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;;; shadowfile.el --- automatic file copying

;; Copyright (C) 1993, 1994, 2001, 2002, 2003, 2004,
;;   2005, 2006, 2007, 2008 Free Software Foundation, Inc.

;; Author: Boris Goldowsky <boris@gnu.org>
;; Keywords: comm files

;; 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 package helps you to keep identical copies of files in more than one
;;  place - possibly on different machines.  When you save a file, it checks
;;  whether it is on the list of files with "shadows", and if so, it tries to
;;  copy it when you exit Emacs (or use the shadow-copy-files command).

;; Installation & Use:

;;  Add clusters (if necessary) and file groups with shadow-define-cluster,
;;  shadow-define-literal-group, and shadow-define-regexp-group (see the
;;  documentation for these functions for information on how and when to use
;;  them).  After doing this once, everything should be automatic.

;;  The lists of clusters and shadows are saved in a file called .shadows,
;;  so that they can be remembered from one Emacs session to another, even
;;  (as much as possible) if the Emacs session terminates abnormally.  The
;;  files needing to be copied are stored in .shadow_todo; if a file cannot
;;  be copied for any reason, it will stay on the list to be tried again
;;  next time.  The .shadows file should itself have shadows on all your
;;  accounts so that the information in it is consistent everywhere, but
;;  .shadow_todo is local information and should have no shadows.

;;  If you do not want to copy a particular file, you can answer "no" and
;;  be asked again next time you hit C-x 4 s or exit Emacs.  If you do not
;;  want to be asked again, use shadow-cancel, and you will not be asked
;;  until you change the file and save it again.  If you do not want to
;;  shadow that file ever again, you can edit it out of the .shadows
;;  buffer.  Anytime you edit the .shadows buffer, you must type M-x
;;  shadow-read-files to load in the new information, or your changes will
;;  be overwritten!

;; Bugs & Warnings:
;;
;;  - It is bad to have two emacses both running shadowfile at the same
;;  time.  It tries to detect this condition, but is not always successful.
;;
;;  - You have to be careful not to edit a file in two locations
;;  before shadowfile has had a chance to copy it; otherwise
;;  "updating shadows" will overwrite one of the changed versions.
;;
;;  - It ought to check modification times of both files to make sure
;;  it is doing the right thing.  This will have to wait until
;;  file-newer-than-file-p works between machines.
;;
;;  - It will not make directories for you, it just fails to copy files
;;  that belong in non-existent directories.
;;
;;  Please report any bugs to me (boris@gnu.org).  Also let me know
;;  if you have suggestions or would like to be informed of updates.


;;; Code:

(require 'ange-ftp)

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Variables
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(defgroup shadow nil
  "Automatic file copying when saving a file."
  :prefix "shadow-"
  :link '(emacs-commentary-link "shadowfile")
  :group 'files)

(defcustom shadow-noquery nil
  "*If t, always copy shadow files without asking.
If nil \(the default), always ask.  If not nil and not t, ask only if there
is no buffer currently visiting the file."
  :type '(choice (const t) (const nil) (other :tag "Ask if no buffer" maybe))
  :group 'shadow)

(defcustom shadow-inhibit-message nil
  "*If non-nil, do not display a message when a file needs copying."
  :type 'boolean
  :group 'shadow)

(defcustom shadow-inhibit-overload nil
  "If non-nil, shadowfile won't redefine \\[save-buffers-kill-emacs].
Normally it overloads the function `save-buffers-kill-emacs' to check for
files that have been changed and need to be copied to other systems."
  :type 'boolean
  :group 'shadow)

(defcustom shadow-info-file nil
  "File to keep shadow information in.
The `shadow-info-file' should be shadowed to all your accounts to
ensure consistency.  Default: ~/.shadows"
  :type '(choice (const nil) file)
  :group 'shadow)

(defcustom shadow-todo-file nil
  "File to store the list of uncopied shadows in.
This means that if a remote system is down, or for any reason you cannot or
decide not to copy your shadow files at the end of one Emacs session, it will
remember and ask you again in your next Emacs session.
This file must NOT be shadowed to any other system, it is host-specific.
Default: ~/.shadow_todo"
  :type '(choice (const nil) file)
  :group 'shadow)


;;; The following two variables should in most cases initialize themselves
;;; correctly.  They are provided as variables in case the defaults are wrong
;;; on your machine \(and for efficiency).

