/* 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.Field;
  import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  import org.hipparchus.geometry.euclidean.threed.Vector3D;
  import org.orekit.signal.AdjustableEmitterSignalTimer;
  import org.orekit.signal.FieldAdjustableEmitterSignalTimer;
  import org.orekit.signal.FieldSignalEmissionCondition;
  import org.orekit.signal.FieldSignalReceptionCondition;
  import org.orekit.signal.SignalEmissionCondition;
  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;
  
  /**
   * Abstract class for angular measurement model.
   * @since 14.0
   * @author Romain Serra
   */
  public abstract class AbstractAngularMeasurementModel extends AbstractSignalBasedModel {
  
      /**
       * Constructor.
       * @param signalTravelTimeModel time delay computer
       */
      protected AbstractAngularMeasurementModel(final SignalTravelTimeModel signalTravelTimeModel) {
          super(signalTravelTimeModel);
      }
  
      /**
       * Compute emitter-to-receiver vector.
       * @param receptionCondition signal reception conditions
       * @param emitter signal emitter coordinates provider
       * @param approxEmissionDate guess for the emission date (shall be adjusted by signal travel time computer)
       * @return emitter-to-receiver vector
       */
      protected Vector3D getEmitterToReceiverVector(final SignalReceptionCondition receptionCondition,
                                                    final PVCoordinatesProvider emitter,
                                                    final AbsoluteDate approxEmissionDate) {
          final AdjustableEmitterSignalTimer signalTravelTime = getSignalTravelTimeModel().getAdjustableEmitterComputer(emitter);
          final SignalEmissionCondition emissionCondition = signalTravelTime.computeEmissionCondition(receptionCondition,
                  approxEmissionDate);
          final Vector3D observedPosition = emissionCondition.emitterPosition();
          return observedPosition.subtract(receptionCondition.receiverPosition()).normalize();
      }
  
      /**
       * Compute emitter-to-receiver vector with FIeld.
       * @param <T> field type
       * @param receptionCondition signal reception conditions
       * @param emitter signal emitter coordinates provider
       * @param approxEmissionDate guess for the emission date (shall be adjusted by signal travel time computer)
       * @return emitter-to-receiver vector
       */
      protected <T extends CalculusFieldElement<T>> FieldVector3D<T> getEmitterToReceiverVector(final FieldSignalReceptionCondition<T> receptionCondition,
                                                                                                final FieldPVCoordinatesProvider<T> emitter,
                                                                                                final FieldAbsoluteDate<T> approxEmissionDate) {
          final Field<T> field = receptionCondition.receptionDate().getField();
          final FieldAdjustableEmitterSignalTimer<T> signalTravelTime = getSignalTravelTimeModel()
                  .getFieldAdjustableEmitterComputer(field, emitter);
          final FieldSignalEmissionCondition<T> emissionCondition = signalTravelTime.computeEmissionCondition(receptionCondition,
                  approxEmissionDate);
          final FieldVector3D<T> observedPosition = emissionCondition.emitterPosition();
          return observedPosition.subtract(receptionCondition.receiverPosition());
      }
  }