;;; nnfolder.el --- mail folder access for Gnus
;; Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000
;;        Free Software Foundation, Inc.

;; Author: Scott Byer <byer@mv.us.adobe.com>
;;	Lars Magne Ingebrigtsen <larsi@gnus.org>
;; 	Masanobu UMEDA <umerin@flab.flab.fujitsu.junet>
;; Keywords: mail

;; 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 2, 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; see the file COPYING.  If not, write to the
;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.

;;; Commentary:

;;; Code:

(require 'nnheader)
(require 'message)
(require 'nnmail)
(require 'nnoo)
(eval-when-compile (require 'cl))
(require 'gnus-util)

(nnoo-declare nnfolder)

(defvoo nnfolder-directory (expand-file-name message-directory)
  "The name of the nnfolder directory.")

(defvoo nnfolder-active-file
    (nnheader-concat nnfolder-directory "active")
  "The name of the active file.")

;; I renamed this variable to something more in keeping with the general GNU
;; style. -SLB

(defvoo nnfolder-ignore-active-file nil
  "If non-nil, the active file is ignored.
This causes nnfolder to do some extra work in order to determine the
true active ranges of an mbox file.  Note that the active file is
still saved, but its values are not used.  This costs some extra time
when scanning an mbox when opening it.")

(defvoo nnfolder-distrust-mbox nil
  "If non-nil, the folder will be distrusted.
This means that nnfolder will not trust the user with respect to
inserting unaccounted for mail in the middle of an mbox file.  This
can greatly slow down scans, which now must scan the entire file for
unmarked messages.  When nil, scans occur forward from the last marked
message, a huge time saver for large mailboxes.")

(defvoo nnfolder-newsgroups-file
    (concat (file-name-as-directory nnfolder-directory) "newsgroups")
  "Mail newsgroups description file.")

(defvoo nnfolder-get-new-mail t
  "If non-nil, nnfolder will check the incoming mail file and split the mail.")

(defvoo nnfolder-prepare-save-mail-hook nil
  "Hook run narrowed to an article before saving.")

(defvoo nnfolder-save-buffer-hook nil
  "Hook run before saving the nnfolder mbox buffer.")

(defvoo nnfolder-inhibit-expiry nil
  "If non-nil, inhibit expiry.")



(defconst nnfolder-version "nnfolder 1.0"
  "nnfolder version.")

(defconst nnfolder-article-marker "X-Gnus-Article-Number: "
  "String used to demarcate what the article number for a message is.")

(defvoo nnfolder-current-group nil)
(defvoo nnfolder-current-buffer nil)
(defvoo nnfolder-status-string "")
(defvoo nnfolder-group-alist nil)
(defvoo nnfolder-buffer-alist nil)
(defvoo nnfolder-scantime-alist nil)
(defvoo nnfolder-active-timestamp nil)
(defvoo nnfolder-active-file-coding-system mm-text-coding-system)
(defvoo nnfolder-active-file-coding-system-for-write 
    nnmail-active-file-coding-system)
(defvoo nnfolder-file-coding-system mm-text-coding-system)
(defvoo nnfolder-file-coding-system-for-write nnheader-file-coding-system
  "Coding system for save nnfolder file.
If NIL, NNFOLDER-FILE-CODING-SYSTEM is used.")



;;; Interface functions

(nnoo-define-basics nnfolder)

(deffoo nnfolder-retrieve-headers (articles &optional group server fetch-old)
  (save-excursion
    (set-buffer nntp-server-buffer)
    (erase-buffer)
    (let (article start stop)
      (nnfolder-possibly-change-group group server)
      (when nnfolder-current-buffer
	(set-buffer nnfolder-current-buffer)
	(goto-char (point-min))
	(if (stringp (car articles))
	    'headers
	  (while (setq article (pop articles))
	    (set-buffer nnfolder-current-buffer)
	    (when (nnfolder-goto-article article)
	      (setq start (point))
	      (setq stop (if (search-forward "\n\n" nil t)
			     (1- (point))
			   (point-max)))
	      (set-buffer nntp-server-buffer)
	      (insert (format "221 %d Article retrieved.\n" article))
	      (insert-buffer-substring nnfolder-current-buffer start stop)
	      (goto-char (point-max))
	      (insert ".\n")))

	  (set-buffer nntp-server-buffer)
	  (nnheader-fold-continuation-lines)
	  'headers)))))