(defvar shadow-system-name (system-name)
  "The complete hostname of this machine.")

(defvar shadow-homedir nil
  "Your home directory on this machine.")

;;;
;;; Internal variables whose values are stored in the info and todo files:
;;;

(defvar shadow-clusters nil
  "List of host clusters \(see `shadow-define-cluster').")

(defvar shadow-literal-groups nil
  "List of files that are shared between hosts.
This list contains shadow structures with literal filenames, created by
`shadow-define-literal-group'.")

(defvar shadow-regexp-groups nil
  "List of file types that are shared between hosts.
This list contains shadow structures with regexps matching filenames,
created by `shadow-define-regexp-group'.")

;;;
;;; Other internal variables:
;;;

(defvar shadow-files-to-copy nil)       ; List of files that need to
                                        ; be copied to remote hosts.

(defvar shadow-hashtable nil)           ; for speed

(defvar shadow-info-buffer nil)         ; buf visiting shadow-info-file
(defvar shadow-todo-buffer nil)         ; buf visiting shadow-todo-file

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Syntactic sugar; General list and string manipulation
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(defun shadow-union (a b)
  "Add members of list A to list B if not equal to items already in B."
  (if (null a)
      b
    (if (member (car a) b)
        (shadow-union (cdr a) b)
      (shadow-union (cdr a) (cons (car a) b)))))

(defun shadow-find (func list)
  "If FUNC applied to some element of LIST is non-nil, return first such element."
  (while (and list (not (funcall func (car list))))
    (setq list (cdr list)))
  (car list))

(defun shadow-remove-if (func list)
  "Remove elements satisfying FUNC from LIST.
Nondestructive; actually returns a copy of the list with the elements removed."
  (if list
      (if (funcall func (car list))
          (shadow-remove-if func (cdr list))
        (cons (car list) (shadow-remove-if func (cdr list))))
    nil))

(defun shadow-regexp-superquote (string)
  "Like `regexp-quote', but includes the ^ and $.
This makes sure regexp matches nothing but STRING."
  (concat "^" (regexp-quote string) "$"))

(defun shadow-suffix (prefix string)
  "If PREFIX begins STRING, return the rest.
Return value is non-nil if PREFIX and STRING are `string=' up to the length of
PREFIX."
  (let ((lp (length prefix))
        (ls (length string)))
    (if (and (>= ls lp)
             (string= prefix (substring string 0 lp)))
        (substring string lp))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Clusters and sites
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;;; I use the term `site' to refer to a string which may be the name of a
;;; cluster or a literal hostname.  All user-level commands should accept
;;; either.

(defun shadow-make-cluster (name primary regexp)
  "Create a shadow cluster.
It is called NAME, uses the PRIMARY hostname and REGEXP matching all
hosts in the cluster.  The variable `shadow-clusters' associates the
names of clusters to these structures.  This function is for program
use: to create clusters interactively, use `shadow-define-cluster'
instead."
  (list name primary regexp))

(defmacro shadow-cluster-name (cluster)
  "Return the name of the CLUSTER."
  (list 'elt cluster 0))

(defmacro shadow-cluster-primary (cluster)
  "Return the primary hostname of a CLUSTER."
  (list 'elt cluster 1))

(defmacro shadow-cluster-regexp (cluster)
  "Return the regexp matching hosts in a CLUSTER."
  (list 'elt cluster 2))

(defun shadow-set-cluster (name primary regexp)
  "Put cluster NAME on the list of clusters.
Replace old definition, if any.  PRIMARY and REGEXP are the
information defining the cluster.  For interactive use, call
`shadow-define-cluster' instead."
  (let ((rest (shadow-remove-if
               (function (lambda (x) (equal name (car x))))
               shadow-clusters)))
    (setq shadow-clusters
          (cons (shadow-make-cluster name primary regexp)
                rest))))

(defmacro shadow-get-cluster (name)
  "Return cluster named NAME, or nil."
  (list 'assoc name 'shadow-clusters))

(defun shadow-site-primary (site)
  "If SITE is a cluster, return primary host, otherwise return SITE."
  (let ((c (shadow-get-cluster site)))
    (if c
        (shadow-cluster-primary c)
      site)))

;;; SITES

(defun shadow-site-cluster (site)
  "Given a SITE \(hostname or cluster name), return cluster it is in, or nil."
  (or (assoc site shadow-clusters)
      (shadow-find
       (function (lambda (x)
                   (string-match (shadow-cluster-regexp x)
                                 site)))
       shadow-clusters)))

