svc: Save display config on change

When the display host updates its monitor configuration by making the
*PUT /display/monitors* HTTP request, the configuration is now saved to
disk.  This will allow the controller to "remember" the configuration
the next time it starts up.

svc/src/hudctrl/api.py

@@ -54,7 +54,8 @@ async def get_monitor_config():
 
 @app.put('/display/monitors')
 async def put_monitor_config(
-    monitors: str = fastapi.Body(..., media_type='text/plain')
+    bgtasks: fastapi.BackgroundTasks,
+    monitors: str = fastapi.Body(..., media_type='text/plain'),
 ):
     try:
         svc.monitor_config = MonitorConfig.from_string(monitors)
@@ -64,6 +65,7 @@ async def put_monitor_config(
             fastapi.status.HTTP_400_BAD_REQUEST,
             detail=f'Invalid monitor config: {e}',
         )
+    bgtasks.add_task(svc.save_config)
     return {'monitor_config': svc.monitor_config}
 
 

svc/src/hudctrl/hud.py

@@ -143,6 +143,19 @@ class HUDService:
             await self.marionette.switch_to_window(self.windows[name])
             await self.marionette.refresh()
 
+    def save_config(self) -> None:
+        log.info('Saving configuration to %s', self.config_file)
+        config = Configuration(
+            monitors=self.monitor_config.monitors
+            if self.monitor_config
+            else [],
+            urls=self.urls,
+            host=self.host,
+            port=self.port,
+        )
+        f = self.config_file.open('w', encoding='utf-8')
+        f.write(config.json())
+
     async def set_display(self, host: str, port: int) -> None:
         if self.marionette:
             log.warning('Closing existing Marionette connection')