;;; shadowfile.el --- automatic file copying  -*- lexical-binding: t; -*-

;; Copyright (C) 1993-1994, 2001-2025 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 <https://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 `shadow-info-file',
;;  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-file'; if a file cannot be copied for any reason, it
;;  will stay on the list to be tried again next time.  The
;;  `shadow-info-file' file should itself have shadows on all your
;;  accounts so that the information in it is consistent everywhere,
;;  but `shadow-todo-file' 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 "M-x 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 Emacsen 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.


;;; Code:

(require 'cl-lib)
(require 'tramp)

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;;; 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)))

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

(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)

(defcustom shadow-info-file (locate-user-emacs-file "shadows" ".shadows")
  "File to keep shadow information in.
The `shadow-info-file' should be shadowed to all your accounts to
ensure consistency.  Default: ~/.emacs.d/shadows"
  :type 'file
  :version "26.2")

(defcustom shadow-todo-file
  (locate-user-emacs-file "shadow_todo" ".shadow_todo")
  "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: ~/.emacs.d/shadow_todo"
  :type 'file
  :version "26.2")


;; 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 (concat "/" (system-name) ":")
  "The identification for local files on this machine.")

(defvar shadow-homedir "~/"
  "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 (make-hash-table :test #'equal)) ; for speed

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

(defvar shadow-debug nil
  "Use for debug messages.")

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

(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 with 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
;; cluster identification "/name:", a remote identification
;; "/method:user@host:", or "/system-name:" (the value of
;; `shadow-system-name') for the location of local files.  All
;; user-level commands should accept either.

(cl-defstruct (shadow-cluster (:type list) :named) name primary regexp)

(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 (cl-remove-if (lambda (x) (equal name (shadow-cluster-name x)))
			    shadow-clusters)))
    (setq shadow-clusters
	  (cons (make-shadow-cluster :name name :primary primary :regexp regexp)
		rest))))

(defun shadow-get-cluster (name)
  "Return cluster named NAME, or nil."
  (seq-find
   (lambda (x) (string-equal (shadow-cluster-name x) name))
   shadow-clusters))

;;; SITES

;; This simplifies it a little bit.  "system-name" is also accepted.
;; But we don't want to make the help echo too long.
(defconst shadow-site-help "\
A cluster identification \"/name:\", a remote identification
\"/method:user@host:\", or \"/system-name:\" (the value of
`shadow-system-name')"
  "The help string describing a valid site.")

(defun shadow-site-name (site)
  "Return name if SITE has the form \"/name:\", otherwise SITE."
  (if (string-match "\\`/\\([-.[:word:]]+\\):\\'" site)
      (match-string 1 site) site))

(defun shadow-name-site (name)
  "Return \"/name:\" if NAME has word syntax, otherwise NAME."
  (if (string-match "\\`[-.[:word:]]+\\'" name)
      (format "/%s:"name) name))

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

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

(defun shadow-read-site ()
  "Read a site name from the minibuffer."
  (let ((ans (completing-read
              (propertize "Site name: " 'help-echo shadow-site-help)
	      shadow-clusters)))
    (when (or (shadow-get-cluster (shadow-site-name ans))
	      (string-equal ans shadow-system-name)
	      (string-equal ans (shadow-site-name shadow-system-name))
	      (setq ans (file-remote-p ans)))
      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)))))

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

(defun shadow-parse-name (name)
  "Parse any NAME into a `tramp-file-name' structure.
Argument can be a simple name, remote file name, or already a
`tramp-file-name' structure."
  (cond
   ((null name) nil)
   ((tramp-file-name-p name) name)
   ((file-remote-p name) (tramp-dissect-file-name name))
   ((shadow-local-file name)
    (make-tramp-file-name
     :host (shadow-site-name shadow-system-name)
     :localname (shadow-local-file name)))
   ;; Cluster name.
   ((string-match "^/\\([^:/]+\\):\\([^:]*\\)$" name)
    (let ((name (match-string 1 name))
          (file (match-string 2 name)))
      (when (shadow-get-cluster name)
        (make-tramp-file-name :host name :localname file))))))

(defsubst shadow-make-fullname (hup &optional host name)
  "Make a Tramp style fullname out of HUP, a `tramp-file-name' structure.
Replace HOST, and NAME when non-nil.  HOST can also be a remote file name."
  (when-let ((hup (copy-tramp-file-name hup)))
    (when host
      (if (file-remote-p host)
          (setq name (or name (and hup (tramp-file-name-localname hup)))
                hup (tramp-dissect-file-name (file-remote-p host)))
        (setf (tramp-file-name-host hup) host)))
    (when name (setf (tramp-file-name-localname hup) name))
    (if (null (tramp-file-name-method hup))
	(format
	 "/%s:%s" (tramp-file-name-host hup) (tramp-file-name-localname hup))
      (tramp-make-tramp-file-name hup))))