(defun shadow-read-site ()
  "Read a cluster name or hostname from the minibuffer."
  (let ((ans (completing-read "Host or cluster name [RET when done]: "
                              shadow-clusters)))
    (if (equal "" ans)
        nil
      ans)))

(defun shadow-site-match (site1 site2)
  "Non-nil if SITE1 is or includes SITE2.
Each may be a host or cluster name; if they are clusters, regexp of SITE1 will
be matched against the primary of SITE2."
  (or (string-equal site1 site2) ; quick check
      (let* ((cluster1 (shadow-get-cluster site1))
             (primary2 (shadow-site-primary site2)))
        (if cluster1
            (string-match (shadow-cluster-regexp cluster1) primary2)
          (string-equal site1 primary2)))))

(defun shadow-get-user (site)
  "Return the default username for a SITE."
  (ange-ftp-get-user (shadow-site-primary site)))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Filename manipulation
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(defun shadow-parse-fullname (fullname)
  "Parse FULLNAME into \(site user path) list.
Leave it alone if it already is one.  Return nil if the argument is
not a full ange-ftp pathname."
  (if (listp fullname)
      fullname
    (ange-ftp-ftp-name fullname)))

(defun shadow-parse-name (name)
  "Parse any NAME into \(site user name) list.
Argument can be a simple name, full ange-ftp name, or already a hup list."
  (or (shadow-parse-fullname name)
      (list shadow-system-name
            (user-login-name)
            name)))

(defsubst shadow-make-fullname (host user name)
  "Make an ange-ftp style fullname out of HOST, USER (optional), and NAME.
This is probably not as general as it ought to be."
  (concat "/"
          (if user (concat user "@"))
          host ":"
          name))

(defun shadow-replace-name-component (fullname newname)
  "Return FULLNAME with the name component changed to NEWNAME."
  (let ((hup (shadow-parse-fullname fullname)))
    (shadow-make-fullname (nth 0 hup) (nth 1 hup) newname)))

(defun shadow-local-file (file)
  "If FILE is at this site, remove /user@host part.
If refers to a different system or a different user on this system,
return nil."
  (let ((hup (shadow-parse-fullname file)))
    (cond ((null hup) file)
          ((and (shadow-site-match (nth 0 hup) shadow-system-name)
                (string-equal (nth 1 hup) (user-login-name)))
           (nth 2 hup))
          (t nil))))

(defun shadow-expand-cluster-in-file-name (file)
  "If hostname part of FILE is a cluster, expand it to cluster's primary hostname.
Will return the name bare if it is a local file."
  (let ((hup (shadow-parse-name file))
        cluster)
    (cond ((null hup) file)
          ((shadow-local-file hup))
          ((shadow-make-fullname (shadow-site-primary (nth 0 hup))
                                 (nth 1 hup)
                                 (nth 2 hup))))))

(defun shadow-expand-file-name (file &optional default)
  "Expand file name and get FILE's true name."
  (file-truename (expand-file-name file default)))

(defun shadow-contract-file-name (file)
  "Simplify FILE.
Do so by replacing (when possible) home directory with ~, and hostname
with cluster name that includes it.  Filename should be absolute and
true."
  (let* ((hup (shadow-parse-name file))
         (homedir (if (shadow-local-file hup)
                      shadow-homedir
                    (file-name-as-directory
                     (nth 2 (shadow-parse-fullname
                             (expand-file-name
                              (shadow-make-fullname
                               (nth 0 hup) (nth 1 hup) "~")))))))
         (suffix (shadow-suffix homedir (nth 2 hup)))
         (cluster (shadow-site-cluster (nth 0 hup))))
    (shadow-make-fullname
     (if cluster
         (shadow-cluster-name cluster)
       (nth 0 hup))
     (nth 1 hup)
     (if suffix
         (concat "~/" suffix)
       (nth 2 hup)))))

(defun shadow-same-site (pattern file)
  "True if the site of PATTERN and of FILE are on the same site.
If usernames are supplied, they must also match exactly.  PATTERN and FILE may
be lists of host, user, name, or ange-ftp file names.  FILE may also be just a
local filename."
  (let ((pattern-sup (shadow-parse-fullname pattern))
        (file-sup    (shadow-parse-name file)))
    (and
     (shadow-site-match (nth 0 pattern-sup) (nth 0 file-sup))
     (or (null (nth 1 pattern-sup))
         (string-equal (nth 1 pattern-sup) (nth 1 file-sup))))))

