From c7a15701a5cc6533e67cd1ae58809a4b048c35b2 Mon Sep 17 00:00:00 2001
From: Clemens Wolff <clewolff@microsoft.com>
Date: Sun, 25 Nov 2018 22:11:23 -0500
Subject: [PATCH] Make singleton decorator explicit

---
 opwen_email_server/integration/azure.py       | 11 ++++----
 opwen_email_server/utils/collections.py       |  6 ++++
 opwen_email_server/utils/log.py               |  8 +++---
 .../utils/test_collections.py                 | 28 +++++++++++++++++++
 4 files changed, 44 insertions(+), 9 deletions(-)

diff --git a/opwen_email_server/integration/azure.py b/opwen_email_server/integration/azure.py
index 70b54abe..127be50a 100644
--- a/opwen_email_server/integration/azure.py
+++ b/opwen_email_server/integration/azure.py
@@ -8,9 +8,10 @@
 from opwen_email_server.services.storage import AzureObjectStorage
 from opwen_email_server.services.storage import AzureObjectsStorage
 from opwen_email_server.services.storage import AzureTextStorage
+from opwen_email_server.utils.collections import singleton
 
 
-@lru_cache(maxsize=1)
+@singleton
 def get_auth() -> AzureAuth:
     return AzureAuth(
         storage=AzureTextStorage(
@@ -20,7 +21,7 @@ def get_auth() -> AzureAuth:
             provider=config.STORAGE_PROVIDER))
 
 
-@lru_cache(maxsize=1)
+@singleton
 def get_client_storage() -> AzureObjectsStorage:
     return AzureObjectsStorage(
         file_storage=AzureFileStorage(
@@ -30,7 +31,7 @@ def get_client_storage() -> AzureObjectsStorage:
             provider=config.STORAGE_PROVIDER))
 
 
-@lru_cache(maxsize=1)
+@singleton
 def get_raw_email_storage() -> AzureTextStorage:
     return AzureTextStorage(
         account=config.BLOBS_ACCOUNT,
@@ -39,13 +40,13 @@ def get_raw_email_storage() -> AzureTextStorage:
         provider=config.STORAGE_PROVIDER)
 
 
-@lru_cache(maxsize=1)
+@singleton
 def get_email_sender() -> SendgridEmailSender:
     return SendgridEmailSender(
         key=config.SENDGRID_KEY)
 
 
-@lru_cache(maxsize=1)
+@singleton
 def get_email_storage() -> AzureObjectStorage:
     return AzureObjectStorage(
         text_storage=AzureTextStorage(
diff --git a/opwen_email_server/utils/collections.py b/opwen_email_server/utils/collections.py
index 9a4ed92c..1a26bae1 100644
--- a/opwen_email_server/utils/collections.py
+++ b/opwen_email_server/utils/collections.py
@@ -1,4 +1,6 @@
+from functools import lru_cache
 from itertools import islice
+from typing import Callable
 from typing import Iterable
 from typing import Optional
 from typing import TypeVar
@@ -18,3 +20,7 @@ def chunks(iterable: Iterable[T], chunk_size: int) -> Iterable[Iterable[T]]:
         if not chunk:
             return
         yield chunk
+
+
+def singleton(func: Callable) -> Callable:
+    return lru_cache(maxsize=1)(func)
diff --git a/opwen_email_server/utils/log.py b/opwen_email_server/utils/log.py
index 61b12abe..98c6bf74 100644
--- a/opwen_email_server/utils/log.py
+++ b/opwen_email_server/utils/log.py
@@ -1,4 +1,3 @@
-from functools import lru_cache
 from logging import Formatter
 from logging import Handler
 from logging import Logger
@@ -17,16 +16,17 @@
 from opwen_email_server.constants.logging import STDERR
 from opwen_email_server.constants.logging import TELEMETRY_QUEUE_ITEMS
 from opwen_email_server.constants.logging import TELEMETRY_QUEUE_SECONDS
+from opwen_email_server.utils.collections import singleton
 
 
-@lru_cache(maxsize=1)
+@singleton
 def _get_log_handlers() -> Iterable[Handler]:
     stderr = StreamHandler()
     stderr.setFormatter(Formatter(STDERR))
     return [stderr]
 
 
-@lru_cache(maxsize=1)
+@singleton
 def _get_logger() -> Logger:
     log = getLogger()
     for handler in _get_log_handlers():
@@ -35,7 +35,7 @@ def _get_logger() -> Logger:
     return log
 
 
-@lru_cache(maxsize=1)
+@singleton
 def _get_telemetry_client() -> Optional[TelemetryClient]:
     if not APPINSIGHTS_KEY:
         return None
diff --git a/tests/opwen_email_server/utils/test_collections.py b/tests/opwen_email_server/utils/test_collections.py
index 5469e74b..33a839b7 100644
--- a/tests/opwen_email_server/utils/test_collections.py
+++ b/tests/opwen_email_server/utils/test_collections.py
@@ -1,3 +1,4 @@
+from collections import Counter
 from unittest import TestCase
 
 from opwen_email_server.utils import collections
@@ -29,3 +30,30 @@ def test_creates_nonfull_chunks(self):
         chunks = collections.chunks([1, 2, 3, 4], 3)
 
         self.assertEqual(list(chunks), [(1, 2, 3), (4, )])
+
+
+class SingletonTests(TestCase):
+    def test_creates_object_only_once(self):
+        value1 = self.function1()
+        value2 = self.function1()
+        value3 = self.function2()
+        value4 = self.function2()
+
+        self.assertIs(value1, value2)
+        self.assertIs(value3, value4)
+        self.assertIsNot(value1, value3)
+        self.assertEqual(self.call_counts['function1'], 1)
+        self.assertEqual(self.call_counts['function2'], 1)
+
+    def setUp(self):
+        self.call_counts = Counter()
+
+    @collections.singleton
+    def function1(self):
+        self.call_counts['function1'] += 1
+        return 'some-value'
+
+    @collections.singleton
+    def function2(self):
+        self.call_counts['function2'] += 1
+        return 'some-other-value'