;;; 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 strikethrough
  (replace-regexp-in-string
   "~~\\(.*\\)~~"
   "<s>\\1</s>"
   ;; Then highlight
   (replace-regexp-in-string
	"==\\(.*\\)=="
	"<mark>\\1</mark>"
	;; Then 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 videos
	  (replace-regexp-in-string
	   "!!\\[\\([^\\[]*\\)](\\([^\\[(]*\\))"
	   (concat (md4tj-begin-tag "video" (list '("src" "\\2") '("type" "video/webm") '("controls" "true"))) "\\1" (md4tj-end-tag "video"))
	   ;; 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)))))))))

(defun md4tj-clean-multiline (line)
  "Clean LINE of markdown syntax for ul."
  (replace-regexp-in-string
   "^```" ""
   (replace-regexp-in-string
	"^[0-9]+\\. " ""
	(replace-regexp-in-string "^- " "" line))))

(defun md4tj-clean-code-for-html (line)
  "Escape characters in LINE that would be misinterpreted by the browser."
  (string-replace
   "<" "&lt;"
   (string-replace ">" "&gt;" line)))
				  
(defun md4tj-convert-line-to-html (line state)
  "Process LINE with STATE and return html."
  (let ((cleanline (md4tj-clean-multiline line)))
	;; If this is a signal to include another file
	(cond ((string-match "^@@INCLUDE" line) (md4tj-parse-to-string (nth 1 (split-string line))))
		  ((string-match "^@@LASTUPDATED" line) (concat "Last updated: " (current-time-string)))
		  ;; If this is some other signal, ignore
		  ((string-match "^@@" line) "")
		  ;; Otherwise, process as normal
		  (t
		   (concat
			;; Beginning multiline block/ending prev multiline block
			(mapconcat #'md4tj-state-to-html state "\n")
			
			;; Body
			(cond ((or (eq (nth 1 state) 'code) (eq (nth 1 state) 'begincode)) (md4tj-clean-code-for-html cleanline))
				  ((string-match "^#+ " cleanline) (md4tj-process-header (md4tj-process-line cleanline)))
				  ((string= "---" cleanline) "<hr>") ;; horizontal line
				  ((= (length cleanline) 0) "<br/>") ;; blank line
				  (t (md4tj-process-paragraph (md4tj-process-line cleanline))))
			
			;; End of multiline block
			(cond ((or (eq (nth 1 state) 'ul) (eq (nth 1 state) 'beginul)) "</li>")
				  ((or (eq (nth 1 state) 'ol) (eq (nth 1 state) 'beginol)) "</li>")
				  ((eq (nth 1 state) 'code) "")
				  (t "")))))))

(defun md4tj-state-to-html (state)
  "Convert STATE to html."
  (cond ((eq state 'beginul) "<ul>\n<li>")
		((eq state 'beginol) "<ol>\n<li>")
		((eq state 'begincode) "<pre>\n<code>")
		((eq state 'ul) "<li>")
		((eq state 'ol) "<li>")
		((eq state 'code) "")
		((eq state 'endul) "</ul>\n")
		((eq state 'endol) "</ol>\n")
		((eq state 'endcode) "</code>\n</pre>\n")
		(t "")))

(defun md4tj-next-state (currline prevstate)
  "Return the state based on CURRLINE and PREVSTATE."
  (list
   ;; End state
   (cond ((and (string-match "^- " currline) (or (eq prevstate 'ol) (eq prevstate 'beginol))) 'endol)
		 ((and (string-match "^[0-9]+\\. " currline) (or (eq prevstate 'ul) (eq prevstate 'beginul))) 'endul)
		 ((and (not (string-match "^- " currline)) (or (eq prevstate 'beginul) (eq prevstate 'ul))) 'endul)
		 ((and (not (string-match "[0-9]+\\.  " currline)) (or (eq prevstate 'beginol) (eq prevstate 'ol))) 'endul)
		 ((and (string-match "```$" currline) (or (eq prevstate 'code) (eq prevstate 'begincode))) 'endcode)
		 (t 'nothing))
   
