etherpad-esync.el

;;; etherpad-esync.el --- Etherpad easysync protocol -*- coding: utf-8; lexical-binding: t -*-

;; Copyright 2020 FoAM
;;
;; Author: nik gaffney <nik@fo.am>
;; Created: 2020-12-12
;; Version: 0.1
;; Keywords: comm, etherpad, collaborative editing
;; URL: https://github.com/zzkt/ethermacs

;; 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 of the License, 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 this program.  If not, see <https://www.gnu.org/licenses/>.


;;; Commentary:

;; Etherpad is a highly customizable Open Source online editor providing
;; collaborative editing in really real-time.
;;
;; The easysync protocol is used for communication of edits, changesets
;; and metadata between etherpad server and clients. It uses websockets
;; for the transport layer
;;
;;  details -> https://etherpad.org/doc/v1.8.5/#index_http_api

;; current issues 2020-12-15 00:52:32
;;  - one ws per buffer. buffer local. shared.
;;  - incorrect newline counts when sending changesets
;;  - problems w. deleting text and/or changing buffer size & change-hooks
;;  - see "Additional Constraints" of easysync
;;  - potential race conditions sending changesets on buffer changes
;;  - doesn't apply attributes or changes from the apool
;;  - general lack of error checking

;;; Code:

(require 'websocket)
(require 'let-alist)
(require 'calc-bin)
(require 'parsec)
(require '0xc)
(require 's)

;; debug details
;; (setq websocket-debug t)

;; local and buffer local variables
(defvar-local etherpad-esync--pre-buffer-length 0)
(defvar-local etherpad-esync--new-buffer-length 0)
(defvar-local etherpad-esync--change-length 0)
(defvar-local etherpad-esync--change-string "")

(defvar-local etherpad-esync--local-rev 0)
(defvar-local etherpad-esync--current-pad "")
(defvar-local etherpad-esync--local-author "") ;; e.g. "a.touCZaixjPgKDSiN"

(defvar-local etherpad-esync--hearbeat-timer nil)
(defvar-local etherpad-esync--current-socket nil)

;; session
(defvar etherpad-esync-session-token "") ;; see also *session-token*

;; buffering
(defvar etherpad-esync-buffer (generate-new-buffer "*etherpad (easysync)*"))


;; keep-alive message & heartbeat timers

(defun etherpad-esync-heartbeat-send ()
  "Send a keep-alive message."
  ;; only send if there is a current socket
  ;; and delete an active timer when there isn't a socket open
  (message "heartbeat?")
  (when (etherpad-esync-current-socket)
    (etherpad-esync-wss-send "2")
    (message "heartbeat sent: %s" etherpad-esync-buffer))
  (when (not (etherpad-esync-current-socket))
    (etherpad-esync-heartbeat-stop)
    (message "heartbeat stopped: %s" etherpad-esync--hearbeat-timer)))

(defun etherpad-esync-heartbeat-start ()
  "Maintain connection to server with periodic pings."
  (message "heartbeat started: %s" etherpad-esync-buffer)
  (setq etherpad-esync--hearbeat-timer
        (run-with-timer 5 15 #'etherpad-esync-heartbeat-send))
  (etherpad-esync-current-socket))

(defun etherpad-esync-heartbeat-stop ()
  "Stop sending keep-alive messages."
  (when etherpad-esync--hearbeat-timer
    (cancel-timer etherpad-esync--hearbeat-timer))
  (setq etherpad-esync--hearbeat-timer nil)
  (message "heartbeat stopped: %s" etherpad-esync-buffer))


;; sockets

(defun etherpad-esync-current-socket (&optional socket)
  "Return currently active socket or set SOCKET as current."
  (when socket
    (setq etherpad-esync--current-socket socket))
  (message "current socket: set")
  etherpad-esync--current-socket)


;; setters

(defun etherpad-esync--set-local-rev (n)
  "Set the local revision to N."
  (message "current rev: %s" etherpad-esync--local-rev)
  (setq etherpad-esync--local-rev n)
  (message "updated rev: %s" etherpad-esync--local-rev)
  (with-current-buffer etherpad-esync-buffer
    (rename-buffer (format "etherpad:%s:%s"
                           etherpad-esync--current-pad
                           etherpad-esync--local-rev))))

