;;; fuel-connection.el -- asynchronous comms with the fuel listener -*- lexical-binding: t -*-

;; Copyright (C) 2018 Björn Lindqvist
;; Copyright (C) 2008, 2009 Jose Antonio Ortega Ruiz
;; See https://factorcode.org/license.txt for BSD license.

;; Author: Jose Antonio Ortega Ruiz <jao@gnu.org>
;; Keywords: languages, fuel, factor
;; Start date: Thu Dec 11, 2008 03:10

;;; Comentary:

;; Handling communications via a comint buffer running a factor
;; listener.

;;; Code:

(require 'fuel-log)
(require 'fuel-base)

(require 'comint)
(require 'advice)


;;; Default connection:

(defvar-local fuel-con--connection nil)

(defun fuel-con--get-connection (buffer/proc)
  (if (processp buffer/proc)
      (fuel-con--get-connection (process-buffer buffer/proc))
    (with-current-buffer buffer/proc fuel-con--connection)))


;;; Request and connection datatypes:

;;; TODO Replace with a defstruct
(defun fuel-con--connection-queue-request (c r)
  (let ((reqs (assoc :requests c)))
    (setcdr reqs (append (cdr reqs) (list r)))))

(defun fuel-con--make-request (str cont &optional sender-buffer)
  (list :fuel-connection-request
        (cons :id (+ 10000 (random 89999)))
        (cons :string str)
        (cons :continuation cont)
        (cons :buffer (or sender-buffer (current-buffer)))))

(defsubst fuel-con--request-p (req)
  (and (listp req) (eq (car req) :fuel-connection-request)))

(defsubst fuel-con--request-deactivate (req)
  (setcdr (assoc :continuation req) nil))

(defsubst fuel-con--request-deactivated-p (req)
  (null (alist-get :continuation req)))

;;; TODO Replace with a defstruct
(defsubst fuel-con--make-connection (buffer)
  (list :fuel-connection
        (cons :requests (list))
        (cons :current nil)
        (cons :completed (make-hash-table :weakness 'value))
        (cons :buffer buffer)
        (cons :timer nil)))

(defsubst fuel-con--connection-p (c)
  (and (listp c) (eq (car c) :fuel-connection)))

(defun fuel-con--connection-clean-current-request (c)
  (let* ((cell (assoc :current c))
         (req (cdr cell)))
    (when req
      (puthash (alist-get :id req) req (alist-get :completed c))
      (setcdr cell nil))))

(defsubst fuel-con--connection-completed-p (c id)
  (gethash id (alist-get :completed c)))

(defun fuel-con--connection-pop-request (c)
  (let ((reqs (assoc :requests c))
        (current (assoc :current c)))
    (setcdr current (prog1 (cadr reqs) (setcdr reqs (cddr reqs))))
    (if (and (cdr current)
             (fuel-con--request-deactivated-p (cdr current)))
        (fuel-con--connection-pop-request c)
      (cdr current))))

(defun fuel-con--connection-start-timer (c)
  (let ((cell (assoc :timer c)))
    (when (cdr cell) (cancel-timer (cdr cell)))
    (setcdr cell (run-at-time t 0.5 'fuel-con--process-next c))))

(defun fuel-con--connection-cancel-timer (c)
  (let ((cell (assoc :timer c)))
    (when (cdr cell) (cancel-timer (cdr cell)))))


;;; Connection setup:

(defun fuel-con--cleanup-connection (c)
  (fuel-con--connection-cancel-timer c))

(defun fuel-con--setup-connection (buffer)
  (set-buffer buffer)
  (fuel-con--cleanup-connection fuel-con--connection)
  (setq fuel-con--connection nil)
  (let ((conn (fuel-con--make-connection buffer)))
    (fuel-con--setup-comint)
    (fuel-con--establish-connection conn buffer)))

(defconst fuel-con--prompt-regex "^IN: [^ ]+\\( auto-use\\)? ")
(defconst fuel-con--eot-marker "<~FUEL~>")
(defconst fuel-con--init-stanza "USE: fuel fuel-retort")

(defconst fuel-con--comint-finished-regex-connected
  (format "^%s$" fuel-con--eot-marker))

(defvar fuel-con--comint-finished-regex fuel-con--prompt-regex)

(defun fuel-con--setup-comint ()
  (setq-local comint-redirect-insert-matching-regexp t)
  (add-hook 'comint-redirect-filter-functions
            'fuel-con--comint-preoutput-filter nil t)
  (add-hook 'comint-redirect-hook
            'fuel-con--comint-redirect-hook nil t))

(defadvice comint-redirect-setup
  (after fuel-con--advice (output-buffer comint-buffer finished-regexp &optional echo))
  (with-current-buffer comint-buffer
    (when fuel-con--connection
      (setq comint-redirect-finished-regexp fuel-con--comint-finished-regex))))
(ad-activate 'comint-redirect-setup)

