;;; md4tj_parse --- Summary

;;; Commentary:

;;; Code:
(require 'cl-lib)

(defun getline ()
  "Get current line from loaded buffer."
  (buffer-substring-no-properties (line-beginning-position) (line-end-position)))

(defun md4tj-begin-tag (tag &optional attrs)
  "Return beginning html tag for TAG with optional ATTRS."
  (concat "<" tag
		  (mapconcat 'identity (cl-map 'listp (lambda (l) (concat " " (nth 0 l) "=" (nth 1 l))) attrs) "")
		  ">"))

(defun md4tj-end-tag (tag)
  "Return end html tag for TAG."
  (concat "</" tag ">"))

(defun md4tj-process-header (line)
  "Process LINE known to be header, return HTML."
  (let ((level (length (nth 0 (split-string line)))))
	(if (or (< level 0) (> level 6))
		(error (concat "Error parsing: " line "\n"))
	  (concat (md4tj-begin-tag (concat "h" (number-to-string level)))
			  (mapconcat 'identity (cdr (split-string line)) " ")
			  (md4tj-end-tag (concat "h" (number-to-string level)))))))

(defun md4tj-process-paragraph (line)
  "Process LINE that is paragraph, return HTML."
  (concat (md4tj-begin-tag "p") line (md4tj-end-tag "p")))

(defun md4tj-process-line (line)
  "Process all inline elements of the LINE, return HTML."
  ;; Finally links
  (replace-regexp-in-string
   "\\[\\(.*\\)\\](\\(.*\\))"
   (concat (md4tj-begin-tag "a" (list '("href" "\\2"))) "\\1" (md4tj-end-tag "a"))
   ;; Then images
   (replace-regexp-in-string
	"!\\[\\(.*\\)\\](\\(.*\\))"
	(md4tj-begin-tag "img" (list '("src" "\\2") '("alt" "\\1")))
	;; Then emphasis
	(replace-regexp-in-string
	 "\\*\\(.*\\)\\*"
	 "<em>\\1</em>"
	 ;; Then strong
	 (replace-regexp-in-string
	  "\\*\\*\\(.*\\)\\*\\*"
	  "<strong>\\1</strong>"
	  ;; First code
	  (replace-regexp-in-string
	   "`\\(.*\\)`"
	   "<code>\\1</code>" line))))))

;; Note: a "block" is the smallest unit of parsing
;; It is normally a line of the code, but can be
;; multiple lines in the case of a block (NI)
(defun md4tj-process-block (codeblock)
  "Process CODEBLOCK and return html."
  (cond ((string-match "^#+ " codeblock) (md4tj-process-header (md4tj-process-line codeblock)))
		((string= "---" codeblock) "<hr>")
		(t (md4tj-process-paragraph (md4tj-process-line codeblock)))))

(defun md4tj-next-block ()
  "Retrieve the next block in the open file."
  (let ((currline (getline)))
	(cond ((string-match "^- " currline) nil) ;; TODO ul's
		  ((string-match "^[0-9]+\\. " currline) nil) ;; TODO ol's
		  (t currline))))

(defun md4tj-parse (mdfile outfile)
  "Entry point to parse MDFILE and output to OUTFILE."
  (let ((inbuf (generate-new-buffer " in"))
		(outbuf (generate-new-buffer " out")))
	(set-buffer inbuf)
	(insert-file-contents mdfile)
	(goto-char (point-min))
	(set-buffer outbuf)
	(while (with-current-buffer inbuf (< (point) (point-max)))
	  ;; Insert next line(s) into output file
	  (insert (concat (md4tj-process-block (with-current-buffer
									   inbuf
									   (md4tj-next-block)))
					  "\n"))
	  ;; Advance input file by a line
	  (with-current-buffer inbuf (forward-line)))
	(write-region nil nil outfile nil)))

(provide 'md4tj_parse)
;;; md4tj_parse.el ends here