/*
    * 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.polynomials;
  
  import org.hipparchus.exception.LocalizedCoreFormats;
  import org.hipparchus.exception.MathIllegalArgumentException;
  import org.hipparchus.exception.MathIllegalStateException;
  import org.hipparchus.util.Binary64;
  import org.junit.jupiter.api.Test;
  
  import java.util.Arrays;
  
  import static org.junit.jupiter.api.Assertions.assertEquals;
  import static org.junit.jupiter.api.Assertions.assertFalse;
  import static org.junit.jupiter.api.Assertions.assertTrue;
  import static org.junit.jupiter.api.Assertions.fail;
  
  /**
   * Tests the PolynomialSplineFunction implementation.
   *
   */
  class PolynomialSplineFunctionTest {
  
      /** Error tolerance for tests */
      protected double tolerance = 1.0e-12;
  
      /**
       * Quadratic polynomials used in tests:
       *
       * x^2 + x            [-1, 0)
       * x^2 + x + 2        [0, 1)
       * x^2 + x + 4        [1, 2)
       *
       * Defined so that evaluation using PolynomialSplineFunction evaluation
       * algorithm agrees at knot point boundaries.
       */
      protected PolynomialFunction[] polynomials = {
          new PolynomialFunction(new double[] {0d, 1d, 1d}),
          new PolynomialFunction(new double[] {2d, 1d, 1d}),
          new PolynomialFunction(new double[] {4d, 1d, 1d})
      };
  
      /** Knot points  */
      protected double[] knots = {-1, 0, 1, 2};
  
      /** Derivative of test polynomials -- 2x + 1  */
      protected PolynomialFunction dp =
          new PolynomialFunction(new double[] {1d, 2d});
  
  
      @Test
      void testConstructor() {
          PolynomialSplineFunction spline =
              new PolynomialSplineFunction(knots, polynomials);
          assertTrue(Arrays.equals(knots, spline.getKnots()));
          assertEquals(1d, spline.getPolynomials()[0].getCoefficients()[2], 0);
          assertEquals(3, spline.getN());
  
          try { // too few knots
              new PolynomialSplineFunction(new double[] {0}, polynomials);
              fail("Expecting MathIllegalArgumentException");
          } catch (MathIllegalArgumentException ex) {
              // expected
          }
  
          try { // too many knots
              new PolynomialSplineFunction(new double[] {0,1,2,3,4}, polynomials);
              fail("Expecting MathIllegalArgumentException");
          } catch (MathIllegalArgumentException ex) {
              // expected
          }
  
          try { // knots not increasing
              new PolynomialSplineFunction(new double[] {0,1, 3, 2}, polynomials);
              fail("Expecting MathIllegalArgumentException");
          } catch (MathIllegalArgumentException ex) {
              // expected
          }
      }
  
     @Test
     void testValues() {
         PolynomialSplineFunction spline =
             new PolynomialSplineFunction(knots, polynomials);
         PolynomialSplineFunction dSpline = spline.polynomialSplineDerivative();
 
         /**
          * interior points -- spline value at x should equal p(x - knot)
          * where knot is the largest knot point less than or equal to x and p
          * is the polynomial defined over the knot segment to which x belongs.
          */
         double x = -1;
         int index = 0;
         for (int i = 0; i < 10; i++) {
            x+=0.25;
            index = findKnot(knots, x);
            assertEquals(polynomials[index].value(x - knots[index]), spline.value(x), tolerance, "spline function evaluation failed for x=" + x);
            assertEquals(dp.value(x - knots[index]), dSpline.value(x), tolerance, "spline derivative evaluation failed for x=" + x);
         }
 
         // knot points -- centering should zero arguments
         for (int i = 0; i < 3; i++) {
             assertEquals(polynomials[i].value(0), spline.value(knots[i]), tolerance, "spline function evaluation failed for knot=" + knots[i]);
             assertEquals(dp.value(0), dSpline.value(new Binary64(knots[i])).getReal(), tolerance, "spline function evaluation failed for knot=" + knots[i]);
         }
 
         try { //outside of domain -- under min
             x = spline.value(-1.5);
             fail("Expecting MathIllegalArgumentException");
         } catch (MathIllegalArgumentException ex) {
             // expected
         }
 
         try { //outside of domain -- over max
             x = spline.value(2.5);
             fail("Expecting MathIllegalArgumentException");
         } catch (MathIllegalArgumentException ex) {
             // expected
         }
     }
 
     @Test
     void testIsValidPoint() {
         final PolynomialSplineFunction spline =
             new PolynomialSplineFunction(knots, polynomials);
         final double xMin = knots[0];
         final double xMax = knots[knots.length - 1];
 
         double x;
 
         x = xMin;
         assertTrue(spline.isValidPoint(x));
         // Ensure that no exception is thrown.
         spline.value(x);
 
         x = xMax;
         assertTrue(spline.isValidPoint(x));
         // Ensure that no exception is thrown.
         spline.value(x);
 
         final double xRange = xMax - xMin;
         x = xMin + xRange / 3.4;
         assertTrue(spline.isValidPoint(x));
         // Ensure that no exception is thrown.
         spline.value(x);
 
         final double small = 1e-8;
         x = xMin - small;
         assertFalse(spline.isValidPoint(x));
         // Ensure that an exception would have been thrown.
         try {
             spline.value(x);
             fail("MathIllegalArgumentException expected");
         } catch (MathIllegalArgumentException expected) {}
     }
 
     /**
      *  Do linear search to find largest knot point less than or equal to x.
      *  Implementation does binary search.
      */
      protected int findKnot(double[] knots, double x) {
          if (x < knots[0] || x >= knots[knots.length -1]) {
              throw new MathIllegalArgumentException(LocalizedCoreFormats.OUT_OF_RANGE_SIMPLE,
                                                     x, knots[0], knots[knots.length -1]);
          }
          for (int i = 0; i < knots.length; i++) {
              if (knots[i] > x) {
                  return i - 1;
              }
          }
          throw new MathIllegalStateException(LocalizedCoreFormats.ILLEGAL_STATE);
      }
 }