/*
    * 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.stat.fitting;
  
  import org.hipparchus.UnitTestUtils;
  import org.hipparchus.analysis.UnivariateFunction;
  import org.hipparchus.analysis.integration.BaseAbstractUnivariateIntegrator;
  import org.hipparchus.analysis.integration.IterativeLegendreGaussIntegrator;
  import org.hipparchus.distribution.RealDistribution;
  import org.hipparchus.distribution.continuous.ConstantRealDistribution;
  import org.hipparchus.distribution.continuous.NormalDistribution;
  import org.hipparchus.distribution.continuous.RealDistributionAbstractTest;
  import org.hipparchus.distribution.continuous.UniformRealDistribution;
  import org.hipparchus.exception.MathIllegalArgumentException;
  import org.hipparchus.exception.MathIllegalStateException;
  import org.hipparchus.exception.NullArgumentException;
  import org.hipparchus.stat.descriptive.StreamingStatistics;
  import org.hipparchus.util.FastMath;
  import org.junit.jupiter.api.BeforeEach;
  import org.junit.jupiter.api.Test;
  
  import java.io.BufferedReader;
  import java.io.File;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.net.URISyntaxException;
  import java.net.URL;
  import java.util.ArrayList;
  import java.util.Arrays;
  
  import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
  import static org.junit.jupiter.api.Assertions.assertEquals;
  import static org.junit.jupiter.api.Assertions.assertFalse;
  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 cases for the EmpiricalDistribution class
   */
  public final class EmpiricalDistributionTest extends RealDistributionAbstractTest {
  
      protected EmpiricalDistribution empiricalDistribution = null;
      protected EmpiricalDistribution empiricalDistribution2 = null;
      protected File file = null;
      protected URL url = null;
      protected double[] dataArray = null;
      protected final int n = 10000;
  
      @Override
      @BeforeEach
      public void setUp() {
          super.setUp();
          empiricalDistribution = new EmpiricalDistribution(100);
          url = getClass().getResource("testData.txt");
          final ArrayList<Double> list = new ArrayList<>();
          assertDoesNotThrow(() -> {
              empiricalDistribution2 = new EmpiricalDistribution(100);
              BufferedReader in =
                  new BufferedReader(new InputStreamReader(
                      url.openStream()));
              String str = null;
              while ((str = in.readLine()) != null) {
                  list.add(Double.valueOf(str));
              }
              in.close();
              in = null;
          }, "IOException ");
  
          dataArray = new double[list.size()];
          int i = 0;
          for (Double data : list) {
              dataArray[i] = data.doubleValue();
              i++;
          }
      }
  
      // MATH-1279
      @Test
      void testPrecondition1() {
         assertThrows(MathIllegalArgumentException.class, () -> {
             new EmpiricalDistribution(0);
         });
     }
 
     /**
      * Test EmpiricalDistrbution.load() using sample data file.<br>
      * Check that the sampleCount, mu and sigma match data in
      * the sample data file. Also verify that load is idempotent.
      */
     @Test
     void testLoad() throws Exception {
         // Load from a URL
         empiricalDistribution.load(url);
         checkDistribution();
 
         // Load again from a file (also verifies idempotency of load)
         File file = new File(url.toURI());
         empiricalDistribution.load(file);
         checkDistribution();
     }
 
     private void checkDistribution() {
         // testData File has 10000 values, with mean ~ 5.0, std dev ~ 1
         // Make sure that loaded distribution matches this
         assertEquals(1000, empiricalDistribution.getSampleStats().getN(), 10E-7);
         //TODO: replace with statistical tests
         assertEquals(
             5.069831575018909, empiricalDistribution.getSampleStats().getMean(), 10E-7);
         assertEquals(
             1.0173699343977738, empiricalDistribution.getSampleStats().getStandardDeviation(), 10E-7);
     }
 
