reconnect and connection cleanup working

sample.py

@@ -0,0 +1,16 @@
+import panel
+
+from watt42_viewlib import attach_w42_state
+
+w42_state = panel.rx(None)
+attach_w42_state(rx_var=w42_state, system_id="fb2b91ce-383e-4356-96b3-b6405dacb353")
+
+state_as_text = panel.bind(lambda s: f"State is {s}", w42_state)
+
+state_pane = panel.pane.Markdown(state_as_text, sizing_mode='stretch_width')
+
+_ = panel.template.FastListTemplate(
+    title="Sample W42 View App",
+    sidebar=[panel.pane.Markdown("This is a sample sidebar.")],
+    main=[panel.pane.Markdown("Welcome to the main content area!"), state_pane],
+).servable()

watt42_viewlib/__init__.py

@@ -1,5 +1,52 @@
+import asyncio
+import json
+import panel
 
-print(f"hello from viewlib")
+from websockets import ConnectionClosed
+from websockets.asyncio.client import connect
 
-def greet(name: str) -> str:
+def attach_w42_state(rx_var: panel.rx, system_id: str):
-    return f"Hello, {name}!"
+
+    WS_URL = "ws://localhost:8000/ws/systems" # TODO: make configurable
+
+    must_reconnect = True
+
+    async def subscribe_to_system():
+
+        print(f"Starting connection to {WS_URL} for system_id {system_id}")
+
+        async for websocket in connect(WS_URL):
+            try:
+                print(f"Connected to {WS_URL}")
+                send_response = await websocket.send(json.dumps({
+                    "action": "subscribe",
+                    "system_id": system_id
+                }))
+                print(f"Subscribed to system {system_id}, waiting for messages..., send_response={send_response}")
+                async for message in websocket:
+                    as_json = json.loads(message)
+                    rx_var.rx.value = as_json['change']['state']
+            except ConnectionClosed:
+                if must_reconnect:
+                    print("connection closed, retrying...")
+                    continue
+                else:
+                    print("Not retrying connection.")
+                    return
+            except Exception as e:
+                print(f"connection error, will retry: {e}")
+                await asyncio.sleep(2)
+
+    print(f"Attaching W42 state for system_id {system_id}")
+    panel.state.execute(subscribe_to_system)
+
+    async def session_destroyed():
+        print("Stop retrying connection (session destroyed)")
+        nonlocal must_reconnect
+        must_reconnect = False
+
+    def on_session_destroyed(session_id):
+        print(f"Session {session_id} destroyed")
+        panel.state.execute(session_destroyed)
+
+    panel.state.on_session_destroyed(on_session_destroyed)