/* Copyright 2002-2024 CS GROUP
    * 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,
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   * 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.hipparchus.util.FastMath;
  import org.hipparchus.util.Precision;
  import org.orekit.bodies.OneAxisEllipsoid;
  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.Constants;
  import org.orekit.utils.ExtendedPVCoordinatesProvider;
  import org.orekit.utils.FrameAdapter;
  import org.orekit.utils.OccultationEngine;
  import org.orekit.utils.ParameterDriver;
  
  import java.lang.reflect.Array;
  import java.util.List;
  
  /** Solar radiation pressure force model.
   * <p>
   * Since Orekit 11.0, it is possible to take into account
   * the eclipses generated by Moon in the solar radiation
   * pressure force model using the
   * {@link #addOccultingBody(ExtendedPVCoordinatesProvider, double)}
   * method.
   * <p>
   * Example:<br>
   * <code> SolarRadiationPressure srp = </code>
   * <code>                      new SolarRadiationPressure(CelestialBodyFactory.getSun(), Constants.EIGEN5C_EARTH_EQUATORIAL_RADIUS,</code>
   * <code>                                     new IsotropicRadiationClassicalConvention(50.0, 0.5, 0.5));</code><br>
   * <code> srp.addOccultingBody(CelestialBodyFactory.getMoon(), Constants.MOON_EQUATORIAL_RADIUS);</code><br>
   *
   * @author Fabien Maussion
   * @author &Eacute;douard Delente
   * @author V&eacute;ronique Pommier-Maurussane
   * @author Pascal Parraud
   */
  public class SolarRadiationPressure extends AbstractRadiationForceModel {
  
      /** Reference distance for the solar radiation pressure (m). */
      private static final double D_REF = 149597870000.0;
  
      /** Reference solar radiation pressure at D_REF (N/m²). */
      private static final double P_REF = 4.56e-6;
  
      /** Margin to force recompute lighting ratio derivatives when we are really inside penumbra. */
      private static final double ANGULAR_MARGIN = 1.0e-10;
  
      /** Threshold to decide whether the S/C frame is Sun-centered. */
      private static final double SUN_CENTERED_FRAME_THRESHOLD = 2. * Constants.SUN_RADIUS;
  
      /** Reference flux normalized for a 1m distance (N). */
      private final double kRef;
  
      /** Sun model. */
      private final ExtendedPVCoordinatesProvider sun;
  
      /** Spacecraft. */
      private final RadiationSensitive spacecraft;
  
      /** Simple constructor with default reference values.
       * <p>When this constructor is used, the reference values are:</p>
       * <ul>
       *   <li>d<sub>ref</sub> = 149597870000.0 m</li>
       *   <li>p<sub>ref</sub> = 4.56 10<sup>-6</sup> N/m²</li>
       * </ul>
       * @param sun Sun model
       * @param centralBody central body shape model (for umbra/penumbra computation)
       * @param spacecraft the object physical and geometrical information
       * @since 12.0
       */
      public SolarRadiationPressure(final ExtendedPVCoordinatesProvider sun,
                                    final OneAxisEllipsoid centralBody,
                                    final RadiationSensitive spacecraft) {
          this(D_REF, P_REF, sun, centralBody, spacecraft);
      }
  
      /** Complete constructor.
       * <p>Note that reference solar radiation pressure <code>pRef</code> in
      * N/m² is linked to solar flux SF in W/m² using
      * formula pRef = SF/c where c is the speed of light (299792458 m/s). So
      * at 1UA a 1367 W/m² solar flux is a 4.56 10<sup>-6</sup>
      * N/m² solar radiation pressure.</p>
      * @param dRef reference distance for the solar radiation pressure (m)
      * @param pRef reference solar radiation pressure at dRef (N/m²)
      * @param sun Sun model
      * @param centralBody central body shape model (for umbra/penumbra computation)
      * @param spacecraft the object physical and geometrical information
      * @since 12.0
      */
     public SolarRadiationPressure(final double dRef, final double pRef,
                                   final ExtendedPVCoordinatesProvider sun,
                                   final OneAxisEllipsoid centralBody,
                                   final RadiationSensitive spacecraft) {
         super(sun, centralBody);
         this.kRef = pRef * dRef * dRef;
         this.sun  = sun;
         this.spacecraft = spacecraft;
     }
 
