Apply singleton pattern to data source

Author: antheia-z

app/data/__init__.py

@@ -1,31 +1,102 @@
 """app.data"""
-from ..services.location import LocationService
+from abc import ABC, abstractmethod
 from ..services.location.csbs import CSBSLocationService
 from ..services.location.jhu import JhuLocationService
 from ..services.location.nyt import NYTLocationService
 
-class dataSourceFactory():
-    def getDataSource():
-        return LocationService()
+class DataSourceFactory(ABC):
+    def __init__(self):
+        pass
+   
+    @abstractmethod 
+    def getInstance():
+        pass
 
-class JhuFactory(dataSourceFactory):
-    def getDataSource():
-        return JhuLocationService()
+    @abstractmethod
+    def getService():
+        pass
 
-class CSBSFactory(dataSourceFactory):
-    def getDataSource():
-        return CSBSLocationService()
+class JhuFactory(DataSourceFactory):
+    __instance = None
+    __service = None
 
-class NYTFactory(dataSourceFactory):
-    def getDataSource():
-        return NYTLocationService()
+    def __init__(self):
+        if JhuFactory.__instance != None:
+            raise Exception("Factory is singleton!")
+        elif JhuFactory.__service != None:
+            raise Exception("Service is singleton!")
+        else:
+            JhuFactory.__instance = self
+            JhuFactory.__service = JhuLocationService()
+        
+    @staticmethod 
+    def getInstance():
+      if JhuFactory.__instance == None:
+         JhuFactory()
+      return JhuFactory.__instance
+        
+    @staticmethod 
+    def getService():
+      if JhuFactory.__service == None:
+         JhuFactory()
+      return JhuFactory.__service
+
+class CSBSFactory(DataSourceFactory):
+    __instance = None
+    __service = None
+
+    def __init__(self):
+        if CSBSFactory.__instance != None:
+            raise Exception("Factory is singleton!")
+        elif CSBSFactory.__service != None:
+            raise Exception("Service is singleton!")
+        else:
+            CSBSFactory.__instance = self
+            CSBSFactory.__service = CSBSLocationService()
+   
+    @staticmethod 
+    def getInstance():
+      if CSBSFactory.__instance == None:
+         CSBSFactory()
+      return CSBSFactory.__instance
+
+    @staticmethod 
+    def getService():
+      if CSBSFactory.__service == None:
+         CSBSFactory()
+      return CSBSFactory.__service
+
+class NYTFactory(DataSourceFactory):
+    __instance = None
+    __service = None
+
+    def __init__(self):
+        if NYTFactory.__instance != None:
+            raise Exception("Factory is singleton!")
+        elif NYTFactory.__service != None:
+            raise Exception("Service is singleton!")
+        else:
+            NYTFactory.__instance = self
+            NYTFactory.__service = NYTLocationService()
+   
+    @staticmethod 
+    def getInstance():
+      if NYTFactory.__instance == None:
+         NYTFactory()
+      return NYTFactory.__instance
+
+    @staticmethod 
+    def getService():
+      if NYTFactory.__service == None:
+         NYTFactory()
+      return NYTFactory.__service
 
 
 # Mapping of factories to data-sources.
 DATA_SOURCES = {
-    "jhu": JhuFactory(),
-    "csbs": CSBSFactory(),
-    "nyt": NYTFactory(),
+    "jhu": JhuFactory.getInstance(),
+    "csbs": CSBSFactory.getInstance(),
+    "nyt": NYTFactory.getInstance(),
 }
 
 def data_source(source):
@@ -35,4 +106,4 @@ def data_source(source):
     :returns: The service.
     :rtype: LocationService
     """
-    return DATA_SOURCES.get(source.lower()).getDataSource()
+    return DATA_SOURCES.get(source.lower()).getService()