feat(server): implement websocket chat backend

app/websocket/chat.py

@@ -0,0 +1,87 @@
+import json
+from datetime import datetime, timezone
+
+from fastapi import APIRouter, WebSocket, WebSocketDisconnect
+
+from app.websocket.manager import manager
+
+router = APIRouter()
+
+
+def now_iso() -> str:
+    return datetime.now(timezone.utc).isoformat()
+
+
+def event(event_type: str, room_id: str, client_id: str, content: str):
+    return {
+        "type": event_type,
+        "room_id": room_id,
+        "client_id": client_id,
+        "content": content,
+        "timestamp": now_iso(),
+    }
+
+
+def clean_value(value: str, fallback: str) -> str:
+    value = value.strip()
+    return value if value else fallback
+
+
+@router.websocket("/ws/{room_id}/{client_id}")
+async def websocket_endpoint(websocket: WebSocket, room_id: str, client_id: str):
+    room_id = clean_value(room_id, "عمومی")
+    client_id = clean_value(client_id, "ناشناس")
+
+    await manager.connect(websocket, room_id, client_id)
+
+    await manager.broadcast_json(
+        event("system", room_id, "سیستم", f"{client_id} وارد اتاق {room_id} شد."),
+        room_id,
+    )
+    await manager.broadcast_json(
+        {
+            "type": "presence",
+            "room_id": room_id,
+            "client_id": "سیستم",
+            "content": "presence-updated",
+            "users": manager.room_users(room_id),
+            "timestamp": now_iso(),
+        },
+        room_id,
+    )
+
+    try:
+        while True:
+            raw_data = await websocket.receive_text()
+
+            try:
+                data = json.loads(raw_data)
+                message = str(data.get("content", "")).strip()
+            except json.JSONDecodeError:
+                message = raw_data.strip()
+
+            if not message:
+                continue
+
+            await manager.broadcast_json(
+                event("message", room_id, client_id, message),
+                room_id,
+            )
+
+    except WebSocketDisconnect:
+        manager.disconnect(websocket, room_id)
+        await manager.broadcast_json(
+            event("system", room_id, "سیستم", f"{client_id} از اتاق {room_id} خارج شد."),
+            room_id,
+        )
+        await manager.broadcast_json(
+            {
+                "type": "presence",
+                "room_id": room_id,
+                "client_id": "سیستم",
+                "content": "presence-updated",
+                "users": manager.room_users(room_id),
+                "timestamp": now_iso(),
+            },
+            room_id,
+        )