;; see also -> inhibit-modification-hooks

(defun etherpad-esync--add-change-hooks ()
  "Add predefined change hooks."
  (interactive)
  (message "setting up buffer change hooks")
  (with-current-buffer etherpad-esync-buffer
    (add-hook 'before-change-functions
              #'etherpad-esync--before-buffer-changes nil t)
    ;; ordering is important...
    (add-hook 'after-change-functions
              #'etherpad-esync--after-buffer-changes 22 t)
    (add-hook 'after-change-functions
              #'etherpad-esync--send-changes 23 t)))

(defun etherpad-esync--remove-change-hooks ()
  "Remove predefined change hooks."
  (interactive)
  (message "removing buffer change hooks")
  (with-current-buffer etherpad-esync-buffer
    (remove-hook 'before-change-functions
                 #'etherpad-esync--before-buffer-changes t)
    (remove-hook 'after-change-functions
                 #'etherpad-esync--after-buffer-changes t)
    (remove-hook 'after-change-functions
                 #'etherpad-esync--send-changes t)))


(defun etherpad-esync--before-buffer-changes (begin end)
  "Length before buffer is synced. BEGIN END."
  ;; (message "before -> b:%s e:%s" begin end)
  (setq-local etherpad-esync--pre-buffer-length (length (buffer-string))
              etherpad-esync--change-length (- end begin)))

(defun etherpad-esync--after-buffer-changes (begin end _pre)
  "Length after buffer is synced. BEGIN END."
  ;; (message "after -> b:%s e:%s p:%s" begin end pre)
  (setq-local etherpad-esync--new-buffer-length (length (buffer-string))
              etherpad-esync--change-string (buffer-substring begin end)
              etherpad-esync--change-length (- end begin)))

;; (message "eabc: pre: %s post: %s changed: %s chars to: %s at: %s(%s)"
;;          etherpad-esync--pre-buffer-length
;;          etherpad-esync--new-buffer-length
;;          etherpad-esync--change-length
;;          etherpad-esync--change-string
;;          (point)
;;          (n-36 (point))))


;; emacs -> etherpad changes

(defun etherpad-esync--send-changes (_b _e _p)
  "Create and encode a changeset."
  (let* ((b0 etherpad-esync--pre-buffer-length)
         (b1 etherpad-esync--new-buffer-length)
         (ops (if (< b0 b1)
                  (format "+%s" (- b1 b0))
                  (format "-%s" (- b0 b1))))
         (changeset
           (etherpad-esync--encode-changeset
            b0
            (- b1 b0)
            ops
            etherpad-esync--change-string)))
    (message "changeset: %s" changeset)
    (etherpad-esync--send-user-changes changeset)))


(defun etherpad-esync--encode-changeset (length change-size ops chars)
  "Create a changeset from some buffer activity. LENGTH CHANGE-SIZE OPS CHARS."
  (cl-labels ((n-36 (n)
                    (let ((calc-number-radix 36))
                      (downcase (math-format-radix n)))))
             (message "encoding: o:%s (%s) cs:%s op:%s ch:%s"
                      length (n-36 length)
                      change-size ops chars)

             (let* ((change (cond ((= 0 change-size) "=0")
                                  ((> 0 change-size)
                                   (format "<%s" (n-36 (abs change-size))))
                                  ((< 0 change-size)
                                   (format ">%s" (n-36 change-size)))))
                    (newline-count (s-count-matches "\n" (buffer-substring
                                                          (point-min)
                                                          (point))))
                    (offset (- (point) (length chars) 1))
                    ;; offset is distance from point-min to point w.out inserted chars and w. newlines
                    (pos-op (if (< 0 newline-count)
                                (format "|%s=%s"
                                        ;; 2 steps reqd. newline insert, then from beginning of line?
                                        (n-36 newline-count)
                                        (let ((p1 (- offset
                                                     (caar
                                                      (reverse
                                                       (s-matched-positions-all
                                                        "\n" (buffer-substring
                                                              (point-min) (point))))))))
                                          (message "offset: %s p1: %s" offset p1)
                                          (if (= 1 p1)
                                              (n-36 (+ 1 offset))
                                              (format "%s=%s"
                                                      (n-36 (- offset p1 -1))
                                                      (n-36 (- p1 1))))))
                                (format "=%s"  (n-36 offset)))))
               (format "Z:%s%s%s%s$%s" (n-36 length) change pos-op ops chars))))


