/* Copyright 2022-2025 Romain Serra
    * 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.forces.radiation;
  
  import org.hipparchus.CalculusFieldElement;
  import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  import org.hipparchus.geometry.euclidean.threed.Vector3D;
  import org.orekit.frames.Frame;
  import org.orekit.propagation.FieldSpacecraftState;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.time.FieldAbsoluteDate;
  import org.orekit.utils.ExtendedPositionProvider;
  
  /**
   * Abstract class for light flux models.
   * Via the definition of the lighting ratio and the unocculted flux vector, derives the final value.
   *
   * @author Romain Serra
   * @see LightFluxModel
   * @since 12.1
   */
  public abstract class AbstractLightFluxModel implements LightFluxModel {
  
      /** Direction provider for the occulted body e.g. the Sun. */
      private final ExtendedPositionProvider occultedBody;
  
      /**
       * Constructor.
       * @param occultedBody position provider for light source
       */
      protected AbstractLightFluxModel(final ExtendedPositionProvider occultedBody) {
          this.occultedBody = occultedBody;
      }
  
      /**
       * Getter for the occulted body's position provider.
       * @return occulted body
       */
      public ExtendedPositionProvider getOccultedBody() {
          return occultedBody;
      }
  
      /** {@inheritDoc} */
      @Override
      public Vector3D getLightFluxVector(final SpacecraftState state) {
          final Vector3D position = state.getPosition();
          final Vector3D lightSourcePosition = getOccultedBodyPosition(state.getDate(), state.getFrame());
          final double lightingRatio = getLightingRatio(position, lightSourcePosition);
          if (lightingRatio != 0.) {
              final Vector3D relativePosition = position.subtract(lightSourcePosition);
              final Vector3D unoccultedFlux = getUnoccultedFluxVector(relativePosition);
              return unoccultedFlux.scalarMultiply(lightingRatio);
          } else {
              return Vector3D.ZERO;
          }
      }
  
      /** {@inheritDoc} */
      @Override
      public <T extends CalculusFieldElement<T>> FieldVector3D<T> getLightFluxVector(final FieldSpacecraftState<T> state) {
          final FieldVector3D<T> position = state.getPosition();
          final FieldVector3D<T> lightSourcePosition = getOccultedBodyPosition(state.getDate(), state.getFrame());
          final T lightingRatio = getLightingRatio(position, lightSourcePosition);
          final FieldVector3D<T> relativePosition = position.subtract(lightSourcePosition);
          final FieldVector3D<T> unoccultedFlux = getUnoccultedFluxVector(relativePosition);
          return unoccultedFlux.scalarMultiply(lightingRatio);
      }
  
      /**
       * Method computing the occulted body's position at a given date and frame.
       * @param date date
       * @param frame frame
       * @return position
       */
      protected Vector3D getOccultedBodyPosition(final AbsoluteDate date, final Frame frame) {
          return occultedBody.getPosition(date, frame);
      }
  
      /**
       * Method computing the occulted body's position at a given date and frame. Field version.
       * @param date date
       * @param frame frame
       * @param <T> field type
       * @return position
      */
     protected <T extends CalculusFieldElement<T>> FieldVector3D<T> getOccultedBodyPosition(final FieldAbsoluteDate<T> date,
                                                                                            final Frame frame) {
         return occultedBody.getPosition(date, frame);
     }
 
     /** Get the light flux vector, not considering any shadowing effect.
      * @param relativePosition relative position w.r.t. light source
      * @return unocculted flux
      */
     protected abstract Vector3D getUnoccultedFluxVector(Vector3D relativePosition);
 
     /** Get the light flux vector, not considering any shadowing effect. Field version.
      * @param relativePosition relative position w.r.t. light source
      * @param <T> field type
      * @return unocculted flux
      */
     protected abstract <T extends CalculusFieldElement<T>> FieldVector3D<T> getUnoccultedFluxVector(FieldVector3D<T> relativePosition);
 
     /** Get the lighting ratio ([0-1]).
      * @param state state
      * @return lighting ratio
      */
     public double getLightingRatio(final SpacecraftState state) {
         final Vector3D position = state.getPosition();
         final Vector3D lightSourcePosition = getOccultedBodyPosition(state.getDate(), state.getFrame());
         return getLightingRatio(position, lightSourcePosition);
     }
 
     /** Get the lighting ratio ([0-1]).
      * @param position object's position
      * @param occultedBodyPosition occulted body position in same frame
      * @return lighting ratio
      */
     protected abstract double getLightingRatio(Vector3D position, Vector3D occultedBodyPosition);
 
     /** Get the lighting ratio ([0-1]).
      * @param state state
      * @param <T> field type
      * @return lighting ratio
      */
     public <T extends CalculusFieldElement<T>> T getLightingRatio(final FieldSpacecraftState<T> state) {
         final FieldVector3D<T> position = state.getPosition();
         final FieldVector3D<T> lightSourcePosition = getOccultedBodyPosition(state.getDate(), state.getFrame());
         return getLightingRatio(position, lightSourcePosition);
     }
 
     /** Get the lighting ratio ([0-1]). Field version.
      * @param position object's position
      * @param occultedBodyPosition occulted body position in same frame
      * @param <T> field type
      * @return lighting ratio
      */
     protected abstract <T extends CalculusFieldElement<T>> T getLightingRatio(FieldVector3D<T> position,
                                                                               FieldVector3D<T> occultedBodyPosition);
 
 }