;;; gnus-registry.el --- article registry for Gnus

;; Copyright (C) 2002-2011  Free Software Foundation, Inc.

;; Author: Ted Zlatanov <tzz@lifelogs.com>
;; Keywords: news registry

;; 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 <http://www.gnu.org/licenses/>.

;;; Commentary:

;; This is the gnus-registry.el package, which works with all
;; Gnus backends, not just nnmail.  The major issue is that it
;; doesn't go across backends, so for instance if an article is in
;; nnml:sys and you see a reference to it in nnimap splitting, the
;; article will end up in nnimap:sys

;; gnus-registry.el intercepts article respooling, moving, deleting,
;; and copying for all backends.  If it doesn't work correctly for
;; you, submit a bug report and I'll be glad to fix it.  It needs
;; documentation in the manual (also on my to-do list).

;; Put this in your startup file (~/.gnus.el for instance)

;; (setq gnus-registry-max-entries 2500)

;; (gnus-registry-initialize)

;; Then use this in your fancy-split:

;; (: gnus-registry-split-fancy-with-parent)

;; You should also consider using the nnregistry backend to look up
;; articles.  See the Gnus manual for more information.

;; TODO:

;; - get the correct group on spool actions

;; - articles that are spooled to a different backend should be moved
;;   after splitting

;;; Code:

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

(eval-when-compile
  (when (null (require 'ert nil t))
    (defmacro* ert-deftest (name () &body docstring-keys-and-body))))

(require 'ert nil t)
(require 'gnus)
(require 'gnus-int)
(require 'gnus-sum)
(require 'gnus-art)
(require 'gnus-util)
(require 'nnmail)
(require 'easymenu)
(require 'registry)

(defvar gnus-adaptive-word-syntax-table)

(defvar gnus-registry-dirty t
 "Boolean set to t when the registry is modified")

(defgroup gnus-registry nil
  "The Gnus registry."
  :version "22.1"
  :group 'gnus)

(defvar gnus-registry-marks
  '((Important
     :char ?i
     :image "summary_important")
    (Work
     :char ?w
     :image "summary_work")
    (Personal
     :char ?p
     :image "summary_personal")
    (To-Do
     :char ?t
     :image "summary_todo")
    (Later
     :char ?l
     :image "summary_later"))

  "List of registry marks and their options.

`gnus-registry-mark-article' will offer symbols from this list
for completion.

Each entry must have a character to be useful for summary mode
line display and for keyboard shortcuts.

Each entry must have an image string to be useful for visual
display.")

(defcustom gnus-registry-default-mark 'To-Do
  "The default mark.  Should be a valid key for `gnus-registry-marks'."
  :group 'gnus-registry
  :type 'symbol)

(defcustom gnus-registry-unfollowed-addresses
  (list (regexp-quote user-mail-address))
  "List of addresses that gnus-registry-split-fancy-with-parent won't trace.
The addresses are matched, they don't have to be fully qualified."
  :group 'gnus-registry
  :type '(repeat regexp))

(defcustom gnus-registry-unfollowed-groups
  '("delayed$" "drafts$" "queue$" "INBOX$" "^nnmairix:" "archive")
  "List of groups that gnus-registry-split-fancy-with-parent won't return.
The group names are matched, they don't have to be fully
qualified.  This parameter tells the Gnus registry 'never split a
message into a group that matches one of these, regardless of
references.'

nnmairix groups are specifically excluded because they are ephemeral."
  :group 'gnus-registry
  :type '(repeat regexp))

(defcustom gnus-registry-install 'ask
  "Whether the registry should be installed."
  :group 'gnus-registry
  :type '(choice (const :tag "Never Install" nil)
                 (const :tag "Always Install" t)
                 (const :tag "Ask Me" ask)))

(defvar gnus-summary-misc-menu) ;; Avoid byte compiler warning.

(defvar gnus-registry-misc-menus nil)   ; ugly way to keep the menus

(make-obsolete-variable 'gnus-registry-clean-empty nil "23.4")
(make-obsolete-variable 'gnus-registry-use-long-group-names nil "23.4")
(make-obsolete-variable 'gnus-registry-max-track-groups nil "23.4")
(make-obsolete-variable 'gnus-registry-entry-caching nil "23.4")
(make-obsolete-variable 'gnus-registry-trim-articles-without-groups nil "23.4")

(defcustom gnus-registry-track-extra '(subject sender)
  "Whether the registry should track extra data about a message.
The Subject and Sender (From:) headers are tracked this way by
default."
  :group 'gnus-registry
  :type
  '(set :tag "Tracking choices"
    (const :tag "Track by subject (Subject: header)" subject)
    (const :tag "Track by sender (From: header)"  sender)))

(defcustom gnus-registry-split-strategy nil
  "The splitting strategy applied to the keys in `gnus-registry-track-extra'.