     @Test
     void testLoadURLError() throws IOException {
         try {
             URL existing = getClass().getResource("testData.txt");
             URL nonexistent = new URL(existing.toString() + "-nonexistent");
             empiricalDistribution.load(nonexistent);
             fail("an exception should have been thrown");
         } catch (IOException ioe) {
             // expected
         }
     }
 
     @Test
     void testLoadFileError() throws IOException, URISyntaxException {
         try {
             File existing = new File(getClass().getResource("testData.txt").toURI());
             File nonexistent = new File(existing.getAbsolutePath() + "-nonexistent");
             empiricalDistribution.load(nonexistent);
             fail("an exception should have been thrown");
         } catch (IOException ioe) {
             // expected
         }
     }
 
     /**
      * Test EmpiricalDistrbution.load(double[]) using data taken from
      * sample data file.<br>
      * Check that the sampleCount, mu and sigma match data in
      * the sample data file.
      */
     @Test
     void testDoubleLoad() throws Exception {
         empiricalDistribution2.load(dataArray);
         // testData File has 10000 values, with mean ~ 5.0, std dev ~ 1
         // Make sure that loaded distribution matches this
         assertEquals(1000, empiricalDistribution2.getSampleStats().getN(), 10E-7);
         //TODO: replace with statistical tests
         assertEquals(
             5.069831575018909, empiricalDistribution2.getSampleStats().getMean(), 10E-7);
         assertEquals(
             1.0173699343977738, empiricalDistribution2.getSampleStats().getStandardDeviation(), 10E-7);
 
         double[] bounds = empiricalDistribution2.getGeneratorUpperBounds();
         assertEquals(100, bounds.length);
         assertEquals(1.0, bounds[99], 10e-12);
 
     }
 
     /**
       * Generate 1000 random values and make sure they look OK.<br>
       * Note that there is a non-zero (but very small) probability that
       * these tests will fail even if the code is working as designed.
       */
     @Test
     void testNext() throws Exception {
         tstGen(0.1);
         tstDoubleGen(0.1);
     }
 
     /**
       * Make sure exception thrown if digest getNext is attempted
       * before loading empiricalDistribution.
      */
     @Test
     void testNexFail() {
         try {
             empiricalDistribution.getNextValue();
             empiricalDistribution2.getNextValue();
             fail("Expecting MathIllegalStateException");
         } catch (MathIllegalStateException ex) {
             // expected
         }
     }
 
     /**
      * Make sure we can handle a grid size that is too fine
      */
     @Test
     void testGridTooFine() throws Exception {
         empiricalDistribution = new EmpiricalDistribution(1001);
         tstGen(0.1);
         empiricalDistribution2 = new EmpiricalDistribution(1001);
         tstDoubleGen(0.1);
     }
 
     /**
      * How about too fat?
      */
     @Test
     void testGridTooFat() throws Exception {
         empiricalDistribution = new EmpiricalDistribution(1);
         tstGen(5); // ridiculous tolerance; but ridiculous grid size
                    // really just checking to make sure we do not bomb
         empiricalDistribution2 = new EmpiricalDistribution(1);
         tstDoubleGen(5);
     }
 
     /**
      * Test bin index overflow problem (BZ 36450)
      */
     @Test
     void testBinIndexOverflow() throws Exception {
         double[] x = new double[] {9474.94326071674, 2080107.8865462579};
         new EmpiricalDistribution().load(x);
     }
 
     @Test
     void testSerialization() {
         // Empty
         EmpiricalDistribution dist = new EmpiricalDistribution();
         EmpiricalDistribution dist2 = (EmpiricalDistribution) UnitTestUtils.serializeAndRecover(dist);
         verifySame(dist, dist2);
 
         // Loaded
         empiricalDistribution2.load(dataArray);
         dist2 = (EmpiricalDistribution) UnitTestUtils.serializeAndRecover(empiricalDistribution2);
         verifySame(empiricalDistribution2, dist2);
     }
 
