math4.legacy.analysis.integration.gauss;
  
  import java.util.List;
  import java.util.ArrayList;
  import java.util.concurrent.ThreadPoolExecutor;
  import java.util.concurrent.ArrayBlockingQueue;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.Callable;
  import java.util.concurrent.Future;
  import java.util.concurrent.ExecutionException;
  import java.util.concurrent.atomic.AtomicInteger;
  
  import org.apache.commons.math4.legacy.core.Pair;
  import org.junit.Test;
  import org.junit.Assert;
  
  /**
   * Test for {@link BaseRuleFactory}.
   *
   */
  public class BaseRuleFactoryTest {
      /**
       * Tests that a given rule rule will be computed and added once to the cache
       * whatever the number of times this rule is called concurrently.
       */
      @Test
          public void testConcurrentCreation() throws InterruptedException,
                                                      ExecutionException {
          // Number of times the same rule will be called.
          final int numTasks = 20;
  
          final ThreadPoolExecutor exec
              = new ThreadPoolExecutor(3, numTasks, 1, TimeUnit.SECONDS,
                                       new ArrayBlockingQueue<>(2));
  
          final List<Future<Pair<double[], double[]>>> results
              = new ArrayList<>();
          for (int i = 0; i < numTasks; i++) {
              results.add(exec.submit(new RuleBuilder()));
          }
  
          // Ensure that all computations have completed.
          for (Future<Pair<double[], double[]>> f : results) {
              f.get();
          }
          exec.shutdown();
  
          // Assertion would fail if "getRuleInternal" were not "synchronized".
          final int n = RuleBuilder.getNumberOfCalls();
          Assert.assertEquals("Rule computation was called " + n + " times", 1, n);
      }
  }
  
  class RuleBuilder implements Callable<Pair<double[], double[]>> {
      private static final DummyRuleFactory factory = new DummyRuleFactory();
  
      @Override
      public Pair<double[], double[]> call() {
          final int dummy = 2; // Always request the same rule.
          return factory.getRule(dummy);
      }
  
      public static int getNumberOfCalls() {
          return factory.getNumberOfCalls();
      }
  }
  
  class DummyRuleFactory extends BaseRuleFactory<Double> {
      /** Rule computations counter. */
      private static AtomicInteger nCalls = new AtomicInteger();
  
      @Override
      protected Pair<Double[], Double[]> computeRule(int order) {
          // Tracks whether this computation has been called more than once.
          nCalls.getAndIncrement();
  
          try {
              // Sleep to simulate computation time.
              Thread.sleep(20);
          } catch (InterruptedException e) {
              Assert.fail("Unexpected interruption");
          }
  
          // Dummy rule (but contents must exist).
         final Double[] p = new Double[order];
         final Double[] w = new Double[order];
         for (int i = 0; i < order; i++) {
             p[i] = Double.valueOf(i);
             w[i] = Double.valueOf(i);
         }
         return new Pair<>(p, w);
     }
 
     public int getNumberOfCalls() {
         return nCalls.get();
     }
 }