/*
    * 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;
  
  /**
   * Test for the {@link AhrensDieterMarsagliaTsangGammaSampler}. The tests hit edge cases for the sampler.
   */
  class AhrensDieterMarsagliaTsangGammaSamplerTest {
      /**
       * Test the constructor with a bad alpha.
       */
      @Test
      void testConstructorThrowsWithZeroAlpha() {
          final UniformRandomProvider rng = RandomAssert.seededRNG();
          final double alpha = 0;
          final double theta = 1;
          Assertions.assertThrows(IllegalArgumentException.class,
              () -> AhrensDieterMarsagliaTsangGammaSampler.of(rng, alpha, theta));
      }
  
      /**
       * Test the constructor with a bad theta.
       */
      @Test
      void testConstructorThrowsWithZeroTheta() {
          final UniformRandomProvider rng = RandomAssert.seededRNG();
          final double alpha = 1;
          final double theta = 0;
          Assertions.assertThrows(IllegalArgumentException.class,
              () -> AhrensDieterMarsagliaTsangGammaSampler.of(rng, alpha, theta));
      }
  
      /**
       * Test the SharedStateSampler implementation.
       */
      @Test
      void testSharedStateSamplerWithAlphaBelowOne() {
          testSharedStateSampler(0.5, 3.456);
      }
  
      /**
       * Test the SharedStateSampler implementation.
       */
      @Test
      void testSharedStateSamplerWithAlphaAboveOne() {
          testSharedStateSampler(3.5, 3.456);
      }
  
      /**
       * Test the SharedStateSampler implementation.
       *
       * @param alpha Alpha.
       * @param theta Theta.
       */
      private static void testSharedStateSampler(double alpha, double theta) {
          final UniformRandomProvider rng1 = RandomAssert.seededRNG();
          final UniformRandomProvider rng2 = RandomAssert.seededRNG();
          // Use instance constructor not factory constructor to exercise 1.X public API
          final AhrensDieterMarsagliaTsangGammaSampler sampler1 =
              new AhrensDieterMarsagliaTsangGammaSampler(rng1, alpha, theta);
          final SharedStateContinuousSampler sampler2 = sampler1.withUniformRandomProvider(rng2);
          RandomAssert.assertProduceSameSequence(sampler1, sampler2);
      }
  
      /**
       * Test the toString method. This is added to ensure coverage as the factory constructor
       * used in other tests does not create an instance of the wrapper class.
       */
      @Test
      void testToString() {
          final UniformRandomProvider rng = RandomAssert.seededRNG();
          Assertions.assertTrue(new AhrensDieterMarsagliaTsangGammaSampler(rng, 1.0, 2.0).toString()
                  .toLowerCase().contains("gamma"));
      }
  }