/* 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.generation;
  
  import org.hipparchus.random.CorrelatedRandomVectorGenerator;
  import org.orekit.estimation.measurements.EstimationModifier;
  import org.orekit.estimation.measurements.InterSatellitesRange;
  import org.orekit.estimation.measurements.ObservableSatellite;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.utils.ParameterDriver;
  
  
  /** Builder for {@link InterSatellitesRange} measurements.
   * @author Luc Maisonobe
   * @since 9.3
   */
  public class InterSatellitesRangeBuilder extends AbstractMeasurementBuilder<InterSatellitesRange> {
  
      /** Flag indicating whether it is a two-way measurement. */
      private final boolean twoway;
  
      /** Simple constructor.
       * @param noiseSource noise source, may be null for generating perfect measurements
       * @param local satellite which receives the signal and performs the measurement
       * @param remote satellite which simply emits the signal in the one-way case,
       * or reflects the signal in the two-way case
       * @param twoWay flag indicating whether it is a two-way measurement
       * @param sigma theoretical standard deviation
       * @param baseWeight base weight
       */
      public InterSatellitesRangeBuilder(final CorrelatedRandomVectorGenerator noiseSource,
                                         final ObservableSatellite local, final ObservableSatellite remote,
                                         final boolean twoWay, final double sigma, final double baseWeight) {
          super(noiseSource, sigma, baseWeight, local, remote);
          this.twoway  = twoWay;
      }
  
      /** {@inheritDoc} */
      @Override
      public InterSatellitesRange build(final SpacecraftState[] states) {
  
          final ObservableSatellite[] satellites = getSatellites();
          final double sigma                     = getTheoreticalStandardDeviation()[0];
          final double baseWeight                = getBaseWeight()[0];
          final SpacecraftState[] relevant       = new SpacecraftState[] {
              states[satellites[0].getPropagatorIndex()],
              states[satellites[1].getPropagatorIndex()]
          };
          final SpacecraftState state            = states[satellites[0].getPropagatorIndex()];
  
          // create a dummy measurement
          final InterSatellitesRange dummy = new InterSatellitesRange(satellites[0], satellites[1], twoway, state.getDate(),
                                                                      Double.NaN, sigma, baseWeight);
          for (final EstimationModifier<InterSatellitesRange> modifier : getModifiers()) {
              dummy.addModifier(modifier);
          }
  
          // set a reference date for parameters missing one
          for (final ParameterDriver driver : dummy.getParametersDrivers()) {
              if (driver.getReferenceDate() == null) {
                  final AbsoluteDate start = getStart();
                  final AbsoluteDate end   = getEnd();
                  driver.setReferenceDate(start.durationFrom(end) <= 0 ? start : end);
              }
          }
  
          // estimate the perfect value of the measurement
          double range = dummy.estimate(0, 0, relevant).getEstimatedValue()[0];
  
          // add the noise
          final double[] noise = getNoise();
          if (noise != null) {
              range += noise[0];
          }
  
          // generate measurement
          final InterSatellitesRange measurement = new InterSatellitesRange(satellites[0], satellites[1], twoway, state.getDate(),
                                                                            range, sigma, baseWeight);
          for (final EstimationModifier<InterSatellitesRange> modifier : getModifiers()) {
              measurement.addModifier(modifier);
          }
          return measurement;
  
      }
 
 }