     @Test
     void testLoadNullDoubleArray() {
         assertThrows(NullArgumentException.class, () -> {
             new EmpiricalDistribution().load((double[]) null);
         });
     }
 
     @Test
     void testLoadNullURL() throws Exception {
         assertThrows(NullArgumentException.class, () -> {
             new EmpiricalDistribution().load((URL) null);
         });
     }
 
     @Test
     void testLoadNullFile() throws Exception {
         assertThrows(NullArgumentException.class, () -> {
             new EmpiricalDistribution().load((File) null);
         });
     }
 
     /**
      * MATH-298
      */
     @Test
     void testGetBinUpperBounds() {
         double[] testData = {0, 1, 1, 2, 3, 4, 4, 5, 6, 7, 8, 9, 10};
         EmpiricalDistribution dist = new EmpiricalDistribution(5);
         dist.load(testData);
         double[] expectedBinUpperBounds = {2, 4, 6, 8, 10};
         double[] expectedGeneratorUpperBounds = {4d/13d, 7d/13d, 9d/13d, 11d/13d, 1};
         double tol = 10E-12;
         UnitTestUtils.customAssertEquals(expectedBinUpperBounds, dist.getUpperBounds(), tol);
         UnitTestUtils.customAssertEquals(expectedGeneratorUpperBounds, dist.getGeneratorUpperBounds(), tol);
     }
 
     @Test
     void testReSeed() throws Exception {
         empiricalDistribution.load(url);
         empiricalDistribution.reSeed(100);
         final double [] values = new double[10];
         for (int i = 0; i < 10; i++) {
             values[i] = empiricalDistribution.getNextValue();
         }
         empiricalDistribution.reSeed(100);
         for (int i = 0; i < 10; i++) {
             assertEquals(values[i],empiricalDistribution.getNextValue(), 0d);
         }
     }
 
     private void verifySame(EmpiricalDistribution d1, EmpiricalDistribution d2) {
         assertEquals(d1.isLoaded(), d2.isLoaded());
         assertEquals(d1.getBinCount(), d2.getBinCount());
         assertEquals(d1.getSampleStats(), d2.getSampleStats());
         if (d1.isLoaded()) {
             for (int i = 0;  i < d1.getUpperBounds().length; i++) {
                 assertEquals(d1.getUpperBounds()[i], d2.getUpperBounds()[i], 0);
             }
             assertEquals(d1.getBinStats(), d2.getBinStats());
         }
     }
 
     private void tstGen(double tolerance)throws Exception {
         empiricalDistribution.load(url);
         empiricalDistribution.reSeed(1000);
         StreamingStatistics stats = new StreamingStatistics();
         for (int i = 1; i < 1000; i++) {
             stats.addValue(empiricalDistribution.getNextValue());
         }
         assertEquals(5.069831575018909, stats.getMean(),tolerance,"mean");
         assertEquals(1.0173699343977738, stats.getStandardDeviation(),tolerance,"std dev");
     }
 
     private void tstDoubleGen(double tolerance)throws Exception {
         empiricalDistribution2.load(dataArray);
         empiricalDistribution2.reSeed(1000);
         StreamingStatistics stats = new StreamingStatistics();
         for (int i = 1; i < 1000; i++) {
             stats.addValue(empiricalDistribution2.getNextValue());
         }
         assertEquals(5.069831575018909, stats.getMean(), tolerance, "mean");
         assertEquals(1.0173699343977738, stats.getStandardDeviation(), tolerance, "std dev");
     }
 
     //  Setup for distribution tests
 
     @Override
     public RealDistribution makeDistribution() {
         // Create a uniform distribution on [0, 10,000]
         final double[] sourceData = new double[n + 1];
         for (int i = 0; i < n + 1; i++) {
             sourceData[i] = i;
         }
         EmpiricalDistribution dist = new EmpiricalDistribution();
         dist.load(sourceData);
         return dist;
     }
 
     /** Uniform bin mass = 10/10001 == mass of all but the first bin */
     private final double binMass = 10d / (n + 1);
 