(deffoo nnfolder-open-server (server &optional defs)
  (nnoo-change-server 'nnfolder server defs)
  (nnmail-activate 'nnfolder t)
  (gnus-make-directory nnfolder-directory)
  (cond
   ((not (file-exists-p nnfolder-directory))
    (nnfolder-close-server)
    (nnheader-report 'nnfolder "Couldn't create directory: %s"
		     nnfolder-directory))
   ((not (file-directory-p (file-truename nnfolder-directory)))
    (nnfolder-close-server)
    (nnheader-report 'nnfolder "Not a directory: %s" nnfolder-directory))
   (t
    (nnmail-activate 'nnfolder)
    (nnheader-report 'nnfolder "Opened server %s using directory %s"
		     server nnfolder-directory)
    t)))

(deffoo nnfolder-request-close ()
  (let ((alist nnfolder-buffer-alist))
    (while alist
      (nnfolder-close-group (caar alist) nil t)
      (setq alist (cdr alist))))
  (nnoo-close-server 'nnfolder)
  (setq nnfolder-buffer-alist nil
	nnfolder-group-alist nil))

(deffoo nnfolder-request-article (article &optional group server buffer)
  (nnfolder-possibly-change-group group server)
  (save-excursion
    (set-buffer nnfolder-current-buffer)
    (goto-char (point-min))
    (when (nnfolder-goto-article article)
      (let (start stop)
	(setq start (point))
	(forward-line 1)
	(unless (and (nnmail-search-unix-mail-delim)
		     (forward-line -1))
	  (goto-char (point-max)))
	(setq stop (point))
	(let ((nntp-server-buffer (or buffer nntp-server-buffer)))
	  (set-buffer nntp-server-buffer)
	  (erase-buffer)
	  (insert-buffer-substring nnfolder-current-buffer start stop)
	  (goto-char (point-min))
	  (while (looking-at "From ")
	    (delete-char 5)
	    (insert "X-From-Line: ")
	    (forward-line 1))
	  (if (numberp article)
	      (cons nnfolder-current-group article)
	    (goto-char (point-min))
	    (cons nnfolder-current-group
		  (if (search-forward (concat "\n" nnfolder-article-marker) 
				      nil t)
		      (string-to-int
		       (buffer-substring
			(point) (progn (end-of-line) (point))))
		    -1))))))))

(deffoo nnfolder-request-group (group &optional server dont-check)
  (nnfolder-possibly-change-group group server t)
  (save-excursion
    (if (not (assoc group nnfolder-group-alist))
	(nnheader-report 'nnfolder "No such group: %s" group)
      (if dont-check
	  (progn
	    (nnheader-report 'nnfolder "Selected group %s" group)
	    t)
	(let* ((active (assoc group nnfolder-group-alist))
	       (group (car active))
	       (range (cadr active)))
	  (cond
	   ((null active)
	    (nnheader-report 'nnfolder "No such group: %s" group))
	   ((null nnfolder-current-group)
	    (nnheader-report 'nnfolder "Empty group: %s" group))
	   (t
	    (nnheader-report 'nnfolder "Selected group %s" group)
	    (nnheader-insert "211 %d %d %d %s\n"
			     (1+ (- (cdr range) (car range)))
			     (car range) (cdr range) group))))))))

(deffoo nnfolder-request-scan (&optional group server)
  (nnfolder-possibly-change-group nil server)
  (when nnfolder-get-new-mail
    (nnfolder-possibly-change-group group server)
    (nnmail-get-new-mail
     'nnfolder
     (lambda ()
       (let ((bufs nnfolder-buffer-alist))
	 (save-excursion
	   (while bufs
	     (if (not (gnus-buffer-live-p (nth 1 (car bufs))))
		 (setq nnfolder-buffer-alist
		       (delq (car bufs) nnfolder-buffer-alist))
	       (set-buffer (nth 1 (car bufs)))
	       (nnfolder-save-buffer)
	       (kill-buffer (current-buffer)))
	     (setq bufs (cdr bufs))))))
     nnfolder-directory
     group)))

;; Don't close the buffer if we're not shutting down the server.  This way,
;; we can keep the buffer in the group buffer cache, and not have to grovel
;; over the buffer again unless we add new mail to it or modify it in some
;; way.

