;;; gnus-cache.el --- cache interface for Gnus  -*- lexical-binding: t; -*-

;; Copyright (C) 1995-2021 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 'gnus-sum)

(declare-function gnus-agent-load-alist "gnus-agent" (group))

(defcustom gnus-cache-active-file
  (expand-file-name "active" gnus-cache-directory)
  "The cache active file."
  :group 'gnus-cache
  :type 'file)

(defcustom gnus-cache-enter-articles '(ticked dormant)
  "Classes of articles to enter into the cache."
  :group 'gnus-cache
  :type '(set (const ticked) (const dormant) (const unread) (const read)))

(defcustom gnus-cache-remove-articles '(read)
  "Classes of articles to remove from the cache."
  :group 'gnus-cache
  :type '(set (const ticked) (const dormant) (const unread) (const read)))

(defcustom gnus-cacheable-groups nil
  "Groups that match this regexp will be cached.

If you only want to cache your nntp groups, you could set this
variable to \"^nntp\".

If a group matches both `gnus-cacheable-groups' and `gnus-uncacheable-groups'
it's not cached."
  :group 'gnus-cache
  :type '(choice (const :tag "off" nil)
		 regexp))

(defcustom gnus-uncacheable-groups nil
  "Groups that match this regexp will not be cached.

If you want to avoid caching your nnml groups, you could set this
variable to \"^nnml\".

If a group matches both gnus-cacheable-groups and gnus-uncacheable-groups
it's not cached."
  :group 'gnus-cache
  :type '(choice (const :tag "off" nil)
		 regexp))

(defvar gnus-cache-overview-coding-system 'raw-text
  "Coding system used on Gnus cache files.")

(defvar gnus-cache-coding-system 'raw-text
  "Coding system used on Gnus cache files.")

\f

;;; Internal variables.

(defvar-local gnus-cache-removable-articles nil)
(defvar gnus-cache-buffer nil)
(defvar gnus-cache-active-hashtb nil)
(defvar gnus-cache-active-altered nil)
(defvar gnus-cache-total-fetched-hashtb nil)

(declare-function nnvirtual-find-group-art "nnvirtual" (group article))

(autoload 'nnml-generate-nov-databases-directory "nnml")
(autoload 'nnvirtual-find-group-art "nnvirtual")
(autoload 'nnselect-article-group "nnselect")
(autoload 'nnselect-article-number  "nnselect")

\f

;;; Functions called from Gnus.

(defun gnus-cache-open ()
  "Initialize the cache."
  (when (or (file-exists-p gnus-cache-directory)
	    (and gnus-use-cache
		 (not (eq gnus-use-cache 'passive))))
    (gnus-cache-read-active)))

;; Complexities of byte-compiling make this kludge necessary.  Eeek.
(ignore-errors
  (gnus-add-shutdown 'gnus-cache-close 'gnus))

(defun gnus-cache-close ()
  "Shut down the cache."
  (gnus-cache-write-active)
  (gnus-cache-save-buffers)
  (setq gnus-cache-active-hashtb nil))

(defun gnus-cache-save-buffers ()
  ;; save the overview buffer if it exists and has been modified
  ;; delete empty cache subdirectories
  (when gnus-cache-buffer
    (let ((buffer (cdr gnus-cache-buffer))
	  (overview-file (gnus-cache-file-name
			  (car gnus-cache-buffer) ".overview")))
      ;; write the overview only if it was modified
      (when (and (buffer-live-p buffer) (buffer-modified-p buffer))
	(with-current-buffer buffer
	  (if (> (buffer-size) 0)
	      ;; Non-empty overview, write it to a file.
	      (let ((coding-system-for-write
		     gnus-cache-overview-coding-system))
		(gnus-write-buffer overview-file))
	    (let ((file-name-coding-system nnmail-pathname-coding-system))
	      ;; Empty overview file, remove it
	      (when (file-exists-p overview-file)
		(delete-file overview-file))
	      ;; If possible, remove group's cache subdirectory.
	      (condition-case nil
		  ;; FIXME: we can detect the error type and warn the user
		  ;; of any inconsistencies (articles w/o nov entries?).
		  ;; for now, just be conservative...delete only if safe -- sj
		  (delete-directory (file-name-directory overview-file))
		(error))))

	  (gnus-cache-update-overview-total-fetched-for
	   (car gnus-cache-buffer) overview-file)))
      ;; Kill the buffer -- it's either unmodified or saved.
      (gnus-kill-buffer buffer)
      (setq gnus-cache-buffer nil))))

