/*
    * 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.interpolation;
  
  import org.hipparchus.analysis.BivariateFunction;
  import org.hipparchus.exception.MathIllegalArgumentException;
  import org.hipparchus.random.RandomDataGenerator;
  import org.hipparchus.util.FastMath;
  import org.hipparchus.util.Precision;
  import org.junit.jupiter.api.Test;
  
  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;
  
  /**
   * Test case for the bicubic function.
   */
  final class BicubicInterpolatingFunctionTest {
      /**
       * Test preconditions.
       */
      @Test
      void testPreconditions() {
          double[] xval = new double[] {3, 4, 5, 6.5};
          double[] yval = new double[] {-4, -3, -1, 2.5};
          double[][] zval = new double[xval.length][yval.length];
  
          @SuppressWarnings("unused")
          BivariateFunction bcf = new BicubicInterpolatingFunction(xval, yval, zval,
                                                                   zval, zval, zval);
  
          try {
              bcf = new BicubicInterpolatingFunction(new double[0], yval,
                                                     zval, zval, zval, zval);
              fail("an exception should have been thrown");
          } catch (MathIllegalArgumentException e) {
              // Expected
          }
          try {
              bcf = new BicubicInterpolatingFunction(xval, new double[0],
                                                     zval, zval, zval, zval);
              fail("an exception should have been thrown");
          } catch (MathIllegalArgumentException e) {
              // Expected
          }
          try {
              bcf = new BicubicInterpolatingFunction(xval, yval,
                                                      new double[0][], zval, zval, zval);
              fail("an exception should have been thrown");
          } catch (MathIllegalArgumentException e) {
              // Expected
          }
          try {
              bcf = new BicubicInterpolatingFunction(xval, yval,
                                                      new double[1][0], zval, zval, zval);
              fail("an exception should have been thrown");
          } catch (MathIllegalArgumentException e) {
              // Expected
          }
  
          double[] wxval = new double[] {3, 2, 5, 6.5};
          try {
              bcf = new BicubicInterpolatingFunction(wxval, yval, zval, zval, zval, zval);
              fail("an exception should have been thrown");
          } catch (MathIllegalArgumentException e) {
              // Expected
          }
          double[] wyval = new double[] {-4, -1, -1, 2.5};
          try {
              bcf = new BicubicInterpolatingFunction(xval, wyval, zval, zval, zval, zval);
              fail("an exception should have been thrown");
          } catch (MathIllegalArgumentException e) {
              // Expected
          }
          double[][] wzval = new double[xval.length][yval.length - 1];
          try {
              bcf = new BicubicInterpolatingFunction(xval, yval, wzval, zval, zval, zval);
              fail("an exception should have been thrown");
         } catch (MathIllegalArgumentException e) {
             // Expected
         }
         try {
             bcf = new BicubicInterpolatingFunction(xval, yval, zval, wzval, zval, zval);
             fail("an exception should have been thrown");
         } catch (MathIllegalArgumentException e) {
             // Expected
         }
         try {
             bcf = new BicubicInterpolatingFunction(xval, yval, zval, zval, wzval, zval);
             fail("an exception should have been thrown");
         } catch (MathIllegalArgumentException e) {
             // Expected
         }
         try {
             bcf = new BicubicInterpolatingFunction(xval, yval, zval, zval, zval, wzval);
             fail("an exception should have been thrown");
         } catch (MathIllegalArgumentException e) {
             // Expected
         }
 
         wzval = new double[xval.length - 1][yval.length];
         try {
             bcf = new BicubicInterpolatingFunction(xval, yval, wzval, zval, zval, zval);
             fail("an exception should have been thrown");
         } catch (MathIllegalArgumentException e) {
             // Expected
         }
         try {
             bcf = new BicubicInterpolatingFunction(xval, yval, zval, wzval, zval, zval);
             fail("an exception should have been thrown");
         } catch (MathIllegalArgumentException e) {
             // Expected
         }
         try {
             bcf = new BicubicInterpolatingFunction(xval, yval, zval, zval, wzval, zval);
             fail("an exception should have been thrown");
         } catch (MathIllegalArgumentException e) {
             // Expected
         }
         try {
             bcf = new BicubicInterpolatingFunction(xval, yval, zval, zval, zval, wzval);
             fail("an exception should have been thrown");
         } catch (MathIllegalArgumentException e) {
             // Expected
         }
     }
 