(deffoo nnfolder-close-group (group &optional server force)
  ;; Make sure we _had_ the group open.
  (when (or (assoc group nnfolder-buffer-alist)
	    (equal group nnfolder-current-group))
    (let ((inf (assoc group nnfolder-buffer-alist)))
      (when inf
	(when (and nnfolder-current-group
		   nnfolder-current-buffer)
	  (push (list nnfolder-current-group nnfolder-current-buffer)
		nnfolder-buffer-alist))
	(setq nnfolder-buffer-alist
	      (delq inf nnfolder-buffer-alist))
	(setq nnfolder-current-buffer (cadr inf)
	      nnfolder-current-group (car inf))))
    (when (and nnfolder-current-buffer
	       (buffer-name nnfolder-current-buffer))
      (save-excursion
	(set-buffer nnfolder-current-buffer)
	;; If the buffer was modified, write the file out now.
	(nnfolder-save-buffer)
	;; If we're shutting the server down, we need to kill the
	;; buffer and remove it from the open buffer list.  Or, of
	;; course, if we're trying to minimize our space impact.
	(kill-buffer (current-buffer))
	(setq nnfolder-buffer-alist (delq (assoc group nnfolder-buffer-alist)
					  nnfolder-buffer-alist)))))
  (setq nnfolder-current-group nil
	nnfolder-current-buffer nil)
  t)

(deffoo nnfolder-request-create-group (group &optional server args)
  (nnfolder-possibly-change-group nil server)
  (nnmail-activate 'nnfolder)
  (when group
    (unless (assoc group nnfolder-group-alist)
      (push (list group (cons 1 0)) nnfolder-group-alist)
      (nnfolder-save-active nnfolder-group-alist nnfolder-active-file)
      (nnfolder-read-folder group)))
  t)

(deffoo nnfolder-request-list (&optional server)
  (nnfolder-possibly-change-group nil server)
  (save-excursion
    (let ((nnmail-file-coding-system nnfolder-active-file-coding-system))
      (nnmail-find-file nnfolder-active-file)
      (setq nnfolder-group-alist (nnmail-get-active)))
    t))

(deffoo nnfolder-request-newgroups (date &optional server)
  (nnfolder-possibly-change-group nil server)
  (nnfolder-request-list server))

(deffoo nnfolder-request-list-newsgroups (&optional server)
  (nnfolder-possibly-change-group nil server)
  (save-excursion
    (let ((nnmail-file-coding-system nnfolder-file-coding-system))
      (nnmail-find-file nnfolder-newsgroups-file))))

;; Return a list consisting of all article numbers existing in the
;; current folder.

(defun nnfolder-existing-articles ()
  (save-excursion
    (when nnfolder-current-buffer
      (set-buffer nnfolder-current-buffer)
      (goto-char (point-min))
      (let ((marker (concat "\n" nnfolder-article-marker))
	    (number "[0-9]+")
	    numbers)
      
	(while (and (search-forward marker nil t)
		    (re-search-forward number nil t))
	  (let ((newnum (string-to-number (match-string 0))))
	    (if (nnmail-within-headers-p)
		(push newnum numbers))))
	numbers))))

(deffoo nnfolder-request-expire-articles
    (articles newsgroup &optional server force)
  (nnfolder-possibly-change-group newsgroup server)
  (let* ((is-old t)
	 ;; The articles we have deleted so far.
	 (deleted-articles nil)
	 ;; The articles that really exist and will
	 ;; be expired if they are old enough.
	 (maybe-expirable
	  (gnus-intersection articles (nnfolder-existing-articles))))
    (nnmail-activate 'nnfolder)

    (save-excursion
      (set-buffer nnfolder-current-buffer)
      ;; Since messages are sorted in arrival order and expired in the
      ;; same order, we can stop as soon as we find a message that is
      ;; too old.
      (while (and maybe-expirable is-old)
	(goto-char (point-min))
	(when (and (nnfolder-goto-article (car maybe-expirable))
		   (search-forward (concat "\n" nnfolder-article-marker)
				   nil t))
	  (forward-sexp)
	  (when (setq is-old
		      (nnmail-expired-article-p
		       newsgroup
		       (buffer-substring
			(point) (progn (end-of-line) (point)))
		       force nnfolder-inhibit-expiry))
	    (nnheader-message 5 "Deleting article %d..."
			      (car maybe-expirable) newsgroup)
	    (nnfolder-delete-mail)
	    ;; Must remember which articles were actually deleted
	    (push (car maybe-expirable) deleted-articles)))
	(setq maybe-expirable (cdr maybe-expirable)))
      (unless nnfolder-inhibit-expiry
	(nnheader-message 5 "Deleting articles...done"))
      (nnfolder-save-buffer)
      (nnfolder-adjust-min-active newsgroup)
      (nnfolder-save-active nnfolder-group-alist nnfolder-active-file)
      (gnus-sorted-complement articles (nreverse deleted-articles)))))