(defvar gnus-article-decode-hook)

(defun gnus-cache-possibly-enter-article
  (group article ticked dormant unread &optional force)
  (when (and (or force (not (eq gnus-use-cache 'passive)))
	     (numberp article)
	     (> article 0))		; This might be a dummy article.
    (let ((number article)
	  file headers lines-chars
	  (file-name-coding-system nnmail-pathname-coding-system))
      ;; If this is a virtual group, we find the real group.
      (when (gnus-virtual-group-p group)
	(let ((result (if (gnus-nnselect-group-p group)
			  (with-current-buffer gnus-summary-buffer
			    (cons (nnselect-article-group article)
				  (nnselect-article-number article)))
			(nnvirtual-find-group-art
			 (gnus-group-real-name group) article))))
	  (setq group (car result)
		number (cdr result))))
      (when (and number
		 (> number 0)		; Reffed article.
		 (or force
		     (and (gnus-cache-fully-p group)
			  (gnus-cache-member-of-class
			   gnus-cache-enter-articles ticked dormant unread)))
		 (not (file-exists-p (setq file (gnus-cache-file-name
						 group number)))))
	;; Possibly create the cache directory.
	(gnus-make-directory (file-name-directory file))
	;; Save the article in the cache.
	(if (file-exists-p file)
	    t				; The article already is saved.
	  (with-current-buffer nntp-server-buffer
	    (require 'gnus-art)
	    (let ((gnus-use-cache nil)
		  (gnus-article-decode-hook nil))
	      (gnus-request-article-this-buffer number group))
	    (when (> (buffer-size) 0)
	      (let ((coding-system-for-write gnus-cache-coding-system))
		(gnus-write-buffer file)
		(gnus-cache-update-file-total-fetched-for group file))
	      (setq lines-chars (nnheader-get-lines-and-char))
	      (nnheader-remove-body)
	      (setq headers (nnheader-parse-head t))
	      (setf (mail-header-number headers) number)
	      (setf (mail-header-lines headers) (car lines-chars))
	      (setf (mail-header-chars headers) (cadr lines-chars))
	      (gnus-cache-change-buffer group)
	      (set-buffer (cdr gnus-cache-buffer))
	      (goto-char (point-max))
	      (forward-line -1)
	      (while (condition-case ()
			 (when (not (bobp))
			   (> (read (current-buffer)) number))
		       (error
			;; The line was malformed, so we just remove it!!
			(gnus-delete-line)
			t))
		(forward-line -1))
	      (if (bobp)
		  (if (not (eobp))
		      (progn
			(beginning-of-line)
			(when (< (read (current-buffer)) number)
			  (forward-line 1)))
		    (beginning-of-line))
		(forward-line 1))
	      (beginning-of-line)
	      (nnheader-insert-nov headers)
	      ;; Update the active info.
	      (set-buffer gnus-summary-buffer)
	      (gnus-cache-possibly-update-active group (cons number number))
	      (setq gnus-newsgroup-cached
		    (gnus-add-to-sorted-list gnus-newsgroup-cached article))
	      (gnus-summary-update-secondary-mark article))
	    t))))))

(defun gnus-cache-enter-remove-article (article)
  "Mark ARTICLE for later possible removal."
  (when article
    (push article gnus-cache-removable-articles)))

(defun gnus-cache-possibly-remove-articles ()
  "Possibly remove some of the removable articles."
  (if (not (gnus-virtual-group-p gnus-newsgroup-name))
      (gnus-cache-possibly-remove-articles-1)
    (let ((arts gnus-cache-removable-articles)
	  ga)
      (while arts
	(when (setq ga
		    (if (gnus-nnselect-group-p gnus-newsgroup-name)
			(with-current-buffer gnus-summary-buffer
			  (let ((article (pop arts)))
			    (cons (nnselect-article-group article)
				  (nnselect-article-number article))))
		      (nnvirtual-find-group-art
		       (gnus-group-real-name gnus-newsgroup-name) (pop arts))))
	  (let ((gnus-cache-removable-articles (list (cdr ga)))
		(gnus-newsgroup-name (car ga)))
	    (gnus-cache-possibly-remove-articles-1)))))
    (setq gnus-cache-removable-articles nil)))

