/* Contributed in the public domain.
    * 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.files.general;
  
  import java.util.List;
  import java.util.stream.Stream;
  
  import org.orekit.attitudes.InertialProvider;
  import org.orekit.errors.OrekitException;
  import org.orekit.errors.OrekitMessages;
  import org.orekit.files.general.EphemerisFile.EphemerisSegment;
  import org.orekit.frames.Frame;
  import org.orekit.orbits.CartesianOrbit;
  import org.orekit.orbits.Orbit;
  import org.orekit.propagation.BoundedPropagator;
  import org.orekit.propagation.Propagator;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.propagation.analytical.AbstractAnalyticalPropagator;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.utils.ImmutableTimeStampedCache;
  import org.orekit.utils.TimeStampedPVCoordinates;
  
  /**
   * A {@link Propagator} based on a {@link EphemerisSegment}.
   *
   * <p> The {@link #getPVCoordinates(AbsoluteDate, Frame)} is implemented without using the
   * {@link #propagate(AbsoluteDate)} methods so using this class as a {@link
   * org.orekit.utils.PVCoordinatesProvider} still behaves as expected when the ephemeris
   * file did not have a valid gravitational parameter.
   * @param <C> type of the Cartesian coordinates
   *
   * @author Evan Ward
   */
  class EphemerisSegmentPropagator<C extends TimeStampedPVCoordinates> extends AbstractAnalyticalPropagator
          implements BoundedPropagator {
  
      /**
       * Sorted cache of state vectors. A duplication of the information in {@link
       * #ephemeris} that could be avoided by duplicating the logic of {@link
       * ImmutableTimeStampedCache#getNeighbors(AbsoluteDate)} for a general {@link List}.
       */
      private final ImmutableTimeStampedCache<C> cache;
      /** Tabular data from which this propagator is built. */
      private final EphemerisSegment<C> ephemeris;
      /** Inertial frame used for creating orbits. */
      private final Frame inertialFrame;
      /** Frame of the ephemeris data. */
      private final Frame ephemerisFrame;
  
      /**
       * Create a {@link Propagator} from an ephemeris segment.
       *
       * @param ephemeris segment containing the data for this propagator.
       */
      EphemerisSegmentPropagator(final EphemerisSegment<C> ephemeris) {
          super(new InertialProvider(ephemeris.getInertialFrame()));
          this.cache = new ImmutableTimeStampedCache<>(
                  ephemeris.getInterpolationSamples(),
                  ephemeris.getCoordinates());
          this.ephemeris = ephemeris;
          this.ephemerisFrame = ephemeris.getFrame();
          this.inertialFrame = ephemeris.getInertialFrame();
          // set the initial state so getFrame() works
          final TimeStampedPVCoordinates ic = cache.getEarliest();
          final TimeStampedPVCoordinates icInertial = ephemerisFrame
                  .getTransformTo(inertialFrame, ic.getDate())
                  .transformPVCoordinates(ic);
          super.resetInitialState(
                  new SpacecraftState(
                          new CartesianOrbit(
                                  icInertial, inertialFrame, ephemeris.getMu()
                          ),
                          getAttitudeProvider().getAttitude(
                                  icInertial.toTaylorProvider(inertialFrame),
                                  ic.getDate(),
                                  inertialFrame),
                          DEFAULT_MASS
                  )
          );
      }
  
      @Override
      public TimeStampedPVCoordinates getPVCoordinates(final AbsoluteDate date, final Frame frame) {
          final Stream<C> neighbors = this.cache.getNeighbors(date);
          final TimeStampedPVCoordinates point =
                 TimeStampedPVCoordinates.interpolate(date, ephemeris.getAvailableDerivatives(), neighbors);
         return ephemerisFrame.getTransformTo(frame, date).transformPVCoordinates(point);
     }
 
     @Override
     protected Orbit propagateOrbit(final AbsoluteDate date) {
         final TimeStampedPVCoordinates pv = this.getPVCoordinates(date, inertialFrame);
         return new CartesianOrbit(pv, inertialFrame, this.ephemeris.getMu());
     }
 
     @Override
     public AbsoluteDate getMinDate() {
         return ephemeris.getStart();
     }
 
     @Override
     public AbsoluteDate getMaxDate() {
         return ephemeris.getStop();
     }
 
     @Override
     protected double getMass(final AbsoluteDate date) {
         return DEFAULT_MASS;
     }
 
     @Override
     public SpacecraftState getInitialState() {
         return this.basicPropagate(this.getMinDate());
     }
 
     @Override
     protected void resetIntermediateState(final SpacecraftState state,
                                           final boolean forward) {
         throw new OrekitException(OrekitMessages.NON_RESETABLE_STATE);
     }
 
     @Override
     public void resetInitialState(final SpacecraftState state) {
         throw new OrekitException(OrekitMessages.NON_RESETABLE_STATE);
     }
 
 }