/*
    * 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.math4.transform;
  
  import org.junit.Assert;
  import org.junit.Test;
  
  import org.apache.commons.numbers.core.Precision;
  
  
  /**
   * Test for {@link FastHadamardTransform}.
   */
  public final class FastHadamardTransformerTest {
      /**
       * Test of transformer for the a 8-point FHT (means n=8)
       */
      @Test
      public void test8Points() {
          checkAllTransforms(new int[] {1, 4, -2, 3, 0, 1, 4, -1},
                             new int[] {10, -4, 2, -4, 2, -12, 6, 8});
      }
  
      /**
       * Test of transformer for the a 4-points FHT (means n=4)
       */
      @Test
      public void test4Points() {
          checkAllTransforms(new int[] {1, 2, 3, 4},
                             new int[] {10, -2, -4, 0});
      }
  
      /**
       * Test the inverse transform of an integer vector is not always an integer vector
       */
      @Test
      public void testNoIntInverse() {
          final FastHadamardTransform transformer = new FastHadamardTransform(true);
          final double[] x = transformer.apply(new double[] {0, 1, 0, 1});
          Assert.assertEquals(0.5, x[0], 0);
          Assert.assertEquals(-0.5, x[1], 0);
          Assert.assertEquals(0.0, x[2], 0);
          Assert.assertEquals(0.0, x[3], 0);
      }
  
      /**
       * Test of transformer for wrong number of points
       */
      @Test
      public void test3Points() {
          try {
              new FastHadamardTransform().apply(new double[3]);
              Assert.fail("an exception should have been thrown");
          } catch (IllegalArgumentException iae) {
              // expected
          }
      }
  
      private void checkAllTransforms(int[] x, int[] y) {
          checkDoubleTransform(x, y);
          checkInverseDoubleTransform(x, y);
          checkIntTransform(x, y);
      }
  
      private void checkDoubleTransform(int[] x, int[] y) {
          // Initiate the transformer
          final FastHadamardTransform transformer = new FastHadamardTransform();
  
          // check double transform
          final double[] dX = new double[x.length];
          for (int i = 0; i < dX.length; ++i) {
              dX[i] = x[i];
          }
          final double[] dResult = transformer.apply(dX);
          for (int i = 0; i < dResult.length; i++) {
              // compare computed results to precomputed results
              Assert.assertTrue(Precision.equals(y[i], dResult[i], 1));
          }
      }
  
      private void checkIntTransform(int[] x, int[] y) {
          // Initiate the transformer
          final FastHadamardTransform transformer = new FastHadamardTransform();
  
          // check integer transform
         final int[] iResult = transformer.apply(x);
         for (int i = 0; i < iResult.length; i++) {
             // compare computed results to precomputed results
             Assert.assertEquals(y[i], iResult[i]);
         }
     }
 
     private void checkInverseDoubleTransform(int[]x, int[] y) {
         // Initiate the transformer
         final FastHadamardTransform transformer = new FastHadamardTransform(true);
 
         // check double transform
         final double[] dY = new double[y.length];
         for (int i = 0; i < dY.length; ++i) {
             dY[i] = y[i];
         }
         final double[] dResult = transformer.apply(dY);
         for (int i = 0; i < dResult.length; i++) {
             // compare computed results to precomputed results
             Assert.assertTrue(Precision.equals(x[i], dResult[i], 1));
         }
     }
 }