(defun etherpad-esync--send-user-changes (cs)
  "Send a `USER_CHANGES' message with changeset CS."
  (let* ((author etherpad-esync--local-author)
         (rev etherpad-esync--local-rev)
         (changeset cs)
         (payload
           (format "42[\"message\",{\"type\":\"COLLABROOM\",\"component\":\"pad\",\"data\":{\"type\":\"USER_CHANGES\",\"baseRev\":%s,\"changeset\":\"%s\",\"apool\":{\"numToAttrib\":{},\"nextNum\":1}}}]"
                   rev changeset))) ;; author?
    (message "send this (as %s) -> %s" payload author)
    (etherpad-esync-wss-send payload)))

;; parsec info https://github.com/cute-jumper/parsec.el

(defun etherpad-esync-parse-changeset (cs)
  "Parse a changeset CS.

  :N : Source text has length N (must be first op)
  >N : Final text is N (positive) characters longer than source text (must be second op)
  <N : Final text is N (positive) characters shorter than source text (must be second op)
  >0 : Final text is same length as source text
  +N : Insert N characters from the bank, none of them newlines
  -N : Skip over (delete) N characters from the source text, none of them newlines
  =N : Keep N characters from the source text, none of them newlines
|L+N : Insert N characters from the source text, containing L newlines.  The last
         character inserted MUST be a newline, but not the (new) document's final newline.
|L-N : Delete N characters from the source text, containing L newlines. The last
         character inserted MUST be a newline, but not the (old) document's final newline.
|L=N : Keep N characters from the source text, containing L newlines.  The last character
         kept MUST be a newline, and the final newline of the document is allowed.
  *I : Apply attribute I from the pool to the following +, =, |+, or |= command.
         In other words, any number of * ops can come before a +, =, or | but not
         between a | and the corresponding + or =.
         If +, text is inserted having this attribute.  If =, text is kept but with
         the attribute applied as an attribute addition or removal.
         Consecutive attributes must be sorted lexically by (key,value) with key
         and value taken as strings.  It's illegal to have duplicate keys
         for (key,value) pairs that apply to the same text.  It's illegal to
         have an empty value for a key in the case of an insertion (+), the
         pair should just be omitted."

  (let* ((changes
           (parsec-with-input
            cs
            ;; a letter Z (the "magic character" and format version identifier)
            (parsec-str "Z")
            (parsec-collect*
             ;; source text length
             (parsec-re ":[0-9a-z]+")
             ;; change in text length
             (parsec-re "[>=<][0-9a-z]+")
             ;; insertion & deletion operations
             (parsec-many
              (parsec-or
               (parsec-re "|[0-9a-z]+[+-=][0-9a-z]+")
               (parsec-re "[><+-=*][0-9a-z]+")))
             ;; separator
             (parsec-str "$")
             ;; a string of characters used by insertion operations (the "char bank")
             (parsec-many-s
              (parsec-any-ch))))))

    (let* ((old-length
             (0xc-string-to-number (substring (car changes) 1) 36))
           (change-sign
             (if (s-equals? ">" (substring (nth 1 changes) 0 1)) 1 -1))
           (change-size
             (0xc-string-to-number (substring (nth 1 changes) 1) 36))
           (new-length
             (+ old-length (* change-sign change-size)))
           (ops
             (nth 2 changes))
           (chars
             (car (last changes))))
      (message "old length: %s new length: %s ops: %s" old-length new-length ops)
      (list old-length ops chars))))



;; operations -> buffer changes

(defun etherpad-esync-apply-ops (ops chars)
  "Apply a series of insert/delete OPS using CHARS.
Numeric offsets are calculated from the beginning of the buffer."
  (with-current-buffer etherpad-esync-buffer
    (save-mark-and-excursion
     (goto-char (point-min))
     (cl-flet
      ;; Convert a base-36 number STRING to decimal.
      ((s-36 (string)
             (0xc-string-to-number string 36)))