     /** Mass of first bin = 11/10001 */
     private final double firstBinMass = 11d / (n + 1);
 
     @Override
     public double[] makeCumulativeTestPoints() {
        final double[] testPoints = new double[] {9, 10, 15, 1000, 5004, 9999};
        return testPoints;
     }
 
 
     @Override
     public double[] makeCumulativeTestValues() {
         /*
          * Bins should be [0, 10], (10, 20], ..., (9990, 10000]
          * Kernels should be N(4.5, 3.02765), N(14.5, 3.02765)...
          * Each bin should have mass 10/10000 = .001
          */
         final double[] testPoints = getCumulativeTestPoints();
         final double[] cumValues = new double[testPoints.length];
         final EmpiricalDistribution empiricalDistribution = (EmpiricalDistribution) makeDistribution();
         final double[] binBounds = empiricalDistribution.getUpperBounds();
         for (int i = 0; i < testPoints.length; i++) {
             final int bin = findBin(testPoints[i]);
             final double lower = bin == 0 ? empiricalDistribution.getSupportLowerBound() :
                 binBounds[bin - 1];
             final double upper = binBounds[bin];
             // Compute bMinus = sum or mass of bins below the bin containing the point
             // First bin has mass 11 / 10000, the rest have mass 10 / 10000.
             final double bMinus = bin == 0 ? 0 : (bin - 1) * binMass + firstBinMass;
             final RealDistribution kernel = findKernel(lower, upper);
             final double withinBinKernelMass = kernel.probability(lower, upper);
             final double kernelCum = kernel.probability(lower, testPoints[i]);
             cumValues[i] = bMinus + (bin == 0 ? firstBinMass : binMass) * kernelCum/withinBinKernelMass;
         }
         return cumValues;
     }
 
     @Override
     public double[] makeDensityTestValues() {
         final double[] testPoints = getCumulativeTestPoints();
         final double[] densityValues = new double[testPoints.length];
         final EmpiricalDistribution empiricalDistribution = (EmpiricalDistribution) makeDistribution();
         final double[] binBounds = empiricalDistribution.getUpperBounds();
         for (int i = 0; i < testPoints.length; i++) {
             final int bin = findBin(testPoints[i]);
             final double lower = bin == 0 ? empiricalDistribution.getSupportLowerBound() :
                 binBounds[bin - 1];
             final double upper = binBounds[bin];
             final RealDistribution kernel = findKernel(lower, upper);
             final double withinBinKernelMass = kernel.probability(lower, upper);
             final double density = kernel.density(testPoints[i]);
             densityValues[i] = density * (bin == 0 ? firstBinMass : binMass) / withinBinKernelMass;
         }
         return densityValues;
     }
 
     /**
      * Modify test integration bounds from the default. Because the distribution
      * has discontinuities at bin boundaries, integrals spanning multiple bins
      * will face convergence problems.  Only test within-bin integrals and spans
      * across no more than 3 bin boundaries.
      */
     @Override
     @Test
     public void testDensityIntegrals() {
         final RealDistribution distribution = makeDistribution();
         final double tol = 1.0e-9;
         final BaseAbstractUnivariateIntegrator integrator =
             new IterativeLegendreGaussIntegrator(5, 1.0e-12, 1.0e-10);
         final UnivariateFunction d = new UnivariateFunction() {
             @Override
             public double value(double x) {
                 return distribution.density(x);
             }
         };
         final double[] lower = {0, 5, 1000, 5001, 9995};
         final double[] upper = {5, 12, 1030, 5010, 10000};
         for (int i = 1; i < 5; i++) {
             assertEquals(
                     distribution.probability(
                             lower[i], upper[i]),
                             integrator.integrate(
                                     1000000, // Triangle integrals are very slow to converge
                                     d, lower[i], upper[i]), tol);
         }
     }
 
