/* Copyright 2002-2021 CS GROUP
    * Licensed to CS GROUP (CS) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
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    * 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.estimation.measurements.modifiers;
  
  import java.util.Collections;
  import java.util.List;
  
  import org.hipparchus.geometry.euclidean.threed.Vector3D;
  import org.orekit.estimation.measurements.EstimatedMeasurement;
  import org.orekit.estimation.measurements.EstimationModifier;
  import org.orekit.estimation.measurements.gnss.InterSatellitesPhase;
  import org.orekit.frames.Transform;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.utils.ParameterDriver;
  import org.orekit.utils.TimeStampedPVCoordinates;
  
  /** On-board antenna offset effect on inter-satellites phase measurements.
   * @author Bryan Cazabonne
   * @since 10.3
   */
  public class OnBoardAntennaInterSatellitesPhaseModifier implements EstimationModifier<InterSatellitesPhase> {
  
      /** Position of the Antenna Phase Center in satellite 1 frame. */
      private final Vector3D antennaPhaseCenter1;
  
      /** Position of the Antenna Phase Center in satellite 2 frame. */
      private final Vector3D antennaPhaseCenter2;
  
      /** Simple constructor.
       * @param antennaPhaseCenter1 position of the Antenna Phase Center in satellite 1 frame
       * (i.e. the satellite which receives the signal and performs the measurement)
       * @param antennaPhaseCenter2 position of the Antenna Phase Center in satellite 2 frame
       * (i.e. the satellite which simply emits the signal in the one-way
       * case, or reflects the signal in the two-way case)
       */
      public OnBoardAntennaInterSatellitesPhaseModifier(final Vector3D antennaPhaseCenter1,
                                                        final Vector3D antennaPhaseCenter2) {
          this.antennaPhaseCenter1 = antennaPhaseCenter1;
          this.antennaPhaseCenter2 = antennaPhaseCenter2;
      }
  
      /** {@inheritDoc} */
      @Override
      public List<ParameterDriver> getParametersDrivers() {
          return Collections.emptyList();
      }
  
      @Override
      public void modify(final EstimatedMeasurement<InterSatellitesPhase> estimated) {
  
          // The participants are satellite 2 at emission, satellite 1 at reception
          final TimeStampedPVCoordinates[] participants  = estimated.getParticipants();
          final AbsoluteDate               emissionDate  = participants[0].getDate();
          final AbsoluteDate               receptionDate = participants[1].getDate();
  
          // transforms from spacecraft to inertial frame at emission/reception dates
          final SpacecraftState localState                 = estimated.getStates()[0];
          final SpacecraftState receptionState             = localState.shiftedBy(receptionDate.durationFrom(localState.getDate()));
          final Transform       receptionSpacecraftToInert = receptionState.toTransform().getInverse();
          final SpacecraftState remoteState                = estimated.getStates()[1];
          final SpacecraftState emissionState              = remoteState.shiftedBy(emissionDate.durationFrom(remoteState.getDate()));
          final Transform       emissionSpacecraftToInert  = emissionState.toTransform().getInverse();
  
          // Compute the geometrical value of the inter-satellites range directly from participants positions.
          final Vector3D pSpacecraftReception = receptionSpacecraftToInert.transformPosition(Vector3D.ZERO);
          final Vector3D pSpacecraftEmission  = emissionSpacecraftToInert.transformPosition(Vector3D.ZERO);
          final double interSatellitesRangeUsingSpacecraftCenter = Vector3D.distance(pSpacecraftEmission, pSpacecraftReception);
  
          // Compute the geometrical value of the range replacing
          // The spacecraft positions with antenna phase center positions
          final Vector3D pAPCReception = receptionSpacecraftToInert.transformPosition(antennaPhaseCenter1);
          final Vector3D pAPCEmission  = emissionSpacecraftToInert.transformPosition(antennaPhaseCenter2);
          final double interSatellitesRangeUsingAntennaPhaseCenter = Vector3D.distance(pAPCEmission, pAPCReception);
  
          // Get the estimated value before this modifier is applied
          final double[] value = estimated.getEstimatedValue();
  
          // Modify the phase value by applying measurement wavelength
          final double wavelength = estimated.getObservedMeasurement().getWavelength();
          value[0] += (interSatellitesRangeUsingAntennaPhaseCenter - interSatellitesRangeUsingSpacecraftCenter) / wavelength;
          estimated.setEstimatedValue(value);
  
      }
  
 
 }