     /**
      * Getter for radiation-sensitive spacecraft.
      * @return radiation-sensitive model
      * @since 12.1
      */
     public RadiationSensitive getRadiationSensitiveSpacecraft() {
         return spacecraft;
     }
 
     /** {@inheritDoc} */
     @Override
     public boolean dependsOnPositionOnly() {
         return spacecraft instanceof IsotropicRadiationClassicalConvention || spacecraft instanceof IsotropicRadiationCNES95Convention || spacecraft instanceof IsotropicRadiationSingleCoefficient;
     }
 
     /** {@inheritDoc} */
     @Override
     public Vector3D acceleration(final SpacecraftState s, final double[] parameters) {
 
         final AbsoluteDate date         = s.getDate();
         final Frame        frame        = s.getFrame();
         final Vector3D     position     = s.getPosition();
         final Vector3D     sunPosition  = sun.getPosition(date, frame);
         final Vector3D     sunSatVector = position.subtract(sunPosition);
         final double       r2           = sunSatVector.getNormSq();
 
         // compute flux
         final double   ratio = getLightingRatio(s, sunPosition);
         final double   rawP  = ratio  * kRef / r2;
         final Vector3D flux  = new Vector3D(rawP / FastMath.sqrt(r2), sunSatVector);
 
         return spacecraft.radiationPressureAcceleration(s, flux, parameters);
 
     }
 
     /** {@inheritDoc} */
     @Override
     public <T extends CalculusFieldElement<T>> FieldVector3D<T> acceleration(final FieldSpacecraftState<T> s,
                                                                              final T[] parameters) {
 
         final FieldAbsoluteDate<T> date         = s.getDate();
         final Frame                frame        = s.getFrame();
         final FieldVector3D<T>     position     = s.getPosition();
         final FieldVector3D<T>     sunPosition  = sun.getPosition(date, frame);
         final FieldVector3D<T>     sunSatVector = position.subtract(sunPosition);
         final T                    r2           = sunSatVector.getNormSq();
 
         // compute flux
         final T                ratio = getLightingRatio(s, sunPosition);
         final T                rawP  = ratio.multiply(kRef).divide(r2);
         final FieldVector3D<T> flux  = new FieldVector3D<>(rawP.divide(r2.sqrt()), sunSatVector);
 
         return spacecraft.radiationPressureAcceleration(s, flux, parameters);
 
     }
 
     /** Check whether the frame is considerer Sun-centered.
      *
      * @param sunPositionInFrame Sun position in frame to test
      * @return true if frame is considered Sun-centered
      * @since 12.0
      */
     private boolean isSunCenteredFrame(final Vector3D sunPositionInFrame) {
         // Frame is considered Sun-centered if Sun (or Solar System barycenter) position
         // in that frame is smaller than SUN_CENTERED_FRAME_THRESHOLD
         return sunPositionInFrame.getNorm() < SUN_CENTERED_FRAME_THRESHOLD;
     }
 
 
     /** Get the lighting ratio ([0-1]).
      * @param state spacecraft state
      * @param sunPosition Sun position in S/C frame at S/C date
      * @return lighting ratio
      * @since 12.0 added to avoid numerous call to sun.getPosition(...)
      */
     private double getLightingRatio(final SpacecraftState state, final Vector3D sunPosition) {
 
