/* 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.propagation.numerical;
  
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.List;
  import java.util.SortedSet;
  import java.util.TreeSet;
  
  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.Rotation;
  import org.apache.commons.math3.geometry.euclidean.threed.Vector3D;
  import org.apache.commons.math3.util.FastMath;
  import org.apache.commons.math3.util.Precision;
  import org.orekit.errors.OrekitException;
  import org.orekit.errors.OrekitMessages;
  import org.orekit.forces.ForceModel;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.propagation.integration.AdditionalEquations;
  
  /** Set of {@link AdditionalEquations additional equations} computing the partial derivatives
   * of the state (orbit) with respect to initial state and force models parameters.
   * <p>
   * This set of equations are automatically added to a {@link NumericalPropagator numerical propagator}
   * in order to compute partial derivatives of the orbit along with the orbit itself. This is
   * useful for example in orbit determination applications.
   * </p>
   * @author V&eacute;ronique Pommier-Maurussane
   */
  public class PartialDerivativesEquations implements AdditionalEquations {
  
      /** Selected parameters for Jacobian computation. */
      private NumericalPropagator propagator;
  
      /** Derivatives providers. */
      private final List<ForceModel> derivativesProviders;
  
      /** List of parameters selected for Jacobians computation. */
      private List<ParameterConfiguration> selectedParameters;
  
      /** Name. */
      private String name;
  
      /** State vector dimension without additional parameters
       * (either 6 or 7 depending on mass derivatives being included or not). */
      private int stateDim;
  
      /** Parameters vector dimension. */
      private int paramDim;
  
      /** Step used for finite difference computation with respect to spacecraft position. */
      private double hPos;
  
      /** Boolean for force models / selected parameters consistency. */
      private boolean dirty = false;
  
      /** Jacobian of acceleration with respect to spacecraft position. */
      private transient double[][] dAccdPos;
  
      /** Jacobian of acceleration with respect to spacecraft velocity. */
      private transient double[][] dAccdVel;
  
      /** Jacobian of acceleration with respect to spacecraft mass. */
      private transient double[]   dAccdM;
  
      /** Jacobian of acceleration with respect to one force model parameter (array reused for all parameters). */
      private transient double[]   dAccdParam;
  
      /** Simple constructor.
       * <p>
       * Upon construction, this set of equations is <em>automatically</em> added to
       * the propagator by calling its {@link
       * NumericalPropagator#addAdditionalEquations(AdditionalEquations)} method. So
       * there is no need to call this method explicitly for these equations.
       * </p>
       * @param name name of the partial derivatives equations
       * @param propagator the propagator that will handle the orbit propagation
       * @exception OrekitException if a set of equations with the same name is already present
       */
      public PartialDerivativesEquations(final String name, final NumericalPropagator propagator)
          throws OrekitException {
          this.name = name;
         derivativesProviders = new ArrayList<ForceModel>();
         dirty = true;
         this.propagator = propagator;
         selectedParameters = new ArrayList<ParameterConfiguration>();
         stateDim = -1;
         paramDim = -1;
         hPos     = Double.NaN;
         propagator.addAdditionalEquations(this);
     }
 
     /** {@inheritDoc} */
     public String getName() {
         return name;
     }
 
     /** Get the names of the available parameters in the propagator.
      * <p>
      * The names returned depend on the force models set up in the propagator,
      * including the Newtonian attraction from the central body.
      * </p>
      * @return available parameters
      */
     public List<String> getAvailableParameters() {
         final List<String> available = new ArrayList<String>();
         available.addAll(propagator.getNewtonianAttractionForceModel().getParametersNames());
         for (final ForceModel model : propagator.getForceModels()) {
             available.addAll(model.getParametersNames());
         }
         return available;
     }
 
     /** Select the parameters to consider for Jacobian processing.
      * <p>Parameters names have to be consistent with some
      * {@link ForceModel} added elsewhere.</p>
      * @param parameters parameters to consider for Jacobian processing
      * @see NumericalPropagator#addForceModel(ForceModel)
      * @see #setInitialJacobians(SpacecraftState, double[][], double[][])
      * @see ForceModel
      * @see org.apache.commons.math3.ode.Parameterizable
 
