;------------------------------------------------------------
;------------------------------------------------------------
;------------------------------------------------------------
;+
;
; @file_comments
; In a string containing an order to execute with EXECUTE by example. 
; We change the value of one of keywords.
; More generally, in a string, we look for the character chain: ', keywdname= ...,
; and we change the value of...
;
; @categories
; String, keywords
;
; 
; @param STRINGIN {in}{required}{type=string}
; it is a string
;
; @param KEYWDNAME {in}{required}{type=string}
; it is a string designating the name of keyword to look for.
;
; @param KEYWDVALUE {in}{required} 
; The new value of the keyword to considerate in STRINGIN
;
; @keyword SEPARATOR
; To look for the keyword, we look for the first sign = which follow 
; the position of keywdname. By default, we substitute the string 
; before the comma. With the keyword SEPARATOR,we can modify the cut 
; of the string. SEPARATOR give a Character before the one we have to 
; look for the comma which delimit the keyword in the string.
; (see examples)
;
; @keyword AFTER
; To look for the keyword, we look for the first sign = which follow 
; the position of keywdname. By default, we substitute the string 
; before the comma. With the keyword AFTER,we can modify the cut 
; of the string. AFTER give a Character after the one we have to 
; look for the comma which delimit the keyword in the string.
; (see examples)
;
; @returns 
; stringout=stringin modified if keywdname has been found in stringin
;
; @uses 
; common.pro
;
; @restrictions
; If keywdvalue is an array, it will be convert in a vector.
;
; @restrictions
; Beware, this function has loops, ifs ad cases everywhere. So it can 
; not be used by big keywords (with a lot of elements which are big 
; arrays). The input keyword must not contain Complex floatings, structure, 
; Double-precision complex, Pointer, Object reference, Unsigned Integer, 
; Unsigned Longword Integer, 64-bit Integer or Unsigned 64-bit Integer.
; 
;
; @examples
;
;   IDL> b='ok=111, year=[1997,1998,1999], age_capitaine=35'
;   IDL> print, b
;   ok=111, year=[1997,1998,1999], age_capitaine=35
;   IDL> print, chkeywd(b,'ok','c''est bon')
;   ok='c''est bon', year=[1997,1998,1999], age_capitaine=35
;   IDL> print, chkeywd(b,'YEAR',indgen(5),sep='=')
;   ok=111, year=[0,1,2,3,4], age_capitaine=35
;   IDL> print, chkeywd(b,'YEAR',indgen(5),sep=']',/after)
;   ok=111, year=[0,1,2,3,4], age_capitaine=35
;   IDL> b='ok=111, /year, /age_capitaine'
;   IDL> print, chkeywd(b,'year','c''est bon')
;   ok=111, year='c''est bon', /age_capitaine
;
; @history
; Sebastien Masson (smasson\@lodyc.jussieu.fr)
;                      18/10/1999
;                      24/11/1999: adaptation for keywords starting by /
; 
; @version
; $Id$
;
;-
;------------------------------------------------------------
;------------------------------------------------------------
;------------------------------------------------------------
FUNCTION chkeywd, stringin, keywdname, keywdvalue, SEPARATOR = separator, AFTER = after
;
  compile_opt idl2, strictarrsubs
;

   stringout = stringin
   poskeywd = strpos(strlowcase(stringout), strlowcase(keywdname))
   if poskeywd EQ -1 then return, stringout
   while poskeywd NE -1 do BEGIN
; change a keyword starting by /toto
      if strmid(stringout,poskeywd-1,1) EQ '/' then BEGIN
         ajoute = keywdname+'='+tostr(keywdvalue)
         stringout = strmid(stringout, 0, poskeywd-1)+ajoute+strmid(stringout,poskeywd+strlen(keywdname) )
         poskeywd = poskeywd+strlen(ajoute)
         poskeywd = strpos(stringout, keywdname, poskeywd)
      ENDIF ELSE BEGIN 
; change a keyword sarting by toto=
         posegal = strpos(stringout, '=', poskeywd)
         if posegal EQ -1 then return, stringout

         if NOT keyword_set(separator) then separator = ','
         posvirgule = strpos(stringout, separator, posegal+1)
         if keyword_set(after) then posvirgule = strpos(stringout, ',', posvirgule-1) $
         ELSE posvirgule = rstrpos(stringout, ',', posvirgule+1)
         if posvirgule EQ -1 then posvirgule = strlen(stringout)
;
         stringout = strmid(stringout, 0, posegal+1)+tostr(keywdvalue)+strmid(stringout, posvirgule)
;
         poskeywd = strpos(stringout, keywdname, posvirgule+1)
      ENDELSE 
   endwhile

   return,  stringout
end