add QMessageBox to display existing backup files

src/gui_qt/main/mainwindow.py

@@ -75,6 +75,8 @@ class NMRMainWindow(QtWidgets.QMainWindow, Ui_BaseWindow):
             if Updater.get_update_information(os.getenv('APPIMAGE'))[0]:
                 self.look_for_update()
 
+        self.check_for_backup()
+
         self.__timer = QtCore.QTimer()
         self.__backup_path = config_paths() / f'{datetime.datetime.now().strftime("%Y-%m-%d_%H%M%S")}.nmr'
         self.__timer.start(3*60*1000)  # every three minutes
@@ -1082,6 +1084,33 @@ class NMRMainWindow(QtWidgets.QMainWindow, Ui_BaseWindow):
         NMRWriter(self.management.graphs, self.management.data).export(self.__backup_path)
         self.status.setText('')
 
+    def check_for_backup(self):
+        backups = []
+        for filename in config_paths().glob('*.nmr'):
+            try:
+                backups.append((filename, datetime.datetime.strptime(filename.stem, "%Y-%m-%d_%H%M%S")))
+            except ValueError:
+                continue
+
+        if backups:
+            backup_by_date = sorted(backups, key=lambda x: x[1])
+            msg = QtWidgets.QMessageBox.information(
+                self, 'Backup found',
+                f'{len(backups)} backup files in directory {backup_by_date[-1][0].parent} found.\n\n'
+                f'Latest backup date: {backup_by_date[-1][1]}\n\n'
+                f'Press Ok to load, Cancel to delete backup, Close to do nothing.',
+                QtWidgets.QMessageBox.Ok | QtWidgets.QMessageBox.Cancel | QtWidgets.QMessageBox.Close
+            )
+
+            if msg == QtWidgets.QMessageBox.Ok:
+                self.management.load_files([str(backup_by_date[-1][0])])
+                backup_by_date[-1][0].unlink()
+            elif msg == QtWidgets.QMessageBox.Cancel:
+                backup_by_date[-1][0].unlink()
+            else:
+                pass
+
+
     @QtCore.pyqtSlot(name='on_actionCreate_starter_triggered')
     def create_starter(self):
         make_starter(os.getenv('APPIMAGE'))