      */
     public void selectParameters(final String ... parameters) {
 
         selectedParameters.clear();
         for (String param : parameters) {
             selectedParameters.add(new ParameterConfiguration(param, Double.NaN));
         }
 
         dirty = true;
 
     }
 
     /** Select the parameters to consider for Jacobian processing.
      * <p>Parameters names have to be consistent with some
      * {@link ForceModel} added elsewhere.</p>
      * @param parameter parameter to consider for Jacobian processing
      * @param hP step to use for computing Jacobian column with respect to the specified parameter
      * @see NumericalPropagator#addForceModel(ForceModel)
      * @see #setInitialJacobians(SpacecraftState, double[][], double[][])
      * @see ForceModel
      * @see org.apache.commons.math3.ode.Parameterizable
      */
     public void selectParamAndStep(final String parameter, final double hP) {
         selectedParameters.add(new ParameterConfiguration(parameter, hP));
         dirty = true;
     }
 
     /** Set the initial value of the Jacobian with respect to state and parameter.
      * <p>
      * This method is equivalent to call {@link #setInitialJacobians(SpacecraftState,
      * double[][], double[][])} with dYdY0 set to the identity matrix and dYdP set
      * to a zero matrix.
      * </p>
      * <p>
      * The returned state must be added to the propagator (it is not done
      * automatically, as the user may need to add more states to it).
      * </p>
      * @param s0 initial state
      * @param stateDimension state dimension, must be either 6 for orbit only or 7 for orbit and mass
      * @param paramDimension parameters dimension
      * @return state with initial Jacobians added
      * @exception OrekitException if the partial equation has not been registered in
      * the propagator or if matrices dimensions are incorrect
      * @see #selectedParameters
      * @see #selectParamAndStep(String, double)
      */
     public SpacecraftState setInitialJacobians(final SpacecraftState s0, final int stateDimension, final int paramDimension)
         throws OrekitException {
         final double[][] dYdY0 = new double[stateDimension][stateDimension];
         final double[][] dYdP  = new double[stateDimension][paramDimension];
         for (int i = 0; i < stateDimension; ++i) {
             dYdY0[i][i] = 1.0;
         }
         return setInitialJacobians(s0, dYdY0, dYdP);
     }
 
     /** Set the initial value of the Jacobian with respect to state and parameter.
      * <p>
      * The returned state must be added to the propagator (it is not done
      * automatically, as the user may need to add more states to it).
      * </p>
      * @param s1 current state
      * @param dY1dY0 Jacobian of current state at time t₁ with respect
      * to state at some previous time t₀ (may be either 6x6 for orbit
      * only or 7x7 for orbit and mass)
      * @param dY1dP Jacobian of current state at time t₁ with respect
      * to parameters (may be null if no parameters are selected)
      * @return state with initial Jacobians added
      * @exception OrekitException if the partial equation has not been registered in
      * the propagator or if matrices dimensions are incorrect
      * @see #selectedParameters
      * @see #selectParamAndStep(String, double)
      */
     public SpacecraftState setInitialJacobians(final SpacecraftState s1,
                                                final double[][] dY1dY0, final double[][] dY1dP)
         throws OrekitException {
 
         // Check dimensions
         stateDim = dY1dY0.length;
         if ((stateDim < 6) || (stateDim > 7) || (stateDim != dY1dY0[0].length)) {
             throw new OrekitException(OrekitMessages.STATE_JACOBIAN_NEITHER_6X6_NOR_7X7,
                                       stateDim, dY1dY0[0].length);
         }
         if ((dY1dP != null) && (stateDim != dY1dP.length)) {
             throw new OrekitException(OrekitMessages.STATE_AND_PARAMETERS_JACOBIANS_ROWS_MISMATCH,
                                       stateDim, dY1dP.length);
         }
 
         paramDim = (dY1dP == null) ? 0 : dY1dP[0].length;
 
