/*
    * 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.rng.sampling.distribution;
  
  import java.time.Duration;
  import org.apache.commons.rng.UniformRandomProvider;
  import org.apache.commons.rng.core.source64.SplitMix64;
  import org.apache.commons.rng.sampling.RandomAssert;
  import org.junit.jupiter.api.Assertions;
  import org.junit.jupiter.api.Test;
  
  /**
   * Test for the {@link AhrensDieterExponentialSampler}. The tests hit edge cases for the sampler.
   */
  class AhrensDieterExponentialSamplerTest {
      /**
       * Test the constructor with a bad mean.
       */
      @Test
      void testConstructorThrowsWithZeroMean() {
          final UniformRandomProvider rng = RandomAssert.seededRNG();
          final double mean = 0;
          Assertions.assertThrows(IllegalArgumentException.class, () -> AhrensDieterExponentialSampler.of(rng, mean));
      }
  
      /**
       * Test the SharedStateSampler implementation.
       */
      @Test
      void testSharedStateSampler() {
          final UniformRandomProvider rng1 = RandomAssert.seededRNG();
          final UniformRandomProvider rng2 = RandomAssert.seededRNG();
          final double mean = 1.23;
          final SharedStateContinuousSampler sampler1 =
              AhrensDieterExponentialSampler.of(rng1, mean);
          final SharedStateContinuousSampler sampler2 = sampler1.withUniformRandomProvider(rng2);
          RandomAssert.assertProduceSameSequence(sampler1, sampler2);
      }
  
      /**
       * Test the sampler is robust to a generator that outputs zeros.
       * See RNG-144.
       */
      @Test
      void testSamplerWithZeroFromRandomGenerator() {
          // A broken generator that returns zero.
          final UniformRandomProvider rng = new SplitMix64(0) {
              @Override
              public long nextLong() {
                  return 0L;
              }
          };
          final SharedStateContinuousSampler sampler = AhrensDieterExponentialSampler.of(rng, 1);
          // This should not infinite loop
          final double[] x = {-1};
          Assertions.assertTimeout(Duration.ofMillis(50), () -> {
              x[0] = sampler.sample();
          });
          Assertions.assertTrue(x[0] >= 0);
      }
  
      /**
       * Test the sampler is robust to a generator that outputs full bits. The uniform random
       * double will be at the top of the range {@code [0, 1]}.
       */
      @Test
      void testSamplerWithOneFromRandomGenerator() {
          // A broken generator that returns all the bits set.
          final UniformRandomProvider rng = new SplitMix64(0) {
              @Override
              public long nextLong() {
                  // All the bits set
                  return -1;
              }
          };
          final SharedStateContinuousSampler sampler = AhrensDieterExponentialSampler.of(rng, 1);
          final double x = sampler.sample();
          Assertions.assertTrue(x >= 0);
      }
  }