PRO dustem_write_align,file,st_align,help=help

;+
; NAME:
;   dustem_write_align
;
; PURPOSE:
;   writes the ALIGN.DAT file
;
; CATEGORY:
;    DustEMWrap, Distributed, LowLevel, Initialization
;
; CALLING SEQUENCE:
;   dustem_write_align,file,st_align
;
;
; INPUTS:
;    file     : name of the file to be written
;    st_align : structure describing alignment parameters for various grains (usually !dustem.grains.align)
;
; OPTIONAL INPUT PARAMETERS:
;    None
;
; OUTPUTS:
;    None
;
; OPTIONAL OUTPUT PARAMETERS:
;    None
;
; ACCEPTED KEY-WORDS:
;    help     : whrites this help
;
; COMMON BLOCKS:
;    None
;
; SIDE EFFECTS:
;    a File is written
;
; RESTRICTIONS:
;    The DustEM fortran code must be installed
;    The DustEMWrap idl code must be installed
;
; PROCEDURES AND SUBROUTINES USED  
;
; EXAMPLES
;
; MODIFICATION HISTORY:
;    Evolution details on the DustEMWrap gitlab.
;    See http://dustemwrap.irap.omp.eu/ for FAQ and help.  
;-

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

Ncomments=13
c=strarr(Ncomments)

;NOTE: In vincent Guillet's model, the alignment parameters of all grains have to be the same.
;As a consquence, there is only one line in the ALIGN.DAT file.
;Here we use the first polarized grain value

;stop

ii=0
c[ii]='# DUSTEM: definition of grain alignment' & ii=ii+1
c[ii]='# for each grain TYPE make sure you have the following files' & ii=ii+1
c[ii]='# Q1_TYPE.DAT and Q2_TYPE in /oprop' & ii=ii+1
c[ii]='# Qc_TYPE.DAT for circular polarization' & ii=ii+1
c[ii]='# QH1_TYPE.DAT QH2_TYPE.DAT for an anistropic radiation field' & ii=ii+1
c[ii]='# Q1_TYPE_RRFxxx.DAT and Q2_TYPE_RRFxxx.DAT when running with RRF option' & ii=ii+1
c[ii]='#' & ii=ii+1
c[ii]='# run keywords' & ii=ii+1
c[ii]='# lin for linear, circ for circular, anis for anistropic extinction and emission, univ for universal alignment law, RRF' & ii=ii+1
c[ii]='# degree of anisotropy of the radiation : if > 0, read QH1 and QH2 files' & ii=ii+1
c[ii]='# alignmentlaw (idg, rat, par), parameters (par1 par2 par3)' & ii=ii+1
c[ii]='# for alignmentlaw = par: parameters are aalign, pstiff, fmax (see Equ. 1 In Guillet et al. 2017' & ii=ii+1
c[ii]='#'

;WHAY IS FMAX in Guillet2017 here called plev ??

openw,unit,file,/get_lun
FOR ii=0,Ncomments-1 DO printf,unit,c[ii]
printf,unit,st_align.keywords,format='(A-40)'
printf,unit,st_align.anisG0,format='(E10.2)'

format='(A-10,2X,10(E18.10,2X))'
IF !run_univ EQ 1 THEN BEGIN
    ind=where(st_align.grains.aligned eq 1,count)
    ii=ind[0]    ;here we use alignment parameters of the first polarized grains and for them to be the same
	printf,unit,st_align.grains[ii].law,st_align.grains[ii].athresh,st_align.grains[ii].pstiff,st_align.grains[ii].plev,format=format
	;stop 
ENDIF ELSE BEGIN
	FOR i=0,n_elements(st_align.grains)-1 DO BEGIN
        IF st_align.grains[i].aligned THEN BEGIN
        	IF st_align.grains[i].law NE '' THEN BEGIN
          		printf,unit,st_align.grains[i].law,st_align.grains[i].athresh,st_align.grains[i].pstiff,st_align.grains[i].plev,format=format
        	ENDIF
        ENDIF
	ENDFOR
ENDELSE

close,unit
free_lun,unit

the_end:

END