/* Copyright 2022-2025 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.generation;
  
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  import java.util.Map;
  
  import org.orekit.estimation.measurements.EstimatedMeasurementBase;
  import org.orekit.estimation.measurements.EstimationModifier;
  import org.orekit.estimation.measurements.MultiplexedMeasurement;
  import org.orekit.estimation.measurements.ObservableSatellite;
  import org.orekit.estimation.measurements.ObservedMeasurement;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.propagation.sampling.OrekitStepInterpolator;
  import org.orekit.time.AbsoluteDate;
  
  
  /** Builder for {@link MultiplexedMeasurement} measurements.
   * @author Luc Maisonobe
   * @since 12.0
   */
  public class MultiplexedMeasurementBuilder implements MeasurementBuilder<MultiplexedMeasurement> {
  
      /** Builders for individual measurements. */
      private final List<MeasurementBuilder<?>> builders;
  
      /** Satellites related to this builder. */
      private final ObservableSatellite[] satellites;
  
      /** Modifiers that apply to the measurement.*/
      private final List<EstimationModifier<MultiplexedMeasurement>> modifiers;
  
      /** Simple constructor.
       * @param builders builders for multiplexed measurements
       */
      public MultiplexedMeasurementBuilder(final List<MeasurementBuilder<?>> builders) {
          this.builders  = builders;
          this.modifiers = new ArrayList<>();
  
          final List<ObservableSatellite> list = new ArrayList<>();
          for (final MeasurementBuilder<?> builder : builders) {
              for (final ObservableSatellite satellite : builder.getSatellites()) {
                  if (!list.contains(satellite)) {
                      list.add(satellite);
                  }
              }
          }
          this.satellites = list.toArray(new ObservableSatellite[0]);
  
      }
  
      /** {@inheritDoc}
       * <p>
       * This implementation stores the time span of the measurements generation.
       * </p>
       */
      @Override
      public void init(final AbsoluteDate start, final AbsoluteDate end) {
          for (final MeasurementBuilder<?> builder : builders) {
              builder.init(start, end);
          }
      }
  
      /** {@inheritDoc} */
      @Override
      public void addModifier(final EstimationModifier<MultiplexedMeasurement> modifier) {
          modifiers.add(modifier);
      }
  
      /** {@inheritDoc} */
      @Override
      public List<EstimationModifier<MultiplexedMeasurement>> getModifiers() {
          return Collections.unmodifiableList(modifiers);
      }
  
      /** {@inheritDoc} */
      @Override
      public EstimatedMeasurementBase<MultiplexedMeasurement> build(final AbsoluteDate date,
                                                                    final Map<ObservableSatellite, OrekitStepInterpolator> interpolators) {
  
          // estimate underlying measurements
          final List<EstimatedMeasurementBase<?>> underlyingEstimated = new ArrayList<>(builders.size());
          final List<ObservedMeasurement<?>>      underlyingObserved  = new ArrayList<>(builders.size());
         for (final MeasurementBuilder<?> builder : builders) {
             final EstimatedMeasurementBase<?> built = builder.build(date, interpolators);
             underlyingEstimated.add(built);
             underlyingObserved.add(built.getObservedMeasurement());
         }
 
         // generate observed multiplexed measurement
         final MultiplexedMeasurement measurement = new MultiplexedMeasurement(underlyingObserved);
         for (final EstimationModifier<MultiplexedMeasurement> modifier : getModifiers()) {
             measurement.addModifier(modifier);
         }
 
         // generate estimated multiplexed measurement
         final SpacecraftState[] states = new SpacecraftState[satellites.length];
         for (int i = 0; i < underlyingEstimated.size(); ++i) {
             final EstimatedMeasurementBase<?> mI = underlyingEstimated.get(i);
             final SpacecraftState[] statesI = mI.getStates();
             for (int j = 0; j < statesI.length; ++j) {
                 states[measurement.getMultiplexedStateIndex(i, j)] = statesI[j];
             }
         }
         return measurement.estimateWithoutDerivatives(states);
 
     }
 
     /** {@inheritDoc} */
     @Override
     public ObservableSatellite[] getSatellites() {
         return satellites.clone();
     }
 
 }