Given a set of unique found groups G and counts for each element
of G, and a key K (typically 'sender or 'subject):

When nil, if G has only one element, use it.  Otherwise give up.
This is the fastest but also least useful strategy.

When 'majority, use the majority by count.  So if there is a
group with the most articles counted by K, use that.  Ties are
resolved in no particular order, simply the first one found wins.
This is the slowest strategy but also the most accurate one.

When 'first, the first element of G wins.  This is fast and
should be OK if your senders and subjects don't \"bleed\" across
groups."
  :group 'gnus-registry
  :type
  '(choice :tag "Splitting strategy"
           (const :tag "Only use single choices, discard multiple matches" nil)
           (const :tag "Majority of matches wins" majority)
           (const :tag "First found wins"  first)))

(defcustom gnus-registry-minimum-subject-length 5
  "The minimum length of a subject before it's considered trackable."
  :group 'gnus-registry
  :type 'integer)

(defcustom gnus-registry-extra-entries-precious '(mark)
  "What extra keys are precious, meaning entries with them won't get pruned.
By default, 'mark is included, so articles with marks are
considered precious.

Before you save the Gnus registry, it's pruned.  Any entries with
keys in this list will not be pruned.  All other entries go to
the Bit Bucket."
  :group 'gnus-registry
  :type '(repeat symbol))

(defcustom gnus-registry-cache-file
  (nnheader-concat
   (or gnus-dribble-directory gnus-home-directory "~/")
   ".gnus.registry.eioio")
  "File where the Gnus registry will be stored."
  :group 'gnus-registry
  :type 'file)

(defcustom gnus-registry-max-entries nil
  "Maximum number of entries in the registry, nil for unlimited."
  :group 'gnus-registry
  :type '(radio (const :format "Unlimited " nil)
                (integer :format "Maximum number: %v")))

(defcustom gnus-registry-max-pruned-entries nil
  "Maximum number of pruned entries in the registry, nil for unlimited."
  :group 'gnus-registry
  :type '(radio (const :format "Unlimited " nil)
                (integer :format "Maximum number: %v")))

(defun gnus-registry-fixup-registry (db)
  (when db
    (oset db :precious
          (append gnus-registry-extra-entries-precious
                  '()))
    (oset db :max-hard
          (or gnus-registry-max-entries
              most-positive-fixnum))
    (oset db :max-soft
          (or gnus-registry-max-pruned-entries
              most-positive-fixnum))
    (oset db :tracked
          (append gnus-registry-track-extra
                  '(mark group keyword))))
  db)

(defun gnus-registry-make-db (&optional file)
  (interactive "fGnus registry persistence file: \n")
  (gnus-registry-fixup-registry
   (registry-db
    "Gnus Registry"
    :file (or file gnus-registry-cache-file)
    ;; these parameters are set in `gnus-registry-fixup-registry'
    :max-hard most-positive-fixnum
    :max-soft most-positive-fixnum
    :precious nil
    :tracked nil)))

(defvar gnus-registry-db (gnus-registry-make-db)
  "*The article registry by Message ID.  See `registry-db'")

;; top-level registry data management
(defun gnus-registry-remake-db (&optional forsure)
  "Remake the registry database after customization.
This is not required after changing `gnus-registry-cache-file'."
  (interactive (list (y-or-n-p "Remake and CLEAR the Gnus registry? ")))
  (when forsure
    (gnus-message 1 "Remaking the Gnus registry")
    (setq gnus-registry-db (gnus-registry-make-db))))

(defun gnus-registry-read ()
  "Read the registry cache file."
  (interactive)
  (let ((file gnus-registry-cache-file))
    (condition-case nil
        (progn
          (gnus-message 5 "Reading Gnus registry from %s..." file)
          (setq gnus-registry-db (gnus-registry-fixup-registry
                                  (eieio-persistent-read file)))
          (gnus-message 5 "Reading Gnus registry from %s...done" file))
      (error
       (gnus-message
        1
        "The Gnus registry could not be loaded from %s, creating a new one"
        file)
       (gnus-registry-remake-db t)))))

(defun gnus-registry-save (&optional file db)
  "Save the registry cache file."
  (interactive)
  (let ((file (or file gnus-registry-cache-file))
        (db (or db gnus-registry-db)))
    (gnus-message 5 "Saving Gnus registry (%d entries) to %s..."
                  (registry-size db) file)
    (registry-prune db)
    ;; TODO: call (gnus-string-remove-all-properties v) on all elements?
    (eieio-persistent-save db file)
    (gnus-message 5 "Saving Gnus registry (size %d) to %s...done"
                  (registry-size db) file)))

