/* Copyright 2002-2021 CS GROUP
    * 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.gnss;
  
  import java.util.Arrays;
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.Map;
  
  import org.hipparchus.analysis.differentiation.Gradient;
  import org.hipparchus.analysis.differentiation.GradientField;
  import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  import org.orekit.estimation.measurements.AbstractMeasurement;
  import org.orekit.estimation.measurements.EstimatedMeasurement;
  import org.orekit.estimation.measurements.GroundStation;
  import org.orekit.estimation.measurements.ObservableSatellite;
  import org.orekit.frames.FieldTransform;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.time.FieldAbsoluteDate;
  import org.orekit.utils.Constants;
  import org.orekit.utils.ParameterDriver;
  import org.orekit.utils.TimeStampedFieldPVCoordinates;
  import org.orekit.utils.TimeStampedPVCoordinates;
  
  /** Class modeling a phase measurement from a ground station.
   * <p>
   * The measurement is considered to be a signal emitted from
   * a spacecraft and received on a ground station.
   * Its value is the number of cycles between emission and
   * reception. The motion of both the station and the
   * spacecraft during the signal flight time are taken into
   * account. The date of the measurement corresponds to the
   * reception on ground of the emitted signal.
   * </p>
   * @author Thierry Ceolin
   * @author Luc Maisonobe
   * @author Maxime Journot
   * @since 9.2
   */
  public class Phase extends AbstractMeasurement<Phase> {
  
      /** Name for ambiguity driver. */
      public static final String AMBIGUITY_NAME = "ambiguity";
  
      /** Driver for ambiguity. */
      private final ParameterDriver ambiguityDriver;
  
      /** Ground station from which measurement is performed. */
      private final GroundStation station;
  
      /** Wavelength of the phase observed value [m]. */
      private final double wavelength;
  
      /** Simple constructor.
       * @param station ground station from which measurement is performed
       * @param date date of the measurement
       * @param phase observed value (cycles)
       * @param wavelength phase observed value wavelength (m)
       * @param sigma theoretical standard deviation
       * @param baseWeight base weight
       * @param satellite satellite related to this measurement
       * @since 9.3
       */
      public Phase(final GroundStation station, final AbsoluteDate date,
                   final double phase, final double wavelength, final double sigma,
                   final double baseWeight, final ObservableSatellite satellite) {
          super(date, phase, sigma, baseWeight, Collections.singletonList(satellite));
          ambiguityDriver = new ParameterDriver(AMBIGUITY_NAME,
                                                 0.0, 1.0,
                                                 Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);
          addParameterDriver(ambiguityDriver);
          addParameterDriver(satellite.getClockOffsetDriver());
          addParameterDriver(station.getClockOffsetDriver());
          addParameterDriver(station.getEastOffsetDriver());
          addParameterDriver(station.getNorthOffsetDriver());
          addParameterDriver(station.getZenithOffsetDriver());
          addParameterDriver(station.getPrimeMeridianOffsetDriver());
          addParameterDriver(station.getPrimeMeridianDriftDriver());
          addParameterDriver(station.getPolarOffsetXDriver());
          addParameterDriver(station.getPolarDriftXDriver());
          addParameterDriver(station.getPolarOffsetYDriver());
          addParameterDriver(station.getPolarDriftYDriver());
          this.station    = station;
          this.wavelength = wavelength;
     }
 
     /** Get the ground station from which measurement is performed.
      * @return ground station from which measurement is performed
      */
     public GroundStation getStation() {
         return station;
     }
 
     /** Get the wavelength.
      * @return wavelength (m)
      */
     public double getWavelength() {
         return wavelength;
     }
 
     /** Get the driver for phase ambiguity.
      * @return the driver for phase ambiguity
      * @since 10.3
      */
     public ParameterDriver getAmbiguityDriver() {
         return ambiguityDriver;
     }
 
     /** {@inheritDoc} */
     @Override
     protected EstimatedMeasurement<Phase> theoreticalEvaluation(final int iteration,
                                                                 final int evaluation,
                                                                 final SpacecraftState[] states) {
 
         final SpacecraftState state = states[0];
 
