/*
    * 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.junit.jupiter.api.Test;
  
  import java.lang.reflect.Constructor;
  import java.lang.reflect.InvocationTargetException;
  import java.lang.reflect.Method;
  import java.util.Comparator;
  import java.util.Iterator;
  import java.util.NoSuchElementException;
  
  import static org.junit.jupiter.api.Assertions.assertEquals;
  import static org.junit.jupiter.api.Assertions.assertFalse;
  import static org.junit.jupiter.api.Assertions.assertThrows;
  import static org.junit.jupiter.api.Assertions.assertTrue;
  import static org.junit.jupiter.api.Assertions.fail;
  
  /**
   * Tests for the {@link Combinations} class.
   */
  class CombinationsTest {
      @Test
      void testAccessor1() {
          final int n = 5;
          final int k = 3;
          assertEquals(n, new Combinations(n, k).getN());
      }
  
      @Test
      void testAccessor2() {
          final int n = 5;
          final int k = 3;
          assertEquals(k, new Combinations(n, k).getK());
      }
  
      @Test
      void testLexicographicIterator() {
          checkLexicographicIterator(new Combinations(5, 3));
          checkLexicographicIterator(new Combinations(6, 4));
          checkLexicographicIterator(new Combinations(8, 2));
          checkLexicographicIterator(new Combinations(6, 1));
          checkLexicographicIterator(new Combinations(3, 3));
          checkLexicographicIterator(new Combinations(1, 1));
          checkLexicographicIterator(new Combinations(1, 0));
          checkLexicographicIterator(new Combinations(0, 0));
          checkLexicographicIterator(new Combinations(4, 2));
          checkLexicographicIterator(new Combinations(123, 2));
      }
  
      @Test
      void testLexicographicComparatorWrongIterate1() {
          assertThrows(MathIllegalArgumentException.class, () -> {
              final int n = 5;
              final int k = 3;
              final Comparator<int[]> comp = new Combinations(n, k).comparator();
              comp.compare(new int[]{1}, new int[]{0, 1, 2});
          });
      }
  
      @Test
      void testLexicographicComparatorWrongIterate2() {
          assertThrows(MathIllegalArgumentException.class, () -> {
              final int n = 5;
              final int k = 3;
              final Comparator<int[]> comp = new Combinations(n, k).comparator();
              comp.compare(new int[]{0, 1, 2}, new int[]{0, 1, 2, 3});
          });
      }
  
      @Test
      void testLexicographicComparatorWrongIterate3() {
          assertThrows(MathIllegalArgumentException.class, () -> {
              final int n = 5;
              final int k = 3;
              final Comparator<int[]> comp = new Combinations(n, k).comparator();
              comp.compare(new int[]{1, 2, 5}, new int[]{0, 1, 2});
          });
     }
 
     @Test
     void testLexicographicComparatorWrongIterate4() {
         assertThrows(MathIllegalArgumentException.class, () -> {
             final int n = 5;
             final int k = 3;
             final Comparator<int[]> comp = new Combinations(n, k).comparator();
             comp.compare(new int[]{1, 2, 4}, new int[]{-1, 1, 2});
         });
     }
 
     @Test
     void testLexicographicComparator() {
         final int n = 5;
         final int k = 3;
         final Comparator<int[]> comp = new Combinations(n, k).comparator();
         assertEquals(1, comp.compare(new int[] {1, 2, 4},
                                             new int[] {1, 2, 3}));
         assertEquals(-1, comp.compare(new int[] {0, 1, 4},
                                              new int[] {0, 2, 4}));
         assertEquals(0, comp.compare(new int[] {1, 3, 4},
                                             new int[] {1, 3, 4}));
     }
 
     /**
      * Check that iterates can be passed unsorted.
      */
     @Test
     void testLexicographicComparatorUnsorted() {
         final int n = 5;
         final int k = 3;
         final Comparator<int[]> comp = new Combinations(n, k).comparator();
         assertEquals(1, comp.compare(new int[] {1, 4, 2},
                                             new int[] {1, 3, 2}));
         assertEquals(-1, comp.compare(new int[] {0, 4, 1},
                                              new int[] {0, 4, 2}));
         assertEquals(0, comp.compare(new int[] {1, 4, 3},
                                             new int[] {1, 3, 4}));
     }
 
     @Test
     void testEmptyCombination() {
         final Iterator<int[]> iter = new Combinations(12345, 0).iterator();
         assertTrue(iter.hasNext());
         final int[] c = iter.next();
         assertEquals(0, c.length);
         assertFalse(iter.hasNext());
     }
 
