EECS 3311: Creational Design Pattern - Singleton

Author: DukeM23

app/data/__init__.py

@@ -3,19 +3,34 @@
 from ..services.location.jhu import JhuLocationService
 from ..services.location.nyt import NYTLocationService
 
-# Mapping of services to data-sources.
-DATA_SOURCES = {
-    "jhu": JhuLocationService(),
-    "csbs": CSBSLocationService(),
-    "nyt": NYTLocationService(),
-}
+class DataSourceSingletonMeta(type):
+    """
+    access point to the DataSourceSingleton
+    """
+    _instances = {}
 
+    def __call__(cls, *args, **kwargs):
+        """
+        Possible changes to the value of the `__init__` argument do not affect
+        the returned instance.
+        """
+        if cls not in cls._instances:
+            instance = super().__call__(*args, **kwargs)
+            cls._instances[cls] = instance
+        return cls._instances[cls]
 
-def data_source(source):
-    """
-    Retrieves the provided data-source service.
 
-    :returns: The service.
-    :rtype: LocationService
-    """
-    return DATA_SOURCES.get(source.lower())
+class DataSourceSingleton(metaclass=DataSourceSingletonMeta):
+        DATA_SOURCES = {
+            "jhu": JhuLocationService(),
+            "csbs": CSBSLocationService(),
+            "nyt": NYTLocationService(),
+        }
+        def get_data_source(self, dataSource):
+            return self.DATA_SOURCES.get(dataSource.lower())
+        ...
+
+        def get_data_source_list(self): 
+            return self.DATA_SOURCES
+
+        

app/main.py

@@ -14,7 +14,8 @@
 from sentry_sdk.integrations.asgi import SentryAsgiMiddleware
 
 from .config import get_settings
-from .data import data_source
+# from .data import data_source
+from .data import DataSourceSingleton
 from .routers import V1, V2
 from .utils.httputils import setup_client_session, teardown_client_session
 
@@ -73,8 +74,12 @@ async def add_datasource(request: Request, call_next):
     """
     Attach the data source to the request.state.
     """
+
+
+
     # Retrieve the datas ource from query param.
-    source = data_source(request.query_params.get("source", default="jhu"))
+    source = DataSourceSingleton().get_data_source(request.query_params.get("source", default="jhu"))
+    # data_source(request.query_params.get("source", default="jhu"))
 
     # Abort with 404 if source cannot be found.
     if not source:

app/routers/v2.py

@@ -3,7 +3,7 @@
 
 from fastapi import APIRouter, HTTPException, Request
 
-from ..data import DATA_SOURCES
+from ..data import DataSourceSingleton
 from ..models import LatestResponse, LocationResponse, LocationsResponse
 
 V2 = APIRouter()
@@ -107,4 +107,4 @@ async def sources():
     """
     Retrieves a list of data-sources that are availble to use.
     """
-    return {"sources": list(DATA_SOURCES.keys())}
+    return {"sources": list(DataSourceSingleton().get_data_source_list().keys())}