(deffoo nnfolder-request-move-article (article group server
					       accept-form &optional last)
  (save-excursion
    (let ((buf (get-buffer-create " *nnfolder move*"))
	  result)
      (and
       (nnfolder-request-article article group server)
       (save-excursion
	 (set-buffer buf)
	 (erase-buffer)
	 (insert-buffer-substring nntp-server-buffer)
	 (goto-char (point-min))
	 (while (re-search-forward
		 (concat "^" nnfolder-article-marker)
		 (save-excursion (and (search-forward "\n\n" nil t) (point))) 
		 t)
	   (delete-region (progn (beginning-of-line) (point))
			  (progn (forward-line 1) (point))))
	 (setq result (eval accept-form))
	 (kill-buffer buf)
	 result)
       (save-excursion
	 (nnfolder-possibly-change-group group server)
	 (set-buffer nnfolder-current-buffer)
	 (goto-char (point-min))
	 (when (nnfolder-goto-article article)
	   (nnfolder-delete-mail))
	 (when last
	   (nnfolder-save-buffer)
	   (nnfolder-adjust-min-active group)
	   (nnfolder-save-active nnfolder-group-alist nnfolder-active-file))))
      result)))

(deffoo nnfolder-request-accept-article (group &optional server last)
  (save-excursion
    (nnfolder-possibly-change-group group server)
    (nnmail-check-syntax)
    (let ((buf (current-buffer))
	  result art-group)
      (goto-char (point-min))
      (when (looking-at "X-From-Line: ")
	(replace-match "From "))
      (and
       (nnfolder-request-list)
       (save-excursion
	 (set-buffer buf)
	 (goto-char (point-min))
	 (if (search-forward "\n\n" nil t)
	     (forward-line -1)
	   (goto-char (point-max)))
	 (while (re-search-backward (concat "^" nnfolder-article-marker) nil t)
	   (delete-region (point) (progn (forward-line 1) (point))))
	 (when nnmail-cache-accepted-message-ids
	   (nnmail-cache-insert (nnmail-fetch-field "message-id")))
	 (setq result (if (stringp group)
			  (list (cons group (nnfolder-active-number group)))
			(setq art-group
			      (nnmail-article-group 'nnfolder-active-number))))
	 (if (and (null result)
		  (yes-or-no-p "Moved to `junk' group; delete article? "))
	     (setq result 'junk)
	   (setq result
		 (car (nnfolder-save-mail result)))))
       (when last
	 (save-excursion
	   (nnfolder-possibly-change-folder (or (caar art-group) group))
	   (nnfolder-save-buffer)
	   (when nnmail-cache-accepted-message-ids
	     (nnmail-cache-close)))))
      (nnfolder-save-active nnfolder-group-alist nnfolder-active-file)
      (unless result
	(nnheader-report 'nnfolder "Couldn't store article"))
      result)))

(deffoo nnfolder-request-replace-article (article group buffer)
  (nnfolder-possibly-change-group group)
  (save-excursion
    (set-buffer buffer)
    (goto-char (point-min))
    (let (xfrom)
      (while (re-search-forward "^X-From-Line: \\(.*\\)$" nil t)
	(setq xfrom (match-string 1))
	(gnus-delete-line))
      (goto-char (point-min))
      (if xfrom
	  (insert "From " xfrom "\n")
	(unless (looking-at "From ")
	  (insert "From nobody " (current-time-string) "\n"))))
    (nnfolder-normalize-buffer)
    (set-buffer nnfolder-current-buffer)
    (goto-char (point-min))
    (if (not (nnfolder-goto-article article))
	nil
      (nnfolder-delete-mail)
      (insert-buffer-substring buffer)
      (nnfolder-save-buffer)
      t)))

