Add external product prices (#47)

Co-authored-by: Niklas Fondberg <niklas.fondberg@photowall.se>

api/lib/utils.py

@@ -1,5 +1,25 @@
 from decimal import Decimal, ROUND_HALF_UP
+import time
+from functools import lru_cache
 
 
 def round_half_up(val):
     return int(Decimal(val).quantize(0, ROUND_HALF_UP))
+
+
+def lru_with_ttl(*, ttl_seconds, maxsize=128):
+    """
+    A decorator to apply LRU in-memory cache to a function with defined maximum(!) TTL in seconds.
+    Be design an actual TTL may be shorter then the passed value (in rare randomized cases). But it can't be higher.
+    :param ttl_seconds: TTL for a cache record in seconds
+    :param maxsize: Maximum size of the LRU cache (a functools.lru_cache argument)
+    :return: decorated function
+    """
+    def deco(foo):
+        @lru_cache(maxsize=maxsize)
+        def cached_with_ttl(*args, ttl_hash, **kwargs):
+            return foo(*args, **kwargs)
+        def inner(*args, **kwargs):
+            return cached_with_ttl(*args, ttl_hash=round(time.time() / ttl_seconds), **kwargs)
+        return inner
+    return deco