/*
    * 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.analysis.differentiation.Gradient;
  import org.hipparchus.analysis.differentiation.GradientField;
  import org.hipparchus.analysis.interpolation.LinearInterpolator;
  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.BeforeEach;
  import org.junit.jupiter.api.Test;
  
  import java.lang.reflect.Array;
  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 FieldFieldPolynomialSplineFunction implementation.
   *
   */
  class FieldPolynomialSplineFunctionTest {
  
      /** Error tolerance for tests */
      private double tolerance;
  
      /**
       * 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 FieldPolynomialSplineFunction evaluation
       * algorithm agrees at knot point boundaries.
       */
      private FieldPolynomialFunction<Binary64>[] polynomials;
  
      /** Knot points  */
      private Binary64[] knots;
  
      /** Derivative of test polynomials -- 2x + 1  */
      protected PolynomialFunction dp =
          new PolynomialFunction(new double[] {1d, 2d});
  
  
      @Test
      void testConstructor() {
          FieldPolynomialSplineFunction<Binary64> spline =
              new FieldPolynomialSplineFunction<>(knots, polynomials);
          assertTrue(Arrays.equals(knots, spline.getKnots()));
          assertEquals(1d, spline.getPolynomials()[0].getCoefficients()[2].getReal(), 0);
          assertEquals(3, spline.getN());
  
          try { // too few knots
              new FieldPolynomialSplineFunction<>(new Binary64[] { new Binary64(0) }, polynomials);
              fail("Expecting MathIllegalArgumentException");
          } catch (MathIllegalArgumentException ex) {
              // expected
          }
  
          try { // too many knots
              new FieldPolynomialSplineFunction<>(new Binary64[] {
                  new Binary64(0), new Binary64(1), new Binary64(2),
                  new Binary64(3), new Binary64(4)
              }, polynomials);
              fail("Expecting MathIllegalArgumentException");
          } catch (MathIllegalArgumentException ex) {
              // expected
          }
  
          try { // knots not increasing
              new FieldPolynomialSplineFunction<>(new Binary64[] {
                  new Binary64(0), new Binary64(1), new Binary64(3), new Binary64(2)
              }, polynomials);
             fail("Expecting MathIllegalArgumentException");
         } catch (MathIllegalArgumentException ex) {
             // expected
         }
     }
 
     @Test
     void testValues() {
         FieldPolynomialSplineFunction<Binary64> spline =
             new FieldPolynomialSplineFunction<>(knots, polynomials);
         FieldPolynomialSplineFunction<Binary64> 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(new Binary64(x).subtract(knots[index])).getReal(),
                                spline.value(x).getReal(),
                                tolerance,
                                "spline function evaluation failed for x=" + x);
            assertEquals(dp.value(new Binary64(x).subtract(knots[index])).getReal(),
                                dSpline.value(x).getReal(),
                                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).getReal(),
                                 spline.value(knots[i]).getReal(),
                                 tolerance,
                                 "spline function evaluation failed for knot=" + knots[i].getReal());
             assertEquals(dp.value(0),
                                 dSpline.value(knots[i]).getReal(),
                                 tolerance,
                                 "spline function evaluation failed for knot=" + knots[i]);
         }
 
         try { //outside of domain -- under min
             spline.value(-1.5);
             fail("Expecting MathIllegalArgumentException");
         } catch (MathIllegalArgumentException ex) {
             // expected
         }
 
         try { //outside of domain -- over max
             spline.value(2.5);
             fail("Expecting MathIllegalArgumentException");
         } catch (MathIllegalArgumentException ex) {
             // expected
         }
     }
 
     @Test
     void testIsValidPoint() {
         final FieldPolynomialSplineFunction<Binary64> spline =
             new FieldPolynomialSplineFunction<>(knots, polynomials);
         final Binary64 xMin = knots[0];
         final Binary64 xMax = knots[knots.length - 1];
 
         Binary64 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 Binary64 xRange = xMax.subtract(xMin);
         x = xMin.add(xRange.divide(3.4));
         assertTrue(spline.isValidPoint(x));
         // Ensure that no exception is thrown.
         spline.value(x);
 
         final Binary64 small = new Binary64(1e-8);
         x = xMin.subtract(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(Binary64[] knots, double x) {
          if (x < knots[0].getReal() || x >= knots[knots.length -1].getReal()) {
              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].getReal() > x) {
                  return i - 1;
              }
          }
          throw new MathIllegalStateException(LocalizedCoreFormats.ILLEGAL_STATE);
      }
 
      private FieldPolynomialFunction<Binary64> buildD64(double...c) {
          Binary64[] array = new Binary64[c.length];
          for (int i = 0; i < c.length; ++i) {
              array[i] = new Binary64(c[i]);
          }
          return new FieldPolynomialFunction<>(array);
      }
 
     @BeforeEach
     @SuppressWarnings("unchecked")
     void setUp() {
          tolerance = 1.0e-12;
          polynomials = (FieldPolynomialFunction<Binary64>[]) Array.newInstance(FieldPolynomialFunction.class, 3);
          polynomials[0] = buildD64(0, 1, 1);
          polynomials[1] = buildD64(2, 1, 1);
          polynomials[2] = buildD64(4, 1, 1);
          knots = new Binary64[] {
              new Binary64(-1), new Binary64(0), new Binary64(1), new Binary64(2)
          };
      }
 
     @Test
     void testValueGradient() {
          // issue #257
          // Given
          final int freeParameters = 1;
          final GradientField field = GradientField.getField(freeParameters);
          final Gradient zero = field.getZero();
          final Gradient time1 = zero.add(1.0);
          final Gradient time2 = zero.add(2.0);
          final Gradient time3 = zero.add(4.0);
          final Gradient x1 = zero.add(4.0);
          final Gradient x2 = Gradient.variable(freeParameters, 0, -2.0);
          final Gradient x3 = zero.add(0.0);
          final Gradient[] times = new Gradient[] {time1, time2, time3};
          final Gradient[] xs = new Gradient[] {x1, x2, x3};
          // When
          final FieldPolynomialSplineFunction<Gradient> spline = new LinearInterpolator().interpolate(times, xs);
          final Gradient actualEvaluation = spline.value(zero.add(3.));
          // Then
          final Gradient expectedEvaluation = Gradient.variable(freeParameters, 0, 0).multiply(0.5).add(-1.0);
          assertEquals(expectedEvaluation, actualEvaluation);
      }
 
 }