(defun shadow-replace-name-component (fullname newname)
  "Return FULLNAME with the name component changed to NEWNAME."
  (concat (file-remote-p fullname) newname))

(defun shadow-local-file (file)
  "If FILE is not remote, return it.
If it refers to a different system, return nil."
  (cond
   ((null file) nil)
   ;; `tramp-file-name' structure.
   ((and (tramp-file-name-p file) (null (tramp-file-name-method file)))
    (tramp-file-name-localname file))
   ((tramp-file-name-p file) nil)
   ;; Local host name.
   ((string-match
     (format "^%s\\([^:]*\\)$" (regexp-quote shadow-system-name)) file)
    (match-string 1 file))
   ;; Cluster name.
   ((and (string-match "^/\\([^:/]+\\):\\([^:]*\\)$" file)
         (shadow-get-cluster (match-string 1 file)))
    (let ((file (match-string 2 file))
	  (primary
	   (shadow-cluster-primary
	    (shadow-get-cluster (match-string 1 file)))))
      (when (string-equal primary shadow-system-name) (setq primary nil))
      (shadow-local-file (concat primary file))))
   ;; Local name.
   ((null (file-remote-p file)) file)))

(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."
  (when (stringp file)
    (cond
     ;; Local file.
     ((shadow-local-file file))
     ;; Cluster name.
     ((string-match "^\\(/[^:/]+:\\)[^:]*$" file)
      (let ((primary
             (save-match-data
	       (shadow-cluster-primary
	        (shadow-get-cluster
                 (shadow-site-name (match-string 1 file)))))))
	(if (not primary)
            file
          (setq file (replace-match primary nil nil file 1))
          (or (shadow-local-file file) file))))
     (t file))))

(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."
  (when-let ((hup (shadow-parse-name file)))
    (let* ((homedir (if (shadow-local-file hup)
		        shadow-homedir
		      (file-name-as-directory
		       (file-local-name
                        (expand-file-name
                         (shadow-make-fullname hup nil shadow-homedir))))))
	   (suffix (shadow-suffix homedir (tramp-file-name-localname hup)))
	   (cluster (shadow-site-cluster (shadow-make-fullname hup nil ""))))
      (when cluster
        (setf (tramp-file-name-method hup) nil
	      (tramp-file-name-host hup) (shadow-cluster-name cluster)))
      (shadow-make-fullname
       hup nil
       (if suffix
           (concat shadow-homedir suffix)
         (tramp-file-name-localname hup))))))

(defun shadow-same-site (pattern file)
  "True if the site of PATTERN and of FILE are on the same site.
PATTERN and FILE may be Tramp vectors, or remote file names.
FILE may also be just a local filename."
  (let ((pattern-sup (shadow-parse-name pattern))
	(file-sup    (shadow-parse-name file)))
    (and
     (shadow-site-match
      (tramp-file-name-host pattern-sup) (tramp-file-name-host file-sup))
     (or (null (tramp-file-name-user pattern-sup))
	 (string-equal
          (tramp-file-name-user pattern-sup)
          (tramp-file-name-user 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 must
match---see `shadow-same-site'.  The pattern must be in full Tramp 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-name pattern))
	(file-sup (shadow-parse-name file)))
   (and (shadow-same-site pattern-sup file-sup)
	(if regexp
	    (string-match
             (tramp-file-name-localname pattern-sup)
             (tramp-file-name-localname file-sup))
	  (string-equal
           (tramp-file-name-localname pattern-sup)
           (tramp-file-name-localname file-sup)))
        t)))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; 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 (let (try-primary)
		    (while (not
			    (or
			     (string-equal
			      (setq try-primary
				    (read-string
				     "Primary host: "
				     (if old (shadow-cluster-primary old)
				       name)))
			      shadow-system-name)
			     (file-remote-p try-primary)))
		      (message "Not a valid primary!")
		      (sit-for 2))
		    try-primary))
	 (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)))
    (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)
  (when-let ((hup (shadow-parse-name
	           (shadow-contract-file-name (buffer-file-name)))))
    (let* ((name (tramp-file-name-localname hup))
	   site group)
      (while (setq site (shadow-read-site))
        (setq name (read-string "Filename: " name)
              hup (shadow-parse-name (shadow-contract-file-name name))
	      group (cons (shadow-make-fullname hup site) group)))
      (when 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
                      (file-local-name (buffer-file-name))))))
	site sites)
    (while (setq site (shadow-read-site))
      (setq sites (cons site sites)))
    (setq shadow-regexp-groups
	  (cons (shadow-make-group regexp sites)
		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 (called-interactively-p 'interactive)
	  (message "No files need to be shadowed."))
    (save-excursion
      (map-y-or-n-p (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 (lambda (pair)
                  (format "Cancel copying %s to %s? "
                          (car pair) (cdr pair)))
                (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)
  "Make a description of a file group---
actually a list of regexp Tramp file names---from REGEXP (name of file to
be shadowed), and list of SITES."
  (if sites
      (cons (shadow-make-fullname
             (shadow-parse-name (shadow-site-primary (car sites))) nil regexp)
	    (shadow-make-group regexp (cdr sites)))
    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)
      (condition-case nil
	  (progn
            (write-region nil nil 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 (gethash 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 (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)))))
          (when shadow-debug
            (message
             "shadow-shadows-of: %s %s %s %s %s"
             file (shadow-local-file file) shadow-homedir
             absolute-file canonical-file))
	  (puthash file shadows shadow-hashtable))))

