;;; edit-server.el --- server that responds to edit requests from Chrome

;; Copyright (C) 2009-2011  Alex Bennee
;; Copyright (C) 2010-2011  Riccardo Murri

;; Author: Alex Bennee <alex@bennee.com>
;; Maintainer: Alex Bennee <alex@bennee.com>
;; Version: 1.10
;; Homepage: https://github.com/stsquad/emacs_chrome

;; This file is not part of GNU Emacs.

;; This file 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 file 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 this program.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; This provides an edit server to respond to requests from the Chrome
;; Emacs Chrome plugin. This is my first attempt at doing something
;; with sockets in Emacs. I based it on the following examples:
;;
;;   http://www.emacswiki.org/emacs/EmacsEchoServer
;;   http://nullprogram.com/blog/2009/05/17/
;;
;; To use it ensure the file is in your load-path and add something
;; like the following examples to your .emacs:
;;
;; To open pages for editing in new buffers in your existing Emacs
;; instance:
;;
;;   (when (require 'edit-server nil t)
;;     (setq edit-server-new-frame nil)
;;     (edit-server-start))
;;
;; To open pages for editing in new frames using a running emacs
;; started in --daemon mode:
;;
;;   (when (and (require 'edit-server nil t) (daemonp))
;;     (edit-server-start))
;;
;; Buffers are edited in `text-mode' by default; to use a different
;; major mode, change `edit-server-default-major-mode' or customize
;; `edit-server-url-major-mode-alist' to specify major modes based
;; on the remote URL:
;;
;;   (setq edit-server-url-major-mode-alist
;;         '(("github\\.com" . markdown-mode)))
;;
;; Alternatively, set the mode in `edit-server-start-hook'.  For
;; example:
;;
;; (add-hook 'edit-server-start-hook
;;          (lambda ()
;;            (when (string-match "github.com" (buffer-name))
;;              (markdown-mode))))


;;; Code:

;; uncomment to debug
;; (setq debug-on-error t)
;; (setq edebug-all-defs t)

(unless (featurep 'make-network-process)
  (error "Incompatible version of [X]Emacs - lacks make-network-process"))

;;; Customization

(defcustom edit-server-port 9292
  "Local port the edit server listens to."
  :group 'edit-server
  :type 'integer)

(defcustom edit-server-host nil
  "If not nil, accept connections from HOST address rather than just
localhost. This may present a security issue."
  :group 'edit-server
  :type 'boolean)

(defcustom edit-server-verbose nil
  "If not nil, log connections and progress also to the echo area."
  :group 'edit-server
  :type 'boolean)

(defcustom edit-server-done-hook nil
  "Hook run when done editing a buffer for the Emacs HTTP edit-server.
Current buffer holds the text that is about to be sent back to the client."
  :group 'edit-server
  :type 'hook)

(defcustom edit-server-start-hook nil
  "Hook run when starting a editing buffer.  Current buffer is
the fully prepared editing buffer.  Use this hook to enable
buffer-specific modes or add key bindings."
  :group 'edit-server
  :type 'hook)

;; frame options

(defcustom edit-server-new-frame t
  "If not nil, edit each buffer in a new frame (and raise it)."
  :group 'edit-server
  :type 'boolean)

(defcustom edit-server-new-frame-alist
  '((name . "Emacs TEXTAREA")
    (width . 80)
    (height . 25)
    (minibuffer . t)
    (menu-bar-lines . t))
  "Frame parameters for new frames.  See `default-frame-alist' for examples.
If nil, the new frame will use the existing `default-frame-alist' values."
  :group 'edit-server
  :type '(repeat (cons :format "%v"
		       (symbol :tag "Parameter")
		       (sexp :tag "Value"))))

(defcustom edit-server-default-major-mode
  'text-mode
  "The default major mode to use in editing buffers, if no other
mode is selected by `edit-server-url-major-mode-alist'."
  :group 'edit-server
  :type 'function)

(defcustom edit-server-url-major-mode-alist
  nil
  "A-list of patterns and corresponding functions; when the first
pattern is encountered which matches `edit-server-url', the
corresponding function will be called in order to set the desired
major mode. If no pattern matches,
`edit-server-default-major-mode' will be used."
  :group 'edit-server
  :type '(alist :key-type (string :tag "Regexp")
		:value-type (function :tag "Major mode function")))

(defcustom edit-server-new-frame-mode-line t
  "Show the emacs frame's mode-line if set to t; hide if nil."
  :group 'edit-server
  :type 'boolean)

;;; Variables

(defconst edit-server-process-buffer-name " *edit-server*"
  "Template name of the edit-server process buffers.")