(defun fuel-con--comint-preoutput-filter (str)
  (when (string-match fuel-con--comint-finished-regex str)
    (setq comint-redirect-finished-regexp fuel-con--prompt-regex))
  str)

(defun fuel-con--establish-connection (conn buffer)
  (with-current-buffer (fuel-con--comint-buffer) (erase-buffer))
  (with-current-buffer buffer
    (setq fuel-con--connection conn)
    (setq fuel-con--comint-finished-regex fuel-con--prompt-regex)
    (fuel-con--send-string/wait buffer
                                fuel-con--init-stanza
                                'fuel-con--establish-connection-cont
                                3000000)
    conn))

(defun fuel-con--establish-connection-cont (ignore)
  (let ((str (with-current-buffer (fuel-con--comint-buffer) (buffer-string))))
    (if (string-match fuel-con--eot-marker str)
        (progn
          (setq fuel-con--comint-finished-regex
                fuel-con--comint-finished-regex-connected)
          (fuel-con--connection-start-timer fuel-con--connection)
          (message "FUEL listener up and running!"))
      (fuel-con--connection-clean-current-request fuel-con--connection)
      (setq fuel-con--connection nil)
      (message "An error occurred initialising FUEL's Factor library!")
      (pop-to-buffer (fuel-con--comint-buffer)))))


;;; Requests handling:

(defsubst fuel-con--comint-buffer ()
  (get-buffer-create " *fuel connection retort*"))

(defun fuel-con--comint-buffer-form ()
  "Parse the text in the comint buffer into a
sexp. fuel-con-error is thrown if the sexp is malformed."
  (with-current-buffer (fuel-con--comint-buffer)
    (goto-char (point-min))
    (condition-case cerr
        (let ((form (read (current-buffer))))
          (if (listp form) form
            (list 'fuel-con-error (buffer-string))))
      (error (list 'fuel-con-error (format "%s" cerr))))))

(defun fuel-con--process-next (con)
  (when (not (alist-get :current con))
    (let* ((buffer (alist-get :buffer con))
           (req (fuel-con--connection-pop-request con))
           (str (and req (alist-get :string req)))
           (cbuf (with-current-buffer (fuel-con--comint-buffer)
                   (erase-buffer)
                   (current-buffer))))
      (if (not (buffer-live-p buffer))
          (fuel-con--connection-cancel-timer con)
        (when (and buffer req str)
          (set-buffer buffer)
          (fuel-log--info "<%s>: %s" (alist-get :id req) str)
          (comint-redirect-send-command (format "%s" str) cbuf nil t))))))

(defun fuel-con--process-completed-request (req)
  (let ((cont (alist-get :continuation req))
        (id (alist-get :id req))
        (rstr (alist-get :string req))
        (buffer (alist-get :buffer req)))
    (if (not cont)
        (fuel-log--warn "<%s> Dropping result for request %S (%s)"
                            id rstr req)
      (condition-case cerr
          (with-current-buffer (or buffer (current-buffer))
            (funcall cont (fuel-con--comint-buffer-form))
            (fuel-log--info "<%s>: processed" id))
        (error (fuel-log--error
                "<%s>: continuation failed %S \n\t%s" id rstr cerr))))))

(defun fuel-con--comint-redirect-hook ()
  (if (not fuel-con--connection)
      (fuel-log--error "No connection in buffer")
    (let ((req (alist-get :current fuel-con--connection)))
      (if (not req) (fuel-log--error "No current request")
        (fuel-con--process-completed-request req)
        (fuel-con--connection-clean-current-request fuel-con--connection)))))


;;; Message sending interface:

(defconst fuel-con--error-message "FUEL connection not active")

(defun fuel-con--send-string (buffer/proc str cont &optional sender-buffer)
  (save-current-buffer
    (let ((con (fuel-con--get-connection buffer/proc)))
      (unless con (error fuel-con--error-message))
      (let ((req (fuel-con--make-request str cont sender-buffer)))
        (fuel-con--connection-queue-request con req)
        (fuel-con--process-next con)
        req))))

(defvar fuel-connection-timeout 30000
  "Time limit, in msecs, blocking on synchronous evaluation requests")

(defun fuel-con--send-string/wait (buffer/proc str cont &optional timeout sbuf)
  (save-current-buffer
    (let ((con (fuel-con--get-connection buffer/proc)))
      (unless con (error fuel-con--error-message))
      (let* ((req (fuel-con--send-string buffer/proc str cont sbuf))
             (id (and req (alist-get :id req)))
             (time (or timeout fuel-connection-timeout))
             (step 100)
             (waitsecs (/ step 1000.0)))
        (when id
          (condition-case nil
              (while (and (> time 0)
                          (not (fuel-con--connection-completed-p con id)))
                (accept-process-output nil waitsecs)
                (setq time (- time step)))
            (error (setq time 0)))
          (or (> time 0)
              (fuel-con--request-deactivate req)
              nil))))))


(provide 'fuel-connection)

;;; fuel-connection.el ends here