         // Check if S/C frame is Sun-centered
         if (isSunCenteredFrame(sunPosition)) {
             // We are in fact computing a trajectory around Sun (or solar system barycenter),
             // not around a planet, we consider lighting ratio will always be 1
             return 1.0;
         }
 
         final List<OccultationEngine> occultingBodies = getOccultingBodies();
         final int n = occultingBodies.size();
 
         final OccultationEngine.OccultationAngles[] angles = new OccultationEngine.OccultationAngles[n];
         for (int i = 0; i < n; ++i) {
             angles[i] = occultingBodies.get(i).angles(state);
         }
         final double alphaSunSq = angles[0].getOccultedApparentRadius() * angles[0].getOccultedApparentRadius();
 
         double result = 0.0;
         for (int i = 0; i < n; ++i) {
 
             // compute lighting ratio considering one occulting body only
             final OccultationEngine oi  = occultingBodies.get(i);
             final double lightingRatioI = maskingRatio(angles[i]);
             if (lightingRatioI == 0.0) {
                 // body totally occults Sun, total eclipse is occurring.
                 return 0.0;
             }
             result += lightingRatioI;
 
             // Mutual occulting body eclipse ratio computations between first and secondary bodies
             for (int j = i + 1; j < n; ++j) {
 
                 final OccultationEngine oj = occultingBodies.get(j);
                 final double lightingRatioJ = maskingRatio(angles[j]);
                 if (lightingRatioJ == 0.0) {
                     // Secondary body totally occults Sun, no more computations are required, total eclipse is occurring.
                     return 0.0;
                 } else if (lightingRatioJ != 1) {
                     // Secondary body partially occults Sun
 
                     final OccultationEngine oij = new OccultationEngine(new FrameAdapter(oi.getOcculting().getBodyFrame()),
                                                                         oi.getOcculting().getEquatorialRadius(),
                                                                         oj.getOcculting());
                     final OccultationEngine.OccultationAngles aij = oij.angles(state);
                     final double maskingRatioIJ = maskingRatio(aij);
                     final double alphaJSq       = aij.getOccultedApparentRadius() * aij.getOccultedApparentRadius();
 
                     final double mutualEclipseCorrection = (1 - maskingRatioIJ) * alphaJSq / alphaSunSq;
                     result -= mutualEclipseCorrection;
 
                 }
 
             }
         }
 
         // Final term
         result -= n - 1;
 
         return result;
     }
 
     /** Get the lighting ratio ([0-1]).
      * @param state spacecraft state
      * @return lighting ratio
      * @since 7.1
      */
     public double getLightingRatio(final SpacecraftState state) {
         return getLightingRatio(state, sun.getPosition(state.getDate(), state.getFrame()));
     }
 
     /** Get the masking ratio ([0-1]) considering one pair of bodies.
      * @param angles occultation angles
      * @return masking ratio: 0.0 body fully masked, 1.0 body fully visible
      * @since 12.0
      */
     private double maskingRatio(final OccultationEngine.OccultationAngles angles) {
 
         // Sat-Occulted/ Sat-Occulting angle
         final double sunSatCentralBodyAngle = angles.getSeparation();
 
         // Occulting apparent radius
         final double alphaCentral = angles.getLimbRadius();
 
         // Occulted apparent radius
         final double alphaSun = angles.getOccultedApparentRadius();
 
         // Is the satellite in complete umbra ?
         if (sunSatCentralBodyAngle - alphaCentral + alphaSun <= ANGULAR_MARGIN) {
             return 0.0;
         } else if (sunSatCentralBodyAngle - alphaCentral - alphaSun < -ANGULAR_MARGIN) {
             // Compute a masking ratio in penumbra
             final double sEA2    = sunSatCentralBodyAngle * sunSatCentralBodyAngle;
             final double oo2sEA  = 1.0 / (2. * sunSatCentralBodyAngle);
             final double aS2     = alphaSun * alphaSun;
             final double aE2     = alphaCentral * alphaCentral;
             final double aE2maS2 = aE2 - aS2;
 
             final double alpha1  = (sEA2 - aE2maS2) * oo2sEA;
             final double alpha2  = (sEA2 + aE2maS2) * oo2sEA;
 
