/*
    * 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.exception.LocalizedCoreFormats;
  import org.hipparchus.exception.MathIllegalArgumentException;
  import org.hipparchus.util.FastMath;
  import org.junit.jupiter.api.Test;
  
  import static org.junit.jupiter.api.Assertions.assertEquals;
  import static org.junit.jupiter.api.Assertions.assertThrows;
  import static org.junit.jupiter.api.Assertions.assertTrue;
  import static org.junit.jupiter.api.Assertions.fail;
  
  /**
   * Test of the LoessInterpolator class.
   */
  class LoessInterpolatorTest {
  
      @Test
      void testOnOnePoint() {
          double[] xval = {0.5};
          double[] yval = {0.7};
          double[] res = new LoessInterpolator().smooth(xval, yval);
          assertEquals(1, res.length);
          assertEquals(0.7, res[0], 0.0);
      }
  
      @Test
      void testOnTwoPoints() {
          double[] xval = {0.5, 0.6};
          double[] yval = {0.7, 0.8};
          double[] res = new LoessInterpolator().smooth(xval, yval);
          assertEquals(2, res.length);
          assertEquals(0.7, res[0], 0.0);
          assertEquals(0.8, res[1], 0.0);
      }
  
      @Test
      void testOnStraightLine() {
          double[] xval = {1,2,3,4,5};
          double[] yval = {2,4,6,8,10};
          LoessInterpolator li = new LoessInterpolator(0.6, 2, 1e-12);
          double[] res = li.smooth(xval, yval);
          assertEquals(5, res.length);
          for(int i = 0; i < 5; ++i) {
              assertEquals(yval[i], res[i], 1e-8);
          }
      }
  
      @Test
      void testOnDistortedSine() {
          int numPoints = 100;
          double[] xval = new double[numPoints];
          double[] yval = new double[numPoints];
          double xnoise = 0.1;
          double ynoise = 0.2;
  
          generateSineData(xval, yval, xnoise, ynoise);
  
          LoessInterpolator li = new LoessInterpolator(0.3, 4, 1e-12);
  
          double[] res = li.smooth(xval, yval);
  
          // Check that the resulting curve differs from
          // the "real" sine less than the jittered one
  
          double noisyResidualSum = 0;
          double fitResidualSum = 0;
  
          for(int i = 0; i < numPoints; ++i) {
              double expected = FastMath.sin(xval[i]);
              double noisy = yval[i];
              double fit = res[i];
  
              noisyResidualSum += FastMath.pow(noisy - expected, 2);
              fitResidualSum += FastMath.pow(fit - expected, 2);
          }
  
          assertTrue(fitResidualSum < noisyResidualSum);
     }
 
     @Test
     void testIncreasingBandwidthIncreasesSmoothness() {
         int numPoints = 100;
         double[] xval = new double[numPoints];
         double[] yval = new double[numPoints];
         double xnoise = 0.1;
         double ynoise = 0.1;
 
         generateSineData(xval, yval, xnoise, ynoise);
 
         // Check that variance decreases as bandwidth increases
 
         double[] bandwidths = {0.1, 0.5, 1.0};
         double[] variances = new double[bandwidths.length];
         for (int i = 0; i < bandwidths.length; i++) {
             double bw = bandwidths[i];
 
             LoessInterpolator li = new LoessInterpolator(bw, 4, 1e-12);
 
             double[] res = li.smooth(xval, yval);
 
             for (int j = 1; j < res.length; ++j) {
                 variances[i] += FastMath.pow(res[j] - res[j-1], 2);
             }
         }
 
         for(int i = 1; i < variances.length; ++i) {
             assertTrue(variances[i] < variances[i-1]);
         }
     }
 
     @Test
     void testIncreasingRobustnessItersIncreasesSmoothnessWithOutliers() {
         int numPoints = 100;
         double[] xval = new double[numPoints];
         double[] yval = new double[numPoints];
         double xnoise = 0.1;
         double ynoise = 0.1;
 
         generateSineData(xval, yval, xnoise, ynoise);
 
         // Introduce a couple of outliers
         yval[numPoints/3] *= 100;
         yval[2 * numPoints/3] *= -100;
 
         // Check that variance decreases as the number of robustness
         // iterations increases
 
         double[] variances = new double[4];
         for (int i = 0; i < 4; i++) {
             LoessInterpolator li = new LoessInterpolator(0.3, i, 1e-12);
 
             double[] res = li.smooth(xval, yval);
 
             for (int j = 1; j < res.length; ++j) {
                 variances[i] += FastMath.abs(res[j] - res[j-1]);
             }
         }
 
         for(int i = 1; i < variances.length; ++i) {
             assertTrue(variances[i] < variances[i-1]);
         }
     }
 
     @Test
     void testUnequalSizeArguments() {
         assertThrows(MathIllegalArgumentException.class, () -> {
             new LoessInterpolator().smooth(new double[]{1, 2, 3}, new double[]{1, 2, 3, 4});
         });
     }
 
     @Test
     void testEmptyData() {
         assertThrows(MathIllegalArgumentException.class, () -> {
             new LoessInterpolator().smooth(new double[]{}, new double[]{});
         });
     }
 