(defun shadow-file-match (pattern file &optional regexp)
 "Return t if PATTERN matches FILE.
If REGEXP is supplied and non-nil, the file part of the pattern is a regular
expression, otherwise it must match exactly.  The sites and usernames must
match---see `shadow-same-site'.  The pattern must be in full ange-ftp format,
but the file can be any valid filename.  This function does not do any
filename expansion or contraction, you must do that yourself first."
 (let* ((pattern-sup (shadow-parse-fullname pattern))
        (file-sup (shadow-parse-name file)))
   (and (shadow-same-site pattern-sup file-sup)
        (if regexp
            (string-match (nth 2 pattern-sup) (nth 2 file-sup))
          (string-equal (nth 2 pattern-sup) (nth 2 file-sup))))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; User-level Commands
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;;;###autoload
(defun shadow-define-cluster (name)
  "Edit \(or create) the definition of a cluster NAME.
This is a group of hosts that share directories, so that copying to or from
one of them is sufficient to update the file on all of them.  Clusters are
defined by a name, the network address of a primary host \(the one we copy
files to), and a regular expression that matches the hostnames of all the
sites in the cluster."
  (interactive (list (completing-read "Cluster name: " shadow-clusters () ())))
  (let* ((old (shadow-get-cluster name))
         (primary (read-string "Primary host: "
                               (if old (shadow-cluster-primary old)
                                 name)))
         (regexp   (let (try-regexp)
                     (while (not
                             (string-match
                              (setq try-regexp
                                    (read-string
                                     "Regexp matching all host names: "
                                     (if old (shadow-cluster-regexp old)
                                       (shadow-regexp-superquote primary))))
                              primary))
                       (message "Regexp doesn't include the primary host!")
                       (sit-for 2))
                     try-regexp))
;        (username (read-no-blanks-input
;                   (format "Username (default %s): "
;                           (shadow-get-user primary))
;                   (if old (or (shadow-cluster-username old) "")
;                     (user-login-name))))
         )
;    (if (string-equal "" username) (setq username nil))
    (shadow-set-cluster name primary regexp)))

;;;###autoload
(defun shadow-define-literal-group ()
  "Declare a single file to be shared between sites.
It may have different filenames on each site.  When this file is edited, the
new version will be copied to each of the other locations.  Sites can be
specific hostnames, or names of clusters \(see `shadow-define-cluster')."
  (interactive)
  (let* ((hup (shadow-parse-fullname
               (shadow-contract-file-name (buffer-file-name))))
         (name (nth 2 hup))
         user site group)
    (while (setq site (shadow-read-site))
      (setq user (read-string (format "Username (default %s): "
                                      (shadow-get-user site)))
            name (read-string "Filename: " name))
      (setq group (cons (shadow-make-fullname site
                                              (if (string-equal "" user)
                                                  (shadow-get-user site)
                                                user)
                                              name)
                        group)))
    (setq shadow-literal-groups (cons group shadow-literal-groups)))
  (shadow-write-info-file))

;;;###autoload
(defun shadow-define-regexp-group ()
  "Make each of a group of files be shared between hosts.
Prompts for regular expression; files matching this are shared between a list
of sites, which are also prompted for.  The filenames must be identical on all
hosts \(if they aren't, use `shadow-define-literal-group' instead of this
function).  Each site can be either a hostname or the name of a cluster \(see
`shadow-define-cluster')."
  (interactive)
  (let ((regexp (read-string
                 "Filename regexp: "
                 (if (buffer-file-name)
                     (shadow-regexp-superquote
                      (nth 2
                           (shadow-parse-name
                            (shadow-contract-file-name
                             (buffer-file-name))))))))
        site sites usernames)
    (while (setq site (shadow-read-site))
      (setq sites (cons site sites))
      (setq usernames
            (cons (read-string (format "Username for %s: " site)
                               (shadow-get-user site))
                  usernames)))
    (setq shadow-regexp-groups
          (cons (shadow-make-group regexp sites usernames)
                shadow-regexp-groups))
    (shadow-write-info-file)))

(defun shadow-shadows ()
  ;; Mostly for debugging.
  "Interactive function to display shadows of a buffer."
  (interactive)
  (let ((msg (mapconcat #'cdr (shadow-shadows-of (buffer-file-name)) " ")))
    (message "%s"
             (if (zerop (length msg))
                 "No shadows."
               msg))))

