//
// Created by Santosh Putta, Nov 2006
//
#ifndef __RD_FOURTHDIMCONTRIB_H__
#define __RD_FOURTHDIMCONTRIB_H__

#include <RDGeneral/Invariant.h>
#include <ForceField/Contrib.h>
#include <ForceField/ForceField.h>

namespace DistGeom {
  //! A term used in penalizing chirality violations
  //!
  class FourthDimContrib : public ForceFields::ForceFieldContrib {
  public:
    FourthDimContrib() : d_idx(0), d_weight(0.0) {};

    //! Constructor
    /*!
      \param owner       pointer to the owning ForceField
      \param idx        the index of the atom to be considered
      \param weight     (optional) the weight to be used for this contrib
                        
    */
    FourthDimContrib(ForceFields::ForceField *owner,unsigned int idx,
                     double weight) : d_idx(idx), d_weight(weight) {
      PRECONDITION(owner,"bad force field");
      PRECONDITION(owner->dimension()==4,"force field has wrong dimension");
      dp_forceField=owner;
    };

    //! return the contribution of this contrib to the energy of a given state 
    double getEnergy(double *pos) const {
      PRECONDITION(dp_forceField,"no owner");
      PRECONDITION(dp_forceField->dimension()==4,"force field has wrong dimension");
      PRECONDITION(pos,"bad vector");
      unsigned int pid = d_idx*dp_forceField->dimension() + 3;
      return d_weight*pos[pid]*pos[pid];
    }
    
    //! calculate the contribution of this contrib to the gradient at a given state
    void getGrad(double *pos, double *grad) const {
      PRECONDITION(dp_forceField,"no owner");
      PRECONDITION(dp_forceField->dimension()==4,"force field has wrong dimension");
      PRECONDITION(pos,"bad vector");
      unsigned int pid = d_idx*dp_forceField->dimension() + 3;
      grad[pid] += d_weight*pos[pid];
    }
    virtual FourthDimContrib *copy() const { return new FourthDimContrib(*this); };
  private:
    unsigned int d_idx;
    double d_weight;
  };
}

#endif
    