(defconst edit-server-log-buffer-name "*edit-server-log*"
  "Template name of the edit-server process buffers.")

(defconst edit-server-edit-buffer-name "TEXTAREA"
  "Template name of the edit-server text editing buffers.")

(defvar edit-server-clients ()
  "List of all client processes associated with the server process.")

;; Buffer local variables
;;
;; These are all required to associate the edit buffer with the
;; correct connection to the client and allow for the buffer to be sent
;; back when ready. They are `permanent-local` to avoid being reset if
;; the buffer changes major modes.

(defvar edit-server-proc nil
  "Network process associated with the current edit.")
(make-variable-buffer-local 'edit-server-proc)
(put 'edit-server-proc 'permanent-local t)

(defvar edit-server-frame nil
  "The frame created for a new edit-server process.")
(make-variable-buffer-local 'edit-server-frame)
(put 'edit-server-frame 'permanent-local t)

(defvar edit-server-phase nil
  "Symbol indicating the state of the HTTP request parsing.")
(make-variable-buffer-local 'edit-server-phase)
(put 'edit-server-phase 'permanent-local t)

(defvar edit-server-received nil
  "Number of bytes received so far in the client buffer.
Depending on the character encoding, may be different from the buffer length.")
(make-variable-buffer-local 'edit-server-received)
(put 'edit-server-received 'permanent-local t)

(defvar edit-server-request nil
  "The HTTP request (GET, HEAD, POST) received.")
(make-variable-buffer-local 'edit-server-request)
(put 'edit-server-request 'permanent-local t)

(defvar edit-server-content-length nil
  "The value gotten from the HTTP `Content-Length' header.")
(make-variable-buffer-local 'edit-server-content-length)
(put 'edit-server-content-length 'permanent-local t)

(defvar edit-server-url nil
  "The value gotten from the HTTP `x-url' header.")
(make-variable-buffer-local 'edit-server-url)
(put 'edit-server-url 'permanent-local t)

(defvar edit-server-file nil
  "The value gotten from the HTTP `x-file' header.")
(make-variable-buffer-local 'edit-server-file)
(put 'edit-server-file 'permanent-local t)

;;; Mode magic
;;
;; We want to re-map some of the keys to trigger edit-server-done
;; instead of the usual emacs like behaviour. However using
;; local-set-key will affect all buffers of the same mode, hence we
;; define a special (derived) mode for handling editing of text areas.


(defvar edit-server-edit-mode-map
  (let ((map (make-sparse-keymap)))
    (define-key map (kbd "C-x C-s") 'edit-server-save)
    (define-key map (kbd "C-x #")   'edit-server-done)
    (define-key map (kbd "C-c C-c") 'edit-server-done)
    (define-key map (kbd "C-x C-c") 'edit-server-abort)
    map)
  "Keymap for minor mode `edit-server-edit-mode'.

Redefine a few common Emacs keystrokes to functions that can
deal with the response to the edit-server request.

Any of the following keys will close the buffer and send the text
to the HTTP client: C-x #, C-c C-c.

Pressing C-x C-s will save the current state to the kill-ring.

If any of the above isused with a prefix argument, the
unmodified text is sent back instead.")

(define-minor-mode edit-server-edit-mode
  "Minor mode enabled on buffers opened by `edit-server-accept'.

Its sole purpose is currently to enable
`edit-server-edit-mode-map', which overrides common keystrokes to
send a response back to the client."
  :group 'edit-server
  :lighter " EditSrv"
  :init-value nil
  :keymap edit-server-edit-mode-map)

(defun turn-on-edit-server-edit-mode-if-server ()
  "Turn on `edit-server-edit-mode' if in an edit-server buffer."
  (when edit-server-proc
    (edit-server-edit-mode t)))

(define-globalized-minor-mode global-edit-server-edit-mode
  edit-server-edit-mode turn-on-edit-server-edit-mode-if-server)
(global-edit-server-edit-mode t)


;; Edit Server socket code

(defun edit-server-start (&optional verbose)
  "Start the edit server.

