/*
    * 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
    *
    *      http://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.
   */
  package org.apache.commons.rng.sampling.shape;
  
  import java.util.Arrays;
  import java.util.stream.DoubleStream;
  import org.apache.commons.rng.UniformRandomProvider;
  import org.apache.commons.rng.sampling.RandomAssert;
  import org.apache.commons.rng.sampling.UnitSphereSampler;
  import org.junit.jupiter.api.Assertions;
  import org.junit.jupiter.api.Test;
  
  /**
   * Test for {@link LineSampler}.
   */
  class LineSamplerTest {
      /**
       * Test an unsupported dimension.
       */
      @Test
      void testInvalidDimensionThrows() {
          final UniformRandomProvider rng = RandomAssert.seededRNG();
          Assertions.assertThrows(IllegalArgumentException.class,
              () -> LineSampler.of(rng, new double[0], new double[0]));
      }
  
      /**
       * Test a dimension mismatch between vertices.
       */
      @Test
      void testDimensionMismatchThrows() {
          final UniformRandomProvider rng = RandomAssert.seededRNG();
          final double[] c2 = new double[2];
          final double[] c3 = new double[3];
          for (double[][] c : new double[][][] {
              {c2, c3},
              {c3, c2},
          }) {
              Assertions.assertThrows(IllegalArgumentException.class,
                  () -> LineSampler.of(rng, c[0], c[1]),
                  () -> String.format("Did not detect dimension mismatch: %d,%d",
                      c[0].length, c[1].length));
          }
      }
  
      /**
       * Test non-finite vertices.
       */
      @Test
      void testNonFiniteVertexCoordinates() {
          final UniformRandomProvider rng = RandomAssert.seededRNG();
          // A valid line
          final double[][] c = new double[][] {
              {0, 1, 2}, {-1, 2, 3}
          };
          Assertions.assertNotNull(LineSampler.of(rng, c[0],  c[1]));
          final double[] bad = {Double.POSITIVE_INFINITY, Double.NEGATIVE_INFINITY, Double.NaN};
          for (int i = 0; i < c.length; i++) {
              final int ii = i;
              for (int j = 0; j < c[0].length; j++) {
                  final int jj = j;
                  for (final double d : bad) {
                      final double value = c[i][j];
                      c[i][j] = d;
                      Assertions.assertThrows(IllegalArgumentException.class,
                          () -> LineSampler.of(rng, c[0], c[1]),
                          () -> String.format("Did not detect non-finite coordinate: %d,%d = %s",
                              ii, jj, d));
                      c[i][j] = value;
                  }
              }
          }
      }
  
      /**
       * Test a line with coordinates that are separated by more than
       * {@link Double#MAX_VALUE} in 1D.
       */
      @Test
      void testExtremeValueCoordinates1D() {
          testExtremeValueCoordinates(1);
      }
  
      /**
       * Test a line with coordinates that are separated by more than
      * {@link Double#MAX_VALUE} in 2D.
      */
     @Test
     void testExtremeValueCoordinates2D() {
         testExtremeValueCoordinates(2);
     }
 
     /**
      * Test a line with coordinates that are separated by more than
      * {@link Double#MAX_VALUE} in 3D.
      */
     @Test
     void testExtremeValueCoordinates3D() {
         testExtremeValueCoordinates(3);
     }
 
     /**
      * Test a line with coordinates that are separated by more than
      * {@link Double#MAX_VALUE} in 4D.
      */
     @Test
     void testExtremeValueCoordinates4D() {
         testExtremeValueCoordinates(4);
     }
 
