/* Copyright 2022-2026 Romain Serra
    * 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.model;
  
  import org.hipparchus.CalculusFieldElement;
  import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  import org.hipparchus.geometry.euclidean.threed.Vector3D;
  import org.hipparchus.util.MathArrays;
  import org.orekit.errors.OrekitException;
  import org.orekit.errors.OrekitMessages;
  import org.orekit.frames.FieldStaticTransform;
  import org.orekit.frames.Frame;
  import org.orekit.frames.StaticTransform;
  import org.orekit.signal.FieldSignalReceptionCondition;
  import org.orekit.signal.SignalReceptionCondition;
  import org.orekit.signal.SignalTravelTimeModel;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.time.FieldAbsoluteDate;
  import org.orekit.utils.FieldPVCoordinatesProvider;
  import org.orekit.utils.PVCoordinatesProvider;
  
  /**
   * Perfect measurement model for right ascension and declination. It is assumed that the signal reception date is known.
   * @since 14.0
   * @author Romain Serra
   */
  public class RaDecModel extends AbstractAngularMeasurementModel {
  
      /** Reference frame defining axis used with right ascension and declination. */
      private final Frame referenceFrame;
  
      /**
       * Constructor.
       * @param referenceFrame reference frame for RA-Dec (must be inertial)
       * @param signalTravelTimeModel time delay computer
       */
      public RaDecModel(final Frame referenceFrame, final SignalTravelTimeModel signalTravelTimeModel) {
          super(signalTravelTimeModel);
          if (!referenceFrame.isPseudoInertial()) {
              throw new OrekitException(OrekitMessages.NON_PSEUDO_INERTIAL_FRAME, referenceFrame.getName());
          }
          this.referenceFrame = referenceFrame;
      }
  
      /**
       * Compute theoretical measurement.
       * @param receptionCondition signal reception condition
       * @param emitter signal emitter coordinates provider
       * @return RA-Dec (radians)
       */
      public double[] value(final SignalReceptionCondition receptionCondition,
                            final PVCoordinatesProvider emitter) {
          return value(receptionCondition, emitter, receptionCondition.receptionDate());
      }
  
      /**
       * Compute theoretical measurement with guess for the emission date.
       * @param receptionCondition signal reception condition
       * @param emitter signal emitter coordinates provider
       * @param approxEmissionDate guess for the emission date (shall be adjusted by signal travel time computer)
       * @return RA-Dec (radians)
       */
      public double[] value(final SignalReceptionCondition receptionCondition,
                            final PVCoordinatesProvider emitter, final AbsoluteDate approxEmissionDate) {
          // Compute line-of-sight
          final Vector3D apparentLineOfSightInInputFrame = getEmitterToReceiverVector(receptionCondition, emitter,
                  approxEmissionDate).normalize();
          final StaticTransform toInertialFrameAtReception = receptionCondition.referenceFrame()
                  .getStaticTransformTo(referenceFrame, receptionCondition.receptionDate());
          final Vector3D apparentLineOfSight = toInertialFrameAtReception.transformVector(apparentLineOfSightInInputFrame);
  
          // Compute right ascension and declination
          final double rightAscension = apparentLineOfSight.getAlpha();
          final double declination = apparentLineOfSight.getDelta();
          return new double[] { rightAscension, declination };
      }
  
      /**
       * Compute theoretical measurement with FIeld.
       * @param <T> field type
       * @param receptionCondition signal reception condition
       * @param emitter signal emitter coordinates provider
       * @return RA-Dec (radians)
       */
      public <T extends CalculusFieldElement<T>> T[] value(final FieldSignalReceptionCondition<T> receptionCondition,
                                                          final FieldPVCoordinatesProvider<T> emitter) {
         return value(receptionCondition, emitter, receptionCondition.receptionDate());
     }
 
     /**
      * Compute theoretical measurement with FIeld with guess for emission date.
      * @param <T> field type
      * @param receptionCondition signal reception condition
      * @param emitter signal emitter coordinates provider
      * @param approxEmissionDate guess for the emission date (shall be adjusted by signal travel time computer)
      * @return RA-Dec (radians)
      */
     public <T extends CalculusFieldElement<T>> T[] value(final FieldSignalReceptionCondition<T> receptionCondition,
                                                          final FieldPVCoordinatesProvider<T> emitter,
                                                          final FieldAbsoluteDate<T> approxEmissionDate) {
         // Compute line-of-sight
         final FieldVector3D<T> apparentLineOfSightInInputFrame = getEmitterToReceiverVector(receptionCondition,
                 emitter, approxEmissionDate).normalize();
         final FieldAbsoluteDate<T> receptionDate = receptionCondition.receptionDate();
         final FieldStaticTransform<T> toInertialFrameAtReception = receptionCondition.referenceFrame()
                 .getStaticTransformTo(referenceFrame, receptionDate);
         final FieldVector3D<T> apparentLineOfSight = toInertialFrameAtReception.transformVector(apparentLineOfSightInInputFrame);
 
         // Compute right ascension and declination
         final T rightAscension = apparentLineOfSight.getAlpha();
         final T declination = apparentLineOfSight.getDelta();
         final T[] output = MathArrays.buildArray(receptionDate.getField(), 2);
         output[0] = rightAscension;
         output[1] = declination;
         return output;
     }
 }