/* Copyright 2022-2025 Thales Alenia Space
    * 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.estimation.measurements;
  
  import org.hipparchus.CalculusFieldElement;
  import org.hipparchus.analysis.differentiation.Gradient;
  import org.hipparchus.util.FastMath;
  import org.orekit.errors.OrekitException;
  import org.orekit.errors.OrekitMessages;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.time.ClockModel;
  import org.orekit.time.ClockOffset;
  import org.orekit.time.FieldAbsoluteDate;
  import org.orekit.time.FieldClockOffset;
  import org.orekit.utils.ParameterDriver;
  
  import java.util.Map;
  
  /** Quadratic clock model.
   *
   * @author Luc Maisonobe
   * @since 12.1
   *
   */
  public class QuadraticClockModel implements ClockModel {
  
      /** Clock offset scaling factor.
       * <p>
       * We use a power of 2 to avoid numeric noise introduction
       * in the multiplications/divisions sequences.
       * </p>
       */
      private static final double CLOCK_OFFSET_SCALE = FastMath.scalb(1.0, -10);
  
      /** Constant term. */
      private final ParameterDriver a0;
  
      /** Linear term. */
      private final ParameterDriver a1;
  
      /** Quadratic term. */
      private final ParameterDriver a2;
  
      /** Simple constructor.
       * @param referenceDate reference date
       * @param a0 constant term
       * @param a1 linear term
       * @param a2 quadratic term
       */
      public QuadraticClockModel(final AbsoluteDate referenceDate,
                                 final double a0, final double a1, final double a2) {
          this(new ParameterDriver("a0",
                                   0.0, CLOCK_OFFSET_SCALE,
                                   Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY),
               new ParameterDriver("a1",
                                   0.0, CLOCK_OFFSET_SCALE,
                                   Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY),
               new ParameterDriver("a2",
                                   0.0, CLOCK_OFFSET_SCALE,
                                   Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY));
          this.a0.setValue(a0);
          this.a0.setReferenceDate(referenceDate);
          this.a1.setValue(a1);
          this.a1.setReferenceDate(referenceDate);
          this.a2.setValue(a2);
          this.a2.setReferenceDate(referenceDate);
      }
  
      /** Simple constructor.
       * @param a0 constant term
       * @param a1 linear term
       * @param a2 quadratic term
       */
      public QuadraticClockModel(final ParameterDriver a0, final ParameterDriver a1, final ParameterDriver a2) {
          this.a0 = a0;
          this.a1 = a1;
          this.a2 = a2;
      }
  
      /** {@inheritDoc} */
      @Override
      public AbsoluteDate getValidityStart() {
          return AbsoluteDate.PAST_INFINITY;
      }
  
     /** {@inheritDoc} */
     @Override
     public AbsoluteDate getValidityEnd() {
         return AbsoluteDate.FUTURE_INFINITY;
     }
 
     /** {@inheritDoc} */
     @Override
     public ClockOffset getOffset(final AbsoluteDate date) {
         final double dt = date.durationFrom(getSafeReference(date));
         final double c0 = a0.getValue(date);
         final double c1 = a1.getValue(date);
         final double c2 = a2.getValue(date);
         return new ClockOffset(date,
                                (c2 * dt + c1) * dt + c0,
                                2 * c2 * dt + c1,
                                2 * c2);
     }
 
     /** {@inheritDoc} */
     @Override
     public <T extends CalculusFieldElement<T>> FieldClockOffset<T> getOffset(final FieldAbsoluteDate<T> date) {
         final AbsoluteDate aDate = date.toAbsoluteDate();
         final T dt = date.durationFrom(getSafeReference(aDate));
         final double c0 = a0.getValue(aDate);
         final double c1 = a1.getValue(aDate);
         final double c2 = a2.getValue(aDate);
         return new FieldClockOffset<>(date,
                                       dt.multiply(dt.multiply(c2).add(c1)).add(c0),
                                       dt.multiply(2 * c2).add(c1),
                                       dt.newInstance(2 * c2));
     }
 
     /** Get a safe reference date.
      * <p>
      * This method deals with parameters drivers for which no reference
      * date has been set, which is acceptable if the model is not
      * time-dependent.
      * </p>
      * @param date date at which values are requested
      * @return safe reference date
      */
     private AbsoluteDate getSafeReference(final AbsoluteDate date) {
         if (a0.getReferenceDate() == null) {
             if (a1.getValue(date) == 0 && a2.getValue(date) == 0) {
                 // it is OK to not have a reference date is clock offset is constant
                 return date;
             } else {
                 throw new OrekitException(OrekitMessages.NO_REFERENCE_DATE_FOR_PARAMETER,
                                           a0.getName());
             }
         } else {
             return a0.getReferenceDate();
         }
     }
 
     /** Convert to gradient model.
      * @param freeParameters total number of free parameters in the gradient
      * @param indices indices of the differentiation parameters in derivatives computations,
      * must be span name and not driver name
      * @param date date at which model must be valid
      * @return converted clock model
      */
     public QuadraticFieldClockModel<Gradient> toGradientModel(final int freeParameters,
                                                               final Map<String, Integer> indices,
                                                               final AbsoluteDate date) {
         final Gradient g0 = a0.getValue(freeParameters, indices, date);
         final Gradient g1 = a1.getValue(freeParameters, indices, date);
         final Gradient g2 = a2.getValue(freeParameters, indices, date);
         final FieldAbsoluteDate<Gradient> referenceDate =
             new FieldAbsoluteDate<>(g0.getField(), getSafeReference(date));
         return new QuadraticFieldClockModel<>(referenceDate, g0, g1, g2);
     }
 
 }