/*
    * 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.analysis.function;
  
  import org.hipparchus.analysis.UnivariateFunction;
  import org.hipparchus.exception.MathIllegalArgumentException;
  import org.hipparchus.exception.NullArgumentException;
  import org.junit.jupiter.api.Test;
  
  import static org.junit.jupiter.api.Assertions.assertEquals;
  import static org.junit.jupiter.api.Assertions.assertThrows;
  
  /**
   * Test for class {@link StepFunction}.
   */
  class StepFunctionTest {
      private final double EPS = Math.ulp(1d);
  
      @Test
      void testPreconditions1() {
          assertThrows(NullArgumentException.class, () -> {
              new StepFunction(null, new double[]{0, -1, -2});
          });
      }
  
      @Test
      void testPreconditions2() {
          assertThrows(NullArgumentException.class, () -> {
              new StepFunction(new double[]{0, 1}, null);
          });
      }
  
      @Test
      void testPreconditions3() {
          assertThrows(MathIllegalArgumentException.class, () -> {
              new StepFunction(new double[]{0}, new double[]{});
          });
      }
  
      @Test
      void testPreconditions4() {
          assertThrows(MathIllegalArgumentException.class, () -> {
              new StepFunction(new double[]{}, new double[]{0});
          });
      }
  
      @Test
      void testPreconditions5() {
          assertThrows(MathIllegalArgumentException.class, () -> {
              new StepFunction(new double[]{0, 1}, new double[]{0, -1, -2});
          });
      }
  
      @Test
      void testPreconditions6() {
          assertThrows(MathIllegalArgumentException.class, () -> {
              new StepFunction(new double[]{1, 0, 1}, new double[]{0, -1, -2});
          });
      }
  
      @Test
      void testSomeValues() {
          final double[] x = { -2, -0.5, 0, 1.9, 7.4, 21.3 };
          final double[] y = { 4, -1, -5.5, 0.4, 5.8, 51.2 };
  
          final UnivariateFunction f = new StepFunction(x, y);
  
          assertEquals(4, f.value(Double.NEGATIVE_INFINITY), EPS);
          assertEquals(4, f.value(-10), EPS);
          assertEquals(-1, f.value(-0.4), EPS);
          assertEquals(-5.5, f.value(0), EPS);
          assertEquals(0.4, f.value(2), EPS);
          assertEquals(5.8, f.value(10), EPS);
          assertEquals(51.2, f.value(30), EPS);
          assertEquals(51.2, f.value(Double.POSITIVE_INFINITY), EPS);
      }
  
      @Test
      void testEndpointBehavior() {
         final double[] x = {0, 1, 2, 3};
         final double[] xp = {-8, 1, 2, 3};
         final double[] y = {1, 2, 3, 4};
         final UnivariateFunction f = new StepFunction(x, y);
         final UnivariateFunction fp = new StepFunction(xp, y);
         assertEquals(f.value(-8), fp.value(-8), EPS);
         assertEquals(f.value(-10), fp.value(-10), EPS);
         assertEquals(f.value(0), fp.value(0), EPS);
         assertEquals(f.value(0.5), fp.value(0.5), EPS);
         for (int i = 0; i < x.length; i++) {
            assertEquals(y[i], f.value(x[i]), EPS);
            if (i > 0) {
                assertEquals(y[i - 1], f.value(x[i] - 0.5), EPS);
            } else {
                assertEquals(y[0], f.value(x[i] - 0.5), EPS);
            }
         }
     }
 
     @Test
     void testHeaviside() {
         final UnivariateFunction h = new StepFunction(new double[] {-1, 0},
                                                           new double[] {0, 1});
 
         assertEquals(0, h.value(Double.NEGATIVE_INFINITY), 0);
         assertEquals(0, h.value(-Double.MAX_VALUE), 0);
         assertEquals(0, h.value(-2), 0);
         assertEquals(0, h.value(-Double.MIN_VALUE), 0);
         assertEquals(1, h.value(0), 0);
         assertEquals(1, h.value(2), 0);
         assertEquals(1, h.value(Double.POSITIVE_INFINITY), 0);
     }
 }