(deffoo nnfolder-request-delete-group (group &optional force server)
  (nnfolder-close-group group server t)
  ;; Delete all articles in GROUP.
  (if (not force)
      ()				; Don't delete the articles.
    ;; Delete the file that holds the group.
    (ignore-errors
      (delete-file (nnfolder-group-pathname group))))
  ;; Remove the group from all structures.
  (setq nnfolder-group-alist
	(delq (assoc group nnfolder-group-alist) nnfolder-group-alist)
	nnfolder-current-group nil
	nnfolder-current-buffer nil)
  ;; Save the active file.
  (nnfolder-save-active nnfolder-group-alist nnfolder-active-file)
  t)

(deffoo nnfolder-request-rename-group (group new-name &optional server)
  (nnfolder-possibly-change-group group server)
  (save-excursion
    (set-buffer nnfolder-current-buffer)
    (and (file-writable-p buffer-file-name)
	 (ignore-errors
	   (rename-file
	    buffer-file-name
	    (let ((new-file (nnfolder-group-pathname new-name)))
	      (gnus-make-directory (file-name-directory new-file))
	      new-file))
	   t)
	 ;; That went ok, so we change the internal structures.
	 (let ((entry (assoc group nnfolder-group-alist)))
	   (and entry (setcar entry new-name))
	   (setq nnfolder-current-buffer nil
		 nnfolder-current-group nil)
	   ;; Save the new group alist.
	   (nnfolder-save-active nnfolder-group-alist nnfolder-active-file)
	   ;; We kill the buffer instead of renaming it and stuff.
	   (kill-buffer (current-buffer))
	   t))))

(defun nnfolder-request-regenerate (server)
  (nnfolder-possibly-change-group nil server)
  (nnfolder-generate-active-file)
  t)


;;; Internal functions.

(defun nnfolder-adjust-min-active (group)
  ;; Find the lowest active article in this group.
  (let* ((active (cadr (assoc group nnfolder-group-alist)))
	 (marker (concat "\n" nnfolder-article-marker))
	 (number "[0-9]+")
	 (activemin (cdr active)))
    (save-excursion
      (set-buffer nnfolder-current-buffer)
      (goto-char (point-min))
      (while (and (search-forward marker nil t)
		  (re-search-forward number nil t))
	(let ((newnum (string-to-number (match-string 0))))
	  (if (nnmail-within-headers-p)
	      (setq activemin (min activemin newnum)))))
      (setcar active activemin))))

(defun nnfolder-article-string (article)
  (if (numberp article)
      (concat "\n" nnfolder-article-marker (int-to-string article) " ")
    (concat "\nMessage-ID: " article)))

(defun nnfolder-goto-article (article)
  "Place point at the start of the headers of ARTICLE.
ARTICLE can be an article number or a Message-ID.
Returns t if successful, nil otherwise."
  (let ((art-string (nnfolder-article-string article))
	start found)
    ;; It is likely that we are at or before the delimiter line.
    ;; We therefore go to the end of the previous line, and start
    ;; searching from there.
    (beginning-of-line)
    (unless (bobp)
      (forward-char -1))
    (setq start (point))
    ;; First search forward.
    (while (and (setq found (search-forward art-string nil t))
		(not (nnmail-within-headers-p))))
    ;; If unsuccessful, search backward from where we started,
    (unless found
      (goto-char start)
      (while (and (setq found (search-backward art-string nil t))
		  (not (nnmail-within-headers-p)))))
    (when found
      (nnmail-search-unix-mail-delim-backward))))

(defun nnfolder-delete-mail (&optional leave-delim)
  "Delete the message that point is in.
If optional argument LEAVE-DELIM is t, then mailbox delimiter is not
deleted.  Point is left where the deleted region was."
  (save-restriction
    (narrow-to-region
     (save-excursion
       ;; In case point is at the beginning of the message already.
       (forward-line 1)
       (nnmail-search-unix-mail-delim-backward)
       (if leave-delim (progn (forward-line 1) (point))
	 (point)))
     (progn
       (forward-line 1)
       (if (nnmail-search-unix-mail-delim)
	   (point)
	 (point-max))))
    (run-hooks 'nnfolder-delete-mail-hook)
    (delete-region (point-min) (point-max))))

