SUBROUTINE read_upf(upf, grid, ierr, unit,  filename) !
   !---------------------------------------------+
   !! Reads pseudopotential in UPF format (either v.1 or v.2 or upf_schema).
   !! Derived-type variable *upf* and optionally *grid* store in output the 
   !! data read from file. 
   !! If unit number is provided with the *unit* argument, only UPF v1 format
   !! is checked; the PP file must be opened and closed outside the routine.  
   !! Otherwise the *filename* argument must be given, file is opened and closed
   !! inside the routine, all formats will be  checked. 
   !! @Note last revision: 01-01-2019 PG - upf fix moved out from here
   !! @Note last revision: 11-05-2018 PG - removed xml_only
   !
   USE pseudo_types, ONLY: pseudo_upf, deallocate_pseudo_upf 
   USE radial_grids, ONLY: radial_grid_type, deallocate_radial_grid
   USE read_upf_v1_module,ONLY: read_upf_v1
   USE read_upf_v2_module,ONLY: read_upf_v2
   USE read_upf_schema_module ,ONLY: read_upf_schema
   USE FoX_DOM,      ONLY: Node, domException, parseFile, getFirstChild, &
        getExceptionCode, getTagName    
   IMPLICIT NONE
   INTEGER,INTENT(IN), OPTIONAL            :: unit
   !! i/o unit:    
   CHARACTER(len=*),INTENT(IN),OPTIONAL    :: filename  
   !! i/o filename
   TYPE(pseudo_upf),INTENT(INOUT) :: upf       
   !! the derived type storing the pseudo data
   TYPE(radial_grid_type),OPTIONAL,INTENT(INOUT),TARGET :: grid
   !! derived type where is possible to store data on the radial mesh
   INTEGER,INTENT(INOUT) :: ierr
   !! On input:
   !! ierr =0:   return if not a valid xml schema or UPF v.2 file
   !! ierr/=0: continue if not a valid xml schema or UPF v.2 file
   !! On output:
   !! ierr=0: xml schema, ierr=-1: UPF v.1,  ierr=-2: UPF v.2
   !! ierr>0: error reading PP file
   !! ierr=-81: error reading PP file, possibly UPF fix needed
   !
   TYPE(Node),POINTER :: u,doc     
   INTEGER            :: u_temp,&    ! i/o unit in case of upf v1
                         iun, ferr  
   TYPE(DOMException) :: ex 
   INTEGER, EXTERNAL  :: find_free_unit

   ferr = ierr
   ierr = 0
   IF ( present ( unit ) ) THEN 
      REWIND (unit) 
      CALL deallocate_pseudo_upf(upf) 
      CALL deallocate_radial_grid( grid ) 
      CALL read_upf_v1 (unit, upf, grid, ierr ) 
      IF (ierr == 0 ) ierr = -1     
      !
   ELSE IF (PRESENT(filename) ) THEN
      doc => parseFile(TRIM(filename), EX = ex )
      ierr = getExceptionCode( ex )
      IF ( ferr == 0 .AND. ierr ==  81 ) THEN
         ierr = -81
         RETURN
      END IF
      IF ( ierr == 0 ) THEN 
         u => getFirstChild(doc) 
         SELECT CASE (TRIM(getTagname(u))) 
         CASE ('UPF') 
            CALL read_upf_v2( u, upf, grid, ierr )
            IF ( ierr == 0 ) ierr = -2
         CASE ('qe_pp:pseudo') 
            CALL read_upf_schema( u, upf, grid, ierr)
         CASE default 
            ierr = 1
            CALL errore('read_upf', 'xml format '//TRIM(getTagName(u))//' not implemented', ierr) 
         END SELECT
         IF ( ierr > 0 ) CALL errore( 'read_upf', 'File is Incomplete or wrong: '//TRIM(filename), ierr)
         !  
      ELSE IF ( ierr > 0 ) THEN
         ! 
         u_temp = find_free_unit()
         OPEN (UNIT = u_temp, FILE = TRIM(filename), STATUS = 'old', FORM = 'formatted', IOSTAT = ierr)
         CALL errore ("upf_module:read_upf", "error while opening file " // TRIM(filename), ierr) 
         CALL deallocate_pseudo_upf( upf )
         CALL deallocate_radial_grid( grid )
         CALL read_upf_v1( u_temp, upf, grid, ierr )
         IF ( ierr == 0 ) ierr = -1
         CLOSE ( u_temp)  
         !
      END IF
   ELSE 
      CALL errore('read_upf', 'Nothing to read !!! Provide either filename or unit optional arguments',1)
   END IF
   !
 END SUBROUTINE read_upf