      (let ((char-bank chars))
        (mapcar
         (lambda (s)
           (let* ((o1 (s-left 1 s))
                  (p1 (substring s 1)))
             (message "op: %s val: %s" o1 p1)
             (pcase o1
                    ("+" (etherpad-esync-insert (s-left (s-36 p1) char-bank))
                         (setq char-bank (s-right (s-36 p1) char-bank)))
                    ("-" (etherpad-esync-delete (s-36 p1)))
                    ("=" (etherpad-esync-keep (s-36 p1)))
                    ("|" (let* ((p2 (s-split "[+=-]" p1))
                                (l1 (s-36 (car p2)))
                                (n1 (s-36 (cadr p2))))
                           ;; doesn't insert or delete newlines correctly (yet)
                           (message "op: | → l1: %s n1: %s" l1 n1)
                           (pcase p1
                                  ((pred (s-matches? "+"))
                                   (etherpad-esync-insert (make-string n1 10)))
                                  ((pred (s-matches? "-")) (etherpad-esync-delete n1))
                                  ((pred (s-matches? "=")) (etherpad-esync-keep n1)))))
                    ("*" t)
                    (_ nil))))
         ops))))))


;; character operations for remote->local sync
;; which should not trigger change hooks

(defun etherpad-esync-insert (chars)
  "Insert CHARS into the source text."
  (let ((inhibit-modification-hooks t))
    (insert chars)))

(defun etherpad-esync-delete (n)
  "Delete (skip over) N chars from the source text."
  (let ((inhibit-modification-hooks t))
    (delete-char n)))

(defun etherpad-esync-keep (n)
  "Keep N chars from the source text."
  (let ((inhibit-modification-hooks t))
    (forward-char n)))

;; start with current pad text

(defun etherpad-esync-init-text (chars)
  "Seeds a buffer with CHARS from a remote pad."
  (with-current-buffer etherpad-esync-buffer
    (let ((inhibit-modification-hooks t))
      (erase-buffer)
      (goto-char (point-min))
      (insert chars))))

(defun etherpad-esync-try-changeset (cs)
  "Try changeset CS."
  (let* ((changes
           (etherpad-esync-parse-changeset cs))
         (len (nth 0 changes))
         (ops (nth 1 changes))
         (chars (nth 2 changes)))
    (etherpad-esync--check-length len)
    (etherpad-esync-apply-ops ops chars)))

(defun etherpad-esync--check-length (size)
  "Check the changeset and buffer SIZE are consistent."
  (when (not (= size (length (buffer-string))))
    (message "changeset and buffer length are inconsistent.")))

;; various stanzas

(defun etherpad-esync--request-client-ready (padId)
  "Ethersync: send CLIENT_READY for PADID."
  (format "42[\"message\",{\"component\":\"pad\",\"type\":\"CLIENT_READY\",\"padId\":\"%s\",\"token\":\"%s\",\"protocolVersion\":2}]" padId etherpad-esync-session-token))

(defun etherpad-esync--request-get-comments (padId)
  "Ethersync: request comments on PADID."
  (format "42/comment,0[\"getComments\",{\"padId\":\"%s\"}]" padId))

(defun etherpad-esync--request-get-comment-replies (padId)
  "Ethersync: request comment replies on PADID."
  (format "42/comment,1[\"getCommentReplies\",{\"padId\":\"%s\"}]" padId))


;; sending via websockets

(defun etherpad-esync-wss-send (msg)
  "Send MSG to a websocket."
  (if (websocket-openp (etherpad-esync-current-socket))
      (when (stringp msg)
        (websocket-send-text
         (etherpad-esync-current-socket) msg))
      (message "websocket is closed. not sending: %s" msg)))


