;;; nnoo.el --- OO Gnus Backends  -*- lexical-binding: t; -*-

;; Copyright (C) 1996-2021 Free Software Foundation, Inc.

;; Author: Lars Magne Ingebrigtsen <larsi@gnus.org>
;; Keywords: news

;; This file is part of GNU Emacs.

;; GNU Emacs 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.

;; GNU Emacs 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 <https://www.gnu.org/licenses/>.

;;; Commentary:

;;; Code:

(require 'nnheader)
(eval-when-compile (require 'cl-lib))

(defvar nnoo-definition-alist nil)
(defvar nnoo-state-alist nil)
(defvar nnoo-parent-backend nil)

(defmacro defvoo (var init &optional doc &rest map)
  "The same as `defvar', only takes list of variables to MAP to."
  (declare (indent 2)
           (debug (var init &optional doc &rest map)))
  `(prog1
       ,(if doc
	    `(defvar ,var ,init ,(concat doc "\n\nThis is a Gnus server variable.  See Info node `(gnus)Select Methods'."))
	  `(defvar ,var ,init))
     (nnoo-define ',var ',map)))

(defmacro deffoo (func args &rest forms)
  "The same as `defun', only register FUNC."
  (declare (indent 2)
           (debug (&define name lambda-list def-body)))
  `(prog1
       (defun ,func ,args ,@forms)
     (nnoo-register-function ',func)))

(defun noo--defalias (fun val)
  (prog1 (defalias fun val) (nnoo-register-function fun)))

(defun nnoo-register-function (func)
  (let ((funcs (nthcdr 3 (assoc (nnoo-backend func)
				nnoo-definition-alist))))
    (unless funcs
      (error "%s belongs to a backend that hasn't been declared" func))
    (setcar funcs (cons func (car funcs)))))

(defmacro nnoo-declare (backend &rest parents)
  (declare (indent 1))
  `(eval-and-compile
     (if (assq ',backend nnoo-definition-alist)
	 (setcar (cdr (assq ',backend nnoo-definition-alist))
		 (mapcar #'list ',parents))
       (push (list ',backend
		   (mapcar #'list ',parents)
		   nil nil)
	     nnoo-definition-alist))
     (unless (assq ',backend nnoo-state-alist)
       (push (list ',backend "*internal-non-initialized-backend*")
	     nnoo-state-alist))))

(defun nnoo-parents (backend)
  (nth 1 (assoc backend nnoo-definition-alist)))

(defun nnoo-variables (backend)
  (nth 2 (assoc backend nnoo-definition-alist)))

(defun nnoo-functions (backend)
  (nth 3 (assoc backend nnoo-definition-alist)))

(defmacro nnoo-import (backend &rest imports)
  (declare (indent 1))
  `(nnoo-import-1 ',backend ',imports))

(defun nnoo-import-1 (backend imports)
  (let ((call-function
	 (if (symbolp (car imports)) (pop imports) #'nnoo-parent-function)))
    (dolist (imp imports)
      (dolist (fun (or (cdr imp) (nnoo-functions (car imp))))
	(let ((function (nnoo-symbol backend (nnoo-rest-symbol fun))))
	  (unless (fboundp function)
	    (noo--defalias function
		           (lambda (&rest args)
		             (funcall call-function backend fun args)))))))))

(defun nnoo-parent-function (backend function args)
  (let ((pbackend (nnoo-backend function))
	(nnoo-parent-backend backend))
    (nnoo-change-server pbackend
			(nnoo-current-server backend)
			(cdr (assq pbackend (nnoo-parents backend))))
    (prog1
	(apply function args)
      ;; Copy the changed variables back into the child.
      (let ((vars (cdr (assq pbackend (nnoo-parents backend)))))
	(while vars
	  (set (cadar vars) (symbol-value (caar vars)))
	  (setq vars (cdr vars)))))))