If argument VERBOSE is non-nil, logs all server activity to buffer
`*edit-server-log*'.  When called interactivity, a prefix argument
will cause it to be verbose."
  (interactive "P")
  (if (or (process-status "edit-server")
	  (null (condition-case err
                    (let ((proc (make-network-process
                                 :name "edit-server"
                                 :buffer edit-server-process-buffer-name
                                 :family 'ipv4
                                 :host (or edit-server-host 'local)
                                 :service edit-server-port
                                 :log 'edit-server-accept
                                 :server t
                                 :noquery t)))
                      (set-process-coding-system proc 'utf-8 'utf-8)
                      proc)
		  (file-error nil))))
      (message "An edit-server process is already running")
    (setq edit-server-clients '())
    (if verbose (get-buffer-create edit-server-log-buffer-name))
    (edit-server-log nil "Created a new edit-server process")))

(defun edit-server-stop nil
  "Stop the edit server"
  (interactive)
  (while edit-server-clients
    (edit-server-kill-client (car edit-server-clients))
    (setq edit-server-clients (cdr edit-server-clients)))
  (if (process-status "edit-server")
      (delete-process "edit-server")
    (message "No edit server running"))
  (when (get-buffer edit-server-process-buffer-name)
    (kill-buffer edit-server-process-buffer-name)))

(defun edit-server-log (proc fmt &rest args)
  "If a `*edit-server-log*' buffer exists, write STRING to it.
This is done for logging purposes.  If `edit-server-verbose' is
non-nil, then STRING is also echoed to the message line."
  (let ((string (apply 'format fmt args)))
    (if edit-server-verbose
	(message string))
    (if (get-buffer edit-server-log-buffer-name)
	(with-current-buffer edit-server-log-buffer-name
	  (goto-char (point-max))
	  (insert (current-time-string)
		  " "
		  (if (processp proc)
		      (concat
		       (buffer-name (process-buffer proc))
		       ": ")
		    "") ; nil is not acceptable to 'insert
		  string)
	  (or (bolp) (newline))))))

(defun edit-server-accept (server client msg)
  "Accept a new client connection."
  (let ((buffer (generate-new-buffer edit-server-process-buffer-name)))
    (when (fboundp 'set-buffer-multibyte)
      (set-buffer-multibyte t)) ; djb
    (buffer-disable-undo buffer)
    (set-process-buffer client buffer)
    (set-process-filter client 'edit-server-filter)
    ;; kill-buffer kills the associated process
    (set-process-query-on-exit-flag client nil)
    (with-current-buffer buffer
      (setq edit-server-phase 'wait
	    edit-server-received 0
	    edit-server-request nil))
    (setq edit-server-content-length nil
	  edit-server-url nil
	  edit-server-file nil))
  (add-to-list 'edit-server-clients client)
  (edit-server-log client msg))

(defun edit-server-filter (proc string)
  "Process data received from the client."
  ;; there is no guarantee that data belonging to the same client
  ;; request will arrive all in one go; therefore, we must accumulate
  ;; data in the buffer and process it in different phases, which
  ;; requires us to keep track of the processing state.
  (with-current-buffer (process-buffer proc)
    (insert string)
    (setq edit-server-received
	  (+ edit-server-received (string-bytes string)))
    (when (eq edit-server-phase 'wait)
      ;; look for a complete HTTP request string
      (save-excursion
	(goto-char (point-min))
	(when (re-search-forward
	       "^\\([A-Z]+\\)\\s-+\\(\\S-+\\)\\s-+\\(HTTP/[0-9\.]+\\)\r?\n"
	       nil t)
	  (edit-server-log
	   proc "Got HTTP `%s' request, processing in buffer `%s'..."
	   (match-string 1) (current-buffer))
	  (setq edit-server-request (match-string 1))
	  (setq edit-server-content-length nil)
	  (setq edit-server-phase 'head))))

