/* Copyright 2022-2026 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.time.clocks;
  
  import java.util.ArrayList;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.function.DoubleFunction;
  
  import org.hipparchus.CalculusFieldElement;
  import org.hipparchus.Field;
  import org.hipparchus.analysis.differentiation.Gradient;
  import org.orekit.errors.OrekitException;
  import org.orekit.errors.OrekitMessages;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.utils.drivers.ParameterDriver;
  import org.orekit.utils.TimeSpanMap;
  
  /**
   * Offset clock model aggregating several other clock models.
   *
   * @author Luc Maisonobe
   * @since 12.1
   */
  public class AggregatedClockModel implements ClockModel {
  
      /** Underlying clock models. */
      private final TimeSpanMap<ClockModel> models;
  
      /** Cached field-based models.
       * @since 14.0
       */
      private final Map<Field<? extends CalculusFieldElement<?>>, AggregatedFieldClockModel<?>> fieldModels;
  
      /** Simple constructor.
       * @param models underlying clock models
       */
      public AggregatedClockModel(final TimeSpanMap<ClockModel> models) {
  
          try {
              // we ignore the result, we just want to check some data is present
              models.getFirstNonNullSpan();
          } catch (OrekitException oe) {
              throw new OrekitException(oe, OrekitMessages.NOT_ENOUGH_DATA, 0);
          }
  
          this.models      = models;
          this.fieldModels = new HashMap<>();
      }
  
      /** Get the underlying models.
       * @return underlying models
       */
      public TimeSpanMap<ClockModel> getModels() {
          return models;
      }
  
      /** {@inheritDoc} */
      @Override
      public AbsoluteDate getValidityStart() {
          return models.getFirstNonNullSpan().getStart();
      }
  
      /** {@inheritDoc} */
      @Override
      public AbsoluteDate getValidityEnd() {
          return models.getLastNonNullSpan().getEnd();
      }
  
      /** {@inheritDoc} */
      @Override
      public List<ParameterDriver> getParametersDrivers() {
          final List<ParameterDriver> drivers = new ArrayList<>();
          models.forEach(model -> drivers.addAll(model.getParametersDrivers()));
          return drivers;
      }
  
      /** {@inheritDoc} */
      @Override
      public ClockOffset getOffset(final AbsoluteDate date) {
          return getModel(date).getOffset(date);
      }
  
      /** {@inheritDoc} */
     @Override
     @SuppressWarnings("unchecked")
     public <T extends CalculusFieldElement<T>> AggregatedFieldClockModel<T> toField(final DoubleFunction<T> converter) {
         // build aggregated models may be costly, so we cache the results
         return (AggregatedFieldClockModel<T>) fieldModels.computeIfAbsent(converter.apply(0.0).getField(),
                                                                           f -> buildFieldModel(converter));
     }
 
     /**
      * Build a field model.
      * @param <T> type of the field elements
      * @param converter converter to field elements
      * @return field version of the instance
      * @since 14.0
      */
     private <T extends CalculusFieldElement<T>> AggregatedFieldClockModel<T> buildFieldModel(final DoubleFunction<T> converter) {
         final TimeSpanMap<FieldClockModel<T>> fieldMap = new TimeSpanMap<>(null);
         for (TimeSpanMap.Span<ClockModel> span = models.getFirstSpan(); span != null; span = span.next()) {
             fieldMap.addValidBetween(span.getData() == null ? null : span.getData().toField(converter),
                                      span.getStart(), span.getEnd());
         }
         return new AggregatedFieldClockModel<>(fieldMap);
     }
 
     /** {@inheritDoc} */
     @Override
     public AggregatedFieldClockModel<Gradient> toGradient(final int freeParameters, final Map<String, Integer> indices) {
         final TimeSpanMap<FieldClockModel<Gradient>> fieldMap = new TimeSpanMap<>(null);
         for (TimeSpanMap.Span<ClockModel> span = models.getFirstSpan(); span != null; span = span.next()) {
             fieldMap.addValidBetween(span.getData() == null ?
                                      null :
                                      span.getData().toGradient(freeParameters, indices),
                                      span.getStart(), span.getEnd());
         }
         return new AggregatedFieldClockModel<>(fieldMap);
     }
 
     /**
      * Get the model valid at specified date.
      *
      * @param date date for which model is requested
      * @return clock model valid at date
      */
     private ClockModel getModel(final AbsoluteDate date) {
         final ClockModel clockModel = models.get(date);
         if (clockModel == null) {
             // this may happen if map is limited or not contiguous
             // typically for models retrieved from SP3Ephemeris
             throw new OrekitException(OrekitMessages.NO_DATA_GENERATED, date);
         }
         return clockModel;
     }
 
 }