;; article move/copy/spool/delete actions
(defun gnus-registry-action (action data-header from &optional to method)
  (let* ((id (mail-header-id data-header))
         (subject (gnus-string-remove-all-properties
                   (gnus-registry-simplify-subject
                    (mail-header-subject data-header))))
         (sender (gnus-string-remove-all-properties
                  (mail-header-from data-header)))
         (from (gnus-group-guess-full-name-from-command-method from))
         (to (if to (gnus-group-guess-full-name-from-command-method to) nil))
         (to-name (if to to "the Bit Bucket")))
    (gnus-message 7 "Gnus registry: article %s %s from %s to %s"
                  id (if method "respooling" "going") from to)

    (gnus-registry-handle-action
     id
     ;; unless copying, remove the old "from" group
     (if (not (equal 'copy action)) from nil)
     to subject sender)))

(defun gnus-registry-spool-action (id group &optional subject sender)
  (let ((to (gnus-group-guess-full-name-from-command-method group)))
    (when (and (stringp id) (string-match "\r$" id))
      (setq id (substring id 0 -1)))
    (gnus-message 7 "Gnus registry: article %s spooled to %s"
                  id
                  to)
    (gnus-registry-handle-action id nil to subject sender)))

(defun gnus-registry-handle-action (id from to subject sender)
  (let ((db gnus-registry-db)
        ;; safe if not found
        (entry (gnus-registry-get-or-make-entry id)))

    ;; this could be done by calling `gnus-registry-set-id-key'
    ;; several times but it's better to bunch the transactions
    ;; together

    (registry-delete db (list id) nil)
    (when from
      (setq entry (cons (delete from (assoc 'group entry))
                        (assq-delete-all 'group entry))))

    (dolist (kv `((group ,to) (sender ,sender) (subject ,subject)))
      (when (second kv)
        (let ((new (or (assq (first kv) entry)
                       (list (first kv)))))
          (add-to-list 'new (second kv) t)
          (setq entry (cons new
                            (assq-delete-all (first kv) entry))))))
    (gnus-message 10 "Gnus registry: new entry for %s is %S"
                  id
                  entry)
    (registry-insert db id entry)))

;; Function for nn{mail|imap}-split-fancy: look up all references in
;; the cache and if a match is found, return that group.
(defun gnus-registry-split-fancy-with-parent ()
  "Split this message into the same group as its parent.  The parent
is obtained from the registry.  This function can be used as an entry
in `nnmail-split-fancy' or `nnimap-split-fancy', for example like
this: (: gnus-registry-split-fancy-with-parent)

This function tracks ALL backends, unlike
`nnmail-split-fancy-with-parent' which tracks only nnmail
messages.

For a message to be split, it looks for the parent message in the
References or In-Reply-To header and then looks in the registry
to see which group that message was put in.  This group is
returned, unless `gnus-registry-follow-group-p' return nil for
that group.

See the Info node `(gnus)Fancy Mail Splitting' for more details."
  (let* ((refstr (or (message-fetch-field "references") "")) ; guaranteed
         (reply-to (message-fetch-field "in-reply-to"))      ; may be nil
         ;; now, if reply-to is valid, append it to the References
         (refstr (if reply-to
                     (concat refstr " " reply-to)
                   refstr))
         (references (and refstr (gnus-extract-references refstr)))
         ;; these may not be used, but the code is cleaner having them up here
         (sender (gnus-string-remove-all-properties
                  (message-fetch-field "from")))
         (subject (gnus-string-remove-all-properties
                   (gnus-registry-simplify-subject
                    (message-fetch-field "subject"))))

         (nnmail-split-fancy-with-parent-ignore-groups
          (if (listp nnmail-split-fancy-with-parent-ignore-groups)
              nnmail-split-fancy-with-parent-ignore-groups
            (list nnmail-split-fancy-with-parent-ignore-groups))))
    (gnus-registry--split-fancy-with-parent-internal
     :references references
     :refstr refstr
     :sender sender
     :subject subject
     :log-agent "Gnus registry fancy splitting with parent")))