(defun gnus-cache-possibly-remove-articles-1 ()
  "Possibly remove some of the removable articles."
  (when (gnus-cache-fully-p gnus-newsgroup-name)
    (let ((cache-articles gnus-newsgroup-cached))
      (gnus-cache-change-buffer gnus-newsgroup-name)
      (dolist (article gnus-cache-removable-articles)
	(when (memq article cache-articles)
	  ;; The article was in the cache, so we see whether we are
	  ;; supposed to remove it from the cache.
	  (gnus-cache-possibly-remove-article
	   article (memq article gnus-newsgroup-marked)
	   (memq article gnus-newsgroup-dormant)
	   (or (memq article gnus-newsgroup-unreads)
	       (memq article gnus-newsgroup-unselected))))))
    ;; The overview file might have been modified, save it
    ;; safe because we're only called at group exit anyway.
    (gnus-cache-save-buffers)))

(defun gnus-cache-request-article (article group)
  "Retrieve ARTICLE in GROUP from the cache."
  (let ((file (gnus-cache-file-name group article))
	(buffer-read-only nil)
	(file-name-coding-system nnmail-pathname-coding-system))
    (when (file-exists-p file)
      (erase-buffer)
      (gnus-kill-all-overlays)
      (let ((coding-system-for-read gnus-cache-coding-system))
	(insert-file-contents file))
      t)))

(defun gnus-cache-possibly-alter-active (group active)
  "Alter the ACTIVE info for GROUP to reflect the articles in the cache."
  (when gnus-cache-active-hashtb
    (let ((cache-active (gethash group gnus-cache-active-hashtb)))
      (when cache-active
	(when (< (car cache-active) (car active))
	  (setcar active (car cache-active)))
	(when (> (cdr cache-active) (cdr active))
	  (setcdr active (cdr cache-active)))))))

(defun gnus-cache-retrieve-headers (articles group &optional fetch-old)
  "Retrieve the headers for ARTICLES in GROUP."
  (let ((cached
	 (setq gnus-newsgroup-cached (gnus-cache-articles-in-group group))))
    (if (not cached)
	;; No cached articles here, so we just retrieve them
	;; the normal way.
	(let ((gnus-use-cache nil))
	  (gnus-retrieve-headers articles group fetch-old))
      (let ((uncached-articles (gnus-sorted-difference articles cached))
	    (cache-file (gnus-cache-file-name group ".overview"))
	    type
	    (file-name-coding-system nnmail-pathname-coding-system))
	;; We first retrieve all the headers that we don't have in
	;; the cache.
	(let ((gnus-use-cache nil))
	  (when uncached-articles
	    (setq type (and articles
			    (gnus-retrieve-headers
			     uncached-articles group fetch-old)))))
	(gnus-cache-save-buffers)
	;; Then we insert the cached headers.
	(save-excursion
	  (cond
	   ((not (file-exists-p cache-file))
	    ;; There are no cached headers.
	    type)
	   ((null type)
	    ;; There were no uncached headers (or retrieval was
	    ;; unsuccessful), so we use the cached headers exclusively.
	    (set-buffer nntp-server-buffer)
	    (erase-buffer)
	    (let ((coding-system-for-read
		   gnus-cache-overview-coding-system))
	      (insert-file-contents cache-file))
	    'nov)
	   ((eq type 'nov)
	    ;; We have both cached and uncached NOV headers, so we
	    ;; braid them.
	    (gnus-cache-braid-nov group cached)
	    type)
	   (t
	    ;; We braid HEADs.
	    (gnus-cache-braid-heads group (gnus-sorted-intersection
					   cached articles))
	    type)))))))

(defun gnus-cache-enter-article (&optional n)
  "Enter the next N articles into the cache.
If not given a prefix, use the process marked articles instead.
Returns the list of articles entered."
  (interactive "P" gnus-summary-mode)
  (let (out)
    (dolist (article (gnus-summary-work-articles n))
      (gnus-summary-remove-process-mark article)
      (if (natnump article)
	  (when (gnus-cache-possibly-enter-article
		 gnus-newsgroup-name article
		 nil nil nil t)
            (setq gnus-newsgroup-undownloaded (delq article gnus-newsgroup-undownloaded))
	    (push article out))
	(gnus-message 2 "Can't cache article %d" article))
      (gnus-summary-update-download-mark article)
      (gnus-summary-update-secondary-mark article))
    (gnus-summary-next-subject 1)
    (gnus-summary-position-point)
    (nreverse out)))

