/*************************************************************************************

  Grid physics library, www.github.com/paboyle/Grid

  Source file: ./lib/qcd/action/gauge/WilsonGaugeAction.h

  Copyright (C) 2015

  Author: Guido Cossu <guido,cossu@ed.ac.uk>

  This program is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation; either version 2 of the License, or
  (at your option) any later version.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License along
  with this program; if not, write to the Free Software Foundation, Inc.,
  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

  See the full license in the file "LICENSE" in the top level distribution
directory
  *************************************************************************************/
/*  END LEGAL */

#ifndef SCALAR_INT_ACTION_H
#define SCALAR_INT_ACTION_H


// Note: this action can completely absorb the ScalarAction for real float fields
// use the scalarObjs to generalise the structure

namespace Grid {
  // FIXME drop the QCD namespace everywhere here

  template <class Impl, int Ndim >
  class ScalarInteractionAction : public QCD::Action<typename Impl::Field> {
  public:
    INHERIT_FIELD_TYPES(Impl);
  private:
    RealD mass_square;
    RealD lambda;


    typedef typename Field::vector_object vobj;
    typedef CartesianStencil<vobj,vobj> Stencil;

    SimpleCompressor<vobj> compressor;
    int npoint = 2*Ndim;
    std::vector<int> directions;//    = {0,1,2,3,0,1,2,3};  // forcing 4 dimensions
    std::vector<int> displacements;//  = {1,1,1,1, -1,-1,-1,-1};


  public:

    ScalarInteractionAction(RealD ms, RealD l) : mass_square(ms), lambda(l), displacements(2*Ndim,0), directions(2*Ndim,0){
      for (int mu = 0 ; mu < Ndim; mu++){
		directions[mu]         = mu; directions[mu+Ndim]    = mu;
		displacements[mu]      =  1; displacements[mu+Ndim] = -1;
      }
    }

    virtual std::string LogParameters() {
      std::stringstream sstream;
      sstream << GridLogMessage << "[ScalarAction] lambda      : " << lambda      << std::endl;
      sstream << GridLogMessage << "[ScalarAction] mass_square : " << mass_square << std::endl;
      return sstream.str();
    }

    virtual std::string action_name() {return "ScalarAction";}

    virtual void refresh(const Field &U, GridParallelRNG &pRNG) {}

    virtual RealD S(const Field &p) {
      assert(p._grid->Nd() == Ndim);
      static Stencil phiStencil(p._grid, npoint, 0, directions, displacements);
      phiStencil.HaloExchange(p, compressor);
      Field action(p._grid), pshift(p._grid), phisquared(p._grid);
      phisquared = p*p;
      action = (2.0*Ndim + mass_square)*phisquared - lambda/24.*phisquared*phisquared;
      for (int mu = 0; mu < Ndim; mu++) {
	//  pshift = Cshift(p, mu, +1);  // not efficient, implement with stencils
	parallel_for (int i = 0; i < p._grid->oSites(); i++) {
	  int permute_type;
	  StencilEntry *SE;
	  vobj temp2;
	  const vobj *temp, *t_p;
	    
	  SE = phiStencil.GetEntry(permute_type, mu, i);
	  t_p  = &p._odata[i];
	  if ( SE->_is_local ) {
	    temp = &p._odata[SE->_offset];
	    if ( SE->_permute ) {
	      permute(temp2, *temp, permute_type);
	      action._odata[i] -= temp2*(*t_p) + (*t_p)*temp2;
	    } else {
	      action._odata[i] -= (*temp)*(*t_p) + (*t_p)*(*temp);
	    }
	  } else {
	    action._odata[i] -= phiStencil.CommBuf()[SE->_offset]*(*t_p) + (*t_p)*phiStencil.CommBuf()[SE->_offset];
	  }
	}
	//  action -= pshift*p + p*pshift;
      }
      // NB the trace in the algebra is normalised to 1/2
      // minus sign coming from the antihermitian fields
      return -(TensorRemove(sum(trace(action)))).real();
    };

    virtual void deriv(const Field &p, Field &force) {
      assert(p._grid->Nd() == Ndim);
      force = (2.0*Ndim + mass_square)*p - lambda/12.*p*p*p;
      // move this outside
      static Stencil phiStencil(p._grid, npoint, 0, directions, displacements);
      phiStencil.HaloExchange(p, compressor);
      
      //for (int mu = 0; mu < QCD::Nd; mu++) force -= Cshift(p, mu, -1) + Cshift(p, mu, 1);
      for (int point = 0; point < npoint; point++) {
	parallel_for (int i = 0; i < p._grid->oSites(); i++) {
	  const vobj *temp;
	  vobj temp2;
	  int permute_type;
	  StencilEntry *SE;
	  SE = phiStencil.GetEntry(permute_type, point, i);
	  
	  if ( SE->_is_local ) {
	    temp = &p._odata[SE->_offset];
	    if ( SE->_permute ) {
	      permute(temp2, *temp, permute_type);
	      force._odata[i] -= temp2;
	    } else {
	      force._odata[i] -= *temp;
	    }
	  } else {
	    force._odata[i] -= phiStencil.CommBuf()[SE->_offset];
	  }
	}
      }
    }
  };
  
}  // namespace Grid

#endif  // SCALAR_INT_ACTION_H