!!*****************************************************************************
!!
!! module: evolution - handling the time evolution of the block structure
!!
!! Copyright (C) 2008 Grzegorz Kowal <kowal@astro.wisc.edu>
!!
!!*****************************************************************************
!!
!!  This file is part of Godunov-AMR.
!!
!!  Godunov-AMR 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 3 of the License, or
!!  (at your option) any later version.
!!
!!  Godunov-AMR 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, see <http://www.gnu.org/licenses/>.
!!
!!*****************************************************************************
!!
!
module evolution

  implicit none

  integer, save :: n
  real   , save :: t, dt, dtn

  contains
!
!===============================================================================
!
! evolve: subroutine sweeps over all leaf blocks and performs one step time
!         evolution for each according to the selected integration scheme
!
!===============================================================================
!
  subroutine evolve

    use blocks, only : block, plist

    implicit none

! local variables
!
    type(block), pointer :: pblock
!
!-------------------------------------------------------------------------------
!
! iterate over all blocks and perform one step of time evolution
!
      pblock => plist
      do while (associated(pblock))

! check if this block is a leaf
!
#ifdef RK2
        if (pblock%leaf .eq. 'T') &
          call evolve_rk2(pblock)
#endif /* RK2 */

! assign pointer to the next block
!
        pblock => pblock%next

      end do

! TODO: boundary conditions
! TODO: new time step
!

!-------------------------------------------------------------------------------
!
  end subroutine evolve
#ifdef RK2
!
!===============================================================================
!
! evolve_rk2: subroutine evolves the current block using RK2 integration
!
!===============================================================================
!
  subroutine evolve_rk2(pblock)

    use blocks, only : block, nvars
    use config, only : igrids, jgrids, kgrids
    use mesh  , only : adxi, adyi, adzi
    use scheme, only : update

    implicit none

! input arguments
!
    type(block), pointer, intent(inout) :: pblock

! local variables
!
    integer :: q, i, j, k
    real    :: dxi, dyi, dzi

! local arrays
!
    real, dimension(nvars,igrids,jgrids,kgrids) :: u1, du
!
!-------------------------------------------------------------------------------
!
! prepare dxi, dyi, and dzi
!
    dxi = adxi(pblock%level)
    dyi = adyi(pblock%level)
    dzi = adzi(pblock%level)

! 1st step of integration
!
    call update(pblock%u, du, dxi, dyi, dzi)

! update solution
!
    do k = 1, kgrids
      do j = 1, jgrids
        do i = 1, igrids
          do q = 1, nvars
            u1(q,i,j,k) = pblock%u(q,i,j,k) + dt*du(q,i,j,k)
          end do
        end do
      end do
    end do

! 2nd step of integration
!
    call update(u1, du, dxi, dyi, dzi)

! update solution
!
    do k = 1, kgrids
      do j = 1, jgrids
        do i = 1, igrids
          do q = 1, nvars
            pblock%u(q,i,j,k) = 0.5 * (pblock%u(q,i,j,k) + u1(q,i,j,k) &
                              + dt*du(q,i,j,k))
          end do
        end do
      end do
    end do

!-------------------------------------------------------------------------------
!
  end subroutine evolve_rk2
#endif /* RK2 */

!===============================================================================
!
end module