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+;;; Haunt --- Static site generator for GNU Guile
+;;; Copyright © 2022 David Thompson <davet@gnu.org>
+;;;
+;;; This file is part of Haunt.
+;;;
+;;; Haunt 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.
+;;;
+;;; Haunt 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 Haunt. If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+;;
+;; Inotify-based file watching for Linux.
+;;
+;;; Code:
+
+(define-module (haunt watch linux)
+ #:use-module (haunt inotify)
+ #:use-module (haunt site)
+ #:use-module (ice-9 ftw)
+ #:export (watch))
+
+;; TODO: Detect new directories and watch them, too.
+(define (watch thunk check-dir? check-file?)
+ (let ((inotify (make-inotify)))
+ (define (no-op name stat result) result)
+ (define (watch-directory name stat result)
+ (and (check-dir? name)
+ (inotify-add-watch! inotify name
+ '(create delete close-write moved-to moved-from))
+ #t))
+ ;; Drop .scm extension, remove working directory,
+ ;; and transform into a symbolic module name.
+ (define (file-name->module-name file-name)
+ (map string->symbol
+ (string-split (string-drop (string-take file-name
+ (- (string-length file-name)
+ 4))
+ (+ (string-length (getcwd)) 1))
+ #\/)))
+ (file-system-fold watch-directory no-op no-op no-op no-op no-op #t (getcwd))
+ (let loop ((processed-event? #f))
+ (cond
+ ((inotify-pending-events? inotify)
+ (let* ((event (inotify-read-event inotify))
+ (type (inotify-event-type event))
+ (file-name (string-append (inotify-watch-file-name
+ (inotify-event-watch event))
+ "/"
+ (inotify-event-file-name event))))
+ (if (and (check-dir? file-name) (check-file? file-name))
+ (let ((action (case type
+ ((create) "create")
+ ((delete) "delete")
+ ((close-write) "write")
+ ((moved-to moved-from) "move"))))
+ (format #t "watch: observed ~a '~a'~%" action file-name)
+ ;; Reload Scheme modules when they are changed.
+ (when (%search-load-path file-name)
+ (let ((module (resolve-module
+ (file-name->module-name file-name))))
+ (when (module-filename module)
+ (format #t "watch: reload module ~s~%"
+ (module-name module))
+ (reload-module module))))
+ (loop #t))
+ (loop processed-event?))))
+ (processed-event?
+ (thunk)
+ (loop #f))
+ (else
+ (sleep 1)
+ (loop #f))))))