(defun* gnus-registry--split-fancy-with-parent-internal
    (&rest spec
           &key references refstr sender subject log-agent
           &allow-other-keys)
  (gnus-message
   10
   "gnus-registry--split-fancy-with-parent-internal: %S" spec)
  (let ((db gnus-registry-db)
        found)
    ;; this is a big if-else statement.  it uses
    ;; gnus-registry-post-process-groups to filter the results after
    ;; every step.
    (cond
     ;; the references string must be valid and parse to valid references
     (references
      (dolist (reference (nreverse references))
        (gnus-message
         9
         "%s is looking for matches for reference %s from [%s]"
         log-agent reference refstr)
        (setq found
              (loop for group in (gnus-registry-get-id-key reference 'group)
                    when (gnus-registry-follow-group-p group)
                    do (gnus-message
                        7
                        "%s traced the reference %s from [%s] to group %s"
                        log-agent reference refstr group)
                    collect group)))
      ;; filter the found groups and return them
      ;; the found groups are the full groups
      (setq found (gnus-registry-post-process-groups
                   "references" refstr found)))

     ;; else: there were no matches, try the extra tracking by sender
     ((and (memq 'sender gnus-registry-track-extra)
           sender
           (gnus-grep-in-list
            sender
            gnus-registry-unfollowed-addresses))
      (let ((groups (apply
                     'append
                     (mapcar
                      (lambda (reference)
                        (gnus-registry-get-id-key reference 'group))
                      (registry-lookup-secondary-value db 'sender sender)))))
        (setq found
              (loop for group in groups
                    when (gnus-registry-follow-group-p group)
                  do (gnus-message
                      ;; raise level of messaging if gnus-registry-track-extra
                      (if gnus-registry-track-extra 7 9)
                      "%s (extra tracking) traced sender '%s' to groups %s"
                      log-agent sender found)
                  collect group)))

      ;; filter the found groups and return them
      ;; the found groups are NOT the full groups
      (setq found (gnus-registry-post-process-groups
                   "sender" sender found)))

     ;; else: there were no matches, now try the extra tracking by subject
     ((and (memq 'subject gnus-registry-track-extra)
           subject
           (< gnus-registry-minimum-subject-length (length subject)))
      (let ((groups (apply
                     'append
                     (mapcar
                      (lambda (reference)
                        (gnus-registry-get-id-key reference 'group))
                      (registry-lookup-secondary-value db 'subject subject)))))
        (setq found
              (loop for group in groups
                    when (gnus-registry-follow-group-p group)
                    do (gnus-message
                        ;; raise level of messaging if gnus-registry-track-extra
                        (if gnus-registry-track-extra 7 9)
                        "%s (extra tracking) traced subject '%s' to groups %s"
                        log-agent subject found)
                    collect group))
      ;; filter the found groups and return them
      ;; the found groups are NOT the full groups
      (setq found (gnus-registry-post-process-groups
                   "subject" subject found)))))
    ;; after the (cond) we extract the actual value safely
    (car-safe found)))

(defun gnus-registry-post-process-groups (mode key groups)
  "Inspects GROUPS found by MODE for KEY to determine which ones to follow.

MODE can be 'subject' or 'sender' for example.  The KEY is the
value by which MODE was searched.

Transforms each group name to the equivalent short name.

Checks if the current Gnus method (from `gnus-command-method' or
from `gnus-newsgroup-name') is the same as the group's method.
Foreign methods are not supported so they are rejected.

Reduces the list to a single group, or complains if that's not
possible.  Uses `gnus-registry-split-strategy'."
  (let ((log-agent "gnus-registry-post-process-group")
        out)

    ;; the strategy can be nil, in which case groups is nil
    (setq groups
          (case gnus-registry-split-strategy
            ;; first strategy
            ((first)
             (and groups (list (car-safe groups))))

            ((majority)
             (let ((freq (make-hash-table
                          :size 256
                          :test 'equal)))
               (mapc (lambda (x) (puthash x (1+ (gethash x freq 0)) freq))
                     groups)
               (list (car-safe
                      (sort groups (lambda (a b)
                                     (> (gethash a freq 0)
                                        (gethash b freq 0))))))))))

    (dolist (group groups)
      (let ((m1 (gnus-find-method-for-group group))
            (m2 (or gnus-command-method
                    (gnus-find-method-for-group gnus-newsgroup-name)))
            (short-name (gnus-group-short-name group)))
        (if (gnus-methods-equal-p m1 m2)
            (progn
              ;; this is REALLY just for debugging
              (gnus-message
               10
               "%s stripped group %s to %s"
               log-agent group short-name)
              (add-to-list 'out short-name))
          ;; else...
          (gnus-message
           7
           "%s ignored foreign group %s"
           log-agent group))))