         // store the matrices as a single dimension array
         final JacobiansMapper mapper = getMapper();
         final double[] p = new double[mapper.getAdditionalStateDimension()];
         mapper.setInitialJacobians(s1, dY1dY0, dY1dP, p);
 
         // set value in propagator
         return s1.addAdditionalState(name, p);
 
     }
 
     /** Get a mapper between two-dimensional Jacobians and one-dimensional additional state.
      * @return a mapper between two-dimensional Jacobians and one-dimensional additional state,
      * with the same name as the instance
      * @exception OrekitException if the initial Jacobians have not been initialized yet
      * @see #setInitialJacobians(SpacecraftState, int, int)
      * @see #setInitialJacobians(SpacecraftState, double[][], double[][])
      */
     public JacobiansMapper getMapper() throws OrekitException {
         if (stateDim < 0) {
             throw new OrekitException(OrekitMessages.STATE_JACOBIAN_NOT_INITIALIZED);
         }
         return new JacobiansMapper(name, stateDim, paramDim,
                                    propagator.getOrbitType(),
                                    propagator.getPositionAngleType());
     }
 
     /** {@inheritDoc} */
     public double[] computeDerivatives(final SpacecraftState s, final double[] pDot)
         throws OrekitException {
 
         final int dim = 3;
 
         // Lazy initialization
         if (dirty) {
 
             // if step has not been set by user, set a default value
             if (Double.isNaN(hPos)) {
                 hPos = FastMath.sqrt(Precision.EPSILON) * s.getPVCoordinates().getPosition().getNorm();
             }
 
              // set up derivatives providers
             derivativesProviders.clear();
             derivativesProviders.addAll(propagator.getForceModels());
             derivativesProviders.add(propagator.getNewtonianAttractionForceModel());
 
             // check all parameters are handled by at least one Jacobian provider
             for (final ParameterConfiguration param : selectedParameters) {
                 final String parameterName = param.getParameterName();
                 boolean found = false;
                 for (final ForceModel provider : derivativesProviders) {
                     if (provider.isSupported(parameterName)) {
                         param.setProvider(provider);
                         found = true;
                     }
                 }
                 if (!found) {
 
                     // build the list of supported parameters, avoiding duplication
                     final SortedSet<String> set = new TreeSet<String>();
                     for (final ForceModel provider : derivativesProviders) {
                         for (final String forceModelParameter : provider.getParametersNames()) {
                             set.add(forceModelParameter);
                         }
                     }
                     final StringBuilder builder = new StringBuilder();
                     for (final String forceModelParameter : set) {
                         if (builder.length() > 0) {
                             builder.append(", ");
                         }
                         builder.append(forceModelParameter);
                     }
 
                     throw new OrekitException(OrekitMessages.UNSUPPORTED_PARAMETER_NAME,
                                               parameterName, builder.toString());
 
                 }
             }
 
             // check the numbers of parameters and matrix size agree
             if (selectedParameters.size() != paramDim) {
                 throw new OrekitException(OrekitMessages.INITIAL_MATRIX_AND_PARAMETERS_NUMBER_MISMATCH,
                                           paramDim, selectedParameters.size());
             }
 
             dAccdParam = new double[dim];
             dAccdPos   = new double[dim][dim];
             dAccdVel   = new double[dim][dim];
             dAccdM     = (stateDim > 6) ? new double[dim] : null;
 
             dirty = false;
 
         }
 
         // initialize acceleration Jacobians to zero
         for (final double[] row : dAccdPos) {
             Arrays.fill(row, 0.0);
         }
         for (final double[] row : dAccdVel) {
             Arrays.fill(row, 0.0);
         }
         if (dAccdM != null) {
             Arrays.fill(dAccdM, 0.0);
         }
 
         // prepare derivation variables, 3 for position, 3 for velocity and optionally 1 for mass
         final int nbVars = (dAccdM == null) ? 6 : 7;
 
