fix: add backward compatibility for Flet 0.19.0

this is needed until more dust settles, for sake of testing.  Flet
0.19.0 was the main version used for initial dev (iirc) and while the
app now runs "fine" (and presumably would prefer) the latest Flet
0.23.2, the global error handler does *not* work there yet..

see also https://github.com/flet-dev/flet/issues/3615

wuttapos/app.py

@@ -169,7 +169,10 @@ def main(page: ft.Page):
         threading.excepthook = thread_exc_hook
 
     page.title = f"WuttaPOS v{wuttapos.__version__}"
-    page.window.full_screen = True
+    if hasattr(page, 'window'):
+        page.window.full_screen = True
+    else:
+        page.window_full_screen = True
 
     # global defaults for button/text styles etc.
     page.data = {
@@ -179,7 +182,10 @@ def main(page: ft.Page):
 
     def clean_exit():
         # TODO: this doesn't do anything interesting now, but it could
-        page.window.destroy()
+        if hasattr(page, 'window'):
+            page.window.destroy()
+        else:
+            page.window_destroy()
 
     def keyboard(e):
         # exit on ctrl+Q
@@ -194,8 +200,12 @@ def main(page: ft.Page):
             clean_exit()
 
     # cf. https://flet.dev/docs/controls/page/#window_destroy
-    page.window.prevent_close = True
-    page.window.on_event = window_event
+    if hasattr(page, 'window'):
+        page.window.prevent_close = True
+        page.window.on_event = window_event
+    else:
+        page.window_prevent_close = True
+        page.window_on_event = window_event
 
     # TODO: probably these should be auto-loaded from spec
     from wuttapos.views.pos import POSView
@@ -227,6 +237,11 @@ def main(page: ft.Page):
         elif page.route == '/login':
             page.views.append(LoginView(config, '/login'))
 
+        if hasattr(page, 'window'):
+            page.window.full_screen = True
+        else:
+            page.window_full_screen = True
+
         page.update()
 
     # TODO: this was in example docs but not sure what it's for?

wuttapos/controls/timestamp.py

@@ -25,6 +25,8 @@ WuttaPOS - timestamp control
 """
 
 import asyncio
+import threading
+import time
 
 import flet as ft
 
@@ -43,7 +45,13 @@ class WuttaTimestamp(ft.Text):
 
     def did_mount(self):
         self.running = True
-        self.page.run_task(self.update_display)
+        if hasattr(self.page, 'run_task'):
+            self.page.run_task(self.update_display)
+        else:
+            # nb. daemonized thread should be stopped when app exits
+            # cf. https://docs.python.org/3/library/threading.html#thread-objects
+            thread = threading.Thread(target=self.update_display_blocking, daemon=True)
+            thread.start()
 
     def will_unmount(self):
         self.running = False
@@ -56,3 +64,9 @@ class WuttaTimestamp(ft.Text):
             self.value = self.render_time(self.app.localtime())
             self.update()
             await asyncio.sleep(0.5)
+
+    def update_display_blocking(self):
+        while self.running:
+            self.value = self.render_time(self.app.localtime())
+            self.update()
+            time.sleep(0.5)