PRO dustem_write_isrf_lv,file,st,help=help

;+
; NAME:
;    dustem_write_isrf_lv
; PURPOSE:
;    Writes file ISRF.DAT used by DustemWrapper
; CATEGORY:
;    Dustem
; CALLING SEQUENCE:
;    dustem_write_isrf_lv,file,st[,/help]
; INPUTS:
;    file : file name 
;    st   : input ISRF structure
; OPTIONAL INPUT PARAMETERS:
;    None
; OUTPUTS:
;    None
; OPTIONAL OUTPUT PARAMETERS:
;    None
; ACCEPTED KEY-WORDS:
;    help      = If set print this help
; COMMON BLOCKS: 
;    None
; SIDE EFFECTS:
;    None
; RESTRICTIONS:
;    The dustem fortran code must be installed
;    The dustem idl wrapper must be installed
; PROCEDURE:
;    a Stellar ISRF is added based on the content of (*(*!dustem_plugin).stellar_population)
;-

IF keyword_set(help) THEN BEGIN
  doc_library,'dustem_write_isrf_lv'
  goto,the_end
ENDIF


IF tag_exist(*!dustem_plugin,'STELLAR_POPULATION') THEN BEGIN
    IF isa((*!dustem_plugin).stellar_population) THEN goto, the_end
ENDIF

;NOW YOU HAVE TO LOOP ON THE COMMENTS TO SEE IF IT IS THE COMPOSITE ISRF FILE OR THE MATHIS ONE.

Ncomments=6
c=strarr(Ncomments)

;MODIFY THIS TO DISPLAY THE ACTUAL VALUES BECAUSE IT IS JUST DISPLAYING EMPTY STRINGS AT THE MOMENT

;First lines of the ISRF.DAT file
c(0)='# DUSTEM: exciting radiation field featuring'
c(1)='# Mathis ISRF'
c(2)='# Blackbody with     T=   0.0000E+00'
c(3)='# dilution factor wdil=   1.0000E+00'
c(4)='# Nbr of points'
c(5)='# wave (microns), 4*pi*Inu (erg/cm2/s/Hz)'

openw,unit,file,/get_lun

FOR i=0,Ncomments-1 DO BEGIN
    printf,unit,c(i)
ENDFOR

n_waves=n_elements(st)
printf,unit,n_waves

FOR i=0L,n_waves-1 DO BEGIN
    printf,unit,st(i).lambisrf,st(i).isrf
ENDFOR

close,unit
free_lun,unit

the_end:


END