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+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2021 Andrew Tropin <andrew@trop.in>
+;;; Copyright © 2021 Xinglu Chen <public@yoctocell.xyz>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix 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 Guix 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 Guix. If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (gnu home services symlink-manager)
+ #:use-module (gnu home-services)
+ #:use-module (guix gexp)
+
+ #:export (home-symlink-manager-service-type))
+
+;;; Comment:
+;;;
+;;; symlink-manager cares about configuration files: it backs up files
+;;; created by user, removes symlinks and directories created by a
+;;; previous generation, and creates new directories and symlinks to
+;;; configuration files according to the content of files/ directory
+;;; (created by home-files-service) of the current home environment
+;;; generation.
+;;;
+;;; Code:
+
+(define (update-symlinks-script)
+ (program-file
+ "update-symlinks"
+ #~(begin
+ (use-modules (ice-9 ftw)
+ (ice-9 curried-definitions)
+ (ice-9 match)
+ (srfi srfi-1))
+ (define ((simplify-file-tree parent) file)
+ "Convert the result produced by `file-system-tree' to less
+verbose and more suitable for further processing format.
+
+Extract dir/file info from stat and compose a relative path to the
+root of the file tree.
+
+Sample output:
+
+((dir . \".\")
+ ((dir . \"config\")
+ ((dir . \"config/fontconfig\")
+ (file . \"config/fontconfig/fonts.conf\"))
+ ((dir . \"config/isync\")
+ (file . \"config/isync/mbsyncrc\"))))
+"
+ (match file
+ ((name stat) `(file . ,(string-append parent name)))
+ ((name stat children ...)
+ (cons `(dir . ,(string-append parent name))
+ (map (simplify-file-tree
+ (if (equal? name ".")
+ ""
+ (string-append parent name "/")))
+ children)))))
+
+ (define ((file-tree-traverse preordering) node)
+ "Traverses the file tree in different orders, depending on PREORDERING.
+
+if PREORDERING is @code{#t} resulting list will contain directories
+before files located in those directories, otherwise directory will
+appear only after all nested items already listed."
+ (let ((prepend (lambda (a b) (append b a))))
+ (match node
+ (('file . path) (list node))
+ ((('dir . path) . rest)
+ ((if preordering append prepend)
+ (list (cons 'dir path))
+ (append-map (file-tree-traverse preordering) rest))))))
+
+ (use-modules (guix build utils))
+
+ (let* ((config-home (or (getenv "XDG_CONFIG_HOME")
+ (string-append (getenv "HOME") "/.config")))
+
+ (he-path (string-append (getenv "HOME") "/.guix-home"))
+ (new-he-path (string-append he-path ".new"))
+ (new-home (getenv "GUIX_NEW_HOME"))
+ (old-home (getenv "GUIX_OLD_HOME"))
+
+ (new-files-path (string-append new-home "/files"))
+ ;; Trailing dot is required, because files itself is symlink and
+ ;; to make file-system-tree works it should be a directory.
+ (new-files-dir-path (string-append new-files-path "/."))
+
+ (home-path (getenv "HOME"))
+ (backup-dir (string-append home-path "/"
+ (number->string (current-time))
+ "-guix-home-legacy-configs-backup"))
+
+ (old-tree (if old-home
+ ((simplify-file-tree "")
+ (file-system-tree
+ (string-append old-home "/files/.")))
+ #f))
+ (new-tree ((simplify-file-tree "")
+ (file-system-tree new-files-dir-path)))
+
+ (get-source-path
+ (lambda (path)
+ (readlink (string-append new-files-path "/" path))))
+
+ (get-target-path
+ (lambda (path)
+ (string-append home-path "/." path)))
+
+ (get-backup-path
+ (lambda (path)
+ (string-append backup-dir "/." path)))
+
+ (directory?
+ (lambda (path)
+ (equal? (stat:type (stat path)) 'directory)))
+
+ (empty-directory?
+ (lambda (dir)
+ (equal? (scandir dir) '("." ".."))))
+
+ (symlink-to-store?
+ (lambda (path)
+ (and
+ (equal? (stat:type (lstat path)) 'symlink)
+ (store-file-name? (readlink path)))))
+
+ (backup-file
+ (lambda (path)
+ (mkdir-p backup-dir)
+ (format #t "Backing up ~a..." (get-target-path path))
+ (mkdir-p (dirname (get-backup-path path)))
+ (rename-file (get-target-path path) (get-backup-path path))
+ (display " done\n")))
+
+ (cleanup-symlinks
+ (lambda ()
+ (let ((to-delete ((file-tree-traverse #f) old-tree)))
+ (display
+ "Cleaning up symlinks from previous home-environment.\n\n")
+ (map
+ (match-lambda
+ (('dir . ".")
+ (display "Cleanup finished.\n\n"))
+
+ (('dir . path)
+ (if (and
+ (file-exists? (get-target-path path))
+ (directory? (get-target-path path))
+ (empty-directory? (get-target-path path)))
+ (begin
+ (format #t "Removing ~a..."
+ (get-target-path path))
+ (rmdir (get-target-path path))
+ (display " done\n"))
+ (format
+ #t "Skipping ~a (not an empty directory)... done\n"
+ (get-target-path path))))
+
+ (('file . path)
+ (when (file-exists? (get-target-path path))
+ ;; DO NOT remove the file if it is no longer
+ ;; a symlink to the store, it will be backed
+ ;; up later during create-symlinks phase.
+ (if (symlink-to-store? (get-target-path path))
+ (begin
+ (format #t "Removing ~a..." (get-target-path path))
+ (delete-file (get-target-path path))
+ (display " done\n"))
+ (format
+ #t
+ "Skipping ~a (not a symlink to store)... done\n"
+ (get-target-path path))))))
+ to-delete))))
+
+ (create-symlinks
+ (lambda ()
+ (let ((to-create ((file-tree-traverse #t) new-tree)))
+ (map
+ (match-lambda
+ (('dir . ".")
+ (display
+ "New symlinks to home-environment will be created soon.\n")
+ (format
+ #t "All conflicting files will go to ~a.\n\n" backup-dir))
+
+ (('dir . path)
+ (let ((target-path (get-target-path path)))
+ (when (and (file-exists? target-path)
+ (not (directory? target-path)))
+ (backup-file path))
+
+ (if (file-exists? target-path)
+ (format
+ #t "Skipping ~a (directory already exists)... done\n"
+ target-path)
+ (begin
+ (format #t "Creating ~a..." target-path)
+ (mkdir target-path)
+ (display " done\n")))))
+
+ (('file . path)
+ (when (file-exists? (get-target-path path))
+ (backup-file path))
+ (format #t "Symlinking ~a -> ~a..."
+ (get-target-path path) (get-source-path path))
+ (symlink (get-source-path path) (get-target-path path))
+ (display " done\n")))
+ to-create)))))
+
+ (when old-tree
+ (cleanup-symlinks))
+
+ (create-symlinks)
+
+ (symlink new-home new-he-path)
+ (rename-file new-he-path he-path)
+
+ (display " done\nFinished updating symlinks.\n\n")))))
+
+
+(define (update-symlinks-gexp _)
+ #~(primitive-load #$(update-symlinks-script)))
+
+(define home-symlink-manager-service-type
+ (service-type (name 'home-symlink-manager)
+ (extensions
+ (list
+ (service-extension
+ home-activation-service-type
+ update-symlinks-gexp)))
+ (default-value #f)
+ (description "Provide an @code{update-symlinks}
+script, which creates symlinks to configuration files and directories
+on every activation. If an existing file would be overwritten by a
+symlink, backs up that file first.")))
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