/* Copyright 2010-2011 Centre National d'Études Spatiales
    * 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.forces.gravity;
  
  import org.apache.commons.math3.analysis.differentiation.DerivativeStructure;
  import org.apache.commons.math3.geometry.euclidean.threed.FieldRotation;
  import org.apache.commons.math3.geometry.euclidean.threed.FieldVector3D;
  import org.apache.commons.math3.geometry.euclidean.threed.Vector3D;
  import org.apache.commons.math3.ode.AbstractParameterizable;
  import org.apache.commons.math3.util.FastMath;
  import org.orekit.errors.OrekitException;
  import org.orekit.forces.ForceModel;
  import org.orekit.frames.Frame;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.propagation.events.EventDetector;
  import org.orekit.propagation.numerical.TimeDerivativesEquations;
  import org.orekit.time.AbsoluteDate;
  
  /** Force model for Newtonian central body attraction.
   * @author Luc Maisonobe
   */
  public class NewtonianAttraction extends AbstractParameterizable implements ForceModel {
  
      /** Name of the single parameter of this model: the central attraction coefficient. */
      public static final String CENTRAL_ATTRACTION_COEFFICIENT = "central attraction coefficient";
  
      /** Central attraction coefficient (m^3/s^2). */
      private double mu;
  
     /** Simple constructor.
       * @param mu central attraction coefficient (m^3/s^2)
       */
      public NewtonianAttraction(final double mu) {
          super(CENTRAL_ATTRACTION_COEFFICIENT);
          this.mu = mu;
      }
  
      /** {@inheritDoc} */
      public FieldVector3D<DerivativeStructure> accelerationDerivatives(final AbsoluteDate date, final Frame frame,
                                                                        final FieldVector3D<DerivativeStructure> position, final FieldVector3D<DerivativeStructure> velocity,
                                                                        final FieldRotation<DerivativeStructure> rotation, final DerivativeStructure mass)
          throws OrekitException {
  
          final DerivativeStructure r2 = position.getNormSq();
          return new FieldVector3D<DerivativeStructure>(r2.sqrt().multiply(r2).reciprocal().multiply(-mu), position);
  
      }
  
      /** {@inheritDoc} */
      public FieldVector3D<DerivativeStructure> accelerationDerivatives(final SpacecraftState s, final String paramName)
          throws OrekitException {
  
          complainIfNotSupported(paramName);
  
          final Vector3D            position = s.getPVCoordinates().getPosition();
          final double              r2       = position.getNormSq();
          final DerivativeStructure muds     = new DerivativeStructure(1, 1, 0, mu);
          return new FieldVector3D<DerivativeStructure>(muds.divide(-r2 * FastMath.sqrt(r2)), position);
  
      }
  
      /** Get the central attraction coefficient μ.
       * @return mu central attraction coefficient (m³/s²)
       */
      public double getMu() {
          return mu;
      }
  
      /** {@inheritDoc} */
      public double getParameter(final String name)
          throws IllegalArgumentException {
          complainIfNotSupported(name);
          return mu;
      }
  
      /** {@inheritDoc} */
      public void setParameter(final String name, final double value)
          throws IllegalArgumentException {
          complainIfNotSupported(name);
          this.mu = value;
      }
  
      /** {@inheritDoc} */
      public void addContribution(final SpacecraftState s, final TimeDerivativesEquations adder)
          throws OrekitException {
         adder.addKeplerContribution(mu);
     }
 
     /** {@inheritDoc} */
     public EventDetector[] getEventsDetectors() {
         return new EventDetector[0];
     }
 
 }