;; parsing & dispatch of incoming frames

(defun etherpad-esync-parse-wsframe (_websocket frame)
  "Parse & dispatch incoming FRAME.
Parsing occurs `with-current-buffer' for constancy with buffer-local variables
use let bindings for multiple connections."
  ;; (message "parsing: %s" frame)
  (with-current-buffer etherpad-esync-buffer
    (let* ((fr0 (websocket-frame-text frame))
           (frp (parsec-with-input
                 fr0
                 (parsec-collect* (parsec-re "[0-9]+")
                                  (parsec-many-s (parsec-any-ch))))))
      (message "frame: %s" (length fr0))
      (when (= 2 (length fr0))
        (message "frame: %s" fr0))
      (pcase (car frp)
             ("0" (etherpad-esync--parse-0 frp))
             ("2" (etherpad-esync--parse-2 frp))
             ("3" (message "3: keep-alive"))
             ("40" (etherpad-esync--parse-40 frp))
             ("42" (etherpad-esync--parse-42 frp))))))


;; parse various incoming message types

(defun etherpad-esync--parse-0 (p0)
  "Parse messages beginning with 0 from P0.
set sid, upgrades, pingInterval and pingTimeout for session."
  (when (listp p0)
    (pcase (length p0)
           (0 nil)
           (1 (car p0))
           (_ (let* ((p1 (json-parse-string (nth 1 p0) :object-type 'alist))
                     (sid (alist-get 'sid p1)))
                (message "sid %s" sid))))))


(defun etherpad-esync--parse-2 (p0)
  "Parse messages beginning with 2 from P0.
set revisions etc."
  (when (listp p0)
    (pcase (length p0)
           (0 nil)
           (1 (car p0))
           (_ (let* ((p1 (json-parse-string (nth 1 p0) :object-type 'alist)))
                (let-alist (aref p1 1)
                           (pcase .type
                                  ("COLLABROOM"
                                   (pcase .data.type
                                          ("ACCEPT_COMMIT"
                                           (message "accepted changes: rev:%s"
                                                    .data.newRev)
                                           (etherpad-esync--set-local-rev .data.newRev)))))))))))


(defun etherpad-esync--parse-40 (p0)
  "Parse messages beginning with 40 from P0.
comments and comment threads."
  (message "40: comments: %s" p0))


(defun etherpad-esync--parse-42 (p0)
  "Parse messages beginning with 42 from P0.
most of the COLLABROOM and update stuff..."
  (when (listp p0)
    (pcase (length p0)
           (0 nil)
           (1 (car p0))
           (_ (let* ((p1 (json-parse-string (nth 1 p0) :object-type 'alist)))
                (let-alist (aref p1 1)
                           (pcase .type
                                  ("COLLABROOM"
                                   (pcase .data.type

                                          ("USER_NEWINFO"
                                           (message "42: new user %s (color %s)"
                                                    .data.userInfo.userId
                                                    .data.userInfo.colorId))

                                          ("NEW_CHANGES"
                                           (message "42: new_changes rev:%s  changeset:%s (by %s)"
                                                    .data.newRev
                                                    .data.changeset
                                                    .data.author)
                                           (etherpad-esync--set-local-rev .data.newRev)
                                           (etherpad-esync-try-changeset .data.changeset))

                                          ("USER_CHANGES"
                                           (message "42: user_changes rev:%s  changeset:%s (by %s)"
                                                    .data.baseRev
                                                    .data.changeset
                                                    .data.apool.author))

                                          ("ACCEPT_COMMIT"
                                           (message "42: accept-commit rev:%s" .data.newRev)
                                           (etherpad-esync--set-local-rev .data.newRev))))

                                  ("CLIENT_READY"
                                   (message "42: ready -> %s and %s" .padId .token))

                                  ("CLIENT_VARS"
                                   (message "42: client_vars (%s) rev:%s -> %s"
                                            .data.padId
                                            .data.collab_client_vars.rev
                                            .data.collab_client_vars.initialAttributedText.text)
                                   (etherpad-esync--set-local-rev
                                    .data.collab_client_vars.rev)
                                   (etherpad-esync-init-text
                                    .data.collab_client_vars.initialAttributedText.text)))

                           (pcase .disconnect
                                  ("badChangeset"
                                   (message "42: disconnect (%s)" .disconnect)))))))))


(provide 'etherpad-esync)

;;; etherpad-esync.el ends here