!-----------------------------------------------------------------------
  ! Copyright (C) 2010-2015 Henry Lambert, Feliciano Giustino
  ! This file is distributed under the terms of the GNU General Public         
  ! License. See the file `LICENSE' in the root directory of the               
  ! present distribution, or http://www.gnu.org/copyleft.gpl.txt .
  !-----------------------------------------------------------------------
SUBROUTINE unfold_w(scrcoul_g_in, iq)
USE kinds,         ONLY : DP
USE symm_base,     ONLY : nsym, s, time_reversal, t_rev, ftau, invs
USE gwsymm,        ONLY : ig_unique, ngmunique, use_symm, sym_ig, sym_friend
USE gvect,         ONLY : g, ngm, nl
USE modes,         ONLY : nsymq, invsymq 
USE freq_gw,       ONLY : fpol, fiu, nfs, nfsmax, nwcoul, wcoul
USE control_gw,    ONLY : zue, convt, rec_code, modielec, eta, godbyneeds, padecont
USE qpoint,        ONLY : xq
USE cell_base,     ONLY : at
USE gwsigma,      ONLY : sigma_c_st
USE noncollin_module, ONLY : noncolin, nspin_mag

IMPLICIT NONE

COMPLEX(DP)  :: scrcoul_g_in(sigma_c_st%ngmt, sigma_c_st%ngmt, nfs, nspin_mag)
COMPLEX(DP)  :: scrcoul_g_tmp(sigma_c_st%ngmt, nfs)
COMPLEX(DP)  :: phase

INTEGER      :: ig, igp, npe, irr, icounter, ir, irp
!counter
INTEGER      :: isym, iwim, iq, iw
INTEGER      :: done, ngmdone, isp
INTEGER      :: ngmdonelist(sigma_c_st%ngmt)
INTEGER      :: gmapsym(ngm,48)
COMPLEX(DP)  :: eigv(ngm,48)
LOGICAL      :: not_unique
REAL(DP)     :: xq_loc(3)

!unpacks the symmetry reduced list of G vectors to fill the whole W 
!matrix before writing this to file, alternatively could just 
!write the symmetry reduced matrix to file... but right now this isn't necessary.

gmapsym(:,:) = 0
CALL gmap_sym(nsym, s, ftau, gmapsym, eigv, invs)
!do isym = 1, nsymq
!   WRITE(6,'(3i4)') s(:,:,isym) 
!   WRITE(6,*)
!   WRITE(6,'(3i4)') s(:,:,invs(isym)) 
!   WRITE(6,*)
!   WRITE(6,*)
!enddo
!Case where no unfolding needs to be done:
if(.not.use_symm)GOTO 126
if(nsymq.eq.1)GOTO 126

!stack ngmdone list with vectors that aren't unique:
xq_loc = xq
CALL cryst_to_cart(1, xq_loc(:), at, -1)
ngmdonelist(:) = 0
ngmdone = 0

do ig = 1, ngmunique
   ngmdone = ngmdone + 1
   ngmdonelist(ngmdone) = ig_unique(ig)
enddo

if(modielec) then
!only diagonal needs unfolding:
   do ig = 1, ngmunique
      do done = 1, ngmdone
         if (ig.eq.ngmdonelist(done)) then
!             write(6,'("Cycling: unique or already unfolded.")')
                CYCLE
         endif
         enddo
         do iwim = 1, nfs
            do isym = 1, nsymq
               scrcoul_g_in(gmapsym(ig_unique(ig),invs(isym)), gmapsym(ig_unique(ig),invs(isym)),iwim,1) &
&                                                  = scrcoul_g_in(ig_unique(ig), ig_unique(ig), iwim, 1)
            enddo
         enddo
      enddo
ELSE
    do ig = 1, sigma_c_st%ngmt
        do done = 1, ngmdone
           if (ig.eq.ngmdonelist(done)) then
!               write(6,'("Cycling: unique or already unfolded.")') 
               GOTO 128
           endif
        enddo 
!still need to unfold this vector so we append it to the done list:
        ngmdone = ngmdone + 1
        ngmdonelist(ngmdone) = ig
        do isp = 1, nspin_mag
!and unfold it with the correct correspondence ig has sym_friend(ig) where R^{-1} ig = ig_unique:
        do iwim = 1, nfs
            do igp = 1, sigma_c_st%ngmt
               scrcoul_g_tmp(igp,iwim) = scrcoul_g_in(sym_friend(ig), igp, iwim, isp)
            enddo
        enddo
!the relationship R between ig and sym_friend(ig) is given by sym_ig.
          do iwim = 1, nfs
             do igp = 1, sigma_c_st%ngmt
!For symmetry operations with fraction translations we need to include:
!the \tau_{r} part which applies to the original G, G' rotation on R
!e^{-i2\pi(G - G')\cdot\tau_{R}} = eigv(G)*conjg(eigv(G'))
                phase = eigv(sym_friend(ig), sym_ig(ig))*conjg(eigv(igp, sym_ig(ig)))
                scrcoul_g_in(ig, gmapsym(igp, invs(sym_ig(ig))), iwim, isp) = scrcoul_g_tmp(igp, iwim)*phase
             enddo
         enddo
        enddo
128 CONTINUE
    enddo
endif

126 CONTINUE
END SUBROUTINE unfold_w