(defvar test-string
  (concat "q"
          "#0;2;0;0;0#1;2;100;100;0#2;2;0;100;0"
          "#1~~@@vv@@~~@@~~$"
          "#2??GG????-"
          "#1!14@"))


(defun sixel-get-params (string)
  "Retrieve the sixel parameters."
  (car (split-string string "q")))

(defun sixel-get-data (string)
  "Retrieve data string."
  (substring string (1+ (string-match "q" string))))

(defvar sixel-colour-map nil
  "Map of two-character names to RGB colour triples.")

(defvar sixel-current-colour nil
  "Current colour.")

(defun sixel-compute-row-length (string)
  (apply 'max
         (mapcar
          (lambda (substr)
            (apply 'max (mapcar
                         (lambda (subsubstr)
                           (length (subsubstr)))
                         (split-string substr "$"))))
          (split-string string -))))

(defun sixel-tag-bits (sixel n tag)
  "Set bits of SIXEL corresponding to N with to the value TAG."
  (dotimes (i 6)
    (if (= (% n 2) 1)
        (aset sixel i tag))
    (setq n (/ n 2))))

(defun sixel-tag-sixel-in-row (row-variable index char tag)
  "Tag the bits of the sixel at INDEX in the list identified by
the variable ROW-VARIABLE corresponding to input character CHAR
with TAG."
  (while (not (< index (length (symbol-value row-variable))))
    (add-to-list row-variable (make-vector 6 nil)))
  (let ((sixel (elt (symbol-value row-variable) index)))
    (sixel-tag-bits sixel (- char 63) tag)))

(defun sixel-process-row (string)
  (let ((idx-in 0)
        (idx-out 0)
        result)
    (while (< idx-in (length string))
      (let (trunc-string (substring string index-in))
        (cond
         ((string-match "^#\\([0-9]+\\);\\([0-9]+\\);\\([0-9]+\\);\\([0-9]+\\);\\([0-9]+\\)"
                        trunc-string)
          (let ((tag (intern (string-to (match-string 1 trunc-string))))
                (mode (match-string 2 trunc-string))
                (r (string-to-number (match-string 3 trunc-string)))
                (g (string-to-number (match-string 4 trunc-string)))
                (b (string-to-number (match-string 5 trunc-string))))
            (add-to-list 'sixel-colour-map (list (tag r g b)))
            (setq idx-in (match-end 0))))
         ((string-match "^#\\([0-9]+\\)" trunc-string)
          (let ((tag (intern (match-string 1 trunc-string))))
            (setq sixel-current-colour tag)
            (setq idx-in (match-end 0))))
         ((string-match "^$" trunc-string)
          (setq idx-out 0)
          (setq idx-in (match-end 0 trunc-string)))
         ((string-match "^!\\([0-9]+\\)\\([?-~]\\)" trunc-string)
          (let ((repeat-count (string-to-number (match-string 1 trunc-string)))
                (char (elt (match-string 2 trunc-string) 0)))
            (dotimes (i repeat-count)
              (sixel-tag-sixel-in-row 'result idx-out char sixel-current-colour)
              (setq idx-out (+1 idx-out)))))
         ((string-match "^\\([?-~]\\)" trunc-string)
          (let ((char (elt (match-string 1 trunc-string) 0)))
            (sixel-tag-sixel-in-row 'result idx-out char sixel-current-colour))
          (setq idx-out (+1 idx-out))))))))
              
(sixel-get-rows test-string)

(defun sixel-to-xpm (string)
  "Converts the given sixel string into an XPM image."

  (let* ((sp (split-string string "q"))
         (control-string (car sp))
         ())))