(defun nnfolder-possibly-change-group (group &optional server dont-check)
  ;; Change servers.
  (when (and server
	     (not (nnfolder-server-opened server)))
    (nnfolder-open-server server))
  (unless (gnus-buffer-live-p nnfolder-current-buffer)
    (setq nnfolder-current-buffer nil
	  nnfolder-current-group nil))
  ;; Change group.
  (when (and group
	     (not (equal group nnfolder-current-group)))
    (let ((file-name-coding-system nnmail-pathname-coding-system))
      (nnmail-activate 'nnfolder)
      (when (and (not (assoc group nnfolder-group-alist))
		 (not (file-exists-p
		       (nnfolder-group-pathname group))))
	;; The group doesn't exist, so we create a new entry for it.
	(push (list group (cons 1 0)) nnfolder-group-alist)
	(nnfolder-save-active nnfolder-group-alist nnfolder-active-file))

      (if dont-check
	  (setq nnfolder-current-group group
		nnfolder-current-buffer nil)
	(let (inf file)
	  ;; If we have to change groups, see if we don't already have the
	  ;; folder in memory.  If we do, verify the modtime and destroy
	  ;; the folder if needed so we can rescan it.
	  (setq nnfolder-current-buffer
		(nth 1 (assoc group nnfolder-buffer-alist)))

	  ;; If the buffer is not live, make sure it isn't in the alist.  If it
	  ;; is live, verify that nobody else has touched the file since last
	  ;; time.
	  (when (and nnfolder-current-buffer
		     (not (gnus-buffer-live-p nnfolder-current-buffer)))
	    (setq nnfolder-buffer-alist (delq inf nnfolder-buffer-alist)
		  nnfolder-current-buffer nil))

	  (setq nnfolder-current-group group)

	  (when (or (not nnfolder-current-buffer)
		    (not (verify-visited-file-modtime
			  nnfolder-current-buffer)))
	    (save-excursion
	      (setq file (nnfolder-group-pathname group))
	      ;; See whether we need to create the new file.
	      (unless (file-exists-p file)
		(gnus-make-directory (file-name-directory file))
		(let ((nnmail-file-coding-system 
		       (or nnfolder-file-coding-system-for-write
			   nnfolder-file-coding-system-for-write)))
		  (nnmail-write-region 1 1 file t 'nomesg)))
	      (when (setq nnfolder-current-buffer (nnfolder-read-folder group))
		(set-buffer nnfolder-current-buffer)
		(push (list group nnfolder-current-buffer)
		      nnfolder-buffer-alist)))))))))

(defun nnfolder-save-mail (group-art-list)
  "Called narrowed to an article."
  (let* (save-list group-art)
    (goto-char (point-min))
    ;; The From line may have been quoted by movemail.
    (when (looking-at ">From")
      (delete-char 1))
    ;; This might come from somewhere else.
    (unless (looking-at "From ")
      (insert "From nobody " (current-time-string) "\n")
      (goto-char (point-min)))
    ;; Quote all "From " lines in the article.
    (forward-line 1)
    (let (case-fold-search)
      (while (re-search-forward "^From " nil t)
	(beginning-of-line)
	(insert "> ")))
    (setq save-list group-art-list)
    (nnmail-insert-lines)
    (nnmail-insert-xref group-art-list)
    (run-hooks 'nnmail-prepare-save-mail-hook)
    (run-hooks 'nnfolder-prepare-save-mail-hook)

    ;; Insert the mail into each of the destination groups.
    (while (setq group-art (pop group-art-list))
      ;; Kill any previous newsgroup markers.
      (goto-char (point-min))
      (if (search-forward "\n\n" nil t)
	  (forward-line -1)
	(goto-char (point-max)))
      (while (search-backward (concat "\n" nnfolder-article-marker) nil t)
	(delete-region (1+ (point)) (progn (forward-line 2) (point))))

      ;; Insert the new newsgroup marker.
      (nnfolder-insert-newsgroup-line group-art)

      (save-excursion
	(let ((beg (point-min))
	      (end (point-max))
	      (obuf (current-buffer)))
	  (nnfolder-possibly-change-folder (car group-art))
	  (let ((buffer-read-only nil))
	    (nnfolder-normalize-buffer)
	    (insert-buffer-substring obuf beg end)))))

    ;; Did we save it anywhere?
    save-list))

(defun nnfolder-normalize-buffer ()
  "Make sure there are two newlines at the end of the buffer."
  (goto-char (point-max))
  (skip-chars-backward "\n")
  (delete-region (point) (point-max))
  (insert "\n\n"))