(defun nnoo-execute (backend function &rest args)
  "Execute FUNCTION on behalf of BACKEND."
  (let ((pbackend (nnoo-backend function))
	(nnoo-parent-backend backend))
    (nnoo-change-server pbackend
			(nnoo-current-server backend)
			(cdr (assq pbackend (nnoo-parents backend))))
    (prog1
	(apply function args)
      ;; Copy the changed variables back into the child.
      (let ((vars (cdr (assq pbackend (nnoo-parents backend)))))
	(while vars
	  (set (cadar vars) (symbol-value (caar vars)))
	  (setq vars (cdr vars)))))))

(defmacro nnoo-map-functions (backend &rest maps)
  (declare (indent 1))
  `(progn
     ,@(mapcar
        (lambda (m)
          (let ((margs nil))
            (dotimes (i (length (cdr m)))
	      (push (if (numberp (nth i (cdr m)))
	                `(nth ,i args)
	              (nth i (cdr m)))
	            margs))
	    `(deffoo ,(nnoo-symbol backend (nnoo-rest-symbol (car m)))
		 (&rest args)
	       (ignore args) ;; Not always used!
	       (nnoo-parent-function ',backend ',(car m)
				     ,(cons 'list (nreverse margs))))))
	maps)))

(defun nnoo-backend (symbol)
  (string-match "^[^-]+-" (symbol-name symbol))
  (intern (substring (symbol-name symbol) 0 (1- (match-end 0)))))

(defun nnoo-rest-symbol (symbol)
  (string-match "^[^-]+-" (symbol-name symbol))
  (intern (substring (symbol-name symbol) (match-end 0))))

(defun nnoo-symbol (backend symbol)
  (intern (format "%s-%s" backend symbol)))

(defun nnoo-define (var map)
  (let* ((backend (nnoo-backend var))
	 (def (assq backend nnoo-definition-alist))
	 (parents (nth 1 def)))
    (unless def
      (error "%s belongs to a backend that hasn't been declared" var))
    (setcar (nthcdr 2 def)
	    (delq (assq var (nth 2 def)) (nth 2 def)))
    (setcar (nthcdr 2 def)
	    (cons (cons var (symbol-value var))
		  (nth 2 def)))
    (while map
      (nconc (assq (nnoo-backend (car map)) parents)
	     (list (list (pop map) var))))))

(defun nnoo-change-server (backend server defs)
  (let* ((bstate (cdr (assq backend nnoo-state-alist)))
	 (current (car bstate))
	 (parents (nnoo-parents backend))
	 (server (if nnoo-parent-backend
		     (format "%s+%s" nnoo-parent-backend server)
		   server))
	 (bvariables (nnoo-variables backend))
	 state def)
    ;; If we don't have a current state, we push an empty state
    ;; onto the alist.
    (unless bstate
      (push (setq bstate (list backend nil))
	    nnoo-state-alist)
      (pop bstate))
    (if (equal server current)
	t
      (nnoo-push-server backend current)
      (setq state (or (cdr (assoc server (cddr bstate)))
		      (nnoo-variables backend)))
      (while state
	(set (caar state) (cdar state))
	(pop state))
      (setcar bstate server)
      (unless (cdr (assoc server (cddr bstate)))
	(while (setq def (pop defs))
	  (unless (assq (car def) bvariables)
	    (nconc bvariables
		   (list (cons (car def) (and (boundp (car def))
					      (symbol-value (car def)))))))
	  (if (equal server "*internal-non-initialized-backend*")
	      (set (car def) (symbol-value (cadr def)))
	    (set (car def) (cadr def)))))
      (while parents
	(nnoo-change-server
	 (caar parents) (format "%s+%s" backend server)
	 (mapcar (lambda (def) (list (car def) (symbol-value (cadr def))))
		 (cdar parents)))
	(pop parents))))
  t)