         // position corresponds three free parameters
         final Vector3D position = s.getPVCoordinates().getPosition();
         final FieldVector3D<DerivativeStructure> dsP = new FieldVector3D<DerivativeStructure>(new DerivativeStructure(nbVars, 1, 0, position.getX()),
                                               new DerivativeStructure(nbVars, 1, 1, position.getY()),
                                               new DerivativeStructure(nbVars, 1, 2, position.getZ()));
 
         // velocity corresponds three free parameters
         final Vector3D velocity = s.getPVCoordinates().getVelocity();
         final FieldVector3D<DerivativeStructure> dsV = new FieldVector3D<DerivativeStructure>(new DerivativeStructure(nbVars, 1, 3, velocity.getX()),
                                               new DerivativeStructure(nbVars, 1, 4, velocity.getY()),
                                               new DerivativeStructure(nbVars, 1, 5, velocity.getZ()));
 
         // mass corresponds either to a constant or to one free parameter
         final DerivativeStructure dsM = (dAccdM == null) ?
                                         new DerivativeStructure(nbVars, 1,    s.getMass()) :
                                         new DerivativeStructure(nbVars, 1, 6, s.getMass());
 
         // TODO:  we should compute attitude partial derivatives with respect to position/velocity
         final Rotation rotation = s.getAttitude().getRotation();
         final FieldRotation<DerivativeStructure> dsR =
                 new FieldRotation<DerivativeStructure>(new DerivativeStructure(nbVars, 1, rotation.getQ0()),
                                new DerivativeStructure(nbVars, 1, rotation.getQ1()),
                                new DerivativeStructure(nbVars, 1, rotation.getQ2()),
                                new DerivativeStructure(nbVars, 1, rotation.getQ3()),
                                false);
 
         // compute acceleration Jacobians
         for (final ForceModel derivativesProvider : derivativesProviders) {
             final FieldVector3D<DerivativeStructure> acceleration =
                     derivativesProvider.accelerationDerivatives(s.getDate(), s.getFrame(),
                                                                 dsP, dsV, dsR, dsM);
             addToRow(acceleration.getX(), 0);
             addToRow(acceleration.getY(), 1);
             addToRow(acceleration.getZ(), 2);
         }
 
         // the variational equations of the complete state Jacobian matrix have the
         // following form for 7x7, i.e. when mass partial derivatives are also considered
         // (when mass is not considered, only the A, B, D and E matrices are used along
         // with their derivatives):
 
         // [       |        |       ]   [                 |                  |               ]   [    |     |    ]
         // [ Adot  |  Bdot  |  Cdot ]   [  dVel/dPos = 0  |  dVel/dVel = Id  |   dVel/dm = 0 ]   [ A  |  B  |  C ]
         // [       |        |       ]   [                 |                  |               ]   [    |     |    ]
         // --------+--------+--- ----   ------------------+------------------+----------------   -----+-----+-----
         // [       |        |       ]   [                 |                  |               ]   [    |     |    ]
         // [ Ddot  |  Edot  |  Fdot ] = [    dAcc/dPos    |     dAcc/dVel    |    dAcc/dm    ] * [ D  |  E  |  F ]
         // [       |        |       ]   [                 |                  |               ]   [    |     |    ]
         // --------+--------+--- ----   ------------------+------------------+----------------   -----+-----+-----
         // [ Gdot  |  Hdot  |  Idot ]   [ dmDot/dPos = 0  |  dmDot/dVel = 0  |  dmDot/dm = 0 ]   [ G  |  H  |  I ]
 
         // The A, B, D and E sub-matrices and their derivatives (Adot ...) are 3x3 matrices,
         // the C and F sub-matrices and their derivatives (Cdot ...) are 3x1 matrices,
         // the G and H sub-matrices and their derivatives (Gdot ...) are 1x3 matrices,
         // the I sub-matrix and its derivative (Idot) is a 1x1 matrix.
 
