/* Copyright 2002-2026 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,
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   * See the License for the specific language governing permissions and
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  package org.orekit.frames;
  
  import java.util.HashMap;
  import java.util.Map;
  
  import org.hipparchus.CalculusFieldElement;
  import org.hipparchus.Field;
  import org.hipparchus.geometry.euclidean.threed.FieldRotation;
  import org.hipparchus.geometry.euclidean.threed.Rotation;
  import org.hipparchus.geometry.euclidean.threed.RotationConvention;
  import org.hipparchus.geometry.euclidean.threed.RotationOrder;
  import org.hipparchus.geometry.euclidean.threed.Vector3D;
  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;
  
  /** Mean Equator, Mean Equinox Frame.
   * <p>This frame handles precession effects according to to selected IERS conventions.</p>
   * <p>Its parent frame is the GCRF frame.
   * <p>It is sometimes called Mean of Date (MoD) frame.
   * @author Pascal Parraud
   */
  class MODProvider implements TransformProvider {
  
      /** Function computing the precession angles. */
      private final TimeVectorFunction precessionFunction;
  
      /** Constant rotation between ecliptic and equator poles at J2000.0. */
      private final Rotation r4;
  
      /** Constant rotations between ecliptic and equator poles at J2000.0. */
      private final Map<Field<? extends CalculusFieldElement<?>>, FieldRotation<? extends CalculusFieldElement<?>>> fieldR4;
  
      /** Simple constructor.
       * @param conventions IERS conventions to apply
       * @param timeScales used to define this frame.
       */
      MODProvider(final IERSConventions conventions, final TimeScales timeScales) {
          this.precessionFunction = conventions.getPrecessionFunction(timeScales);
          final TimeScalarFunction epsilonAFunction =
                  conventions.getMeanObliquityFunction(timeScales);
          final AbsoluteDate date0 = conventions.getNutationReferenceEpoch(timeScales);
          final double epsilon0 = epsilonAFunction.value(date0);
          r4 = new Rotation(Vector3D.PLUS_I, epsilon0, RotationConvention.FRAME_TRANSFORM);
          fieldR4 = new HashMap<>();
      }
  
      /** {@inheritDoc} */
      @Override
      public Transform getTransform(final AbsoluteDate date) {
  
          // compute the precession angles phiA, omegaA, chiA
          final double[] angles = precessionFunction.value(date);
  
          // complete precession
          final Rotation precession = r4.compose(new Rotation(RotationOrder.ZXZ, RotationConvention.FRAME_TRANSFORM,
                                                              -angles[0], -angles[1], angles[2]),
                                                 RotationConvention.FRAME_TRANSFORM);
  
          // set up the transform from parent GCRF
          return new Transform(date, precession);
  
      }
  
      /** {@inheritDoc} */
      @SuppressWarnings("unchecked")
      @Override
      public <T extends CalculusFieldElement<T>> FieldTransform<T> getTransform(final FieldAbsoluteDate<T> date) {
  
          // compute the precession angles phiA, omegaA, chiA
          final T[] angles = precessionFunction.value(date);
  
          final FieldRotation<T> fR4;
          synchronized (fieldR4) {
              fR4 = (FieldRotation<T>) fieldR4.computeIfAbsent(date.getField(),
                                                               f -> new FieldRotation<>((Field<T>) f, r4));
          }
  
          // complete precession
          final FieldRotation<T> precession = fR4.compose(new FieldRotation<>(RotationOrder.ZXZ, RotationConvention.FRAME_TRANSFORM,
                                                                             angles[0].negate(),
                                                                             angles[1].negate(),
                                                                             angles[2]),
                                                         RotationConvention.FRAME_TRANSFORM);
 
         // set up the transform from parent GCRF
         return new FieldTransform<>(date, precession);
 
     }
 
 }