Scan opened book/data folders for changes to extra files for a few minutes after they are opened, updating caches and the GUI as changes are detected

src/calibre/gui2/actions/view.py

@@ -272,24 +272,23 @@ class ViewAction(InterfaceAction):
             return
         if not self._view_check(len(rows), max_=10, skip_dialog_name='open-folder-many-check'):
             return
-        for i, row in enumerate(rows):
         db = self.gui.current_db
-            db.new_api.clear_extra_files_cache(self.gui.library_view.model().id(row))
+        for i, row in enumerate(rows):
+            self.gui.extra_files_watcher.watch_book(db.id(row.row()))
             path = db.abspath(row.row())
+            if path:
                 open_local_file(path)
                 if ismacos and i < len(rows) - 1:
                     time.sleep(0.1)  # Finder cannot handle multiple folder opens
 
     def view_folder_for_id(self, id_):
-        db = self.gui.current_db
-        db.new_api.clear_extra_files_cache(id_)
-        path = db.abspath(id_, index_is_id=True)
+        self.gui.extra_files_watcher.watch_book(id_)
+        path = self.gui.current_db.abspath(id_, index_is_id=True)
         open_local_file(path)
 
     def view_data_folder_for_id(self, id_):
-        db = self.gui.current_db
-        db.new_api.clear_extra_files_cache(id_)
-        path = db.abspath(id_, index_is_id=True)
+        self.gui.extra_files_watcher.watch_book(id_)
+        path = self.gui.current_db.abspath(id_, index_is_id=True)
         open_local_file(os.path.join(path, DATA_DIR_NAME))
 
     def view_book(self, triggered):

src/calibre/gui2/extra_files_watcher.py

@@ -0,0 +1,87 @@
+#!/usr/bin/env python
+# License: GPLv3 Copyright: 2023, Kovid Goyal <kovid at kovidgoyal.net>
+
+
+from qt.core import QObject, QTimer
+from time import monotonic
+from typing import NamedTuple, Tuple
+
+from calibre.db.constants import DATA_FILE_PATTERN
+
+
+class ExtraFile(NamedTuple):
+    relpath: str
+    mtime: float
+    size: int
+
+
+class ExtraFiles(NamedTuple):
+    last_changed_at: float
+    files: Tuple[ExtraFile, ...]
+
+
+class ExtraFilesWatcher(QObject):
+
+    WATCH_FOR = 300  # seconds
+    TICK_INTERVAL = 1 # seconds
+
+    def __init__(self, parent=None):
+        super().__init__(parent)
+        self.watched_book_ids = {}
+        self.timer = QTimer(self)
+        self.timer.setInterval(int(self.TICK_INTERVAL * 1000))
+        self.timer.timeout.connect(self.check_registered_books)
+
+    def clear(self):
+        self.watched_book_ids.clear()
+        self.timer.stop()
+
+    def watch_book(self, book_id):
+        if book_id not in self.watched_book_ids:
+            try:
+                self.watched_book_ids[book_id] = ExtraFiles(monotonic(), self.get_extra_files(book_id))
+            except Exception:
+                import traceback
+                traceback.print_exc()
+                return
+        self.timer.start()
+
+    @property
+    def gui(self):
+        ans = self.parent()
+        if hasattr(ans, 'current_db'):
+            return ans
+        from calibre.gui2.ui import get_gui
+        return get_gui()
+
+    def get_extra_files(self, book_id):
+        db = self.gui.current_db.new_api
+        return tuple(ExtraFile(relpath, stat_result.st_mtime, stat_result.st_size) for
+                     relpath, file_path, stat_result in db.list_extra_files(book_id, pattern=DATA_FILE_PATTERN))
+
+    def check_registered_books(self):
+        changed = {}
+        remove = set()
+        now = monotonic()
+        for book_id, extra_files in self.watched_book_ids.items():
+            try:
+                ef = self.get_extra_files(book_id)
+            except Exception:
+                # book probably deleted
+                remove.add(book_id)
+                continue
+            if ef != extra_files.files:
+                changed[book_id] = ef
+            elif now - extra_files.last_changed_at > self.WATCH_FOR:
+                remove.add(book_id)
+        if changed:
+            self.refresh_gui(changed)
+            for book_id, files in changed.items():
+                self.watched_book_ids[book_id] = self.watched_book_ids[book_id]._replace(files=files, last_changed_at=now)
+        for book_id in remove:
+            self.watched_book_ids.pop(book_id, None)
+        if not self.watched_book_ids:
+            self.timer.stop()
+
+    def refresh_gui(self, book_ids):
+        self.gui.library_view.model().refresh_ids(frozenset(book_ids), current_row=self.gui.library_view.currentIndex().row())

src/calibre/gui2/ui.py

@@ -30,6 +30,7 @@ from calibre.constants import (
 from calibre.customize import PluginInstallationType
 from calibre.customize.ui import available_store_plugins, interface_actions
 from calibre.db.legacy import LibraryDatabase
+from calibre.gui2.extra_files_watcher import ExtraFilesWatcher
 from calibre.gui2 import (
     Dispatcher, GetMetadata, config, error_dialog, gprefs, info_dialog,
     max_available_height, open_url, question_dialog, warning_dialog,
@@ -118,6 +119,7 @@ class Main(MainWindow, MainWindowMixin, DeviceMixin, EmailMixin,  # {{{
     def __init__(self, opts, parent=None, gui_debug=None):
         MainWindow.__init__(self, opts, parent=parent, disable_automatic_gc=True)
         self.setWindowIcon(QApplication.instance().windowIcon())
+        self.extra_files_watcher = ExtraFilesWatcher(self)
         self.jobs_pointer = Pointer(self)
         self.proceed_requested.connect(self.do_proceed,
                 type=Qt.ConnectionType.QueuedConnection)
@@ -914,6 +916,7 @@ class Main(MainWindow, MainWindowMixin, DeviceMixin, EmailMixin,  # {{{
                     import traceback
                     traceback.print_exc()
             self.library_path = newloc
+            self.extra_files_watcher.clear()
             prefs['library_path'] = self.library_path
             self.book_on_device(None, reset=True)
             db.set_book_on_device_func(self.book_on_device)
@@ -1148,6 +1151,7 @@ class Main(MainWindow, MainWindowMixin, DeviceMixin, EmailMixin,  # {{{
         self.shutdown_started.emit()
         self.show_shutdown_message()
         self.server_change_notification_timer.stop()
+        self.extra_files_watcher.clear()
         try:
             self.event_in_db.disconnect()
         except Exception: