/* Copyright 2002-2025 CS GROUP
    * 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.frames;
  
  
  import org.hipparchus.CalculusFieldElement;
  import org.hipparchus.geometry.euclidean.threed.FieldRotation;
  import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  import org.hipparchus.geometry.euclidean.threed.Rotation;
  import org.hipparchus.geometry.euclidean.threed.RotationConvention;
  import org.hipparchus.geometry.euclidean.threed.Vector3D;
  import org.hipparchus.util.FastMath;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.time.FieldAbsoluteDate;
  import org.orekit.time.TimeScalarFunction;
  import org.orekit.time.TimeScales;
  import org.orekit.time.TimeVectorFunction;
  import org.orekit.utils.IERSConventions;
  
  /** True Equator Mean Equinox Frame.
   * <p>This frame is used for the SGP4 model in TLE propagation. This frame has <em>no</em>
   * official definition and there are some ambiguities about whether it should be used
   * as "of date" or "of epoch". This frame should therefore be used <em>only</em> for
   * TLE propagation and not for anything else, as recommended by the CCSDS Orbit Data Message
   * blue book.</p>
   * @author Luc Maisonobe
   */
  class TEMEProvider implements EOPBasedTransformProvider {
  
      /** Conventions. */
      private final IERSConventions conventions;
  
      /** EOP history. */
      private final EOPHistory eopHistory;
  
      /** Function computing the mean obliquity. */
      private final TimeScalarFunction obliquityFunction;
  
      /** Function computing the nutation angles. */
      private final TimeVectorFunction nutationFunction;
  
      /**
       * Simple constructor.
       *  @param conventions IERS conventions to apply
       * @param eopHistory  EOP history or {@code null} if no corrections should be
       *                    applied.
       * @param timeScales  other time scales used in computing the transform.
       */
      TEMEProvider(final IERSConventions conventions,
                   final EOPHistory eopHistory,
                   final TimeScales timeScales) {
          this.conventions       = conventions;
          this.eopHistory        = eopHistory;
          this.obliquityFunction = conventions.getMeanObliquityFunction(timeScales);
          this.nutationFunction  = conventions.getNutationFunction(timeScales);
      }
  
      /**
       * Private constructor.
       *
       * @param conventions       IERS conventions to apply
       * @param eopHistory        EOP history
       * @param obliquityFunction to use.
       * @param nutationFunction  to use.
       */
      private TEMEProvider(final IERSConventions conventions,
                           final EOPHistory eopHistory,
                           final TimeScalarFunction obliquityFunction,
                           final TimeVectorFunction nutationFunction) {
          this.conventions = conventions;
          this.eopHistory = eopHistory;
          this.obliquityFunction = obliquityFunction;
          this.nutationFunction = nutationFunction;
      }
  
      /** {@inheritDoc} */
      @Override
      public EOPHistory getEOPHistory() {
          return eopHistory;
      }
  
      /** {@inheritDoc} */
      @Override
      public TEMEProvider getNonInterpolatingProvider() {
          return new TEMEProvider(conventions, eopHistory.getEOPHistoryWithoutCachedTidalCorrection(),
                 obliquityFunction, nutationFunction);
     }
 
     /** {@inheritDoc} */
     @Override
     public Transform getTransform(final AbsoluteDate date) {
         final double eqe = getEquationOfEquinoxes(date);
         return new Transform(date, new Rotation(Vector3D.PLUS_K, eqe, RotationConvention.FRAME_TRANSFORM));
     }
 
     /** {@inheritDoc} */
     @Override
     public <T extends CalculusFieldElement<T>> FieldTransform<T> getTransform(final FieldAbsoluteDate<T> date) {
         final T eqe = getEquationOfEquinoxes(date);
         return new FieldTransform<>(date, new FieldRotation<>(FieldVector3D.getPlusK(date.getField()),
                                                               eqe,
                                                               RotationConvention.FRAME_TRANSFORM));
     }
 
     /** Get the Equation of the Equinoxes at the current date.
      * @param  date the date
      * @return equation of the equinoxes
      */
     private double getEquationOfEquinoxes(final AbsoluteDate date) {
 
         // compute nutation angles
         final double[] angles = nutationFunction.value(date);
 
         // nutation in longitude
         double dPsi = angles[0];
 
         if (eopHistory != null) {
             // apply the corrections for the nutation parameters
             final double[] correction = eopHistory.getEquinoxNutationCorrection(date);
             dPsi += correction[0];
         }
 
         // mean obliquity of ecliptic
         final double moe = obliquityFunction.value(date);
 
         // original definition of equation of equinoxes
         final double eqe = dPsi * FastMath.cos(moe);
 
         // apply correction if needed
         return eqe + angles[2];
 
     }
 
     /** Get the Equation of the Equinoxes at the current date.
      * @param  date the date
      * @param <T> type of the field elements
      * @return equation of the equinoxes
      */
     private <T extends CalculusFieldElement<T>> T getEquationOfEquinoxes(final FieldAbsoluteDate<T> date) {
 
         // compute nutation angles
         final T[] angles = nutationFunction.value(date);
 
         // nutation in longitude
         T dPsi = angles[0];
 
         if (eopHistory != null) {
             // apply the corrections for the nutation parameters
             final T[] correction = eopHistory.getEquinoxNutationCorrection(date);
             dPsi = dPsi.add(correction[0]);
         }
 
         // mean obliquity of ecliptic
         final T moe = obliquityFunction.value(date);
 
         // original definition of equation of equinoxes
         final T eqe = dPsi.multiply(moe.cos());
 
         // apply correction if needed
         return eqe.add(angles[2]);
 
     }
 
 }