FUNCTION dustem_compute_ext,p_dim,$
                            st=st,$
                            EXT_spec=EXT_spec,$
                            help=help

;+
; NAME:
;    dustem_compute_ext
;  
; PURPOSE:
;    Computes Extinction in units of optical depth for a given Dustem spectrum
;
; CATEGORY:
;    DustEMWrap, Mid-level, Distributed
;
; CALLING SEQUENCE:
;    ext=dustem_compute_ext(p_dim[,st=][,ext_spec=][,/help])
;
; INPUTS:
;    p_dim      = parameter values
;
; OPTIONAL INPUT PARAMETERS:
;    st        = Dustem output structure
;
; OUTPUTS:
;    ext_spec  = computed EXT for spectrum points in !dustem_data 
;
; OPTIONAL OUTPUT PARAMETERS:
  ;    st        = Dustem output structure
;
; ACCEPTED KEY-WORDS:
;    help      = If set, print this help
;
; COMMON BLOCKS:
;    None
;
; SIDE EFFECTS:
;    None
;
; RESTRICTIONS:
;    The DustEMWrap IDL code must be installed
;  
; MODIFICATION HISTORY:
;    Written ?
;    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_compute_ext'
  dustem_ext=0.
  goto,the_end
ENDIF
;stop
IF not keyword_set(st) THEN BEGIN
    
  dustem_activate_plugins,p_dim/(*(*!dustem_fit).param_init_values),st=st  ; what about the 0/0 division case?
    
ENDIF

;if not keyword_set(wave0) then wave0 = 0.


EXT_spec = st.ext.ext_tot * (*!dustem_HCD)/1.0e21 ;For any column density. Default is 10^20 H/cm^2



;ADDING PLUGIN TO SPECTRUM----------------
scopes=tag_names((*!dustem_plugin))
IF scopes[0] NE 'NONE' THEN BEGIN
;IF ptr_valid(!dustem_plugin) THEN BEGIN
  for i=0L,n_tags(*!dustem_plugin)-1 do begin
    if total(strsplit((*(*!dustem_plugin).(i).scope),'+',/extract) eq 'ADD_EXT') then EXT_spec+=(*(*!dustem_plugin).(i).spec)[*,0]
  endfor
ENDIF
;------------------------------------------

if not isarray(EXT_spec) THEN stop 
    
;COMPUTE THE MODEL SED

dustem_ext = (*(*!dustem_data).ext).values * 0.

;####For now no color corrections are performed (spectrum points)####

; IF !dustem_do_cc NE 0 AND !dustem_never_do_cc EQ 0 THEN BEGIN
;   message,'DOING color correction calculations',/info
; ENDIF ELSE BEGIN
;   message,'SKIPPING color correction calculations: we take previous values of cc',/info
; ENDELSE

; ind_sed=where((*(*!dustem_data).sed).filt_names NE 'SPECTRUM' and (*(*!dustem_data).sed).wav gt wave0,count_sed)
; IF count_sed NE 0 THEN BEGIN
;   filter_names=((*(*!dustem_data).sed).filt_names)[ind_sed]
;   ssed=dustem_cc(st.sed.wav,SED_spec,filter_names,cc=cc)  
;   dustem_sed[ind_sed]=ssed
; ENDIF ELSE BEGIN
;   print,"**** WARNING **** NO FILTER defined in DATA for COLOUR CORRECTION" 
; ENDELSE

;For spectrum data points, interpolate in log-log
;Linear interpolation leads to wrong values, in particular where few
;wavelengths points exist in the model (long wavelengths). (done automatically because the dustem grid is sampled in already log-log space)
ind_spec=where((*(*!dustem_data).ext).filt_names EQ 'SPECTRUM',count_spec)
IF count_spec NE 0 THEN BEGIN
    dustem_ext[ind_spec]=interpol(EXT_spec,st.ext.wav,(((*(*!dustem_data).ext).wav)[ind_spec]))
ENDIF
out_st=st

;clean pointers
heap_gc


;VG : error in cc IRAS1 when no PAH 
; j=where(dustem_sed ne dustem_sed,count)
; if count gt 0 then dustem_sed[j]=0.
;stop
the_end:
RETURN,dustem_ext


END