/* Copyright 2002-2020 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;
  
  import java.util.Arrays;
  
  import org.hipparchus.analysis.UnivariateFunction;
  import org.hipparchus.analysis.solvers.BracketingNthOrderBrentSolver;
  import org.hipparchus.analysis.solvers.UnivariateSolver;
  import org.hipparchus.geometry.euclidean.threed.Vector3D;
  import org.hipparchus.util.FastMath;
  import org.orekit.estimation.Context;
  import org.orekit.frames.Frame;
  import org.orekit.frames.Transform;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.utils.Constants;
  import org.orekit.utils.ParameterDriver;
  
  public class AngularAzElMeasurementCreator extends MeasurementCreator {
  
      private final Context context;
      private final ObservableSatellite satellite;
  
      public AngularAzElMeasurementCreator(final Context context) {
          this.context   = context;
          this.satellite = new ObservableSatellite(0);
      }
  
      public void init(SpacecraftState s0, AbsoluteDate t, double step) {
          for (final GroundStation station : context.stations) {
              for (ParameterDriver driver : Arrays.asList(station.getClockOffsetDriver(),
                                                          station.getEastOffsetDriver(),
                                                          station.getNorthOffsetDriver(),
                                                          station.getZenithOffsetDriver(),
                                                          station.getPrimeMeridianOffsetDriver(),
                                                          station.getPrimeMeridianDriftDriver(),
                                                          station.getPolarOffsetXDriver(),
                                                          station.getPolarDriftXDriver(),
                                                          station.getPolarOffsetYDriver(),
                                                          station.getPolarDriftYDriver())) {
                  if (driver.getReferenceDate() == null) {
                      driver.setReferenceDate(s0.getDate());
                  }
              }
  
          }
      }
  
      public void handleStep(final SpacecraftState currentState, final boolean isLast) {
          for (final GroundStation station : context.stations) {
  
              final AbsoluteDate     date      = currentState.getDate();
              final Frame            inertial  = currentState.getFrame();
              final Vector3D         position  = currentState.getPVCoordinates().getPosition();
  
              if (station.getBaseFrame().getElevation(position, inertial, date) > FastMath.toRadians(30.0)) {
                  final UnivariateSolver solver = new BracketingNthOrderBrentSolver(1.0e-12, 5);
  
                  final double downLinkDelay  = solver.solve(1000, new UnivariateFunction() {
                      public double value(final double x) {
                          final Transform t = station.getOffsetToInertial(inertial, date.shiftedBy(x));
                          final double d = Vector3D.distance(position, t.transformPosition(Vector3D.ZERO));
                          return d - x * Constants.SPEED_OF_LIGHT;
                      }
                  }, -1.0, 1.0);
  
                  // Satellite position at signal departure
                  final Vector3D satelliteAtDeparture = currentState.shiftedBy(-downLinkDelay).getPVCoordinates().getPosition();
  
                  // Initialize measurement
                  final double[] angular = new double[2];
                  final double[] sigma = {1.0, 1.0};
                  final double[] baseweight = {10.0, 10.0};
  
                  // Compute measurement
                  // Elevation
                  angular[1] = station.getBaseFrame().getElevation(satelliteAtDeparture,
                                                                   currentState.getFrame(),
                                                                   currentState.getDate());
                  // Azimuth
                  angular[0] = station.getBaseFrame().getAzimuth(satelliteAtDeparture,
                                                                 currentState.getFrame(),
                                                                 currentState.getDate());
  
                 addMeasurement(new AngularAzEl(station, date, angular, sigma, baseweight, satellite));
             }
 
         }
     }
 
 }