(defun gnus-cache-remove-article (&optional n)
  "Remove the next N articles from the cache.
If not given a prefix, use the process marked articles instead.
Returns the list of articles removed."
  (interactive "P" gnus-summary-mode)
  (gnus-cache-change-buffer gnus-newsgroup-name)
  (let (out)
    (dolist (article (gnus-summary-work-articles n))
      (gnus-summary-remove-process-mark article)
      (when (gnus-cache-possibly-remove-article article nil nil nil t)
        (when gnus-newsgroup-agentized
          (let ((alist (gnus-agent-load-alist gnus-newsgroup-name)))
            (unless (cdr (assoc article alist))
              (setq gnus-newsgroup-undownloaded
                    (gnus-add-to-sorted-list
                     gnus-newsgroup-undownloaded article)))))
	(push article out))
      (gnus-summary-update-download-mark article)
      (gnus-summary-update-secondary-mark article))
    (gnus-summary-next-subject 1)
    (gnus-summary-position-point)
    (nreverse out)))

(defun gnus-cached-article-p (article)
  "Say whether ARTICLE is cached in the current group."
  (memq article gnus-newsgroup-cached))

(defun gnus-summary-insert-cached-articles ()
  "Insert all the articles cached for this group into the current buffer."
  (interactive nil gnus-summary-mode)
  (let ((gnus-verbose (max 6 gnus-verbose)))
    (cond
     ((not gnus-newsgroup-cached)
      (gnus-message 3 "No cached articles for this group"))
     ;; This is faster if there are few articles to insert.
     ((< (length gnus-newsgroup-cached) 20)
      (gnus-summary-goto-subjects gnus-newsgroup-cached))
     (t
      (gnus-summary-include-articles gnus-newsgroup-cached)))))

(defun gnus-summary-limit-include-cached ()
  "Limit the summary buffer to articles that are cached."
  (interactive nil gnus-summary-mode)
  (let ((gnus-verbose (max 6 gnus-verbose)))
    (if gnus-newsgroup-cached
	(progn
	  (gnus-summary-limit gnus-newsgroup-cached)
	  (gnus-summary-position-point))
      (gnus-message 3 "No cached articles for this group"))))

;;; Internal functions.

(defun gnus-cache-change-buffer (group)
  (and gnus-cache-buffer
       ;; See if the current group's overview cache has been loaded.
       (or (string= group (car gnus-cache-buffer))
	   ;; Another overview cache is current, save it.
	   (gnus-cache-save-buffers)))
  ;; if gnus-cache buffer is nil, create it
  (unless gnus-cache-buffer
    ;; Create cache buffer
    (save-excursion
      (setq gnus-cache-buffer
	    (cons group
		  (set-buffer (gnus-get-buffer-create
			       " *gnus-cache-overview*"))))
      ;; Insert the contents of this group's cache overview.
      (erase-buffer)
      (let ((file (gnus-cache-file-name group ".overview"))
	    (file-name-coding-system nnmail-pathname-coding-system))
	(when (file-exists-p file)
	  (nnheader-insert-file-contents file)))
      ;; We have a fresh (empty/just loaded) buffer,
      ;; mark it as unmodified to save a redundant write later.
      (set-buffer-modified-p nil))))

;; Return whether an article is a member of a class.
(defun gnus-cache-member-of-class (class ticked dormant unread)
  (or (and ticked (memq 'ticked class))
      (and dormant (memq 'dormant class))
      (and unread (memq 'unread class))
      (and (not unread) (not ticked) (not dormant) (memq 'read class))))

(defun gnus-cache-file-name (group article)
  (expand-file-name
   (if (stringp article) article (int-to-string article))
   (file-name-as-directory
    (expand-file-name
     (nnheader-translate-file-chars
      (if (gnus-use-long-file-name 'not-cache)
	  group
	(let ((group (nnheader-replace-duplicate-chars-in-string
		      (nnheader-replace-chars-in-string group ?/ ?_)
		      ?. ?_)))
	  ;; Translate the first colon into a slash.
	  (when (string-match ":" group)
		  (setq group (concat (substring group 0 (match-beginning 0))
				      "/" (substring group (match-end 0)))))
	  (nnheader-replace-chars-in-string group ?. ?/)))
      t)
     gnus-cache-directory))))