(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
	     (cl-remove-if (lambda (x) (shadow-file-match x file regexp))
			   (car groups))))
	(append (cond ((equal nonmatching (car groups)) nil)
		      (regexp
		       (let ((realname
                              (tramp-file-name-localname
                               (shadow-parse-name file))))
                         (when shadow-debug
                           (message
                            "shadow-shadows-of-1: %s %s %s"
                            file (shadow-parse-name file) realname))
			 (mapcar
                          (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."
  (when shadow-debug
    (message
     "shadow-add-to-todo: %s %s"
     (buffer-file-name (current-buffer))
     (shadow-expand-file-name (buffer-file-name (current-buffer)))))
  (let ((shadows (shadow-shadows-of
		  (shadow-expand-file-name
		   (buffer-file-name (current-buffer))))))
    (when shadow-debug
      (message
       "shadow-add-to-todo: %s %s\n%s"
       shadows shadow-files-to-copy (with-output-to-string (backtrace))))
    (when shadows
      (setq shadow-files-to-copy
            (nreverse (cl-union shadows shadow-files-to-copy :test #'equal)))
      (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."
  (when shadow-debug
    (message
     "shadow-remove-from-todo: %s %s\n%s"
     pair shadow-files-to-copy (with-output-to-string (backtrace))))
  (setq shadow-files-to-copy
	(cl-remove-if (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 (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-current-buffer
      (when shadow-info-file
	(set-buffer (setq shadow-info-buffer
			  (find-file-noselect shadow-info-file 'nowarn)))
	(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 'nowarn)))
	(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-current-buffer
	(if (not shadow-info-buffer)
	    (setq shadow-info-buffer (find-file-noselect shadow-info-file)))
	(set-buffer shadow-info-buffer)
        (setq buffer-read-only nil)
	(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)
    (setq buffer-read-only nil)
    (delete-region (point-min) (point-max))
    (shadow-insert-var 'shadow-files-to-copy)
    (if save (shadow-save-todo-file))))

(defun shadow-save-todo-file ()
  (when shadow-debug
    (message "shadow-save-todo-file:\n%s" (with-output-to-string (backtrace))))
  (if (and shadow-todo-buffer (buffer-modified-p shadow-todo-buffer))
      (with-current-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 ()
  (clrhash shadow-hashtable))

(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 (symbol-value variable))
	   (insert "\n  '(")
	   (prin1 (car (symbol-value variable)))
	   (let ((rest (cdr (symbol-value variable))))
	     (while rest
	       (insert "\n    ")
	       (prin1 (car rest))
	       (setq rest (cdr rest)))
	     (insert "))\n\n")))
	  (t (insert " ")
	     (prin1 (symbol-value 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."
  (interactive "P")
  (shadow--save-buffers-kill-emacs arg)
  (save-buffers-kill-emacs arg))

(defun shadow--save-buffers-kill-emacs (&optional arg &rest _)
  ;; 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.
  (shadow-save-todo-file)
  (save-some-buffers arg t)
  (shadow-copy-files)
  (shadow-save-todo-file))

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

;;;###autoload
(defun shadow-initialize ()
  "Set up file shadowing."
  (interactive)
  (setq shadow-homedir
        (file-name-as-directory (shadow-expand-file-name shadow-homedir))
        shadow-info-file (shadow-expand-file-name shadow-info-file)
        shadow-todo-file (shadow-expand-file-name shadow-todo-file))
  (if (not (shadow-read-files))
      (progn
	(message "Shadowfile information files not found - aborting")
	(beep)
	(sit-for 3))
    (unless shadow-inhibit-overload
      (advice-add 'save-buffers-kill-emacs :before
	          #'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)
  (advice-remove 'save-buffers-kill-emacs #'shadow--save-buffers-kill-emacs)
  ;; continue standard unloading
  nil)

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Obsolete
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(defun shadow-union (a b)
  "Add members of list A to list B if not equal to items already in B."
  (declare (obsolete cl-union "28.1"))
  (nreverse (cl-union a b :test #'equal)))

(define-obsolete-function-alias 'shadow-find #'seq-find "28.1")

(provide 'shadowfile)

;;; shadowfile.el ends here