/* Copyright 2002-2018 CS Systèmes d'Information
    * Licensed to CS Systèmes d'Information (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.gnss.attitude;
  
  import org.hipparchus.RealFieldElement;
  import org.orekit.attitudes.Attitude;
  import org.orekit.attitudes.FieldAttitude;
  import org.orekit.errors.OrekitException;
  import org.orekit.frames.Frame;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.time.FieldAbsoluteDate;
  import org.orekit.utils.ExtendedPVCoordinatesProvider;
  import org.orekit.utils.FieldPVCoordinatesProvider;
  import org.orekit.utils.PVCoordinatesProvider;
  import org.orekit.utils.TimeStampedAngularCoordinates;
  import org.orekit.utils.TimeStampedFieldAngularCoordinates;
  import org.orekit.utils.TimeStampedFieldPVCoordinates;
  import org.orekit.utils.TimeStampedPVCoordinates;
  
  /**
   * Base class for attitude providers for navigation satellites.
   *
   * @author Luc Maisonobe
   * @since 9.2
   */
  public abstract class AbstractGNSSAttitudeProvider implements GNSSAttitudeProvider {
  
      /** Serializable UID. */
      private static final long serialVersionUID = 20171114L;
  
      /** Start of validity for this provider. */
      private final AbsoluteDate validityStart;
  
      /** End of validity for this provider. */
      private final AbsoluteDate validityEnd;
  
      /** Provider for Sun position. */
      private final ExtendedPVCoordinatesProvider sun;
  
      /** Inertial frame where velocity are computed. */
      private final Frame inertialFrame;
  
      /** Simple constructor.
       * @param validityStart start of validity for this provider
       * @param validityEnd end of validity for this provider
       * @param sun provider for Sun position
       * @param inertialFrame inertial frame where velocity are computed
       */
      protected AbstractGNSSAttitudeProvider(final AbsoluteDate validityStart,
                                             final AbsoluteDate validityEnd,
                                             final ExtendedPVCoordinatesProvider sun,
                                             final Frame inertialFrame) {
          this.validityStart = validityStart;
          this.validityEnd   = validityEnd;
          this.sun           = sun;
          this.inertialFrame = inertialFrame;
      }
  
      /** {@inheritDoc} */
      @Override
      public AbsoluteDate validityStart() {
          return validityStart;
      }
  
      /** {@inheritDoc} */
      @Override
      public AbsoluteDate validityEnd() {
          return validityEnd;
      }
  
      /** {@inheritDoc} */
      @Override
      public Attitude getAttitude(final PVCoordinatesProvider pvProv,
                                  final AbsoluteDate date,
                                  final Frame frame)
          throws OrekitException {
  
          // Sun/spacecraft geometry
          // computed in inertial frame so orbital plane (which depends on spacecraft velocity) is correct
          final TimeStampedPVCoordinates sunPV = sun.getPVCoordinates(date, inertialFrame);
          final TimeStampedPVCoordinates svPV  = pvProv.getPVCoordinates(date, inertialFrame);
  
          // compute yaw correction
          final TimeStampedAngularCoordinates corrected = correctedYaw(new GNSSAttitudeContext(sunPV, svPV));
  
         return new Attitude(inertialFrame, corrected).withReferenceFrame(frame);
 
     }
 
     /** {@inheritDoc} */
     @Override
     public <T extends RealFieldElement<T>> FieldAttitude<T> getAttitude(final FieldPVCoordinatesProvider<T> pvProv,
                                                                         final FieldAbsoluteDate<T> date,
                                                                         final Frame frame)
         throws OrekitException {
 
         // Sun/spacecraft geometry
         // computed in inertial frame so orbital plane (which depends on spacecraft velocity) is correct
         final TimeStampedFieldPVCoordinates<T> sunPV = sun.getPVCoordinates(date, inertialFrame);
         final TimeStampedFieldPVCoordinates<T> svPV  = pvProv.getPVCoordinates(date, inertialFrame);
 
         // compute yaw correction
         final TimeStampedFieldAngularCoordinates<T> corrected = correctedYaw(new GNSSFieldAttitudeContext<>(sunPV, svPV));
 
         return new FieldAttitude<>(inertialFrame, corrected).withReferenceFrame(frame);
 
     }
 
     /** Compute GNSS attitude with midnight/noon yaw turn correction.
      * @param context context data for attitude computation
      * @return corrected yaw, using inertial frame as the reference
      * @exception OrekitException if yaw corrected attitude cannot be computed
      */
     protected abstract TimeStampedAngularCoordinates correctedYaw(GNSSAttitudeContext context)
         throws OrekitException;
 
     /** Compute GNSS attitude with midnight/noon yaw turn correction.
      * @param context context data for attitude computation
      * @param <T> type of the field elements
      * @return corrected yaw, using inertial frame as the reference
      * @exception OrekitException if yaw corrected attitude cannot be computed
      */
     protected abstract <T extends RealFieldElement<T>> TimeStampedFieldAngularCoordinates<T>
         correctedYaw(GNSSFieldAttitudeContext<T> context)
         throws OrekitException;
 
 }