    (when (eq edit-server-phase 'head)
      ;; look for "Content-length" header
      (save-excursion
	(goto-char (point-min))
	(when (re-search-forward "^Content-Length:\\s-+\\([0-9]+\\)" nil t)
	  (setq edit-server-content-length
		(string-to-number (match-string 1)))))
      ;; look for "x-url" header
      (save-excursion
	(goto-char (point-min))
	(when (re-search-forward "^x-url: .*/\\{2,3\\}\\([^?\r\n
]+\\)" nil t)
	  (setq edit-server-url (match-string 1))))
      ;; look for "x-file" header
      (save-excursion
	(goto-char (point-min))
	(when (re-search-forward "^x-file: \\([^?\r\n
]+\\)" nil t)
	  (edit-server-log proc "Found x-file: %s" (match-string 1))
	  (setq edit-server-file (match-string 1))))
      ;; look for head/body separator
      (save-excursion
	(goto-char (point-min))
	(when (re-search-forward "\\(\r?\n\\)\\{2\\}" nil t)
	  ;; HTTP headers are pure ASCII (1 char = 1 byte), so we can subtract
	  ;; the buffer position from the count of received bytes
	  (setq edit-server-received
		(- edit-server-received (- (match-end 0) (point-min))))
	  ;; discard headers - keep only HTTP content in buffer
	  (delete-region (point-min) (match-end 0))
	  (edit-server-log proc
			   "Processed headers, length: %s, url: %s, file: %s"
			   edit-server-content-length edit-server-url edit-server-file)
	  (setq edit-server-phase 'body))))

    (when (eq edit-server-phase 'body)
      (if (and edit-server-content-length
	       (> edit-server-content-length edit-server-received))
	  (edit-server-log proc
			   "Received %d bytes of %d ..."
			   edit-server-received edit-server-content-length)
	;; all content transferred - process request now
	(cond
	 ((string= edit-server-request "POST")
	  ;; create editing buffer, and move content to it
	  (edit-server-find-or-create-edit-buffer proc edit-server-file))
	 (t
	  ;; send 200 OK response to any other request
	  (edit-server-send-response proc "edit-server is running.\n")
	  (edit-server-kill-client proc)))
	;; wait for another connection to arrive
	(setq edit-server-received 0)
	(setq edit-server-phase 'wait)))))

(defun edit-server-show-edit-buffer (buffer)
  "Show edit buffer by creating a frame or raising the selected
frame."
  (if edit-server-new-frame
      (let ((new-frame
	     (if (memq window-system '(ns mac))
		 ;; Aquamacs, Emacs NS, Emacs (experimental) Mac port
		 (make-frame edit-server-new-frame-alist)
	       (make-frame-on-display (getenv "DISPLAY")
				      edit-server-new-frame-alist))))
	(unless edit-server-new-frame-mode-line
	  (setq mode-line-format nil))
	(select-frame new-frame)
	(when (and (eq window-system 'x)
		   (fboundp 'x-send-client-message))
	  (x-send-client-message nil 0 nil
				 "_NET_ACTIVE_WINDOW" 32
				 '(1 0 0)))
	(raise-frame new-frame)
	(set-window-buffer (frame-selected-window new-frame) buffer)
	new-frame)
    (select-frame-set-input-focus (window-frame (selected-window)))
    (pop-to-buffer buffer)
    (raise-frame)
    nil))

(defun edit-server-choose-major-mode ()
  "Use `edit-server-url-major-mode-alist' to choose a major mode
initialization function based on `edit-server-url', or fall back
to `edit-server-default-major-mode'"
  (let ((pairs edit-server-url-major-mode-alist)
	(mode edit-server-default-major-mode))
    (while pairs
      (let ((entry (car pairs)))
	(if (string-match (car entry) edit-server-url)
	    (setq mode (cdr entry)
		  pairs nil)
	  (setq pairs (cdr pairs)))))
    (funcall mode)))

(defun edit-server-find-or-create-edit-buffer(proc &optional existing)
  "Find and existing or create an new edit buffer, place content in it
and save the network process for the final call back"
  (let ((buffer (or (and (stringp existing)
			 (get-buffer existing))
		    (generate-new-buffer
		     (or edit-server-url
			 edit-server-edit-buffer-name)))))
    (with-current-buffer buffer
      (when (fboundp 'set-buffer-multibyte)
	(set-buffer-multibyte t))) ; djb
    (copy-to-buffer buffer (point-min) (point-max))
    (with-current-buffer buffer
      (setq edit-server-url (with-current-buffer (process-buffer proc) edit-server-url))
      (edit-server-choose-major-mode)
      ;; Allow `edit-server-start-hook' to override the major mode.
      ;; (re)setting the minor mode seems to clear the buffer-local
      ;; variables that we depend upon for the response, so call the
      ;; hooks early on
      (run-hooks 'edit-server-start-hook)
      (not-modified)
      (add-hook 'kill-buffer-hook 'edit-server-abort* nil t)
      (buffer-enable-undo)
      (setq edit-server-proc proc
	    edit-server-frame (edit-server-show-edit-buffer buffer))
      (edit-server-edit-mode))))