    ;; is there just one group?
    (cond
     ((= (length out) 1) out)
     ((null out)
      (gnus-message
       5
       "%s: no matches for %s %s."
       log-agent out mode key)
      nil)
     (t (gnus-message
         5
         "%s: too many extra matches (%s) for %s %s.  Returning none."
         log-agent out mode key)
        nil))))

(defun gnus-registry-follow-group-p (group)
  "Determines if a group name should be followed.
Consults `gnus-registry-unfollowed-groups' and
`nnmail-split-fancy-with-parent-ignore-groups'."
  (and group
       (not (or (gnus-grep-in-list
                 group
                 gnus-registry-unfollowed-groups)
                (gnus-grep-in-list
                 group
                 nnmail-split-fancy-with-parent-ignore-groups)))))

(defun gnus-registry-wash-for-keywords (&optional force)
  "Get the keywords of the current article.
Overrides existing keywords with FORCE set non-nil."
  (interactive)
  (let ((id (gnus-registry-fetch-message-id-fast gnus-current-article))
        word words)
    (if (or (not (gnus-registry-get-id-key id 'keyword))
            force)
        (with-current-buffer gnus-article-buffer
          (article-goto-body)
          (save-window-excursion
            (save-restriction
              (narrow-to-region (point) (point-max))
              (with-syntax-table gnus-adaptive-word-syntax-table
                (while (re-search-forward "\\b\\w+\\b" nil t)
                  (setq word (gnus-string-remove-all-properties
                              (downcase (buffer-substring
                                         (match-beginning 0) (match-end 0)))))
                  (if (> (length word) 2)
                      (push word words))))))
          (gnus-registry-set-id-key id 'keyword words)))))

(defun gnus-registry-keywords ()
  (let ((table (registry-lookup-secondary gnus-registry-db 'keyword)))
    (when table (maphash (lambda (k v) k) table))))

(defun gnus-registry-find-keywords (keyword)
  (interactive (list
                (completing-read "Keyword: " (gnus-registry-keywords) nil t)))
  (registry-lookup-secondary-value gnus-registry-db 'keyword keyword))

(defun gnus-registry-register-message-ids ()
  "Register the Message-ID of every article in the group"
  (unless (gnus-parameter-registry-ignore gnus-newsgroup-name)
    (dolist (article gnus-newsgroup-articles)
      (let* ((id (gnus-registry-fetch-message-id-fast article))
             (groups (gnus-registry-get-id-key id 'group)))
        (unless (member gnus-newsgroup-name groups)
          (gnus-message 9 "Registry: Registering article %d with group %s"
                        article gnus-newsgroup-name)
          (gnus-registry-handle-action id nil gnus-newsgroup-name
           (gnus-registry-fetch-simplified-message-subject-fast article)
           (gnus-registry-fetch-sender-fast article)))))))

;; message field fetchers
(defun gnus-registry-fetch-message-id-fast (article)
  "Fetch the Message-ID quickly, using the internal gnus-data-list function"
  (if (and (numberp article)
           (assoc article (gnus-data-list nil)))
      (mail-header-id (gnus-data-header (assoc article (gnus-data-list nil))))
    nil))

(defun gnus-registry-simplify-subject (subject)
  (if (stringp subject)
      (gnus-simplify-subject subject)
    nil))

(defun gnus-registry-fetch-simplified-message-subject-fast (article)
  "Fetch the Subject quickly, using the internal gnus-data-list function"
  (if (and (numberp article)
           (assoc article (gnus-data-list nil)))
      (gnus-string-remove-all-properties
       (gnus-registry-simplify-subject
        (mail-header-subject (gnus-data-header
                              (assoc article (gnus-data-list nil))))))
    nil))

(defun gnus-registry-fetch-sender-fast (article)
  "Fetch the Sender quickly, using the internal gnus-data-list function"
  (if (and (numberp article)
           (assoc article (gnus-data-list nil)))
      (gnus-string-remove-all-properties
       (mail-header-from (gnus-data-header
                          (assoc article (gnus-data-list nil)))))
    nil))

;; registry marks glue
(defun gnus-registry-do-marks (type function)
  "For each known mark, call FUNCTION for each cell of type TYPE.