(defun shadow-copy-files (&optional arg)
  "Copy all pending shadow files.
With prefix argument, copy all pending files without query.
Pending copies are stored in variable `shadow-files-to-copy', and in
`shadow-todo-file' if necessary.  This function is invoked by
`shadow-save-buffers-kill-emacs', so it is not usually necessary to
call it manually."
  (interactive "P")
  (if (not shadow-files-to-copy)
      (if (interactive-p)
          (message "No files need to be shadowed."))
    (save-excursion
      (map-y-or-n-p (function
                     (lambda (pair)
                       (or arg shadow-noquery
                           (format "Copy shadow file %s? " (cdr pair)))))
                    (function shadow-copy-file)
                    shadow-files-to-copy
                    '("shadow" "shadows" "copy"))
      (shadow-write-todo-file t))))

(defun shadow-cancel ()
  "Cancel the instruction to copy some files.
Prompts for which copy operations to cancel.  You will not be asked to copy
them again, unless you make more changes to the files.  To cancel a shadow
permanently, remove the group from `shadow-literal-groups' or
`shadow-regexp-groups'."
  (interactive)
  (map-y-or-n-p (function (lambda (pair)
                            (format "Cancel copying %s to %s? "
                                    (car pair) (cdr pair))))
                (function (lambda (pair)
                            (shadow-remove-from-todo pair)))
                shadow-files-to-copy
                '("shadow" "shadows" "cancel copy"))
  (message "There are %d shadows to be updated."
           (length shadow-files-to-copy))
  (shadow-write-todo-file))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Internal functions
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(defun shadow-make-group (regexp sites usernames)
  "Make a description of a file group---
actually a list of regexp ange-ftp file names---from REGEXP \(name of file to
be shadowed), list of SITES, and corresponding list of USERNAMES for each
site."
  (if sites
      (cons (shadow-make-fullname (car sites) (car usernames) regexp)
            (shadow-make-group regexp (cdr sites) (cdr usernames)))
    nil))

(defun shadow-copy-file (s)
  "Copy one shadow file."
  (let* ((buffer
          (cond ((get-file-buffer
                  (abbreviate-file-name (shadow-expand-file-name (car s)))))
                ((not (file-readable-p (car s)))
                 (if (y-or-n-p
                      (format "Cannot find file %s--cancel copy request? "
                              (car s)))
                     (shadow-remove-from-todo s))
                 nil)
                ((or (eq t shadow-noquery)
                     (y-or-n-p
                      (format "No buffer for %s -- update shadow anyway? "
                              (car s))))
                 (find-file-noselect (car s)))))
         (to (shadow-expand-cluster-in-file-name (cdr s))))
    (when buffer
      (set-buffer buffer)
      (save-restriction
        (widen)
        (condition-case i
            (progn
              (write-region (point-min) (point-max) to)
              (shadow-remove-from-todo s))
          (error (message "Shadow %s not updated!" (cdr s))))))))

(defun shadow-shadows-of (file)
  "Return copy operations needed to update FILE.
Filename should have clusters expanded, but otherwise can have any format.
Return value is a list of dotted pairs like \(from . to), where from
and to are absolute file names."
  (or (symbol-value (intern-soft file shadow-hashtable))
      (let* ((absolute-file (shadow-expand-file-name
                             (or (shadow-local-file file) file)
                             shadow-homedir))
             (canonical-file (shadow-contract-file-name absolute-file))
             (shadows
              (mapcar (function (lambda (shadow)
                                  (cons absolute-file shadow)))
                      (append
                       (shadow-shadows-of-1
                        canonical-file shadow-literal-groups nil)
                       (shadow-shadows-of-1
                        canonical-file shadow-regexp-groups t)))))
        (set (intern file shadow-hashtable) shadows))))

(defun shadow-shadows-of-1 (file groups regexp)
  "Return list of FILE's shadows in GROUPS.
Consider them as regular expressions if third arg REGEXP is true."
  (if groups
      (let ((nonmatching
             (shadow-remove-if
              (function (lambda (x) (shadow-file-match x file regexp)))
              (car groups))))
        (append (cond ((equal nonmatching (car groups)) nil)
                      (regexp
                       (let ((realname (nth 2 (shadow-parse-fullname file))))
                         (mapcar
                          (function
                           (lambda (x)
                             (shadow-replace-name-component x realname)))
                          nonmatching)))
                      (t nonmatching))
                (shadow-shadows-of-1 file (cdr groups) regexp)))))