(defun gnus-cache-update-article (group article)
  "If ARTICLE is in the cache, remove it and re-enter it."
  (gnus-cache-change-buffer group)
  (when (gnus-cache-possibly-remove-article article nil nil nil t)
    (let ((gnus-use-cache nil))
      (gnus-cache-possibly-enter-article
       gnus-newsgroup-name article
       nil nil nil t))))

(defun gnus-cache-possibly-remove-article (article ticked dormant unread
						   &optional force)
  "Possibly remove ARTICLE from the cache."
  (let ((group gnus-newsgroup-name)
	(number article)
	file
	(file-name-coding-system nnmail-pathname-coding-system))
    ;; If this is a virtual group, we find the real group.
    (when (gnus-virtual-group-p group)
      (let ((result (if (gnus-nnselect-group-p group)
			(with-current-buffer gnus-summary-buffer
			  (cons (nnselect-article-group article)
				(nnselect-article-number article)))
		      (nnvirtual-find-group-art
		       (gnus-group-real-name group) article))))
	(setq group (car result)
	      number (cdr result))))
    (setq file (gnus-cache-file-name group number))
    (when (and (file-exists-p file)
	       (or force
		   (gnus-cache-member-of-class
		    gnus-cache-remove-articles ticked dormant unread)))
      (save-excursion
	(gnus-cache-update-file-total-fetched-for group file t)
	(delete-file file)

	(set-buffer (cdr gnus-cache-buffer))
	(goto-char (point-min))
	(when (or (looking-at (concat (int-to-string number) "\t"))
		  (search-forward (concat "\n" (int-to-string number) "\t")
				  (point-max) t))
	    (gnus-delete-line)))
      (unless (setq gnus-newsgroup-cached
		    (delq article gnus-newsgroup-cached))
	(remhash gnus-newsgroup-name gnus-cache-active-hashtb)
	(setq gnus-cache-active-altered t))
      (gnus-summary-update-secondary-mark article)
      t)))

(defun gnus-cache-articles-in-group (group)
  "Return a sorted list of cached articles in GROUP."
  (let ((dir (file-name-directory (gnus-cache-file-name group 1)))
	articles
	(file-name-coding-system nnmail-pathname-coding-system))
    (when (file-exists-p dir)
      (setq articles
	    (sort (mapcar (lambda (name) (string-to-number name))
			  (directory-files dir nil "\\`[0-9]+\\'" t))
		  #'<))
      ;; Update the cache active file, just to synch more.
      (if articles
	  (progn
	    (gnus-cache-update-active group (car articles) t)
	    (gnus-cache-update-active group (car (last articles))))
	(when (gethash group gnus-cache-active-hashtb)
	  (remhash group gnus-cache-active-hashtb)
	  (setq gnus-cache-active-altered t)))
      articles)))

(defun gnus-cache-braid-nov (group cached &optional file)
  (let ((cache-buf (gnus-get-buffer-create " *gnus-cache*"))
	beg end)
    (gnus-cache-save-buffers)
    (with-current-buffer cache-buf
      (erase-buffer)
      (let ((coding-system-for-read gnus-cache-overview-coding-system)
	    (file-name-coding-system nnmail-pathname-coding-system))
	(insert-file-contents
	 (or file (gnus-cache-file-name group ".overview"))))
      (goto-char (point-min))
      (insert "\n")
      (goto-char (point-min)))
    (set-buffer nntp-server-buffer)
    (goto-char (point-min))
    (while cached
      (while (and (not (eobp))
		  (< (read (current-buffer)) (car cached)))
	(forward-line 1))
      (beginning-of-line)
      (set-buffer cache-buf)
      (if (search-forward (concat "\n" (int-to-string (car cached)) "\t")
			  nil t)
	  (setq beg (point-at-bol)
		end (progn (end-of-line) (point)))
	(setq beg nil))
      (set-buffer nntp-server-buffer)
      (when beg
	(insert-buffer-substring cache-buf beg end)
	(insert "\n"))
      (setq cached (cdr cached)))
    (kill-buffer cache-buf)))

