;;; sixel.el --- minor mode for processing sixel graphics

;; Copyright (C) 2019 Tim Vaughan

;; Author: Tim Vaughan <tgvaughan@gmail.com>
;; Created: 19 May 2019
;; Version: 1.0.0
;; Keywords: 
;; Homepage: https://github.com/tgvaughan/sixel
;; Package-Requires: ((emacs "25"))

;;; Commentary:

;;; Code:

(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))))

(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 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 row)))
    (push (make-vector 6 nil) row))
  (let ((sixel (elt row (- (length row) 1 index))))
    (sixel-tag-bits sixel (- char 63) tag))
  row)

(defun sixel-process-data (string)
  "Convert STRING into a list of lists representing individual sixels."
  (with-temp-buffer
    (insert string)
    (goto-char (point-min))
    (let ((idx-out 0)
          this-row rows
          current-colour colour-map
          finished)
      (while  (not finished)
        (cond
         ((looking-at "#\\([0-9]+\\);\\([0-9]+\\);\\([0-9]+\\);\\([0-9]+\\);\\([0-9]+\\)")
          (let ((tag (intern (match-string 1)))
                (mode (match-string 2))
                (r (string-to-number (match-string 3)))
                (g (string-to-number (match-string 4)))
                (b (string-to-number (match-string 5))))
            (push (list tag r g b) colour-map)))

         ((looking-at "#\\([0-9]+\\)")
          (let ((tag (intern (match-string 1))))
            (setq current-colour tag)))

         ((looking-at "\\$")
          (setq idx-out 0))

         ((looking-at "-")
          (push (reverse this-row) rows)
          (setq this-row nil)
          (setq idx-out 0))

         ((looking-at "!\\([0-9]+\\)\\([?-~]\\)")
          (let ((repeat-count (string-to-number (match-string 1)))
                (char (elt (match-string 2) 0)))
            (dotimes (i repeat-count)
              (setq this-row
                    (sixel-tag-sixel-in-row this-row idx-out char current-colour))
              (setq idx-out (1+ idx-out)))))

         ((looking-at "\\([?-~]\\)")
          (let ((char (elt (match-string 1) 0)))
            (setq this-row
                  (sixel-tag-sixel-in-row this-row idx-out char current-colour))
            (setq idx-out (1+ idx-out))))

         (t (setq finished t)))

        (goto-char (match-end 0)))
      (push (reverse this-row) rows)
      (list color-map
            (reverse rows)))))

;; sixel.el ends here