[CHORE] cleanup cache and exception on make test (#1899)

* [CHORE] cleanup cache and exception on `make test`

moved the invalidate_forever task to proper location and use `create_permanent_task`.
and there was a Task never awaited Exception when running tests

* imrpove expiration test

* move cache into utils

* fix issue with pytest_asyncio

s

---------

Co-authored-by: jacksn <jkranawetter05@gmail.com>

lnbits/utils/cache.py

@@ -0,0 +1,66 @@
+from __future__ import annotations
+
+import asyncio
+from time import time
+from typing import Any, NamedTuple, Optional
+
+from loguru import logger
+
+
+class Cached(NamedTuple):
+    value: Any
+    expiry: float
+
+
+class Cache:
+    """
+    Small caching utility providing simple get/set interface (very much like redis)
+    """
+
+    def __init__(self, interval: float = 10) -> None:
+        self.interval = interval
+        self._values: dict[Any, Cached] = {}
+
+    def get(self, key: str, default=None) -> Optional[Any]:
+        cached = self._values.get(key)
+        if cached is not None:
+            if cached.expiry > time():
+                return cached.value
+            else:
+                self._values.pop(key)
+        return default
+
+    def set(self, key: str, value: Any, expiry: float = 10):
+        self._values[key] = Cached(value, time() + expiry)
+
+    def pop(self, key: str, default=None) -> Optional[Any]:
+        cached = self._values.pop(key, None)
+        if cached and cached.expiry > time():
+            return cached.value
+        return default
+
+    async def save_result(self, coro, key: str, expiry: float = 10):
+        """
+        If `key` exists, return its value, otherwise call coro and cache its result
+        """
+        cached = self.get(key)
+        if cached:
+            return cached
+        else:
+            value = await coro()
+            self.set(key, value, expiry=expiry)
+            return value
+
+    async def invalidate_forever(self):
+        while True:
+            try:
+                await asyncio.sleep(self.interval)
+                ts = time()
+                expired = [k for k, v in self._values.items() if v.expiry < ts]
+                for k in expired:
+                    self._values.pop(k)
+            except Exception:
+                logger.error("Error invalidating cache")
+
+
+cache = Cache()

lnbits/utils/exchange_rates.py

@@ -4,7 +4,7 @@ from typing import Callable, NamedTuple
 import httpx
 from loguru import logger
 
-from lnbits.cache import cache
+from lnbits.utils.cache import cache
 
 currencies = {
     "AED": "United Arab Emirates Dirham",