(defun gnus-cache-braid-heads (group cached)
  (let ((cache-buf (gnus-get-buffer-create " *gnus-cache*")))
    (with-current-buffer cache-buf
      (erase-buffer))
    (set-buffer nntp-server-buffer)
    (goto-char (point-min))
    (dolist (entry cached)
      (while (and (not (eobp))
		  (looking-at "2.. +\\([0-9]+\\) ")
		  (< (progn (goto-char (match-beginning 1))
			    (read (current-buffer)))
		     entry))
	(search-forward "\n.\n" nil 'move))
      (beginning-of-line)
      (set-buffer cache-buf)
      (erase-buffer)
      (let ((coding-system-for-read gnus-cache-coding-system)
	    (file-name-coding-system nnmail-pathname-coding-system))
	(insert-file-contents (gnus-cache-file-name group entry)))
      (goto-char (point-min))
      (insert "220 ")
      (princ (pop cached) (current-buffer))
      (insert " Article retrieved.\n")
      (search-forward "\n\n" nil 'move)
      (delete-region (point) (point-max))
      (forward-char -1)
      (insert ".")
      (set-buffer nntp-server-buffer)
      (insert-buffer-substring cache-buf))
    (kill-buffer cache-buf)))

;;;###autoload
(defun gnus-jog-cache ()
  "Go through all groups and put the articles into the cache.

Usage:
$ emacs -batch -l ~/.emacs -l gnus -f gnus-jog-cache"
  (interactive)
  (let ((gnus-mark-article-hook nil)
	(gnus-expert-user t)
	(mail-sources nil)
	(gnus-use-dribble-file nil)
	(gnus-novice-user nil)
	(gnus-large-newsgroup nil))
    ;; Start Gnus.
    (gnus)
    ;; Go through all groups...
    (gnus-group-mark-buffer)
    (gnus-group-iterate nil
      (lambda (group)
	(let (gnus-auto-select-next)
	  (gnus-summary-read-group group nil t)
	  ;; ... and enter the articles into the cache.
	  (when (eq major-mode 'gnus-summary-mode)
	    (gnus-uu-mark-buffer)
	    (gnus-cache-enter-article)
	    (kill-buffer (current-buffer))))))))

(defun gnus-cache-read-active (&optional force)
  "Read the cache active file."
  (gnus-make-directory gnus-cache-directory)
  (if (or (not (file-exists-p gnus-cache-active-file))
	  (zerop (file-attribute-size
		  (file-attributes gnus-cache-active-file)))
	  force)
      ;; There is no active file, so we generate one.
      (gnus-cache-generate-active)
    ;; We simply read the active file.
    (gnus-with-temp-buffer
      (nnheader-insert-file-contents gnus-cache-active-file)
      (gnus-active-to-gnus-format
       nil (setq gnus-cache-active-hashtb
		 (gnus-make-hashtable
		  (count-lines (point-min) (point-max)))))
      (setq gnus-cache-active-altered nil))))

(defun gnus-cache-write-active (&optional force)
  "Write the active hashtb to the active file."
  (when (or force
	    (and gnus-cache-active-hashtb
		 gnus-cache-active-altered))
    (gnus-write-active-file gnus-cache-active-file gnus-cache-active-hashtb t)
    ;; Mark the active hashtb as unaltered.
    (setq gnus-cache-active-altered nil)))

;; FIXME: Why is there a `gnus-cache-possibly-alter-active',
;; `gnus-cache-possibly-update-active', and
;; `gnus-cache-update-active'?  Do we really need all three?
(defun gnus-cache-possibly-update-active (group active)
  "Update active info bounds of GROUP with ACTIVE if necessary.
The update is performed if ACTIVE contains a higher or lower bound
than the current."
  (let ((lower t) (higher t))
    (if gnus-cache-active-hashtb
	(let ((cache-active (gethash group gnus-cache-active-hashtb)))
	  (when cache-active
	    (unless (< (car active) (car cache-active))
	      (setq lower nil))
	    (unless (> (cdr active) (cdr cache-active))
	      (setq higher nil))))
      (gnus-cache-read-active))
    (when lower
      (gnus-cache-update-active group (car active) t))
    (when higher
      (gnus-cache-update-active group (cdr active)))))

(defun gnus-cache-update-active (group number &optional low)
  "Update the upper bound of the active info of GROUP to NUMBER.
If LOW, update the lower bound instead."
  (let ((active (gethash group gnus-cache-active-hashtb)))
    (if (null active)
	;; We just create a new active entry for this group.
	(puthash group (cons number number) gnus-cache-active-hashtb)
      ;; Update the lower or upper bound.
      (if low
	  (setcar active number)
	(setcdr active number)))
    ;; Mark the active hashtb as altered.
    (setq gnus-cache-active-altered t)))