             // Protection against numerical inaccuracy at boundaries
             final double almost0 = Precision.SAFE_MIN;
             final double almost1 = FastMath.nextDown(1.0);
             final double a1oaS   = FastMath.min(almost1, FastMath.max(-almost1, alpha1 / alphaSun));
             final double aS2ma12 = FastMath.max(almost0, aS2 - alpha1 * alpha1);
             final double a2oaE   = FastMath.min(almost1, FastMath.max(-almost1, alpha2 / alphaCentral));
             final double aE2ma22 = FastMath.max(almost0, aE2 - alpha2 * alpha2);
 
             final double P1 = aS2 * FastMath.acos(a1oaS) - alpha1 * FastMath.sqrt(aS2ma12);
             final double P2 = aE2 * FastMath.acos(a2oaE) - alpha2 * FastMath.sqrt(aE2ma22);
 
             return 1. - (P1 + P2) / (FastMath.PI * aS2);
         } else {
             return 1.0;
         }
 
     }
 
     /** Get the lighting ratio ([0-1]).
      * @param state spacecraft state
      * @param sunPosition Sun position in S/C frame at S/C date
      * @param <T> extends CalculusFieldElement
      * @return lighting ratio
      * @since 12.0 added to avoid numerous call to sun.getPosition(...)
      */
     private <T extends CalculusFieldElement<T>> T getLightingRatio(final FieldSpacecraftState<T> state, final FieldVector3D<T> sunPosition) {
 
         final T one  = state.getDate().getField().getOne();
         if (isSunCenteredFrame(sunPosition.toVector3D())) {
             // We are in fact computing a trajectory around Sun (or solar system barycenter),
             // not around a planet, we consider lighting ratio will always be 1
             return one;
         }
         final T zero = state.getDate().getField().getZero();
         final List<OccultationEngine> occultingBodies = getOccultingBodies();
         final int n = occultingBodies.size();
 
         @SuppressWarnings("unchecked")
         final OccultationEngine.FieldOccultationAngles<T>[] angles =
         (OccultationEngine.FieldOccultationAngles<T>[]) Array.newInstance(OccultationEngine.FieldOccultationAngles.class, n);
         for (int i = 0; i < n; ++i) {
             angles[i] = occultingBodies.get(i).angles(state);
         }
         final T alphaSunSq = angles[0].getOccultedApparentRadius().multiply(angles[0].getOccultedApparentRadius());
 
         T result = state.getDate().getField().getZero();
         for (int i = 0; i < n; ++i) {
 
             // compute lighting ratio considering one occulting body only
             final OccultationEngine oi  = occultingBodies.get(i);
             final T lightingRatioI = maskingRatio(angles[i]);
             if (lightingRatioI.isZero()) {
                 // body totally occults Sun, total eclipse is occurring.
                 return zero;
             }
             result = result.add(lightingRatioI);
 
             // Mutual occulting body eclipse ratio computations between first and secondary bodies
             for (int j = i + 1; j < n; ++j) {
 
                 final OccultationEngine oj = occultingBodies.get(j);
                 final T lightingRatioJ = maskingRatio(angles[j]);
                 if (lightingRatioJ.isZero()) {
                     // Secondary body totally occults Sun, no more computations are required, total eclipse is occurring.
                     return zero;
                 } else if (lightingRatioJ.getReal() != 1) {
                     // Secondary body partially occults Sun
 
                     final OccultationEngine oij = new OccultationEngine(new FrameAdapter(oi.getOcculting().getBodyFrame()),
                                                                         oi.getOcculting().getEquatorialRadius(),
                                                                         oj.getOcculting());
                     final OccultationEngine.FieldOccultationAngles<T> aij = oij.angles(state);
                     final T maskingRatioIJ = maskingRatio(aij);
                     final T alphaJSq       = aij.getOccultedApparentRadius().multiply(aij.getOccultedApparentRadius());
 
                     final T mutualEclipseCorrection = one.subtract(maskingRatioIJ).multiply(alphaJSq).divide(alphaSunSq);
                     result = result.subtract(mutualEclipseCorrection);
 
