/*
    * 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
    *
    *      https://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.
   */
  
  /*
   * This is not the original file distributed by the Apache Software Foundation
   * It has been modified by the Hipparchus project
   */
  package org.hipparchus.analysis.integration.gauss;
  
  import org.hipparchus.util.Pair;
  import org.junit.jupiter.api.Test;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.concurrent.ArrayBlockingQueue;
  import java.util.concurrent.Callable;
  import java.util.concurrent.ExecutionException;
  import java.util.concurrent.Future;
  import java.util.concurrent.ThreadPoolExecutor;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicInteger;
  
  import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
  import static org.junit.jupiter.api.Assertions.assertEquals;
  
  /**
   * Test for {@link AbstractRuleFactory}.
   *
   */
  class RuleFactoryTest {
      /**
       * 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
      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<Runnable>(2));
  
          final List<Future<Pair<double[], double[]>>> results
              = new ArrayList<Future<Pair<double[], double[]>>>();
          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();
          }
  
          // Assertion would fail if "getRuleInternal" were not "synchronized".
          final int n = RuleBuilder.getNumberOfCalls();
          assertEquals(1, n, "Rule computation was called " + n + " times");
      }
  
      private static class RuleBuilder implements Callable<Pair<double[], double[]>> {
          private static final DummyRuleFactory factory = new DummyRuleFactory();
  
          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();
          }
      }
  
      private static class DummyRuleFactory extends AbstractRuleFactory {
          /** 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();
  
              assertDoesNotThrow(() -> {
                  // Sleep to simulate computation time.
                  Thread.sleep(20);
             }, "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();
         }
 
     }
 
 }