/* Copyright 2002-2024 Thales Alenia Space
    * 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.AbstractMeasurement;
  import org.orekit.estimation.measurements.EstimatedMeasurementBase;
  import org.orekit.estimation.measurements.InterSatellitesRange;
  import org.orekit.frames.StaticTransform;
  import org.orekit.gnss.antenna.FrequencyPattern;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.utils.TimeStampedPVCoordinates;
  
  /** On-board antenna offset effect on inter-satellites phase measurements.
   * @param <T> type of the measurement
   * @author Luc Maisonobe
   * @since 12.1
   */
  public class PhaseCentersInterSatellitesBaseModifier<T extends AbstractMeasurement<T>> {
  
      /** Uplink offset model. */
      private final PhaseCentersOffsetComputer uplink;
  
      /** Downlink offset model. */
      private final PhaseCentersOffsetComputer downlink;
  
      /** Simple constructor.
       * @param pattern1 pattern for satellite 1
       * (i.e. the satellite which receives the signal and performs the measurement)
       * @param pattern2  pattern for satellite 2
       * (i.e. the satellite which simply emits the signal in the one-way
       * case, or reflects the signal in the two-way case)
       */
      public PhaseCentersInterSatellitesBaseModifier(final FrequencyPattern pattern1,
                                                     final FrequencyPattern pattern2) {
          this.uplink   = new PhaseCentersOffsetComputer(pattern1, pattern2);
          this.downlink = new PhaseCentersOffsetComputer(pattern2, pattern1);
      }
  
      /** 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) {
  
          // 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 StaticTransform receptionSpacecraftToInert = receptionState.toStaticTransform().getInverse();
          final SpacecraftState remoteState                = estimated.getStates()[1];
          final SpacecraftState emissionState              = remoteState.shiftedBy(emissionDate.durationFrom(remoteState.getDate()));
          final StaticTransform emissionSpacecraftToInert  = emissionState.toStaticTransform().getInverse();
  
          // compute offset due to phase centers
          return downlink.offset(emissionSpacecraftToInert, receptionSpacecraftToInert);
  
      }
  
      /** Compute distance modification for two way measurement.
       * @param estimated estimated measurement to modify
       * @return distance modification to add to raw measurement
       */
      public double twoWayDistanceModification(final EstimatedMeasurementBase<InterSatellitesRange> estimated) {
  
          // the participants are satellite 1 at emission, satellite 2 at transit, satellite 1 at reception
          final TimeStampedPVCoordinates[] participants  = estimated.getParticipants();
          final AbsoluteDate               emissionDate  = participants[0].getDate();
          final AbsoluteDate               transitDate   = participants[1].getDate();
          final AbsoluteDate               receptionDate = participants[2].getDate();
  
          // transforms from spacecraft to inertial frame at emission/reception dates
          final SpacecraftState refState1                  = estimated.getStates()[0];
          final SpacecraftState receptionState             = refState1.shiftedBy(receptionDate.durationFrom(refState1.getDate()));
          final StaticTransform receptionSpacecraftToInert = receptionState.toStaticTransform().getInverse();
          final SpacecraftState refState2                  = estimated.getStates()[1];
          final SpacecraftState transitState               = refState2.shiftedBy(transitDate.durationFrom(refState2.getDate()));
          final StaticTransform transitSpacecraftToInert   = transitState.toStaticTransform().getInverse();
          final SpacecraftState emissionState              = refState1.shiftedBy(emissionDate.durationFrom(refState1.getDate()));
          final StaticTransform emissionSpacecraftToInert  = emissionState.toStaticTransform().getInverse();
  
         // compute offsets due to phase centers
         final double uplinkOffset   = uplink.offset(emissionSpacecraftToInert, transitSpacecraftToInert);
         final double downlinkOffset = downlink.offset(transitSpacecraftToInert, receptionSpacecraftToInert);
 
         return 0.5 * (uplinkOffset + downlinkOffset);
 
     }
 
 }