/* Contributed in the public domain.
    * Licensed to CS GROUP (CS) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * CS 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.orekit.forces.gravity.potential;
  
  import org.hipparchus.util.Precision;
  import org.junit.jupiter.api.Assertions;
  import org.junit.jupiter.api.BeforeEach;
  import org.junit.jupiter.api.Test;
  import org.orekit.forces.gravity.potential.NormalizedSphericalHarmonicsProvider.NormalizedSphericalHarmonics;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.utils.Constants;
  
  /** @author Evan Ward */
  public class CachedNormalizedSphericalHarmonicsProviderTest {
  
  
      private static final AbsoluteDate date = AbsoluteDate.J2000_EPOCH;
      private NormalizedSphericalHarmonicsProvider raw;
      private static final double step = 60 * 60, slotSpan = Constants.JULIAN_DAY, newSlotInterval = Constants.JULIAN_DAY;
      private static final int interpolationPoints = 3, maxSlots = 100;
      private CachedNormalizedSphericalHarmonicsProvider cache;
  
      @BeforeEach
      public void setUp() {
          raw = new QuadraticProvider(date);
          cache = new CachedNormalizedSphericalHarmonicsProvider(raw, step, interpolationPoints, maxSlots, slotSpan, newSlotInterval);
      }
  
      @Test
      void testGetReferenceDate() {
          AbsoluteDate actualDate = cache.getReferenceDate();
          Assertions.assertEquals(actualDate, date);
      }
  
      @Test
      void testLimits() {
          Assertions.assertEquals(2, cache.getMaxDegree());
          Assertions.assertEquals(2, cache.getMaxOrder());
      }
  
      @Test
      void testBody() {
          Assertions.assertEquals(1, cache.getMu(), 1.0e-15);
          Assertions.assertEquals(1, cache.getAe(), 1.0e-15);
      }
  
      @Test
      void testGetTideSystem() {
          TideSystem actualSystem = cache.getTideSystem();
          Assertions.assertEquals(actualSystem, TideSystem.UNKNOWN);
      }
  
      @Test
      void testInterpolation() {
          //setup
          //generate points on grid with date as the origin
          cache.onDate(date);
          //sample at step/2
          AbsoluteDate sampleDate = date.shiftedBy(step / 2.0);
          //expected values
          NormalizedSphericalHarmonics expected = raw.onDate(sampleDate);
  
          //action
          NormalizedSphericalHarmonics actual = cache.onDate(sampleDate);
  
          //verify
          double tol = Precision.EPSILON;
          for (int n = 0; n < raw.getMaxDegree(); n++) {
              for (int m = 0; m < n; m++) {
                  Assertions.assertEquals(expected.getNormalizedCnm(n, m), actual.getNormalizedCnm(n, m), tol);
                  Assertions.assertEquals(expected.getNormalizedSnm(n, m), actual.getNormalizedSnm(n, m), tol);
              }
          }
      }
  
      @Test
      void testReverseEntryGeneration() {
          //setup
          //generate points on grid with date as the origin
          cache.onDate(date);
          //sample before the current cached values
          AbsoluteDate sampleDate = date.shiftedBy(-step * 3);
          NormalizedSphericalHarmonics expected = raw.onDate(sampleDate);
  
          //action
         NormalizedSphericalHarmonics actual = cache.onDate(sampleDate);
 
         //verify
         double tol = Precision.EPSILON;
         for (int n = 0; n < raw.getMaxDegree(); n++) {
             for (int m = 0; m < n; m++) {
                 Assertions.assertEquals(expected.getNormalizedCnm(n, m), actual.getNormalizedCnm(n, m), tol);
                 Assertions.assertEquals(expected.getNormalizedSnm(n, m), actual.getNormalizedSnm(n, m), tol);
             }
         }
     }
 
     private static class QuadraticProvider implements NormalizedSphericalHarmonicsProvider {
 
         private final AbsoluteDate date;
 
         private QuadraticProvider(AbsoluteDate date) {
             this.date = date;
         }
 
         @Override
         public NormalizedSphericalHarmonics onDate(final AbsoluteDate date) {
             final double t = date.durationFrom(this.date);
             return new NormalizedSphericalHarmonics() {
                 @Override
                 public double getNormalizedCnm(int n, int m) {
                     return n + m + t * t;
                 }
 
                 @Override
                 public double getNormalizedSnm(int n, int m) {
                     return n + m + t * t + 1;
                 }
 
                 @Override
                 public AbsoluteDate getDate() {
                     return date;
                 }
             };
         }
 
         @Override
         public int getMaxDegree() {
             return 2;
         }
 
         @Override
         public int getMaxOrder() {
             return 2;
         }
 
         @Override
         public double getMu() {
             return 1;
         }
 
         @Override
         public double getAe() {
             return 1;
         }
 
         @Override
         public AbsoluteDate getReferenceDate() {
             return date;
         }
 
        @Override
         public TideSystem getTideSystem() {
             return TideSystem.UNKNOWN;
         }
 
     }
 }