;;;###autoload
(defun gnus-cache-generate-active (&optional directory)
  "Generate the cache active file."
  (interactive)
  (let* ((top (null directory))
	 (directory (expand-file-name (or directory gnus-cache-directory)))
	 (file-name-coding-system nnmail-pathname-coding-system)
	 (files (directory-files directory 'full))
	 (group
	  (if top
	      ""
	    (string-match
	     (concat "^" (regexp-quote
			  (file-name-as-directory
			   (expand-file-name gnus-cache-directory))))
	     (directory-file-name directory))
	    (nnheader-replace-chars-in-string
	     (substring (directory-file-name directory) (match-end 0))
	     ?/ ?.)))
	 nums alphs)
    (when top
      (gnus-message 5 "Generating the cache active file...")
      (setq gnus-cache-active-hashtb (gnus-make-hashtable 123)))
    (when (string-match "^\\(nn[^_]+\\)_" group)
      (setq group (replace-match "\\1:" t nil group)))
    ;; Separate articles from all other files and directories.
    (while files
      (if (string-match "^[0-9]+$" (file-name-nondirectory (car files)))
	  (push (string-to-number (file-name-nondirectory (pop files))) nums)
	(push (pop files) alphs)))
    ;; If we have nums, then this is probably a valid group.
    (when (setq nums (sort nums #'<))
      (puthash group
	       (cons (car nums) (car (last nums)))
	       gnus-cache-active-hashtb))
    ;; Go through all the other files.
    (dolist (file alphs)
      (when (and (file-directory-p file)
		 (not (string-match "^\\."
				    (file-name-nondirectory file))))
	;; We descend directories.
	(gnus-cache-generate-active file)))
    ;; Write the new active file.
    (when top
      (gnus-cache-write-active t)
      (gnus-message 5 "Generating the cache active file...done"))))

(defvar nnml-generate-active-function)

;;;###autoload
(defun gnus-cache-generate-nov-databases (dir)
  "Generate NOV files recursively starting in DIR."
  (interactive (list gnus-cache-directory))
  (gnus-cache-close)
  (let ((nnml-generate-active-function 'identity))
    (nnml-generate-nov-databases-directory dir))

  (setq gnus-cache-total-fetched-hashtb nil)

  (gnus-cache-open))

(defun gnus-cache-move-cache (dir)
  "Move the cache tree to somewhere else."
  (interactive "FMove the cache tree to: ")
  (rename-file gnus-cache-directory dir))

(defun gnus-cache-fully-p (&optional group)
  "Return non-nil if the cache should be fully used.
If GROUP is non-nil, also cater to `gnus-cacheable-groups' and
`gnus-uncacheable-groups'."
  (and gnus-use-cache
       (not (eq gnus-use-cache 'passive))
       (if (null group)
	   t
	 (and (or (not gnus-cacheable-groups)
		  (string-match gnus-cacheable-groups group))
	      (or (not gnus-uncacheable-groups)
		  (not (string-match gnus-uncacheable-groups group)))))))

;;;###autoload
(defun gnus-cache-rename-group (old-group new-group)
  "Rename OLD-GROUP as NEW-GROUP.
Always updates the cache, even when disabled, as the old cache
files would corrupt Gnus when the cache was next enabled.  It
depends on the caller to determine whether group renaming is
supported."
  (let ((old-dir (gnus-cache-file-name old-group ""))
	(new-dir (gnus-cache-file-name new-group ""))
	(file-name-coding-system nnmail-pathname-coding-system))
    (gnus-rename-file old-dir new-dir t))

  (gnus-cache-rename-group-total-fetched-for old-group new-group)

  (let ((no-save gnus-cache-active-hashtb))
    (unless gnus-cache-active-hashtb
      (gnus-cache-read-active))
    (let* ((old-group-hash-value
	    (gethash old-group gnus-cache-active-hashtb))
	   (new-group-hash-value
	    (gethash new-group gnus-cache-active-hashtb))
	   (delta
	    (or old-group-hash-value new-group-hash-value)))
      (puthash new-group old-group-hash-value gnus-cache-active-hashtb)
      (puthash old-group nil gnus-cache-active-hashtb)

      (if no-save
	  (setq gnus-cache-active-altered delta)
	(gnus-cache-write-active delta)))))

;;;###autoload
(defun gnus-cache-delete-group (group)
  "Delete GROUP from the cache.
Always updates the cache, even when disabled, as the old cache
files would corrupt gnus when the cache was next enabled.
Depends upon the caller to determine whether group deletion is
supported."
  (let ((dir (gnus-cache-file-name group ""))
	(file-name-coding-system nnmail-pathname-coding-system))
    (gnus-delete-directory dir))