     /**
      * Test a line with coordinates that are separated by more than
      * {@link Double#MAX_VALUE}.
      *
      * @param dimension the dimension
      */
     private static void testExtremeValueCoordinates(int dimension) {
         final double[][] c1 = new double[2][dimension];
         final double[][] c2 = new double[2][dimension];
         // Create a valid line that can be scaled
         Arrays.fill(c1[0], -1);
         Arrays.fill(c1[1], 1);
         // Extremely large value for scaling. Use a power of 2 for exact scaling.
         final double scale = 0x1.0p1023;
         for (int i = 0; i < c1.length; i++) {
             // Scale the second line
             for (int j = 0; j < dimension; j++) {
                 c2[i][j] = c1[i][j] * scale;
             }
         }
         // Show the line is too big to compute vectors between points.
         Assertions.assertEquals(Double.POSITIVE_INFINITY, c2[1][0] - c2[0][0],
             "Expect vector b - a to be infinite in the x dimension");
 
         final LineSampler sampler1 = LineSampler.of(
             RandomAssert.seededRNG(), c1[0], c1[1]);
         final LineSampler sampler2 = LineSampler.of(
             RandomAssert.seededRNG(), c2[0], c2[1]);
 
         for (int n = 0; n < 10; n++) {
             final double[] a = sampler1.sample();
             final double[] b = sampler2.sample();
             for (int i = 0; i < a.length; i++) {
                 a[i] *= scale;
             }
             Assertions.assertArrayEquals(a, b);
         }
     }
 
     /**
      * Test the distribution of points in 1D.
      */
     @Test
     void testDistribution1D() {
         testDistributionND(1);
     }
 
     /**
      * Test the distribution of points in 2D.
      */
     @Test
     void testDistribution2D() {
         testDistributionND(2);
     }
 
     /**
      * Test the distribution of points in 3D.
      */
     @Test
     void testDistribution3D() {
         testDistributionND(3);
     }
 
     /**
      * Test the distribution of points in 4D.
      */
     @Test
     void testDistribution4D() {
         testDistributionND(4);
     }
 
     /**
      * Test the distribution of points in N dimensions. The output coordinates
      * should be uniform in the line.
      *
      * @param dimension the dimension
      */
     private static void testDistributionND(int dimension) {
         final UniformRandomProvider rng = RandomAssert.createRNG();
 
         double[] a;
         double[] b;
         if (dimension == 1) {
             a = new double[] {rng.nextDouble()};
             b = new double[] {-rng.nextDouble()};
         } else {
             final UnitSphereSampler sphere = UnitSphereSampler.of(rng, dimension);
             a = sphere.sample();
             b = sphere.sample();
         }
 
         // To test uniformity on the line all fractional lengths along each dimension
         // should be the same constant:
         // x - a
         // ----- = C
         // b - a
         // This should be uniformly distributed in the range [0, 1].
         // Pre-compute scaling:
         final double[] scale = new double[dimension];
         for (int i = 0; i < dimension; i++) {
             scale[i] = 1.0 / (b[i] - a[i]);
         }
 
         // Use two RNGs with the same output. The line sampler only uses a single double
         // per sample so we can assert that the point is approximately located along the
         // line vector is each dimension by the constant C. Floating-point tolerance
         // is required to validate the equality.
         final UniformRandomProvider[] rngs = RandomAssert.createRNG(2);
         final UniformRandomProvider rng1 = rngs[0];
         final UniformRandomProvider rng2 = rngs[1];
         final LineSampler sampler = LineSampler.of(rng1, a, b);
         final double relEps = 1e-10;
         final int n = 1000;
         final DoubleStream.Builder errors = DoubleStream.builder();
         for (int i = 0; i < n; i++) {
             final double[] x = sampler.sample();
             Assertions.assertEquals(dimension, x.length);
             final double c = rng2.nextDouble();
             for (int j = 0; j < dimension; j++) {
                 final double u = (x[j] - a[j]) * scale[j];
                 Assertions.assertTrue(u >= 0.0 && u <= 1.0, "Not within the line");
                 final double e = Math.abs(c - u) / u;
                 errors.add(e);
                 Assertions.assertEquals(c, u, c * relEps,
                     () -> "Not on the expected line: rel.error = " + e);
             }
         }
         final double averageRelError = errors.build().sum() / n;
         Assertions.assertTrue(averageRelError < 1e-12,
             () -> "Average relative error is too large = " + averageRelError);
     }
 