                 }
 
             }
         }
 
         // Final term
         result = result.subtract(n - 1);
 
         return result;
     }
 
     /** Get the lighting ratio ([0-1]).
      * @param state spacecraft state
      * @param <T> extends CalculusFieldElement
      * @return lighting ratio
      * @since 7.1
      */
     public <T extends CalculusFieldElement<T>> T getLightingRatio(final FieldSpacecraftState<T> state) {
         return getLightingRatio(state, sun.getPosition(state.getDate(), state.getFrame()));
     }
 
     /** Get the masking ratio ([0-1]) considering one pair of bodies.
      * @param angles occultation angles
      * @param <T> type of the field elements
      * @return masking ratio: 0.0 body fully masked, 1.0 body fully visible
      * @since 12.0
      */
     private <T extends CalculusFieldElement<T>> T maskingRatio(final OccultationEngine.FieldOccultationAngles<T> angles) {
 
 
         // Sat-Occulted/ Sat-Occulting angle
         final T occultedSatOcculting = angles.getSeparation();
 
         // Occulting apparent radius
         final T alphaOcculting = angles.getLimbRadius();
 
         // Occulted apparent radius
         final T alphaOcculted = angles.getOccultedApparentRadius();
 
         // Is the satellite in complete umbra ?
         if (occultedSatOcculting.getReal() - alphaOcculting.getReal() + alphaOcculted.getReal() <= ANGULAR_MARGIN) {
             return occultedSatOcculting.getField().getZero();
         } else if (occultedSatOcculting.getReal() - alphaOcculting.getReal() - alphaOcculted.getReal() < -ANGULAR_MARGIN) {
             // Compute a masking ratio in penumbra
             final T sEA2    = occultedSatOcculting.multiply(occultedSatOcculting);
             final T oo2sEA  = occultedSatOcculting.multiply(2).reciprocal();
             final T aS2     = alphaOcculted.multiply(alphaOcculted);
             final T aE2     = alphaOcculting.multiply(alphaOcculting);
             final T aE2maS2 = aE2.subtract(aS2);
 
             final T alpha1  = sEA2.subtract(aE2maS2).multiply(oo2sEA);
             final T alpha2  = sEA2.add(aE2maS2).multiply(oo2sEA);
 
             // Protection against numerical inaccuracy at boundaries
             final double almost0 = Precision.SAFE_MIN;
             final double almost1 = FastMath.nextDown(1.0);
             final T a1oaS   = min(almost1, max(-almost1, alpha1.divide(alphaOcculted)));
             final T aS2ma12 = max(almost0, aS2.subtract(alpha1.multiply(alpha1)));
             final T a2oaE   = min(almost1, max(-almost1, alpha2.divide(alphaOcculting)));
             final T aE2ma22 = max(almost0, aE2.subtract(alpha2.multiply(alpha2)));
 
             final T P1 = aS2.multiply(a1oaS.acos()).subtract(alpha1.multiply(aS2ma12.sqrt()));
             final T P2 = aE2.multiply(a2oaE.acos()).subtract(alpha2.multiply(aE2ma22.sqrt()));
 
             return occultedSatOcculting.getField().getOne().subtract(P1.add(P2).divide(aS2.multiply(occultedSatOcculting.getPi())));
         } else {
             return occultedSatOcculting.getField().getOne();
         }
 
     }
 
     /** {@inheritDoc} */
     @Override
     public List<ParameterDriver> getParametersDrivers() {
         return spacecraft.getRadiationParametersDrivers();
     }
 
     /** Compute min of two values, one double and one field element.
      * @param d double value
      * @param f field element
      * @param <T> type of the field elements
      * @return min value
      */
     private <T extends CalculusFieldElement<T>> T min(final double d, final T f) {
         return (f.getReal() > d) ? f.getField().getZero().newInstance(d) : f;
     }
 
     /** Compute max of two values, one double and one field element.
      * @param d double value
      * @param f field element
      * @param <T> type of the field elements
      * @return max value
      */
     private <T extends CalculusFieldElement<T>> T max(final double d, final T f) {
         return (f.getReal() <= d) ? f.getField().getZero().newInstance(d) : f;
     }
 
 }