  (gnus-cache-delete-group-total-fetched-for group)

  (let ((no-save gnus-cache-active-hashtb))
    (unless gnus-cache-active-hashtb
      (gnus-cache-read-active))
    (let* ((group-hash-value (gethash group gnus-cache-active-hashtb)))
      (remhash group gnus-cache-active-hashtb)

      (if no-save
	  (setq gnus-cache-active-altered group-hash-value)
	(gnus-cache-write-active group-hash-value)))))

(defvar gnus-cache-inhibit-update-total-fetched-for nil)
(defvar gnus-cache-need-update-total-fetched-for nil)

(defmacro gnus-cache-with-refreshed-group (group &rest body)
  `(prog1 (let ((gnus-cache-inhibit-update-total-fetched-for t))
	    ,@body)
     (when (and gnus-cache-need-update-total-fetched-for
		(not gnus-cache-inhibit-update-total-fetched-for))
	(with-current-buffer gnus-group-buffer
	  (setq gnus-cache-need-update-total-fetched-for nil)
	  (gnus-group-update-group ,group t)))))

(defun gnus-cache-update-file-total-fetched-for (group file &optional subtract)
  (when gnus-cache-total-fetched-hashtb
    (gnus-cache-with-refreshed-group
     group
     (let* ((entry (or (gethash group gnus-cache-total-fetched-hashtb)
		       (puthash group (make-vector 2 0)
				gnus-cache-total-fetched-hashtb)))
	    size)

       (if file
	   (setq size (or (file-attribute-size (file-attributes file)) 0))
	 (let* ((file-name-coding-system nnmail-pathname-coding-system)
		(files (directory-files (gnus-cache-file-name group "")
					t nil t))
		file attrs)
	   (setq size 0.0)
	   (while (setq file (pop files))
	     (setq attrs (file-attributes file))
	     (unless (file-attribute-type attrs)
	       (cl-incf size (float (file-attribute-size attrs)))))))

       (setq gnus-cache-need-update-total-fetched-for t)

       (cl-incf (nth 1 entry) (if subtract (- size) size))))))

(defun gnus-cache-update-overview-total-fetched-for (group file)
  (when gnus-cache-total-fetched-hashtb
    (gnus-cache-with-refreshed-group
     group
     (let* ((entry (or (gethash group gnus-cache-total-fetched-hashtb)
		       (puthash group (make-list 2 0)
				     gnus-cache-total-fetched-hashtb)))
	    (file-name-coding-system nnmail-pathname-coding-system)
	    (size (or (file-attribute-size (file-attributes
			      (or file
				  (gnus-cache-file-name group ".overview"))))
		      0)))
       (setq gnus-cache-need-update-total-fetched-for t)
       (setf (nth 0 entry) size)))))

(defun gnus-cache-rename-group-total-fetched-for (old-group new-group)
  "Record of disk space used by OLD-GROUP now associated with NEW-GROUP."
  (when gnus-cache-total-fetched-hashtb
    (let ((entry (gethash old-group gnus-cache-total-fetched-hashtb)))
      (puthash new-group entry gnus-cache-total-fetched-hashtb)
      (remhash old-group gnus-cache-total-fetched-hashtb))))

(defun gnus-cache-delete-group-total-fetched-for (group)
  "Delete record of disk space used by GROUP being deleted."
  (when gnus-cache-total-fetched-hashtb
      (remhash group gnus-cache-total-fetched-hashtb)))

(defun gnus-cache-total-fetched-for (group &optional no-inhibit)
  "Get total disk space used by the cache for the specified GROUP."
  (unless (equal group "dummy.group")
    (unless gnus-cache-total-fetched-hashtb
      (setq gnus-cache-total-fetched-hashtb (gnus-make-hashtable 1000)))
    (let* ((entry (gethash group gnus-cache-total-fetched-hashtb)))
      (if entry
	  (apply #'+ entry)
	(let ((gnus-cache-inhibit-update-total-fetched-for (not no-inhibit)))
	  (+
	   (gnus-cache-update-overview-total-fetched-for group nil)
	   (gnus-cache-update-file-total-fetched-for     group nil)))))))

(provide 'gnus-cache)

;;; gnus-cache.el ends here