; docformat = 'rst'

;+
; Decode a string in Base64.
;
; :Examples:
;    Try::
;
;       enc = mg_base64encode('username: password')
;       print, enc
;       dec = mg_base64decode(enc)
;       print, dec
;
; :Returns:
;    string
; 
; :Params:
;    s : in, required, type=string
;       string to decode
;-
function mg_base64decode, s
  compile_opt strictarr
  
  _translate = bytarr(123)
  _translate[bindgen(26) + 65B] = bindgen(26)       ; A-Z
  _translate[bindgen(26) + 97B] = bindgen(26) + 26  ; a-z
  _translate[bindgen(10) + 48B] = bindgen(10) + 52  ; a-z  
  _translate[43] = 62B                              ; +
  _translate[47] = 63B                              ; /  
  
  ns = strlen(s)
  ind = where(byte(strmid(s, 3, /reverse_offset)) eq (byte('='))[0], npadding)
  ind = _translate[byte(strmid(s, 0, ns - npadding))]
  
  b = bytarr(3 * (ns - npadding) / 4)
  reads, string(ind, format='(' + strtrim(n_elements(ind), 2) + 'B06)'), b, $
         format='(' + strtrim(3 * (ns - npadding) / 4, 2) + 'B8)'
                 
  return, string(b)
end


; main-level example program

enc = mg_base64encode('username: password')
print, enc
dec = mg_base64decode(enc)
print, dec

end