     @Test
     void testIsValidPoint() {
         final double xMin = -12;
         final double xMax = 34;
         final double yMin = 5;
         final double yMax = 67;
         final double[] xval = new double[] { xMin, xMax };
         final double[] yval = new double[] { yMin, yMax };
         final double[][] f = new double[][] { { 1, 2 },
                                               { 3, 4 } };
         final double[][] dFdX = f;
         final double[][] dFdY = f;
         final double[][] dFdXdY = f;
 
         final BicubicInterpolatingFunction bcf
             = new BicubicInterpolatingFunction(xval, yval, f,
                                                      dFdX, dFdY, dFdXdY);
 
         double x, y;
 
         x = xMin;
         y = yMin;
         assertTrue(bcf.isValidPoint(x, y));
         // Ensure that no exception is thrown.
         bcf.value(x, y);
 
         x = xMax;
         y = yMax;
         assertTrue(bcf.isValidPoint(x, y));
         // Ensure that no exception is thrown.
         bcf.value(x, y);
 
         final double xRange = xMax - xMin;
         final double yRange = yMax - yMin;
         x = xMin + xRange / 3.4;
         y = yMin + yRange / 1.2;
         assertTrue(bcf.isValidPoint(x, y));
         // Ensure that no exception is thrown.
         bcf.value(x, y);
 
         final double small = 1e-8;
         x = xMin - small;
         y = yMax;
         assertFalse(bcf.isValidPoint(x, y));
         // Ensure that an exception would have been thrown.
         try {
             bcf.value(x, y);
             fail("MathIllegalArgumentException expected");
         } catch (MathIllegalArgumentException expected) {}
 
         x = xMin;
         y = yMax + small;
         assertFalse(bcf.isValidPoint(x, y));
         // Ensure that an exception would have been thrown.
         try {
             bcf.value(x, y);
             fail("MathIllegalArgumentException expected");
         } catch (MathIllegalArgumentException expected) {}
     }
 
     /**
      * Interpolating a plane.
      * <p>
      * z = 2 x - 3 y + 5
      */
     @Test
     void testPlane() {
         final int numberOfElements = 10;
         final double minimumX = -10;
         final double maximumX = 10;
         final double minimumY = -10;
         final double maximumY = 10;
         final int numberOfSamples = 1000;
 
         final double interpolationTolerance = 1e-15;
         final double maxTolerance = 1e-14;
 
         // Function values
         BivariateFunction f = new BivariateFunction() {
                 @Override
                 public double value(double x, double y) {
                     return 2 * x - 3 * y + 5;
                 }
             };
         BivariateFunction dfdx = new BivariateFunction() {
                 @Override
                 public double value(double x, double y) {
                     return 2;
                 }
             };
         BivariateFunction dfdy = new BivariateFunction() {
                 @Override
                 public double value(double x, double y) {
                     return -3;
                 }
             };
         BivariateFunction d2fdxdy = new BivariateFunction() {
                 @Override
                 public double value(double x, double y) {
                     return 0;
                 }
             };
 
         testInterpolation(minimumX,
                           maximumX,
                           minimumY,
                           maximumY,
                           numberOfElements,
                           numberOfSamples,
                           f,
                           dfdx,
                           dfdy,
                           d2fdxdy,
                           interpolationTolerance,
                           maxTolerance,
                           false);
     }
 
     /**
      * Interpolating a paraboloid.
      * <p>
      * z = 2 x<sup>2</sup> - 3 y<sup>2</sup> + 4 x y - 5
      */
     @Test
     void testParaboloid() {
         final int numberOfElements = 10;
         final double minimumX = -10;
         final double maximumX = 10;
         final double minimumY = -10;
         final double maximumY = 10;
         final int numberOfSamples = 1000;
 
         final double interpolationTolerance = 2e-14;
         final double maxTolerance = 1e-12;
 
         // Function values
         BivariateFunction f = new BivariateFunction() {
                 @Override
                 public double value(double x, double y) {
                     return 2 * x * x - 3 * y * y + 4 * x * y - 5;
                 }
             };
         BivariateFunction dfdx = new BivariateFunction() {
                 @Override
                 public double value(double x, double y) {
                     return 4 * (x + y);
                 }
             };
         BivariateFunction dfdy = new BivariateFunction() {
                 @Override
                 public double value(double x, double y) {
                     return 4 * x - 6 * y;
                 }
             };
         BivariateFunction d2fdxdy = new BivariateFunction() {
                 @Override
                 public double value(double x, double y) {
                     return 4;
                 }
             };
 
         testInterpolation(minimumX,
                           maximumX,
                           minimumY,
                           maximumY,
                           numberOfElements,
                           numberOfSamples,
                           f,
                           dfdx,
                           dfdy,
                           d2fdxdy,
                           interpolationTolerance,
                           maxTolerance,
                           false);
     }
 