         // The expanded multiplication above can be rewritten to take into account
         // the fixed values found in the sub-matrices in the left factor. This leads to:
 
         //     [ Adot ] = [ D ]
         //     [ Bdot ] = [ E ]
         //     [ Cdot ] = [ F ]
         //     [ Ddot ] = [ dAcc/dPos ] * [ A ] + [ dAcc/dVel ] * [ D ] + [ dAcc/dm ] * [ G ]
         //     [ Edot ] = [ dAcc/dPos ] * [ B ] + [ dAcc/dVel ] * [ E ] + [ dAcc/dm ] * [ H ]
         //     [ Fdot ] = [ dAcc/dPos ] * [ C ] + [ dAcc/dVel ] * [ F ] + [ dAcc/dm ] * [ I ]
         //     [ Gdot ] = [ 0 ]
         //     [ Hdot ] = [ 0 ]
         //     [ Idot ] = [ 0 ]
 
         // The following loops compute these expressions taking care of the mapping of the
         // (A, B, ... I) matrices into the single dimension array p and of the mapping of the
         // (Adot, Bdot, ... Idot) matrices into the single dimension array pDot.
 
         // copy D, E and F into Adot, Bdot and Cdot
         final double[] p = s.getAdditionalState(getName());
         System.arraycopy(p, dim * stateDim, pDot, 0, dim * stateDim);
 
         // compute Ddot, Edot and Fdot
         for (int i = 0; i < dim; ++i) {
             final double[] dAdPi = dAccdPos[i];
             final double[] dAdVi = dAccdVel[i];
             for (int j = 0; j < stateDim; ++j) {
                 pDot[(dim + i) * stateDim + j] =
                     dAdPi[0] * p[j]                + dAdPi[1] * p[j +     stateDim] + dAdPi[2] * p[j + 2 * stateDim] +
                     dAdVi[0] * p[j + 3 * stateDim] + dAdVi[1] * p[j + 4 * stateDim] + dAdVi[2] * p[j + 5 * stateDim] +
                     ((dAccdM == null) ? 0.0 : dAccdM[i] * p[j + 6 * stateDim]);
             }
         }
 
         if (dAccdM != null) {
             // set Gdot, Hdot and Idot to 0
             Arrays.fill(pDot, 6 * stateDim, 7 * stateDim, 0.0);
         }
 
         for (int k = 0; k < paramDim; ++k) {
 
             // compute the acceleration gradient with respect to current parameter
             final ParameterConfiguration param = selectedParameters.get(k);
             final ForceModel provider = param.getProvider();
             final FieldVector3D<DerivativeStructure> accDer =
                     provider.accelerationDerivatives(s, param.getParameterName());
             dAccdParam[0] = accDer.getX().getPartialDerivative(1);
             dAccdParam[1] = accDer.getY().getPartialDerivative(1);
             dAccdParam[2] = accDer.getZ().getPartialDerivative(1);
 
             // the variational equations of the parameters Jacobian matrix are computed
             // one column at a time, they have the following form:
             // [      ]   [                 |                  |               ]   [   ]   [                  ]
             // [ Jdot ]   [  dVel/dPos = 0  |  dVel/dVel = Id  |   dVel/dm = 0 ]   [ J ]   [  dVel/dParam = 0 ]
             // [      ]   [                 |                  |               ]   [   ]   [                  ]
             // --------   ------------------+------------------+----------------   -----   --------------------
             // [      ]   [                 |                  |               ]   [   ]   [                  ]
             // [ Kdot ] = [    dAcc/dPos    |     dAcc/dVel    |    dAcc/dm    ] * [ K ] + [    dAcc/dParam   ]
             // [      ]   [                 |                  |               ]   [   ]   [                  ]
             // --------   ------------------+------------------+----------------   -----   --------------------
             // [ Ldot ]   [ dmDot/dPos = 0  |  dmDot/dVel = 0  |  dmDot/dm = 0 ]   [ L ]   [ dmDot/dParam = 0 ]
 
             // The J and K sub-columns and their derivatives (Jdot ...) are 3 elements columns,
             // the L sub-colums and its derivative (Ldot) are 1 elements columns.
 