(defun shadow-add-to-todo ()
  "If current buffer has shadows, add them to the list needing to be copied."
  (let ((shadows (shadow-shadows-of
                  (shadow-expand-file-name
                   (buffer-file-name (current-buffer))))))
    (when shadows
      (setq shadow-files-to-copy
            (shadow-union shadows shadow-files-to-copy))
      (when (not shadow-inhibit-message)
        (message "%s" (substitute-command-keys
                       "Use \\[shadow-copy-files] to update shadows."))
        (sit-for 1))
      (shadow-write-todo-file)))
  nil)     ; Return nil for write-file-functions

(defun shadow-remove-from-todo (pair)
  "Remove PAIR from `shadow-files-to-copy'.
PAIR must be `eq' to one of the elements of that list."
  (setq shadow-files-to-copy
        (shadow-remove-if (function (lambda (s) (eq s pair)))
                          shadow-files-to-copy)))

(defun shadow-read-files ()
  "Visit and load `shadow-info-file' and `shadow-todo-file'.
Thus restores shadowfile's state from your last Emacs session.
Return t unless files were locked; then return nil."
  (interactive)
  (if (and (fboundp 'file-locked-p)
           (or (stringp (file-locked-p shadow-info-file))
               (stringp (file-locked-p shadow-todo-file))))
      (progn
        (message "Shadowfile is running in another Emacs; can't have two.")
        (beep)
        (sit-for 3)
        nil)
    (save-excursion
      (when shadow-info-file
        (set-buffer (setq shadow-info-buffer
                          (find-file-noselect shadow-info-file)))
        (when (and (not (buffer-modified-p))
                   (file-newer-than-file-p (make-auto-save-file-name)
                                           shadow-info-file))
          (erase-buffer)
          (message "Data recovered from %s."
                   (car (insert-file-contents (make-auto-save-file-name))))
          (sit-for 1))
        (eval-buffer))
      (when shadow-todo-file
        (set-buffer (setq shadow-todo-buffer
                          (find-file-noselect shadow-todo-file)))
        (when (and (not (buffer-modified-p))
                   (file-newer-than-file-p (make-auto-save-file-name)
                                           shadow-todo-file))
          (erase-buffer)
          (message "Data recovered from %s."
                   (car (insert-file-contents (make-auto-save-file-name))))
          (sit-for 1))
        (eval-buffer nil))
      (shadow-invalidate-hashtable))
    t))

(defun shadow-write-info-file ()
  "Write out information to `shadow-info-file'.
Also clear `shadow-hashtable', since when there are new shadows
defined, the old hashtable info is invalid."
  (shadow-invalidate-hashtable)
  (if shadow-info-file
      (save-excursion
        (if (not shadow-info-buffer)
            (setq shadow-info-buffer (find-file-noselect shadow-info-file)))
        (set-buffer shadow-info-buffer)
        (delete-region (point-min) (point-max))
        (shadow-insert-var 'shadow-clusters)
        (shadow-insert-var 'shadow-literal-groups)
        (shadow-insert-var 'shadow-regexp-groups))))

(defun shadow-write-todo-file (&optional save)
  "Write out information to `shadow-todo-file'.
With non-nil argument also saves the buffer."
  (save-excursion
    (if (not shadow-todo-buffer)
        (setq shadow-todo-buffer (find-file-noselect shadow-todo-file)))
    (set-buffer shadow-todo-buffer)
    (delete-region (point-min) (point-max))
    (shadow-insert-var 'shadow-files-to-copy)
    (if save (shadow-save-todo-file))))

(defun shadow-save-todo-file ()
  (if (and shadow-todo-buffer (buffer-modified-p shadow-todo-buffer))
      (save-excursion
        (set-buffer shadow-todo-buffer)
        (condition-case nil             ; have to continue even in case of
            (basic-save-buffer)         ; error, otherwise kill-emacs might
          (error                        ; not work!
           (message "WARNING: Can't save shadow todo file; it is locked!")
           (sit-for 1))))))

(defun shadow-invalidate-hashtable ()
  (setq shadow-hashtable (make-vector 37 0)))