FUNCTION should take two parameters, a mark symbol and the cell value."
  (dolist (mark-info gnus-registry-marks)
    (let* ((mark (car-safe mark-info))
           (data (cdr-safe mark-info))
           (cell-data (plist-get data type)))
      (when cell-data
        (funcall function mark cell-data)))))

;;; this is ugly code, but I don't know how to do it better
(defun gnus-registry-install-shortcuts ()
  "Install the keyboard shortcuts and menus for the registry.
Uses `gnus-registry-marks' to find what shortcuts to install."
  (let (keys-plist)
    (setq gnus-registry-misc-menus nil)
    (gnus-registry-do-marks
     :char
     (lambda (mark data)
       (let ((function-format
              (format "gnus-registry-%%s-article-%s-mark" mark)))

;;; The following generates these functions:
;;; (defun gnus-registry-set-article-Important-mark (&rest articles)
;;;   "Apply the Important mark to process-marked ARTICLES."
;;;   (interactive (gnus-summary-work-articles current-prefix-arg))
;;;   (gnus-registry-set-article-mark-internal 'Important articles nil t))
;;; (defun gnus-registry-remove-article-Important-mark (&rest articles)
;;;   "Apply the Important mark to process-marked ARTICLES."
;;;   (interactive (gnus-summary-work-articles current-prefix-arg))
;;;   (gnus-registry-set-article-mark-internal 'Important articles t t))

         (dolist (remove '(t nil))
           (let* ((variant-name (if remove "remove" "set"))
                  (function-name (format function-format variant-name))
                  (shortcut (format "%c" data))
                  (shortcut (if remove (upcase shortcut) shortcut)))
             (unintern function-name obarray)
             (eval
              `(defun
                 ;; function name
                 ,(intern function-name)
                 ;; parameter definition
                 (&rest articles)
                 ;; documentation
                 ,(format
                   "%s the %s mark over process-marked ARTICLES."
                   (upcase-initials variant-name)
                   mark)
                 ;; interactive definition
                 (interactive
                  (gnus-summary-work-articles current-prefix-arg))
                 ;; actual code

                 ;; if this is called and the user doesn't want the
                 ;; registry enabled, we'll ask anyhow
                 (when (eq gnus-registry-install nil)
                   (setq gnus-registry-install 'ask))

                 ;; now the user is asked if gnus-registry-install is 'ask
                 (when (gnus-registry-install-p)
                   (gnus-registry-set-article-mark-internal
                    ;; all this just to get the mark, I must be doing it wrong
                    (intern ,(symbol-name mark))
                    articles ,remove t)
                   (gnus-message
                    9
                    "Applying mark %s to %d articles"
                    ,(symbol-name mark) (length articles))
                   (dolist (article articles)
                     (gnus-summary-update-article
                      article
                      (assoc article (gnus-data-list nil)))))))
             (push (intern function-name) keys-plist)
             (push shortcut keys-plist)
             (push (vector (format "%s %s"
                                   (upcase-initials variant-name)
                                   (symbol-name mark))
                           (intern function-name) t)
                   gnus-registry-misc-menus)
             (gnus-message
              9
              "Defined mark handling function %s"
              function-name))))))
    (gnus-define-keys-1
     '(gnus-registry-mark-map "M" gnus-summary-mark-map)
     keys-plist)
    (add-hook 'gnus-summary-menu-hook
              (lambda ()
                (easy-menu-add-item
                 gnus-summary-misc-menu
                 nil
                 (cons "Registry Marks" gnus-registry-misc-menus))))))

;;; use like this:
;;; (defalias 'gnus-user-format-function-M
;;;           'gnus-registry-user-format-function-M)
(defun gnus-registry-user-format-function-M (headers)
  (let* ((id (mail-header-message-id headers))
         (marks (when id (gnus-registry-get-id-key id 'mark))))
    (apply 'concat (mapcar (lambda (mark)
                             (let ((c
                                    (plist-get
                                     (cdr-safe
                                      (assoc mark gnus-registry-marks))
                                     :char)))
                               (if c
                                   (list c)
                                 nil)))
                           marks))))

(defun gnus-registry-read-mark ()
  "Read a mark name from the user with completion."
  (let ((mark (gnus-completing-read
               "Label"
               (mapcar 'symbol-name (mapcar 'car gnus-registry-marks))
               nil nil nil
               (symbol-name gnus-registry-default-mark))))
    (when (stringp mark)
      (intern mark))))

(defun gnus-registry-set-article-mark (&rest articles)
  "Apply a mark to process-marked ARTICLES."
  (interactive (gnus-summary-work-articles current-prefix-arg))
  (gnus-registry-set-article-mark-internal (gnus-registry-read-mark)
                                           articles nil t))

(defun gnus-registry-remove-article-mark (&rest articles)
  "Remove a mark from process-marked ARTICLES."
  (interactive (gnus-summary-work-articles current-prefix-arg))
  (gnus-registry-set-article-mark-internal (gnus-registry-read-mark)
                                           articles t t))