     /**
      * MATH-984
      * Verify that sampled values do not go outside of the range of the data.
      */
     @Test
     void testSampleValuesRange() {
         // Concentrate values near the endpoints of (0, 1).
         // Unconstrained Gaussian kernel would generate values outside the interval.
         final double[] data = new double[100];
         for (int i = 0; i < 50; i++) {
             data[i] = 1 / ((double) i + 1);
         }
         for (int i = 51; i < 100; i++) {
             data[i] = 1 - 1 / (100 - (double) i + 2);
         }
         EmpiricalDistribution dist = new EmpiricalDistribution(10);
         dist.load(data);
         dist.reseedRandomGenerator(1000);
         for (int i = 0; i < 1000; i++) {
             final double dev = dist.getNextValue();
             assertTrue(dev < 1);
             assertTrue(dev > 0);
         }
     }
 
     /**
      * MATH-1203, MATH-1208
      */
     @Test
     void testNoBinVariance() {
         final double[] data = {0, 0, 1, 1};
         EmpiricalDistribution dist = new EmpiricalDistribution(2);
         dist.load(data);
         dist.reseedRandomGenerator(1000);
         for (int i = 0; i < 1000; i++) {
             final double dev = dist.getNextValue();
             assertTrue(dev == 0 || dev == 1);
         }
         assertEquals(0.5, dist.cumulativeProbability(0), Double.MIN_VALUE);
         assertEquals(1.0, dist.cumulativeProbability(1), Double.MIN_VALUE);
         assertEquals(0.5, dist.cumulativeProbability(0.5), Double.MIN_VALUE);
         assertEquals(0.5, dist.cumulativeProbability(0.7), Double.MIN_VALUE);
     }
 
     /**
      * Find the bin that x belongs (relative to {@link #makeDistribution()}).
      */
     private int findBin(double x) {
         // Number of bins below x should be trunc(x/10)
         final double nMinus = FastMath.floor(x / 10);
         final int bin =  (int) FastMath.round(nMinus);
         // If x falls on a bin boundary, it is in the lower bin
         return FastMath.floor(x / 10) == x / 10 ? bin - 1 : bin;
     }
 
     /**
      * Find the within-bin kernel for the bin with lower bound lower
      * and upper bound upper. All bins other than the first contain 10 points
      * exclusive of the lower bound and are centered at (lower + upper + 1) / 2.
      * The first bin includes its lower bound, 0, so has different mean and
      * standard deviation.
      */
     private RealDistribution findKernel(double lower, double upper) {
         if (lower < 1) {
             return new NormalDistribution(5d, 3.3166247903554);
         } else {
             return new NormalDistribution((upper + lower + 1) / 2d, 3.0276503540974917);
         }
     }
 
     @Test
     void testKernelOverrideConstant() {
         final EmpiricalDistribution dist = new ConstantKernelEmpiricalDistribution(5);
         final double[] data = {1d,2d,3d, 4d,5d,6d, 7d,8d,9d, 10d,11d,12d, 13d,14d,15d};
         dist.load(data);
         // Bin masses concentrated on 2, 5, 8, 11, 14 <- effectively discrete uniform distribution over these
         double[] values = {2d, 5d, 8d, 11d, 14d};
         for (int i = 0; i < 20; i++) {
             assertTrue(Arrays.binarySearch(values, dist.getNextValue()) >= 0);
         }
         final double tol = 10E-12;
         assertEquals(0.0, dist.cumulativeProbability(1), tol);
         assertEquals(0.2, dist.cumulativeProbability(2), tol);
         assertEquals(0.6, dist.cumulativeProbability(10), tol);
         assertEquals(0.8, dist.cumulativeProbability(12), tol);
         assertEquals(0.8, dist.cumulativeProbability(13), tol);
         assertEquals(1.0, dist.cumulativeProbability(15), tol);
 
         assertEquals(2.0, dist.inverseCumulativeProbability(0.1), tol);
         assertEquals(2.0, dist.inverseCumulativeProbability(0.2), tol);
         assertEquals(5.0, dist.inverseCumulativeProbability(0.3), tol);
         assertEquals(5.0, dist.inverseCumulativeProbability(0.4), tol);
         assertEquals(8.0, dist.inverseCumulativeProbability(0.5), tol);
         assertEquals(8.0, dist.inverseCumulativeProbability(0.6), tol);
     }
 
