!>
!> @file counter.f90
!>
!> @brief
!>
!> @copyright
!> Copyright (©) 2021 EPFL (Ecole Polytechnique Fédérale de Lausanne)
!> SPC (Swiss Plasma Center)
!>
!> futils is free software: you can redistribute it and/or modify it under
!> the terms of the GNU Lesser General Public License as published by the Free
!> Software Foundation, either version 3 of the License, or (at your option)
!> any later version.
!>
!> futils 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 Lesser General Public License
!> along with this program. If not, see <https://www.gnu.org/licenses/>.
!>
!> @authors
!> (in alphabetical order)
!> @author Trach-Minh Tran <trach-minh.tran@epfl.ch>
!>
MODULE counter
  IMPLICIT NONE
  INTEGER, PARAMETER :: nfmax=32
  LOGICAL :: used(nfmax) = .FALSE.
  INTEGER :: current_fid=0
CONTAINS

  INTEGER FUNCTION next_fid
    IMPLICIT NONE
    INTEGER :: i
    DO i=1,nfmax
       IF( .NOT. used(i) ) THEN
          used(i) = .TRUE.
          next_fid = i
          RETURN
       END IF
    END DO
    PRINT*, "Number of created files exceeds NFMAX =", nfmax
    STOP
  END FUNCTION next_fid

  SUBROUTINE closef(fid)
    IMPLICIT NONE
    INTEGER, intent(in) :: fid
    IF( fid .GT. nfmax) PRINT*, 'Invalid fid', fid
    used(fid) = .FALSE.
  END SUBROUTINE closef
END MODULE counter

PROGRAM main
  USE counter
  IMPLICIT NONE
  INTEGER :: fid1, fid2, fid3, fid4
  !
  fid1 = next_fid(); PRINT*, 'Get fid =', fid1
  fid2 = next_fid(); PRINT*, 'Get fid =', fid2
  fid3 = next_fid(); PRINT*, 'Get fid =', fid3

  CALL closef(fid2); PRINT*, 'Close fid =', fid2
  fid4 = next_fid(); PRINT*, 'Get fid =', fid4
END PROGRAM main