/* Copyright 2002-2024 Luc Maisonobe
    * 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.modifiers;
  
  import org.orekit.estimation.measurements.EstimatedMeasurementBase;
  import org.orekit.estimation.measurements.GroundReceiverMeasurement;
  import org.orekit.estimation.measurements.GroundStation;
  import org.orekit.frames.Frame;
  import org.orekit.frames.Transform;
  import org.orekit.gnss.antenna.FrequencyPattern;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.utils.TimeStampedPVCoordinates;
  
  /** Ground and on-board antennas offsets effect on range measurements.
   * @param <T> the type of the measurement
   * @author Luc Maisonobe
   * @since 12.0
   */
  public class PhaseCentersGroundReceiverBaseModifier<T extends GroundReceiverMeasurement<T>> {
  
      /** Uplink offset model. */
      private final PhaseCentersOffsetComputer uplink;
  
      /** Downlink offset model. */
      private final PhaseCentersOffsetComputer downlink;
  
      /** Simple constructor.
       * @param stationPattern station pattern
       * @param satellitePattern satellite pattern
       */
      public PhaseCentersGroundReceiverBaseModifier(final FrequencyPattern stationPattern,
                                                    final FrequencyPattern satellitePattern) {
          this.uplink   = new PhaseCentersOffsetComputer(stationPattern, satellitePattern);
          this.downlink = new PhaseCentersOffsetComputer(satellitePattern, stationPattern);
      }
  
      /** Compute distance modification for one way measurement.
       * @param estimated estimated measurement to modify
       * @return distance modification to add to raw measurement
       */
      public double oneWayDistanceModification(final EstimatedMeasurementBase<T> estimated) {
  
          // get all participants
          // note that clock offset is compensated in participants,
          // so the dates included there are more accurate than the measurement date
          final TimeStampedPVCoordinates[] participants = estimated.getParticipants();
  
          // station at reception date
          final Frame         inertial       = estimated.getStates()[0].getFrame();
          final GroundStation station        = estimated.getObservedMeasurement().getStation();
          final AbsoluteDate  receptionDate  = participants[1].getDate();
          final Transform     stationToInert = station.getOffsetToInertial(inertial, receptionDate, false);
  
          // spacecraft at emission date
          final AbsoluteDate    emissionDate      = participants[0].getDate();
          final SpacecraftState refState          = estimated.getStates()[0];
          final SpacecraftState emissionState     = refState.shiftedBy(emissionDate.durationFrom(refState.getDate()));
          final Transform       spacecraftToInert = emissionState.toTransform().getInverse();
  
          // compute offset due to phase centers
          return downlink.offset(spacecraftToInert, stationToInert);
  
      }
  
      /** Apply a modifier to a two-way range measurement.
       * @param estimated estimated measurement to modify
       * @return distance modification to add to raw measurement
       */
      public double twoWayDistanceModification(final EstimatedMeasurementBase<T> estimated) {
  
          // get all participants
          // note that clock offset is compensated in participants,
          // so the dates included there are more accurate than the measurement date
          final TimeStampedPVCoordinates[] participants = estimated.getParticipants();
  
          // station at reception date
          final Frame         inertial                = estimated.getStates()[0].getFrame();
          final GroundStation station                 = estimated.getObservedMeasurement().getStation();
          final AbsoluteDate  receptionDate           = participants[2].getDate();
          final Transform     stationToInertReception = station.getOffsetToInertial(inertial, receptionDate, false);
  
          // transform from spacecraft to inertial frame at transit date
          final AbsoluteDate    transitDate           = participants[1].getDate();
          final SpacecraftState refState              = estimated.getStates()[0];
         final SpacecraftState transitState          = refState.shiftedBy(transitDate.durationFrom(refState.getDate()));
         final Transform       spacecraftToInert     = transitState.toTransform().getInverse();
 
         // station at emission date
         final AbsoluteDate emissionDate             = participants[0].getDate();
         final Transform    stationToInertEmission   = station.getOffsetToInertial(inertial, emissionDate, true);
 
         // compute offsets due to phase centers
         final double uplinkOffset   = uplink.offset(stationToInertEmission, spacecraftToInert);
         final double downlinkOffset = downlink.offset(spacecraftToInert, stationToInertReception);
 
         return 0.5 * (uplinkOffset + downlinkOffset);
 
     }
 
 }