add redis backend for storage of gameboards

server/GameStateStore.py

@@ -0,0 +1,55 @@
+import pickle
+
+class GameStateStore:
+  def __init__(self, backend:str="memory", redis_url:str="redis://localhost:6379/0", key_prefix:str="snake:gameboard", ttl_seconds:int=900,):
+    self.backend = (backend or "memory").strip().lower()
+    self.redis_url = redis_url
+    self.key_prefix = key_prefix
+    self.ttl_seconds = max(60, int(ttl_seconds))
+    self._redis = None
+
+  async def _get_redis(self):
+    if self._redis is not None:
+      return self._redis
+
+    try:
+      from redis.asyncio import from_url  # type: ignore[import-not-found]
+    except ImportError as error:  # pragma: no cover
+      raise RuntimeError("Redis backend selected but 'redis' package is not installed") from error
+
+    self._redis = from_url(self.redis_url)
+    return self._redis
+
+  def _key(self, game_id:str) -> str:
+    return f"{self.key_prefix}:{game_id}"
+
+  async def save(self, game_id:str, game_board) -> None:
+    if self.backend != "redis":
+      return
+
+    redis = await self._get_redis()
+    payload = pickle.dumps(game_board, protocol=pickle.HIGHEST_PROTOCOL)
+    await redis.set(self._key(game_id), payload, ex=self.ttl_seconds)
+
+  async def load(self, game_id:str):
+    if self.backend != "redis":
+      return None
+
+    redis = await self._get_redis()
+    payload = await redis.get(self._key(game_id))
+    if payload is None:
+      return None
+    return pickle.loads(payload)
+
+  async def delete(self, game_id:str) -> None:
+    if self.backend != "redis":
+      return
+
+    redis = await self._get_redis()
+    await redis.delete(self._key(game_id))
+
+  async def close(self) -> None:
+    if self._redis is None:
+      return
+    await self._redis.aclose()
+    self._redis = None