(defun gnus-registry-set-article-mark-internal (mark
                                                articles
                                                &optional remove
                                                show-message)
  "Apply or remove MARK across a list of ARTICLES."
  (let ((article-id-list
         (mapcar 'gnus-registry-fetch-message-id-fast articles)))
    (dolist (id article-id-list)
      (let* ((marks (delq mark (gnus-registry-get-id-key id 'mark)))
             (marks (if remove marks (cons mark marks))))
        (when show-message
          (gnus-message 1 "%s mark %s with message ID %s, resulting in %S"
                        (if remove "Removing" "Adding")
                        mark id marks))
        (gnus-registry-set-id-key id 'mark marks)))))

(defun gnus-registry-get-article-marks (&rest articles)
  "Get the Gnus registry marks for ARTICLES and show them if interactive.
Uses process/prefix conventions.  For multiple articles,
only the last one's marks are returned."
  (interactive (gnus-summary-work-articles 1))
  (let* ((article (last articles))
         (id (gnus-registry-fetch-message-id-fast article))
         (marks (when id (gnus-registry-get-id-key id 'mark))))
    (when (interactive-p)
      (gnus-message 1 "Marks are %S" marks))
    marks))

(defun gnus-registry-group-count (id)
  "Get the number of groups of a message, based on the message ID."
  (length (gnus-registry-get-id-key id 'group)))

(defun gnus-registry-get-or-make-entry (id)
  (let* ((db gnus-registry-db)
         ;; safe if not found
         (entries (registry-lookup db (list id))))

    (when (null entries)
      (registry-insert db id (list (list 'creation-time (current-time))
                                   '(group) '(sender) '(subject)))
      (setq entries (registry-lookup db (list id))))

    (nth 1 (assoc id entries))))

(defun gnus-registry-delete-entries (idlist)
  (registry-delete gnus-registry-db idlist nil))

(defun gnus-registry-get-id-key (id key)
  (cdr-safe (assq key (gnus-registry-get-or-make-entry id))))

(defun gnus-registry-set-id-key (id key vals)
  (let* ((db gnus-registry-db)
         (entry (gnus-registry-get-or-make-entry id)))
    (registry-delete db (list id) nil)
    (setq entry (cons (cons key vals) (assq-delete-all key entry)))
    (registry-insert db id entry)
    entry))

(defun gnus-registry-import-eld (file)
  (interactive "fOld registry file to import? ")
  ;; example content:
  ;;   (setq gnus-registry-alist '(
  ;; ("<messageID>" ((marks nil)
  ;;                 (mtime 19365 1776 440496)
  ;;                 (sender . "root (Cron Daemon)")
  ;;                 (subject . "Cron"))
  ;;  "cron" "nnml+private:cron")
  (load file t)
  (when (boundp 'gnus-registry-alist)
    (let* ((old (symbol-value 'gnus-registry-alist))
           (count 0)
           (expected (length old))
           entry)
      (while (car-safe old)
        (incf count)
        ;; don't use progress reporters for backwards compatibility
        (when (and (< 0 expected)
                   (= 0 (mod count 100)))
          (message "importing: %d of %d (%.2f%%)"
                   count expected (/ (* 100 count) expected)))
        (setq entry (car-safe old)
              old (cdr-safe old))
        (let* ((id (car-safe entry))
               (new-entry (gnus-registry-get-or-make-entry id))
               (rest (cdr-safe entry))
               (groups (loop for p in rest
                             when (stringp p)
                             collect p))
               extra-cell key val)
          ;; remove all the strings from the entry
          (delete* nil rest :test (lambda (a b) (stringp b)))
          (gnus-registry-set-id-key id 'group groups)
          ;; just use the first extra element
          (setq rest (car-safe rest))
          (while (car-safe rest)
            (setq extra-cell (car-safe rest)
                  key (car-safe extra-cell)
                  val (cdr-safe extra-cell)
                  rest (cdr-safe rest))
            (when (and val (atom val))
              (setq val (list val)))
            (gnus-registry-set-id-key id key val))))
      (message "Import done, collected %d entries" count))))

(ert-deftest gnus-registry-usage-test ()
  (let* ((n 100)
         (tempfile (make-temp-file "gnus-registry-persist"))
         (db (gnus-registry-make-db tempfile))
         (gnus-registry-db db)
         back size)
    (message "Adding %d keys to the test Gnus registry" n)
    (dotimes (i n)
      (let ((id (number-to-string i)))
        (gnus-registry-handle-action id
                                     (if (>= 50 i) "fromgroup" nil)
                                     "togroup"
                                     (when (>= 70 i)
                                       (format "subject %d" (mod i 10)))
                                     (when (>= 80 i)
                                       (format "sender %d" (mod i 10))))))
    (message "Testing Gnus registry size is %d" n)
    (should (= n (registry-size db)))
    (message "Looking up individual keys (registry-lookup)")
    (should (equal (loop for e
                         in (mapcar 'cadr
                                    (registry-lookup db '("20" "83" "72")))
                         collect (assq 'subject e)
                         collect (assq 'sender e)
                         collect (assq 'group e))
                   '((subject "subject 0") (sender "sender 0") (group "togroup")
                     (subject) (sender) (group "togroup")
                     (subject) (sender "sender 2") (group "togroup"))))

