/*
    * 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 org.apache.commons.rng.UniformRandomProvider;
  import org.apache.commons.rng.sampling.RandomAssert;
  import org.junit.jupiter.api.Assertions;
  import org.junit.jupiter.api.Test;
  import org.junit.jupiter.params.ParameterizedTest;
  import org.junit.jupiter.params.provider.ValueSource;
  
  /**
   * Test for the {@link SmallMeanPoissonSampler}. The tests hit edge cases for the sampler.
   */
  class SmallMeanPoissonSamplerTest {
      /**
       * Test the constructor with a bad mean.
       */
      @Test
      void testConstructorThrowsWithMeanThatSetsProbabilityP0ToZero() {
          final UniformRandomProvider rng =
              RandomAssert.seededRNG();
          final double p0 = Double.MIN_VALUE;
          // Note: p0 = Math.exp(-mean) => mean = -Math.log(p0).
          // Add to the limit on the mean to cause p0 to be zero.
          final double mean = -Math.log(p0) + 1;
          Assertions.assertThrows(IllegalArgumentException.class,
              () -> SmallMeanPoissonSampler.of(rng, mean));
      }
  
      /**
       * Test the constructor with a bad mean.
       */
      @Test
      void testConstructorThrowsWithZeroMean() {
          final UniformRandomProvider rng =
              RandomAssert.seededRNG();
          final double mean = 0;
          Assertions.assertThrows(IllegalArgumentException.class,
              () -> SmallMeanPoissonSampler.of(rng, mean));
      }
  
      /**
       * Test the sample is bounded to 1000 * mean.
       */
      @ParameterizedTest
      @ValueSource(doubles = {0.5, 1, 1.5, 2.2})
      void testSampleUpperBounds(double mean) {
          // If the nextDouble() is always ~1 then the sample will hit the upper bounds.
          // nextLong() returns -1; nextDouble returns Math.nextDown(1.0).
          final UniformRandomProvider rng = () -> -1;
          final SharedStateDiscreteSampler sampler = SmallMeanPoissonSampler.of(rng, mean);
          final int expected = (int) Math.ceil(1000 * mean);
          Assertions.assertEquals(expected, sampler.sample());
      }
  
      /**
       * Test the SharedStateSampler implementation.
       */
      @Test
      void testSharedStateSampler() {
          final UniformRandomProvider rng1 = RandomAssert.seededRNG();
          final UniformRandomProvider rng2 = RandomAssert.seededRNG();
          final double mean = 1.23;
          final SharedStateDiscreteSampler sampler1 =
              SmallMeanPoissonSampler.of(rng1, mean);
          final SharedStateDiscreteSampler sampler2 = sampler1.withUniformRandomProvider(rng2);
          RandomAssert.assertProduceSameSequence(sampler1, sampler2);
      }
  }