     /**
      * Test the SharedStateSampler implementation for 1D.
      */
     @Test
     void testSharedStateSampler1D() {
         testSharedStateSampler(1);
     }
 
     /**
      * Test the SharedStateSampler implementation for 2D.
      */
     @Test
     void testSharedStateSampler2D() {
         testSharedStateSampler(2);
     }
 
     /**
      * Test the SharedStateSampler implementation for 3D.
      */
     @Test
     void testSharedStateSampler3D() {
         testSharedStateSampler(3);
     }
 
     /**
      * Test the SharedStateSampler implementation for 4D.
      */
     @Test
     void testSharedStateSampler4D() {
         testSharedStateSampler(4);
     }
 
     /**
      * Test the SharedStateSampler implementation for the given dimension.
      */
     private static void testSharedStateSampler(int dimension) {
         final UniformRandomProvider rng1 = RandomAssert.seededRNG();
         final UniformRandomProvider rng2 = RandomAssert.seededRNG();
         final double[] c1 = createCoordinate(1, dimension);
         final double[] c2 = createCoordinate(2, dimension);
         final LineSampler sampler1 = LineSampler.of(rng1, c1, c2);
         final LineSampler sampler2 = sampler1.withUniformRandomProvider(rng2);
         RandomAssert.assertProduceSameSequence(sampler1, sampler2);
     }
 
     /**
      * Test the input vectors are copied and not used by reference for 1D.
      */
     @Test
     void testChangedInputCoordinates1D() {
         testChangedInputCoordinates(1);
     }
 
     /**
      * Test the input vectors are copied and not used by reference for 2D.
      */
     @Test
     void testChangedInputCoordinates2D() {
         testChangedInputCoordinates(2);
     }
 
     /**
      * Test the input vectors are copied and not used by reference for 3D.
      */
     @Test
     void testChangedInputCoordinates3D() {
         testChangedInputCoordinates(3);
     }
 
     /**
      * Test the input vectors are copied and not used by reference for 4D.
      */
     @Test
     void testChangedInputCoordinates4D() {
         testChangedInputCoordinates(4);
     }
 
     /**
      * Test the input vectors are copied and not used by reference for the given
      * dimension.
      *
      * @param dimension the dimension
      */
     private static void testChangedInputCoordinates(int dimension) {
         final UniformRandomProvider rng1 = RandomAssert.seededRNG();
         final UniformRandomProvider rng2 = RandomAssert.seededRNG();
         final double[] c1 = createCoordinate(1, dimension);
         final double[] c2 = createCoordinate(2, dimension);
         final LineSampler sampler1 = LineSampler.of(rng1, c1, c2);
         // Check the input vectors are copied and not used by reference.
         // Change them in place and create a new sampler. It should have different output
         // translated by the offset.
         final double offset = 10;
         for (int i = 0; i < dimension; i++) {
             c1[i] += offset;
             c2[i] += offset;
         }
         final LineSampler sampler2 = LineSampler.of(rng2, c1, c2);
         for (int n = 0; n < 3; n++) {
             final double[] s1 = sampler1.sample();
             final double[] s2 = sampler2.sample();
             Assertions.assertEquals(s1.length, s2.length);
             Assertions.assertFalse(Arrays.equals(s1, s2),
                 "First sampler has used the vertices by reference");
             for (int i = 0; i < dimension; i++) {
                 Assertions.assertEquals(s1[i] + offset, s2[i], 1e-10);
             }
         }
     }
 
     /**
      * Creates the coordinate of length specified by the dimension filled with
      * the given value and the dimension index: x + i.
      *
      * @param x the value for index 0
      * @param dimension the dimension
      * @return the coordinate
      */
     private static double[] createCoordinate(double x, int dimension) {
         final double[] coord = new double[dimension];
         for (int i = 0; i < dimension; i++) {
             coord[0] = x + i;
         }
         return coord;
     }
 }