     @Test
     void testNonStrictlyIncreasing1() {
         assertThrows(MathIllegalArgumentException.class, () -> {
             new LoessInterpolator().smooth(new double[]{4, 3, 1, 2}, new double[]{3, 4, 5, 6});
         });
     }
 
     @Test
     void testNonStrictlyIncreasing2() {
         assertThrows(MathIllegalArgumentException.class, () -> {
             new LoessInterpolator().smooth(new double[]{1, 2, 2, 3}, new double[]{3, 4, 5, 6});
         });
     }
 
     @Test
     void testNotAllFiniteReal1() {
         try {
             new LoessInterpolator().smooth(new double[] {1,2,Double.NaN}, new double[] {3,4,5});
             fail("an exception should have been thrown");
         } catch (MathIllegalArgumentException e) {
             assertEquals(LocalizedCoreFormats.NOT_FINITE_NUMBER, e.getSpecifier());
         }
     }
 
     @Test
     void testNotAllFiniteReal2() {
         try {
             new LoessInterpolator().smooth(new double[] {1,2,Double.POSITIVE_INFINITY}, new double[] {3,4,5});
         } catch (MathIllegalArgumentException e) {
             assertEquals(LocalizedCoreFormats.NOT_FINITE_NUMBER, e.getSpecifier());
         }
     }
 
     @Test
     void testNotAllFiniteReal3() {
         try {
             new LoessInterpolator().smooth(new double[] {1,2,Double.NEGATIVE_INFINITY}, new double[] {3,4,5});
         } catch (MathIllegalArgumentException e) {
             assertEquals(LocalizedCoreFormats.NOT_FINITE_NUMBER, e.getSpecifier());
         }
     }
 
     @Test
     void testNotAllFiniteReal4() {
         try {
             new LoessInterpolator().smooth(new double[] {3,4,5}, new double[] {1,2,Double.NaN});
         } catch (MathIllegalArgumentException e) {
             assertEquals(LocalizedCoreFormats.NOT_FINITE_NUMBER, e.getSpecifier());
         }
     }
 
     @Test
     void testNotAllFiniteReal5() {
         try {
             new LoessInterpolator().smooth(new double[] {3,4,5}, new double[] {1,2,Double.POSITIVE_INFINITY});
         } catch (MathIllegalArgumentException e) {
             assertEquals(LocalizedCoreFormats.NOT_FINITE_NUMBER, e.getSpecifier());
         }
     }
 
     @Test
     void testNotAllFiniteReal6() {
         try {
             new LoessInterpolator().smooth(new double[] {3,4,5}, new double[] {1,2,Double.NEGATIVE_INFINITY});
         } catch (MathIllegalArgumentException e) {
             assertEquals(LocalizedCoreFormats.NOT_FINITE_NUMBER, e.getSpecifier());
         }
     }
 
     @Test
     void testInsufficientBandwidth() {
         assertThrows(MathIllegalArgumentException.class, () -> {
             LoessInterpolator li = new LoessInterpolator(0.1, 3, 1e-12);
             li.smooth(new double[]{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12}, new double[]{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12});
         });
     }
 
     @Test
     void testCompletelyIncorrectBandwidth1() {
         assertThrows(MathIllegalArgumentException.class, () -> {
             new LoessInterpolator(-0.2, 3, 1e-12);
         });
     }
 
     @Test
     void testCompletelyIncorrectBandwidth2() {
         assertThrows(MathIllegalArgumentException.class, () -> {
             new LoessInterpolator(1.1, 3, 1e-12);
         });
     }
 
     @Test
     void testMath296withoutWeights() {
         double[] xval = {
                 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0,
                  1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0};
         double[] yval = {
                 0.47, 0.48, 0.55, 0.56, -0.08, -0.04, -0.07, -0.07,
                 -0.56, -0.46, -0.56, -0.52, -3.03, -3.08, -3.09,
                 -3.04, 3.54, 3.46, 3.36, 3.35};
         // Output from R, rounded to .001
         double[] yref = {
                 0.461, 0.499, 0.541, 0.308, 0.175, -0.042, -0.072,
                 -0.196, -0.311, -0.446, -0.557, -1.497, -2.133,
                 -3.08, -3.09, -0.621, 0.982, 3.449, 3.389, 3.336
         };
         LoessInterpolator li = new LoessInterpolator(0.3, 4, 1e-12);
         double[] res = li.smooth(xval, yval);
         assertEquals(xval.length, res.length);
         for(int i = 0; i < res.length; ++i) {
             assertEquals(yref[i], res[i], 0.02);
         }
     }
 
     private void generateSineData(double[] xval, double[] yval, double xnoise, double ynoise) {
         double dx = 2 * FastMath.PI / xval.length;
         double x = 0;
         for(int i = 0; i < xval.length; ++i) {
             xval[i] = x;
             yval[i] = FastMath.sin(x) + (2 * FastMath.random() - 1) * ynoise;
             x += dx * (1 + (2 * FastMath.random() - 1) * xnoise);
         }
     }
 }