     @Test
     void testFullSetCombination() {
         final int n = 67;
         final Iterator<int[]> iter = new Combinations(n, n).iterator();
         assertTrue(iter.hasNext());
         final int[] c = iter.next();
         assertEquals(n, c.length);
 
         for (int i = 0; i < n; i++) {
             assertEquals(i, c[i]);
         }
 
         assertFalse(iter.hasNext());
     }
 
     /**
      * Verifies that the iterator generates a lexicographically
      * increasing sequence of b(n,k) arrays, each having length k
      * and each array itself increasing.
      *
      * @param c Combinations.
      */
     private void checkLexicographicIterator(Combinations c) {
         final Comparator<int[]> comp = c.comparator();
         final int n = c.getN();
         final int k = c.getK();
 
         int[] lastIterate = null;
 
         long numIterates = 0;
         for (int[] iterate : c) {
             assertEquals(k, iterate.length);
 
             // Check that the sequence of iterates is ordered.
             if (lastIterate != null) {
                 assertEquals(1, comp.compare(iterate, lastIterate));
             }
 
             // Check that each iterate is ordered.
             for (int i = 1; i < iterate.length; i++) {
                 assertTrue(iterate[i] > iterate[i - 1]);
             }
 
             lastIterate = iterate;
             ++numIterates;
         }
 
         // Check the number of iterates.
         assertEquals(CombinatoricsUtils.binomialCoefficient(n, k),
                             numIterates);
     }
 
     @Test
     void testCombinationsIteratorFail() {
         try {
             new Combinations(4, 5).iterator();
             fail("expecting MathIllegalArgumentException");
         } catch (MathIllegalArgumentException ex) {
             // ignored
         }
 
         try {
             new Combinations(-1, -2).iterator();
             fail("expecting MathIllegalArgumentException");
         } catch (MathIllegalArgumentException ex) {
             // ignored
         }
     }
 
     @Test
     void testLexicographicIteratorUnreachable() {
         // this tests things that could really never happen,
         // as the conditions are tested in the enclosing class before
         // the lexicographic iterator is built
         try {
             Class<?> lexicographicIteratorClass = null;
             for (Class<?> c : Combinations.class.getDeclaredClasses()) {
                 if (c.getCanonicalName().endsWith(".LexicographicIterator")) {
                     lexicographicIteratorClass = c;
                 }
             }
             Constructor<?> ctr = lexicographicIteratorClass.getDeclaredConstructor(Integer.TYPE, Integer.TYPE);
             Method hasNext = lexicographicIteratorClass.getDeclaredMethod("hasNext");
             Method next = lexicographicIteratorClass.getDeclaredMethod("next");
             Method remove = lexicographicIteratorClass.getDeclaredMethod("remove");
             assertFalse((Boolean) hasNext.invoke(ctr.newInstance(3, 0)));
             assertFalse((Boolean) hasNext.invoke(ctr.newInstance(3, 3)));
             assertTrue((Boolean) hasNext.invoke(ctr.newInstance(3, 2)));
             try {
                 next.invoke(ctr.newInstance(3, 0));
                 fail("an exception should have been thrown");
             } catch (InvocationTargetException ite) {
                 assertTrue(ite.getCause() instanceof NoSuchElementException);
             }
             try {
                 remove.invoke(ctr.newInstance(3, 2));
                 fail("an exception should have been thrown");
             } catch (InvocationTargetException ite) {
                 assertTrue(ite.getCause() instanceof UnsupportedOperationException);
             }
         } catch (NoSuchMethodException | IllegalAccessException | IllegalArgumentException |
                  InvocationTargetException | InstantiationException e) {
             fail(e.getLocalizedMessage());
         }
     }
 
     @Test
     void testSingletonIteratorUnreachable() {
         // this tests things that could really never happen,
         try {
             Class<?> singletonIteratorClass = null;
             for (Class<?> c : Combinations.class.getDeclaredClasses()) {
                 if (c.getCanonicalName().endsWith(".SingletonIterator")) {
                     singletonIteratorClass = c;
                 }
             }
             Constructor<?> ctr = singletonIteratorClass.getDeclaredConstructor(Integer.TYPE);
             Method hasNext = singletonIteratorClass.getDeclaredMethod("hasNext");
             Method next = singletonIteratorClass.getDeclaredMethod("next");
             Method remove = singletonIteratorClass.getDeclaredMethod("remove");
             Object iterator = ctr.newInstance(3);
             assertTrue((Boolean) hasNext.invoke(iterator));
             int[] ret = (int[]) next.invoke(iterator);
             assertEquals(3, ret.length);
             assertEquals(0, ret[0]);
             assertEquals(1, ret[1]);
             assertEquals(2, ret[2]);
             assertFalse((Boolean) hasNext.invoke(iterator));
             try {
                 next.invoke(iterator);
                 fail("an exception should have been thrown");
             } catch (InvocationTargetException ite) {
                 assertTrue(ite.getCause() instanceof NoSuchElementException);
             }
             try {
                 remove.invoke(iterator);
                 fail("an exception should have been thrown");
             } catch (InvocationTargetException ite) {
                 assertTrue(ite.getCause() instanceof UnsupportedOperationException);
             }
         } catch (NoSuchMethodException | IllegalAccessException | IllegalArgumentException |
                  InvocationTargetException | InstantiationException e) {
             fail(e.getLocalizedMessage());
         }
     }
 
 }