markdown-preview-mode/markdown-preview-mode.el

;;; markdown-preview-mode.el --- markdown realtime preview minor mode.

;; Copyright (C) 2014 <igor.shimko@gmail.com>

;; Author: Igor Shymko <igor.shimko@gmail.com>
;; URL: https://github.com/ancane/markdown-preview-mode
;; Keywords: markdown, preview
;; Version: 0.6
;; Package-Requires: ((websocket "1.6") (markdown-mode "2.1") (cl-lib "0.5"))

;; This file is not part of GNU Emacs.

;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 3, or (at your option)
;; any later version.
;;
;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.
;;
;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:
;;
;; This package makes use of websockets to deliver rendered markdown to a web browser.
;; Updates happen upon buffer save or on idle.
;;
;;; Code:

(require 'cl-lib)
(require 'websocket)
(require 'markdown-mode)

(defgroup markdown-preview nil
  "Markdown preview mode."
  :group 'text
  :prefix "markdown-preview-"
  :link '(url-link "https://github.com/ancane/markdown-preview-mode"))

(defcustom markdown-preview-host 'local
  "Markdown preview websocket server address."
  :group 'markdown-preview
  :type '(choice (const :tag "localhost" local)
                 (string :tag "Custom host")))

(defcustom markdown-preview-port 7379
  "Markdown preview websocket server port."
  :group 'markdown-preview
  :type 'integer)

(defcustom markdown-preview-style
  "http://thomasf.github.io/solarized-css/solarized-dark.min.css"
  "Markdown preview style URI."
  :group 'markdown-preview
  :type 'string)

(defcustom markdown-preview-file-name ".markdown-preview.html"
  "Markdown preview file name."
  :group 'markdown-preview
  :type 'string)

(defvar markdown-preview--websocket-server nil
  "`markdown-preview' Websocket server.")

(defvar markdown-preview--local-client nil
  "`markdown-preview' local client.")

(defvar markdown-preview--remote-clients nil
  "List of `markdown-preview' websocket remote clients.")

(defvar markdown-preview--preview-url
  (concat (file-name-directory load-file-name) "preview.html")
  "Location of `markdown-preview' html.")

(defvar markdown-preview--idle-timer nil
  "Preview idle timer.")

(defun markdown-preview--stop-idle-timer ()
  "Stop the `markdown-preview' idle timer."
  (when (timerp markdown-preview--idle-timer)
    (cancel-timer markdown-preview--idle-timer)))

(defun markdown-preview--open-browser-preview ()
  "Open the markdown preview in the browser."
  (let* ((dir-of-buffer-to-preview (file-name-directory (buffer-file-name)))
         (preview-file (concat dir-of-buffer-to-preview markdown-preview-file-name)))
    (if (not (file-exists-p preview-file))
        (copy-file markdown-preview--preview-url preview-file))
    (browse-url preview-file)))

(defun markdown-preview--stop-websocket-server ()
  "Stop the `markdown-preview' websocket server."
  (when markdown-preview--local-client
    (websocket-close markdown-preview--local-client))
  (when markdown-preview--websocket-server
    (delete-process markdown-preview--websocket-server)
    (setq markdown-preview--websocket-server nil
          markdown-preview--remote-clients nil)))

(defun markdown-preview--drop-closed-clients ()
  "Clean closed clients in `markdown-preview--remote-clients' list."
  (setq markdown-preview--remote-clients
        (cl-remove-if-not #'websocket-openp markdown-preview--remote-clients)))

(defun markdown-preview--start-websocket-server ()
  "Start `markdown-preview' websocket server."
  (when (not markdown-preview--websocket-server)
    (setq markdown-preview--websocket-server
          (websocket-server
           markdown-preview-port
           :host markdown-preview-host
           :on-message (lambda (websocket frame)
                         (mapc (lambda (ws) (websocket-send ws frame))
                               markdown-preview--remote-clients))
           :on-open (lambda (websocket)
                      (push websocket markdown-preview--remote-clients)
                      (markdown-preview--send-preview-to websocket))
           :on-error (lambda (websocket type err) (message (concat "====> Error:" err)))
           :on-close (lambda (websocket) (markdown-preview--drop-closed-clients))))
    (add-hook 'kill-emacs-hook 'markdown-preview--stop-websocket-server)
    (markdown-preview--open-browser-preview)))

(defun markdown-preview--start-local-client ()
  "Start the `markdown-preview' local client."
  (when (not markdown-preview--local-client)
    (setq markdown-preview--local-client
          (websocket-open
           (format "ws://localhost:%d" markdown-preview-port)
           :on-error (lambda (ws type err)
                       (message "error connecting"))
           :on-close (lambda (websocket)
                       (setq markdown-preview--local-client nil))))))

(defun markdown-preview--send-preview ()
  "Send the `markdown-preview' preview to clients."
  (when (bound-and-true-p markdown-preview-mode)
    (markdown-preview--send-preview-to markdown-preview--local-client)))

(defun markdown-preview--send-preview-to (websocket)
  "Send the `markdown-preview' to a specific WEBSOCKET."
  (let ((mark-position-percent
         (number-to-string
          (truncate
           (* 100
              (/
               (float (-  (line-number-at-pos) (/ (count-screen-lines (window-start) (point)) 2)))
               (count-lines (point-min) (point-max))))))))
    (markdown markdown-output-buffer-name)
    (with-current-buffer (get-buffer markdown-output-buffer-name)
      (websocket-send-text websocket
                           (concat
                            "<div>"
                            "<span id='style'>"
                            markdown-preview-style
                            "</span>"
                            "<span id='position-percentage'>"
                            mark-position-percent
                            "</span>"
                            "<div id='content'>"
                            (buffer-substring-no-properties (point-min) (point-max))
                            "</div>"
                            "</div>")
                           ))))

(defun markdown-preview--start ()
  "Start `markdown-preview' mode."
  (markdown-preview--start-websocket-server)
  (markdown-preview--start-local-client)
  (setq markdown-preview--idle-timer
        (run-with-idle-timer 2 t (lambda () (markdown-preview--send-preview))))
  (add-hook 'after-save-hook 'markdown-preview--send-preview nil t))

(defun markdown-preview--stop ()
  "Stop `markdown-preview' mode."
  (remove-hook 'after-save-hook 'markdown-preview--send-preview t)
  (markdown-preview--stop-idle-timer)
  (let ((preview-file (concat (file-name-directory (buffer-file-name)) markdown-preview-file-name)))
    (if (file-exists-p preview-file)
        (delete-file preview-file)))
  )

;;;###autoload
(defun markdown-preview-open-browser ()
  "Open the `markdown-preview' in the browser."
  (interactive)
  (markdown-preview--open-browser-preview))

;;;###autoload
(defun markdown-preview-cleanup ()
  "Cleanup `markdown-preview' mode."
  (interactive)
  (markdown-preview--stop-websocket-server))

;;;###autoload
(define-minor-mode markdown-preview-mode
  "Markdown preview mode."
  :group 'markdown-preview
  :init-value nil
  (when (not (or
              (equal major-mode 'markdown-mode)
              (equal major-mode 'gfm-mode)))
    (markdown-mode))
  (if markdown-preview-mode
      (markdown-preview--start)
    (markdown-preview--stop)))

(provide 'markdown-preview-mode)

;;; markdown-preview-mode.el ends here