(defun edit-server-send-response (proc &optional body progress)
  "Send an HTTP 200 OK response back to process PROC.
Optional second argument BODY specifies the response content:
    - If nil, the HTTP response will have null content.
    - If a string, the string is sent as response content.
    - Any other value will cause the contents of the current
      buffer to be sent.
If optional third argument progress is non-nil, then the response
will include x-file and x-open headers to allow continuation of editing."
  (interactive)
  (edit-server-log proc "sending edit-server response")
  (if (processp proc)
      (let ((response-header (concat
			      "HTTP/1.0 200 OK\n"
			      (format "Server: Emacs/%s\n" emacs-version)
			      "Date: "
			      (format-time-string
			       "%a, %d %b %Y %H:%M:%S GMT\n"
			       (current-time))
			      (when progress
				(format "x-file: %s\nx-open: true\n" (buffer-name))))))
	(process-send-string proc response-header)
	(process-send-string proc "\n")
	(cond
	 ((stringp body)
	  (process-send-string proc (encode-coding-string body 'utf-8)))
	 ((not body) nil)
	 (t
	  (encode-coding-region (point-min) (point-max) 'utf-8)
	  (process-send-region proc (point-min) (point-max))))
	(process-send-eof proc)
	(edit-server-log proc "Editing done, sent HTTP OK response."))
    (message "edit-server-send-response: invalid proc (bug?)")))

(defun edit-server-kill-client (proc)
  "Kill client process PROC and remove it from the list."
  (let ((procbuf (process-buffer proc)))
    (delete-process proc)
    (when (buffer-live-p procbuf)
      (kill-buffer procbuf))
    (setq edit-server-clients (delq proc edit-server-clients))))

(defun edit-server-done (&optional abort nokill)
  "Finish editing: send HTTP response back, close client and editing buffers.

The current contents of the buffer are sent back to the HTTP
client, unless argument ABORT is non-nil, in which case then the
original text is sent back.
If optional second argument NOKILL is non-nil, then the editing
buffer is not killed and the buffer name is passed to calling process.

When called interactively, use prefix arg to abort editing."
  (interactive "P")
  ;; Do nothing if the connection is closed by the browser (tab killed, etc.)
  (unless (eq (process-status edit-server-proc) 'closed)
    (let ((buffer (current-buffer))
	  (proc edit-server-proc)
	  (procbuf (process-buffer edit-server-proc)))
      ;; edit-server-* vars are buffer-local,
      ;; so they must be used before issuing kill-buffer
      (if abort
	  ;; send back original content
	  (with-current-buffer procbuf
	    (run-hooks 'edit-server-done-hook)
	    (edit-server-send-response proc t))
	;; send back edited content
	(save-restriction
	  (widen)
	  (buffer-disable-undo)
	  ;; ensure any format encoding is done (like longlines)
	  (dolist (format buffer-file-format)
	    (format-encode-region (point-min) (point-max) format))
	  ;; send back
	  (run-hooks 'edit-server-done-hook)
	  (edit-server-send-response proc t nokill)
	  ;; restore formats (only useful if we keep the buffer)
	  (dolist (format buffer-file-format)
	    (format-decode-region (point-min) (point-max) format))
	  (buffer-enable-undo)))
      (when edit-server-frame
	(delete-frame edit-server-frame))
      ;; delete-frame may change the current buffer
      (unless nokill
	(kill-buffer buffer))
      (edit-server-kill-client proc))))

;; edit-server-save uses the iterative edit-server option (send a
;; buffer back to the client which then returns new request to
;; continue the session). The edit-server then switches back to the
;; buffer referenced by the x-file header.
;;

(defun edit-server-save ()
  "Save the current state of the edit buffer but don't close it."
  (interactive)
  (edit-server-done nil t))

(defun edit-server-abort ()
  "Discard editing and send the original text back to the browser."
  (interactive)
  (edit-server-done t))

(defun edit-server-abort* ()
  "Discard editing and send the original text back to the browser,
but don't kill the editing buffer."
  (interactive)
  (edit-server-done t t))

(provide 'edit-server)

;;; edit-server.el ends here