    (message "Looking up individual keys (gnus-registry-id-key)")
    (should (equal (gnus-registry-get-id-key "34" 'group) '("togroup")))
    (should (equal (gnus-registry-get-id-key "34" 'subject) '("subject 4")))
    (message "Trying to insert a duplicate key")
    (should-error (registry-insert db "55" '()))
    (message "Looking up individual keys (gnus-registry-get-or-make-entry)")
    (should (gnus-registry-get-or-make-entry "22"))
    (message "Saving the Gnus registry to %s" tempfile)
    (should (gnus-registry-save tempfile db))
    (setq size (nth 7 (file-attributes tempfile)))
    (message "Saving the Gnus registry to %s: size %d" tempfile size)
    (should (< 0 size))
    (with-temp-buffer
      (insert-file-contents-literally tempfile)
      (should (looking-at (concat ";; Object "
                                  "Gnus Registry"
                                  "\n;; EIEIO PERSISTENT OBJECT"))))
    (message "Reading Gnus registry back")
    (setq back (eieio-persistent-read tempfile))
    (should back)
    (message "Read Gnus registry back: %d keys, expected %d==%d"
             (registry-size back) n (registry-size db))
    (should (= (registry-size back) n))
    (should (= (registry-size back) (registry-size db)))
    (delete-file tempfile)
    (message "Pruning Gnus registry to 0 by setting :max-soft")
    (oset db :max-soft 0)
    (registry-prune db)
    (should (= (registry-size db) 0)))
  (message "Done with Gnus registry usage testing."))

;;;###autoload
(defun gnus-registry-initialize ()
"Initialize the Gnus registry."
  (interactive)
  (gnus-message 5 "Initializing the registry")
  (setq gnus-registry-install t)        ; in case it was 'ask or nil
  (gnus-registry-install-hooks)
  (gnus-registry-install-shortcuts)
  (gnus-registry-read))

;;;###autoload
(defun gnus-registry-install-hooks ()
  "Install the registry hooks."
  (interactive)
  (add-hook 'gnus-summary-article-move-hook 'gnus-registry-action)
  (add-hook 'gnus-summary-article-delete-hook 'gnus-registry-action)
  (add-hook 'gnus-summary-article-expire-hook 'gnus-registry-action)
  (add-hook 'nnmail-spool-hook 'gnus-registry-spool-action)

  (add-hook 'gnus-save-newsrc-hook 'gnus-registry-save)
  (add-hook 'gnus-read-newsrc-el-hook 'gnus-registry-read)

  (add-hook 'gnus-summary-prepare-hook 'gnus-registry-register-message-ids))

(defun gnus-registry-unload-hook ()
  "Uninstall the registry hooks."
  (interactive)
  (remove-hook 'gnus-summary-article-move-hook 'gnus-registry-action)
  (remove-hook 'gnus-summary-article-delete-hook 'gnus-registry-action)
  (remove-hook 'gnus-summary-article-expire-hook 'gnus-registry-action)
  (remove-hook 'nnmail-spool-hook 'gnus-registry-spool-action)

  (remove-hook 'gnus-save-newsrc-hook 'gnus-registry-save)
  (remove-hook 'gnus-read-newsrc-el-hook 'gnus-registry-read)

  (remove-hook 'gnus-summary-prepare-hook 'gnus-registry-register-message-ids))

(add-hook 'gnus-registry-unload-hook 'gnus-registry-unload-hook)

(defun gnus-registry-install-p ()
  (interactive)
  (when (eq gnus-registry-install 'ask)
    (setq gnus-registry-install
          (gnus-y-or-n-p
           (concat "Enable the Gnus registry?  "
                   "See the variable `gnus-registry-install' "
                   "to get rid of this query permanently. ")))
    (when gnus-registry-install
      ;; we just set gnus-registry-install to t, so initialize the registry!
      (gnus-registry-initialize)))
;;; we could call it here: (customize-variable 'gnus-registry-install)
  gnus-registry-install)

;; TODO: a few things

(provide 'gnus-registry)

;;; gnus-registry.el ends here