(defun nnfolder-insert-newsgroup-line (group-art)
  (save-excursion
    (goto-char (point-min))
    (unless (search-forward "\n\n" nil t)
      (goto-char (point-max))
      (insert "\n"))
    (forward-char -1)
    (insert (format (concat nnfolder-article-marker "%d   %s\n")
		    (cdr group-art) (current-time-string)))))

(defun nnfolder-active-number (group)
  ;; Find the next article number in GROUP.
  (let ((active (cadr (assoc group nnfolder-group-alist))))
    (if active
	(setcdr active (1+ (cdr active)))
      ;; This group is new, so we create a new entry for it.
      ;; This might be a bit naughty... creating groups on the drop of
      ;; a hat, but I don't know...
      (push (list group (setq active (cons 1 1)))
	    nnfolder-group-alist))
    (cdr active)))

(defun nnfolder-possibly-change-folder (group)
  (let ((inf (assoc group nnfolder-buffer-alist)))
    (if (and inf
	     (gnus-buffer-live-p (cadr inf)))
	(set-buffer (cadr inf))
      (when inf
	(setq nnfolder-buffer-alist (delq inf nnfolder-buffer-alist)))
      (when nnfolder-group-alist
	(nnfolder-save-active nnfolder-group-alist nnfolder-active-file))
      (push (list group (nnfolder-read-folder group))
	    nnfolder-buffer-alist))))

;; This method has a problem if you've accidentally let the active list get
;; out of sync with the files.  This could happen, say, if you've
;; accidentally gotten new mail with something other than Gnus (but why
;; would _that_ ever happen? :-).  In that case, we will be in the middle of
;; processing the file, ready to add new X-Gnus article number markers, and
;; we'll run across a message with no ID yet - the active list _may_not_ be
;; ready for us yet.

;; To handle this, I'm modifying this routine to maintain the maximum ID seen
;; so far, and when we hit a message with no ID, we will _manually_ scan the
;; rest of the message looking for any more, possibly higher IDs.  We'll
;; assume the maximum that we find is the highest active.  Note that this
;; shouldn't cost us much extra time at all, but will be a lot less
;; vulnerable to glitches between the mbox and the active file.

(defun nnfolder-read-folder (group)
  (let* ((file (nnfolder-group-pathname group))
	 (buffer (set-buffer
		  (let ((nnheader-file-coding-system 
			 nnfolder-file-coding-system))
		    (nnheader-find-file-noselect file)))))
    (if (equal (cadr (assoc group nnfolder-scantime-alist))
	       (nth 5 (file-attributes file)))
	;; This looks up-to-date, so we don't do any scanning.
	(if (file-exists-p file)
	    buffer
	  (push (list group buffer) nnfolder-buffer-alist)
	  (set-buffer-modified-p t)
	  (nnfolder-save-buffer))
      ;; Parse the damn thing.
      (save-excursion
	(goto-char (point-min))
	;; Remove any blank lines at the start.
	(while (eq (following-char) ?\n)
	  (delete-char 1))
	(nnmail-activate 'nnfolder)
	;; Read in the file.
	(let ((delim "^From ")
	      (marker (concat "\n" nnfolder-article-marker))
	      (number "[0-9]+")
	      (active (or (cadr (assoc group nnfolder-group-alist))
			  (cons 1 0)))
	      (scantime (assoc group nnfolder-scantime-alist))
	      (minid (lsh -1 -1))
	      maxid start end newscantime
	      buffer-read-only)
	  (buffer-disable-undo)
	  (setq maxid (cdr active))
	  (goto-char (point-min))

	  ;; Anytime the active number is 1 or 0, it is suspect.  In that
	  ;; case, search the file manually to find the active number.  Or,
	  ;; of course, if we're being paranoid.  (This would also be the
	  ;; place to build other lists from the header markers, such as
	  ;; expunge lists, etc., if we ever desired to abandon the active
	  ;; file entirely for mboxes.)
	  (when (or nnfolder-ignore-active-file
		    (< maxid 2))
	    (while (and (search-forward marker nil t)
			(re-search-forward number nil t))
	      (let ((newnum (string-to-number (match-string 0))))
		(if (nnmail-within-headers-p)
		    (setq maxid (max maxid newnum)
		          minid (min minid newnum)))))
	    (setcar active (max 1 (min minid maxid)))
	    (setcdr active (max maxid (cdr active)))
	    (goto-char (point-min)))