(defun shadow-insert-var (variable)
  "Build a `setq' to restore VARIABLE.
Prettily insert a `setq' command which, when later evaluated,
will restore VARIABLE to its current setting.
VARIABLE must be the name of a variable whose value is a list."
  (let ((standard-output (current-buffer)))
    (insert (format "(setq %s" variable))
    (cond ((consp (eval variable))
           (insert "\n  '(")
           (prin1 (car (eval variable)))
           (let ((rest (cdr (eval variable))))
             (while rest
               (insert "\n    ")
               (prin1 (car rest))
               (setq rest (cdr rest)))
             (insert "))\n\n")))
          (t (insert " ")
             (prin1 (eval variable))
             (insert ")\n\n")))))

(defun shadow-save-buffers-kill-emacs (&optional arg)
  "Offer to save each buffer and copy shadows, then kill this Emacs process.
With prefix arg, silently save all file-visiting buffers, then kill.

Extended by shadowfile to automatically save `shadow-todo-file' and
look for files that have been changed and need to be copied to other systems."
  ;; This function is necessary because we need to get control and save
  ;; the todo file /after/ saving other files, but /before/ the warning
  ;; message about unsaved buffers (because it can get modified by the
  ;; action of saving other buffers).  `kill-emacs-hook' is no good
  ;; because it is not called at the correct time, and also because it is
  ;; called when the terminal is disconnected and we cannot ask whether
  ;; to copy files.
  (interactive "P")
  (shadow-save-todo-file)
  (save-some-buffers arg t)
  (shadow-copy-files)
  (shadow-save-todo-file)
  (and (or (not (memq t (mapcar (function
                                 (lambda (buf) (and (buffer-file-name buf)
                                                    (buffer-modified-p buf))))
                                (buffer-list))))
           (yes-or-no-p "Modified buffers exist; exit anyway? "))
       (or (not (fboundp 'process-list))
           ;; process-list is not defined on VMS.
           (let ((processes (process-list))
                 active)
             (while processes
               (and (memq (process-status (car processes)) '(run stop open listen))
                    (process-query-on-exit-flag (car processes))
                    (setq active t))
               (setq processes (cdr processes)))
             (or (not active)
                 (yes-or-no-p "Active processes exist; kill them and exit anyway? "))))
       (kill-emacs)))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Lucid Emacs compatibility
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;; This is on hold until someone tells me about a working version of
;; map-ynp for Lucid Emacs.

;(when (string-match "Lucid" emacs-version)
;  (require 'symlink-fix)
;  (require 'ange-ftp)
;  (require 'map-ynp)
;  (if (not (fboundp 'file-truename))
;      (fset 'shadow-expand-file-name
;           (symbol-function 'symlink-expand-file-name)))
;  (if (not (fboundp 'ange-ftp-ftp-name))
;      (fset 'ange-ftp-ftp-name
;           (symbol-function 'ange-ftp-ftp-name))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Hook us up
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;;;###autoload
(defun shadow-initialize ()
  "Set up file shadowing."
  (interactive)
  (if (null shadow-homedir)
      (setq shadow-homedir
            (file-name-as-directory (shadow-expand-file-name "~"))))
  (if (null shadow-info-file)
      (setq shadow-info-file
            (shadow-expand-file-name "~/.shadows")))
  (if (null shadow-todo-file)
      (setq shadow-todo-file
            (shadow-expand-file-name "~/.shadow_todo")))
  (if (not (shadow-read-files))
      (progn
        (message "Shadowfile information files not found - aborting")
        (beep)
        (sit-for 3))
    (when (and (not shadow-inhibit-overload)
               (not (fboundp 'shadow-orig-save-buffers-kill-emacs)))
      (defalias 'shadow-orig-save-buffers-kill-emacs
        (symbol-function 'save-buffers-kill-emacs))
      (defalias 'save-buffers-kill-emacs 'shadow-save-buffers-kill-emacs))
    (add-hook 'write-file-functions 'shadow-add-to-todo)
    (define-key ctl-x-4-map "s" 'shadow-copy-files)))

(defun shadowfile-unload-function ()
  (substitute-key-definition 'shadow-copy-files nil ctl-x-4-map)
  (when (fboundp 'shadow-orig-save-buffers-kill-emacs)
    (fset 'save-buffers-kill-emacs
          (symbol-function 'shadow-orig-save-buffers-kill-emacs)))
  ;; continue standard unloading
  nil)

(provide 'shadowfile)

;; arch-tag: e2f4cdd7-2bab-4def-9130-9e69b412b79e
;;; shadowfile.el ends here