     /**
      * @param minimumX Lower bound of interpolation range along the x-coordinate.
      * @param maximumX Higher bound of interpolation range along the x-coordinate.
      * @param minimumY Lower bound of interpolation range along the y-coordinate.
      * @param maximumY Higher bound of interpolation range along the y-coordinate.
      * @param numberOfElements Number of data points (along each dimension).
      * @param numberOfSamples Number of test points.
      * @param f Function to test.
      * @param dfdx Partial derivative w.r.t. x of the function to test.
      * @param dfdy Partial derivative w.r.t. y of the function to test.
      * @param d2fdxdy Second partial cross-derivative of the function to test.
      * @param meanTolerance Allowed average error (mean error on all interpolated values).
      * @param maxTolerance Allowed error on each interpolated value.
      */
     private void testInterpolation(double minimumX,
                                    double maximumX,
                                    double minimumY,
                                    double maximumY,
                                    int numberOfElements,
                                    int numberOfSamples,
                                    BivariateFunction f,
                                    BivariateFunction dfdx,
                                    BivariateFunction dfdy,
                                    BivariateFunction d2fdxdy,
                                    double meanTolerance,
                                    double maxTolerance,
                                    boolean print) {
         double expected;
         double actual;
         double currentX;
         double currentY;
         final double deltaX = (maximumX - minimumX) / numberOfElements;
         final double deltaY = (maximumY - minimumY) / numberOfElements;
         final double[] xValues = new double[numberOfElements];
         final double[] yValues = new double[numberOfElements];
         final double[][] zValues = new double[numberOfElements][numberOfElements];
         final double[][] dzdx = new double[numberOfElements][numberOfElements];
         final double[][] dzdy = new double[numberOfElements][numberOfElements];
         final double[][] d2zdxdy = new double[numberOfElements][numberOfElements];
 
         for (int i = 0; i < numberOfElements; i++) {
             xValues[i] = minimumX + deltaX * i;
             final double x = xValues[i];
             for (int j = 0; j < numberOfElements; j++) {
                 yValues[j] = minimumY + deltaY * j;
                 final double y = yValues[j];
                 zValues[i][j] = f.value(x, y);
                 dzdx[i][j] = dfdx.value(x, y);
                 dzdy[i][j] = dfdy.value(x, y);
                 d2zdxdy[i][j] = d2fdxdy.value(x, y);
             }
         }
 
         final BivariateFunction interpolation
             = new BicubicInterpolatingFunction(xValues,
                                                yValues,
                                                zValues,
                                                dzdx,
                                                dzdy,
                                                d2zdxdy);
 
         for (int i = 0; i < numberOfElements; i++) {
             currentX = xValues[i];
             for (int j = 0; j < numberOfElements; j++) {
                 currentY = yValues[j];
                 expected = f.value(currentX, currentY);
                 actual = interpolation.value(currentX, currentY);
                 assertTrue(Precision.equals(expected, actual),
                                   "On data point: " + expected + " != " + actual);
             }
         }
 
         final RandomDataGenerator randomDataGenerator = new RandomDataGenerator(100);
 
         double sumError = 0;
         for (int i = 0; i < numberOfSamples; i++) {
             currentX = randomDataGenerator.nextUniform(xValues[0], xValues[xValues.length - 1]);
             currentY = randomDataGenerator.nextUniform(yValues[0], yValues[yValues.length - 1]);
             expected = f.value(currentX, currentY);
 
             if (print) {
                 System.out.println(currentX + " " + currentY + " -> ");
             }
 
             actual = interpolation.value(currentX, currentY);
             sumError += FastMath.abs(actual - expected);
 
             if (print) {
                 System.out.println(actual + " (diff=" + (expected - actual) + ")");
             }
 
             assertEquals(expected, actual, maxTolerance);
         }
 
         final double meanError = sumError / numberOfSamples;
         assertEquals(0, meanError, meanTolerance);
     }
 }