	  ;; As long as we trust that the user will only insert unmarked mail
	  ;; at the end, go to the end and search backwards for the last
	  ;; marker.  Find the start of that message, and begin to search for
	  ;; unmarked messages from there.
	  (when (not (or nnfolder-distrust-mbox
			 (< maxid 2)))
	    (goto-char (point-max))
	    (unless (re-search-backward marker nil t)
	      (goto-char (point-min)))
	    (when (nnmail-search-unix-mail-delim)
	      (goto-char (point-min))))

	  ;; Keep track of the active number on our own, and insert it back
	  ;; into the active list when we're done.  Also, prime the pump to
	  ;; cut down on the number of searches we do.
	  (unless (nnmail-search-unix-mail-delim)
	    (goto-char (point-max)))
	  (setq end (point-marker))
	  (while (not (= end (point-max)))
	    (setq start (marker-position end))
	    (goto-char end)
	    ;; There may be more than one "From " line, so we skip past
	    ;; them.
	    (while (looking-at delim)
	      (forward-line 1))
	    (set-marker end (if (nnmail-search-unix-mail-delim)
				(point)
			      (point-max)))
	    (goto-char start)
	    (when (not (search-forward marker end t))
	      (narrow-to-region start end)
	      (nnmail-insert-lines)
	      (nnfolder-insert-newsgroup-line
	       (cons nil (nnfolder-active-number nnfolder-current-group)))
	      (widen)))

	  (set-marker end nil)
	  ;; Make absolutely sure that the active list reflects reality!
	  (nnfolder-save-active nnfolder-group-alist nnfolder-active-file)
	  ;; Set the scantime for this group.
	  (setq newscantime (visited-file-modtime))
	  (if scantime
	      (setcdr scantime (list newscantime))
	    (push (list nnfolder-current-group newscantime)
		  nnfolder-scantime-alist))
	  (current-buffer))))))

;;;###autoload
(defun nnfolder-generate-active-file ()
  "Look for mbox folders in the nnfolder directory and make them into groups.
This command does not work if you use short group names."
  (interactive)
  (nnmail-activate 'nnfolder)
  (let ((files (directory-files nnfolder-directory))
        file)
    (while (setq file (pop files))
      (when (and (not (backup-file-name-p file))
                 (message-mail-file-mbox-p
		  (nnheader-concat nnfolder-directory file)))
        (let ((oldgroup (assoc file nnfolder-group-alist)))
          (if oldgroup
              (nnheader-message 5 "Refreshing group %s..." file)
            (nnheader-message 5 "Adding group %s..." file))
	  (if oldgroup
	      (setq nnfolder-group-alist
		    (delq oldgroup (copy-sequence nnfolder-group-alist))))
          (push (list file (cons 1 0)) nnfolder-group-alist)
          (nnfolder-possibly-change-folder file)
          (nnfolder-possibly-change-group file)
          (nnfolder-close-group file))))
    (nnheader-message 5 "")))

(defun nnfolder-group-pathname (group)
  "Make pathname for GROUP."
  (setq group
	(mm-encode-coding-string group nnmail-pathname-coding-system))
  (let ((dir (file-name-as-directory (expand-file-name nnfolder-directory))))
    ;; If this file exists, we use it directly.
    (if (or nnmail-use-long-file-names
	    (file-exists-p (concat dir group)))
	(concat dir group)
      ;; If not, we translate dots into slashes.
      (concat dir (nnheader-replace-chars-in-string group ?. ?/)))))

(defun nnfolder-save-buffer ()
  "Save the buffer."
  (when (buffer-modified-p)
    (run-hooks 'nnfolder-save-buffer-hook)
    (gnus-make-directory (file-name-directory (buffer-file-name)))
    (let ((coding-system-for-write 
	   (or nnfolder-file-coding-system-for-write
	       nnfolder-file-coding-system)))
      (save-buffer))))

(defun nnfolder-save-active (group-alist active-file)
  (let ((nnmail-active-file-coding-system
	 (or nnfolder-active-file-coding-system-for-write
	     nnfolder-active-file-coding-system)))
    (nnmail-save-active group-alist active-file)))

(provide 'nnfolder)

;;; nnfolder.el ends here