   ;; Begin state (or next line's prevstate)
   (cond ((and (string-match "^- " currline) (not (or (eq prevstate 'beginul) (eq prevstate 'ul))) 'beginul))
		 ((and (string-match "^- " currline) (or (eq prevstate 'beginul) (eq prevstate 'ul)) 'ul))
		 ((and (string-match "^[0-9]+\\. " currline) (not (or (eq prevstate 'beginol) (eq prevstate 'ol))) 'beginol))
		 ((and (string-match "^[0-9]+\\. " currline) (or (eq prevstate 'beginol) (eq prevstate 'ol)) 'ol))
		 ((and (string-match "^```" currline) (not (or (eq prevstate 'begincode) (eq prevstate 'code))) 'begincode))
		 ((and (not (string-match "```$" currline)) (or (eq prevstate 'begincode) (eq prevstate 'code)) 'code))
		 (t 'normal))))

(defun md4tj-begin ()
  "Insert beginning code for all html."
  (concat "<!DOCTYPE html>\n"
		  (md4tj-begin-tag "html"
						   (list (list "lang"
									   (or (nth 1 (car (cl-remove-if-not (lambda (meta) (string= (car meta) "@@LANG")) (md4tj-find-metas)))) "en"))))
		  "\n"))

(defun md4tj-finalize (state)
  "Finalizes HTML document by inserting missing end tags based on STATE."
  (concat
   (cond ((or (eq state 'beginul) (eq state 'ul)) "</ul>")
		 ((or (eq state 'beginol) (eq state 'ol)) "</ol>")
		 ((or (eq state 'begincode) (eq state 'code)) "</code>")
		 (t ""))
   "</body>\n"
   "</html>"))

(defun md4tj-find-metas ()
  "Return all lines starting with @@ as list of split strings."
  (save-excursion
	(let ((meta-list nil))
	  (goto-char (point-min))
	  (while (re-search-forward "^@@" nil t)
		(setq meta-list (cons (split-string (getline)) meta-list)))
	  meta-list)))

(defun md4tj-list-to-tuple-list (list)
  "Convert LIST to tuple list."
  (let ((tuples nil))
	(dolist (i (number-sequence 0 (- (length list) 1) 2))
	  (setq tuples (cons (cons (nth i list) (list (nth (+ i 1) list))) tuples)))
	(reverse tuples)))

(defun md4tj-meta-to-html (meta)
  "Convert META to html."
  (cond ((string= (nth 0 meta) "@@TITLE")
		 (concat "<title>" (mapconcat 'identity (cdr meta) " ") "</title>\n"))
		((string= (nth 0 meta) "@@META")
		 (concat (md4tj-begin-tag "meta" (md4tj-list-to-tuple-list (cdr meta)))))
		((string= (nth 0 meta) "@@CSS")
		 (concat (md4tj-begin-tag "link" (list (list "rel" "stylesheet") (list "href" (nth 1 meta))))))))

(defun md4tj-head ()
  "Return text for head element on current buffer."
  (concat
   (md4tj-begin-tag "head") "\n"
   (mapconcat 'md4tj-meta-to-html (md4tj-find-metas) "\n")
   "\n"
   (md4tj-end-tag "head") "\n"))

(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"))
		(fullstate (list 'nothing 'normal))
		(line nil))
	(set-buffer inbuf)
	(insert-file-contents mdfile)
	(goto-char (point-min))
	(set-buffer outbuf)
	(insert (md4tj-begin))
	(insert (with-current-buffer inbuf (md4tj-head)))
	(insert (md4tj-begin-tag "body"))
	(while (with-current-buffer inbuf (< (point) (point-max)))
	  (setq line (with-current-buffer inbuf (getline)))
	  (setq fullstate (md4tj-next-state line (nth 1 fullstate)))
	  ;; Insert next line(s) into output file
	  (insert (concat (md4tj-convert-line-to-html line fullstate) "\n"))
	  ;; Advance input file by a line
	  (with-current-buffer inbuf (forward-line)))
	(insert (md4tj-finalize (nth 1 fullstate)))
	;; Write outbuf to outfile
	(write-region nil nil outfile nil)))

(defun md4tj-parse-to-string (mdfile)
  "Parse MDFILE, return conversion to HTML as string."
  (with-temp-buffer
	(let ((acc nil)
		  (line nil)
		  (fullstate (list 'nothing 'normal)))
	  (insert-file-contents mdfile)
	  (goto-char (point-min))
	  (while (< (point) (point-max))
		(setq line (getline))
		(setq fullstate (md4tj-next-state line (nth 1 fullstate)))
		(setq acc (concat acc (md4tj-convert-line-to-html line fullstate) "\n"))
		(forward-line))
	  acc)))
(provide 'md4tj_parse)
;;; md4tj_parse.el ends here