         // Phase derivatives are computed with respect to spacecraft state in inertial frame
         // and station parameters
         // ----------------------
         //
         // Parameters:
         //  - 0..2 - Position of the spacecraft in inertial frame
         //  - 3..5 - Velocity of the spacecraft in inertial frame
         //  - 6..n - station parameters (ambiguity, clock offset, station offsets, pole, prime meridian...)
         int nbParams = 6;
         final Map<String, Integer> indices = new HashMap<>();
         for (ParameterDriver driver : getParametersDrivers()) {
             if (driver.isSelected()) {
                 indices.put(driver.getName(), nbParams++);
             }
         }
         final FieldVector3D<Gradient> zero = FieldVector3D.getZero(GradientField.getField(nbParams));
 
         // Coordinates of the spacecraft expressed as a gradient
         final TimeStampedFieldPVCoordinates<Gradient> pvaDS = getCoordinates(state, 0, nbParams);
 
         // transform between station and inertial frame, expressed as a gradient
         // The components of station's position in offset frame are the 3 last derivative parameters
         final FieldTransform<Gradient> offsetToInertialDownlink =
                         station.getOffsetToInertial(state.getFrame(), getDate(), nbParams, indices);
         final FieldAbsoluteDate<Gradient> downlinkDateDS =
                         offsetToInertialDownlink.getFieldDate();
 
         // Station position in inertial frame at end of the downlink leg
         final TimeStampedFieldPVCoordinates<Gradient> stationDownlink =
                         offsetToInertialDownlink.transformPVCoordinates(new TimeStampedFieldPVCoordinates<>(downlinkDateDS,
                                                                                                             zero, zero, zero));
 
         // Compute propagation times
         // (if state has already been set up to pre-compensate propagation delay,
         //  we will have delta == tauD and transitState will be the same as state)
 
         // Downlink delay
         final Gradient tauD = signalTimeOfFlight(pvaDS, stationDownlink.getPosition(), downlinkDateDS);
 
         // Transit state & Transit state (re)computed with gradients
         final Gradient        delta        = downlinkDateDS.durationFrom(state.getDate());
         final Gradient        deltaMTauD   = tauD.negate().add(delta);
         final SpacecraftState transitState = state.shiftedBy(deltaMTauD.getValue());
         final TimeStampedFieldPVCoordinates<Gradient> transitStateDS = pvaDS.shiftedBy(deltaMTauD);
 
         // prepare the evaluation
         final EstimatedMeasurement<Phase> estimated =
                         new EstimatedMeasurement<Phase>(this, iteration, evaluation,
                                                         new SpacecraftState[] {
                                                             transitState
                                                         }, new TimeStampedPVCoordinates[] {
                                                             transitStateDS.toTimeStampedPVCoordinates(),
                                                             stationDownlink.toTimeStampedPVCoordinates()
                                                         });
 
         // Clock offsets
         final ObservableSatellite satellite = getSatellites().get(0);
         final Gradient            dts       = satellite.getClockOffsetDriver().getValue(nbParams, indices);
         final Gradient            dtg       = station.getClockOffsetDriver().getValue(nbParams, indices);
 
         // Phase value
         final double   cOverLambda = Constants.SPEED_OF_LIGHT / wavelength;
         final Gradient ambiguity   = ambiguityDriver.getValue(nbParams, indices);
         final Gradient phase       = tauD.add(dtg).subtract(dts).multiply(cOverLambda).add(ambiguity);
 
         estimated.setEstimatedValue(phase.getValue());
 
         // Phase partial derivatives with respect to state
         final double[] derivatives = phase.getGradient();
         estimated.setStateDerivatives(0, Arrays.copyOfRange(derivatives, 0, 6));
 
         // set partial derivatives with respect to parameters
         // (beware element at index 0 is the value, not a derivative)
         for (final ParameterDriver driver : getParametersDrivers()) {
             final Integer index = indices.get(driver.getName());
             if (index != null) {
                 estimated.setParameterDerivatives(driver, derivatives[index]);
             }
         }
 
         return estimated;
 
     }
 
 }