/*
    * 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.util;
  
  import org.hipparchus.exception.MathIllegalArgumentException;
  import org.hipparchus.special.Gamma;
  import org.junit.jupiter.api.Test;
  
  import static org.junit.jupiter.api.Assertions.assertEquals;
  import static org.junit.jupiter.api.Assertions.assertThrows;
  
  /**
   * Test cases for the {@link CombinatoricsUtils.FactorialLog} class.
   */
  class FactorialLogTest {
  
      @Test
      void testPrecondition1() {
          assertThrows(MathIllegalArgumentException.class, () -> {
              CombinatoricsUtils.FactorialLog.create().withCache(-1);
          });
      }
  
      @Test
      void testNonPositiveArgument() {
          assertThrows(MathIllegalArgumentException.class, () -> {
              final CombinatoricsUtils.FactorialLog f = CombinatoricsUtils.FactorialLog.create();
              f.value(-1);
          });
      }
  
      @Test
      void testDelegation() {
          final CombinatoricsUtils.FactorialLog f = CombinatoricsUtils.FactorialLog.create();
  
          // Starting at 21 because for smaller arguments, there is no delegation to the
          // "Gamma" class.
          for (int i = 21; i < 10000; i++) {
              final double expected = Gamma.logGamma(i + 1);
              assertEquals(expected, f.value(i), 0d, i + "! ");
          }
      }
  
      @Test
      void testCompareDirectWithoutCache() {
          // This test shows that delegating to the "Gamma" class will also lead to a
          // less accurate result.
  
          final int max = 100;
          final CombinatoricsUtils.FactorialLog f = CombinatoricsUtils.FactorialLog.create();
  
          for (int i = 0; i < max; i++) {
              final double expected = factorialLog(i);
              assertEquals(expected, f.value(i), 2 * Math.ulp(expected), i + "! ");
          }
      }
  
      @Test
      void testCompareDirectWithCache() {
          final int max = 1000;
          final CombinatoricsUtils.FactorialLog f = CombinatoricsUtils.FactorialLog.create().withCache(max);
  
          for (int i = 0; i < max; i++) {
              final double expected = factorialLog(i);
              assertEquals(expected, f.value(i), 0d, i + "! ");
          }
      }
  
      @Test
      void testCacheIncrease() {
          final int max = 100;
          final CombinatoricsUtils.FactorialLog f1 = CombinatoricsUtils.FactorialLog.create().withCache(max);
          final CombinatoricsUtils.FactorialLog f2 = f1.withCache(2 * max);
  
          final int val = max + max / 2;
          final double expected = factorialLog(val);
          assertEquals(expected, f2.value(val), 0d);
      }
  
      @Test
     void testCacheDecrease() {
         final int max = 100;
         final CombinatoricsUtils.FactorialLog f1 = CombinatoricsUtils.FactorialLog.create().withCache(max);
         final CombinatoricsUtils.FactorialLog f2 = f1.withCache(max / 2);
 
         final int val = max / 4;
         final double expected = factorialLog(val);
         assertEquals(expected, f2.value(val), 0d);
     }
 
     // Direct implementation.
     private double factorialLog(final int n) {
         double logSum = 0;
         for (int i = 2; i <= n; i++) {
             logSum += FastMath.log(i);
         }
         return logSum;
     }
 }