Add minimum to ItemCounter and refactor redis client init

allianceauth/authentication/task_statistics/helpers.py

@@ -1,21 +1,62 @@
 """Helpers for Task Statistics."""
 
+import logging
 from typing import Optional
 
+from app_utils.allianceauth import get_redis_client
+from redis import Redis, RedisError
+
 from django.core.cache import cache
 
+logger = logging.getLogger(__name__)
+
+
+class _RedisStub:
+    """Stub of a Redis client.
+
+    It's purpose is to prevent EventSeries objects from trying to access Redis
+    when it is not available. e.g. when the Sphinx docs are rendered by readthedocs.org.
+    """
+
+    IS_STUB = True
+
+    def delete(self, *args, **kwargs):
+        pass
+
+    def incr(self, *args, **kwargs):
+        return 0
+
+    def zadd(self, *args, **kwargs):
+        pass
+
+    def zcount(self, *args, **kwargs):
+        pass
+
+    def zrangebyscore(self, *args, **kwargs):
+        pass
+
 
 class ItemCounter:
-    """A process safe item counter."""
+    """A process safe item counter.
+
+    Args:
+        - name: Unique name for the counter
+        - minimum: Counter can not go below the minimum, when set
+        - redis: A Redis client. Will use AA's cache client by default
+    """
 
     CACHE_KEY_BASE = "allianceauth-item-counter"
     DEFAULT_CACHE_TIMEOUT = 24 * 3600
 
-    def __init__(self, name: str) -> None:
+    def __init__(
+        self, name: str, minimum: Optional[int] = None, redis: Optional[Redis] = None
+    ) -> None:
         if not name:
             raise ValueError("Must define a name")
 
         self._name = str(name)
+        self._minimum = minimum
+        self._redis = redis if redis else get_redis_client()
 
     @property
     def _cache_key(self) -> str:
@@ -23,6 +64,9 @@ class ItemCounter:
 
     def reset(self, init_value: int = 0):
         """Reset counter to initial value."""
+        if self._minimum is not None and init_value < self._minimum:
+            raise ValueError("Can not reset below minimum")
+
         cache.set(self._cache_key, init_value, self.DEFAULT_CACHE_TIMEOUT)
 
     def incr(self, delta: int = 1):
@@ -34,6 +78,8 @@ class ItemCounter:
 
     def decr(self, delta: int = 1):
         """Decrement counter by delta."""
+        if self._minimum is not None and self.value() == self._minimum:
+            return
         try:
             cache.decr(self._cache_key, delta)
         except ValueError:
@@ -42,3 +88,18 @@ class ItemCounter:
     def value(self) -> Optional[int]:
         """Return current value or None if not yet initialized."""
         return cache.get(self._cache_key)
+
+
+def get_redis_client_or_stub():
+    """Return AA's default cache client or a stub if Redis is not available."""
+    redis = get_redis_client()
+    try:
+        if not redis.ping():
+            raise RuntimeError()
+    except (AttributeError, RedisError, RuntimeError):
+        logger.exception(
+            "Failed to establish a connection with Redis. "
+            "This EventSeries object is disabled.",
+        )
+        return _RedisStub()
+    return redis