(defun nnoo-push-server (backend current)
  (let ((bstate (assq backend nnoo-state-alist))
	(defs (nnoo-variables backend)))
    ;; Remove the old definition.
    (setcdr (cdr bstate) (delq (assoc current (cddr bstate)) (cddr bstate)))
    ;; If this is the first time we push the server (i. e., this is
    ;; the nil server), then we update the default values of
    ;; all the variables to reflect the current values.
    (when (equal current "*internal-non-initialized-backend*")
      (let ((defaults (nnoo-variables backend))
	    def)
	(while (setq def (pop defaults))
	  (setcdr def (symbol-value (car def))))))
    (let (state)
      (while defs
	(push (cons (caar defs) (symbol-value (caar defs)))
	      state)
	(pop defs))
      (nconc bstate (list (cons current state))))))

(defsubst nnoo-current-server-p (backend server)
  (equal (nnoo-current-server backend)
	 (if nnoo-parent-backend
	     (format "%s+%s" nnoo-parent-backend server)
	   server)))

(defun nnoo-current-server (backend)
  (nth 1 (assq backend nnoo-state-alist)))

(defun nnoo-close-server (backend &optional server)
  (unless server
    (setq server (nnoo-current-server backend)))
  (when server
    (let* ((bstate (cdr (assq backend nnoo-state-alist)))
	   (defs (assoc server (cdr bstate))))
      (when bstate
	(setcar bstate nil)
	(setcdr bstate (delq defs (cdr bstate)))
	(pop defs)
	(while defs
	  (set (car (pop defs)) nil)))))
  t)

(defun nnoo-close (backend)
  (setq nnoo-state-alist
	(delq (assq backend nnoo-state-alist)
	      nnoo-state-alist))
  t)

(defun nnoo-status-message (backend _server)
  (nnheader-get-report backend))

(defun nnoo-server-opened (backend server)
  (and (nnoo-current-server-p backend server)
       (buffer-live-p nntp-server-buffer)))

(defmacro nnoo-define-basics (backend)
  "Define `close-server', `server-opened' and `status-message'."
  (let ((form
         ;; We wrap the definitions in `when t' here so that a subsequent
         ;; "real" definition of one those doesn't trigger a "defined multiple
         ;; times" warning.
         `(when t
            ,@(mapcar (lambda (fun)
                       `(deffoo ,(nnoo-symbol backend fun) (&optional server)
	                  (,(nnoo-symbol 'nnoo fun) ',backend server)))
	             '(server-opened status-message))
	   (deffoo ,(nnoo-symbol backend 'close-server) (&optional server _defs)
             (,(nnoo-symbol 'nnoo 'close-server) ',backend server))
           (deffoo ,(nnoo-symbol backend 'open-server) (server &optional defs)
             (nnoo-change-server ',backend server defs)))))
    ;; Wrapping with `when' has the downside that the compiler now doesn't
    ;; "know" that these functions are defined, so to avoid "not known to be
    ;; defined" warnings we eagerly define them during the compilation.
    ;; This is fairly nasty since it will override previous "real" definitions
    ;; (e.g. when compiling this in an Emacs instance that's running Gnus), but
    ;; that's also what the previous code did, so it sucks but is not worse.
    (eval form t)
    form))

(defmacro nnoo-define-skeleton (backend)
  "Define all required backend functions for BACKEND.
All functions will return nil and report an error."
  `(eval-and-compile
     (nnoo-define-skeleton-1 ',backend)))

(defun nnoo-define-skeleton-1 (backend)
  (dolist (op '(retrieve-headers
		request-close request-article
		request-group close-group
		request-list request-post request-list-newsgroups))
    (let ((fun (nnoo-symbol backend op)))
      (unless (fboundp fun)
	(let ((msg (format "%s-%s not implemented" backend op)))
	  (noo--defalias fun
	                 (lambda (&rest _args) (nnheader-report backend msg))))))))

(defun nnoo-set (server &rest args)
  (let ((parents (nnoo-parents (car server)))
	(nnoo-parent-backend (car server)))
    (while parents
      (nnoo-change-server (caar parents)
			  (cadr server)
			  (cdar parents))
      (pop parents)))
  (nnoo-change-server (car server)
		      (cadr server) (cddr server))
  (while args
    (set (pop args) (pop args))))

(provide 'nnoo)

;;; nnoo.el ends here