     @Test
     void testKernelOverrideUniform() {
         final EmpiricalDistribution dist = new UniformKernelEmpiricalDistribution(5);
         final double[] data = {1d,2d,3d, 4d,5d,6d, 7d,8d,9d, 10d,11d,12d, 13d,14d,15d};
         dist.load(data);
         // Kernels are uniform distributions on [1,3], [4,6], [7,9], [10,12], [13,15]
         final double[] bounds = {3d, 6d, 9d, 12d};
         final double tol = 10E-12;
         for (int i = 0; i < 20; i++) {
             final double v = dist.getNextValue();
             // Make sure v is not in the excluded range between bins - that is (bounds[i], bounds[i] + 1)
             for (int j = 0; j < bounds.length; j++) {
                 assertFalse(v > bounds[j] + tol && v < bounds[j] + 1 - tol);
             }
         }
         assertEquals(0.0, dist.cumulativeProbability(1), tol);
         assertEquals(0.1, dist.cumulativeProbability(2), tol);
         assertEquals(0.6, dist.cumulativeProbability(10), tol);
         assertEquals(0.8, dist.cumulativeProbability(12), tol);
         assertEquals(0.8, dist.cumulativeProbability(13), tol);
         assertEquals(1.0, dist.cumulativeProbability(15), tol);
 
         assertEquals(2.0, dist.inverseCumulativeProbability(0.1), tol);
         assertEquals(3.0, dist.inverseCumulativeProbability(0.2), tol);
         assertEquals(5.0, dist.inverseCumulativeProbability(0.3), tol);
         assertEquals(6.0, dist.inverseCumulativeProbability(0.4), tol);
         assertEquals(8.0, dist.inverseCumulativeProbability(0.5), tol);
         assertEquals(9.0, dist.inverseCumulativeProbability(0.6), tol);
     }
 
     @Test
     void testEmptyBins() {
         double[] data = new double[10];
         for (int i = 0; i < 10; ++i) {
             data[i] = i < 5 ? 0 : 1;
         }
         EmpiricalDistribution edist = new EmpiricalDistribution(100);
         edist.load(data);
         assertEquals(0.5, edist.cumulativeProbability(0), Double.MIN_VALUE);
         assertEquals(0.5, edist.cumulativeProbability(0.3), Double.MIN_VALUE);
         assertEquals(0.5, edist.cumulativeProbability(0.9), Double.MIN_VALUE);
         assertEquals(1, edist.cumulativeProbability(1), Double.MIN_VALUE);
         assertEquals(1, edist.cumulativeProbability(1.5), Double.MIN_VALUE);
     }
 
 
     /**
      * Empirical distribution using a constant smoothing kernel.
      */
     private class ConstantKernelEmpiricalDistribution extends EmpiricalDistribution {
         private static final long serialVersionUID = 1L;
         public ConstantKernelEmpiricalDistribution(int i) {
             super(i);
         }
         // Use constant distribution equal to bin mean within bin
         @Override
         protected RealDistribution getKernel(StreamingStatistics bStats) {
             return new ConstantRealDistribution(bStats.getMean());
         }
     }
 
     /**
      * Empirical distribution using a uniform smoothing kernel.
      */
     private class UniformKernelEmpiricalDistribution extends EmpiricalDistribution {
         private static final long serialVersionUID = 2963149194515159653L;
         public UniformKernelEmpiricalDistribution(int i) {
             super(i);
         }
         @Override
         protected RealDistribution getKernel(StreamingStatistics bStats) {
             return new UniformRealDistribution(bStats.getMin(), bStats.getMax());
         }
     }
 }