             // The expanded multiplication and addition above can be rewritten to take into
             // account the fixed values found in the sub-matrices in the left factor. This leads to:
 
             //     [ Jdot ] = [ K ]
             //     [ Kdot ] = [ dAcc/dPos ] * [ J ] + [ dAcc/dVel ] * [ K ] + [ dAcc/dm ] * [ L ] + [ dAcc/dParam ]
             //     [ Ldot ] = [ 0 ]
 
             // The following loops compute these expressions taking care of the mapping of the
             // (J, K, L) columns into the single dimension array p and of the mapping of the
             // (Jdot, Kdot, Ldot) columns into the single dimension array pDot.
 
             // copy K into Jdot
             final int columnTop = stateDim * stateDim + k;
             pDot[columnTop]                = p[columnTop + 3 * paramDim];
             pDot[columnTop +     paramDim] = p[columnTop + 4 * paramDim];
             pDot[columnTop + 2 * paramDim] = p[columnTop + 5 * paramDim];
 
             // compute Kdot
             for (int i = 0; i < dim; ++i) {
                 final double[] dAdPi = dAccdPos[i];
                 final double[] dAdVi = dAccdVel[i];
                 pDot[columnTop + (dim + i) * paramDim] =
                     dAccdParam[i] +
                     dAdPi[0] * p[columnTop]                + dAdPi[1] * p[columnTop +     paramDim] + dAdPi[2] * p[columnTop + 2 * paramDim] +
                     dAdVi[0] * p[columnTop + 3 * paramDim] + dAdVi[1] * p[columnTop + 4 * paramDim] + dAdVi[2] * p[columnTop + 5 * paramDim] +
                     ((dAccdM == null) ? 0.0 : dAccdM[i] * p[columnTop + 6 * paramDim]);
             }
 
             if (dAccdM != null) {
                 // set Ldot to 0
                 pDot[columnTop + 6 * paramDim] = 0;
             }
 
         }
 
         // these equations have no effect of the main state itself
         return null;
 
     }
 
     /** Fill Jacobians rows when mass is needed.
      * @param accelerationComponent component of acceleration (along either x, y or z)
      * @param index component index (0 for x, 1 for y, 2 for z)
      */
     private void addToRow(final DerivativeStructure accelerationComponent, final int index) {
 
         if (dAccdM == null) {
 
             // free parameters 0, 1, 2 are for position
             dAccdPos[index][0] += accelerationComponent.getPartialDerivative(1, 0, 0, 0, 0, 0);
             dAccdPos[index][1] += accelerationComponent.getPartialDerivative(0, 1, 0, 0, 0, 0);
             dAccdPos[index][2] += accelerationComponent.getPartialDerivative(0, 0, 1, 0, 0, 0);
 
             // free parameters 3, 4, 5 are for velocity
             dAccdVel[index][0] += accelerationComponent.getPartialDerivative(0, 0, 0, 1, 0, 0);
             dAccdVel[index][1] += accelerationComponent.getPartialDerivative(0, 0, 0, 0, 1, 0);
             dAccdVel[index][2] += accelerationComponent.getPartialDerivative(0, 0, 0, 0, 0, 1);
 
         } else {
 
             // free parameters 0, 1, 2 are for position
             dAccdPos[index][0] += accelerationComponent.getPartialDerivative(1, 0, 0, 0, 0, 0, 0);
             dAccdPos[index][1] += accelerationComponent.getPartialDerivative(0, 1, 0, 0, 0, 0, 0);
             dAccdPos[index][2] += accelerationComponent.getPartialDerivative(0, 0, 1, 0, 0, 0, 0);
 
             // free parameters 3, 4, 5 are for velocity
             dAccdVel[index][0] += accelerationComponent.getPartialDerivative(0, 0, 0, 1, 0, 0, 0);
             dAccdVel[index][1] += accelerationComponent.getPartialDerivative(0, 0, 0, 0, 1, 0, 0);
             dAccdVel[index][2] += accelerationComponent.getPartialDerivative(0, 0, 0, 0, 0, 1, 0);
 
             // free parameter 6 is for mass
             dAccdM[index]      += accelerationComponent.getPartialDerivative(0, 0, 0, 0, 0, 0, 1);
 
         }
 
     }
 
 }