lots of typing fixes

app/terraform/bridge/__init__.py

@@ -1,5 +1,5 @@
 import datetime
-from typing import Iterable, Optional, Any
+from typing import Iterable, Optional, Any, List
 
 from app import app
 from app.extensions import db
@@ -9,7 +9,18 @@ from app.terraform.terraform import TerraformAutomation
 
 
 class BridgeAutomation(TerraformAutomation):
-    def create_missing(self):
+    template: str
+    """
+    Terraform configuration template using Jinja 2.
+    """
+
+    template_parameters: List[str]
+    """
+    List of parameters to be read from the application configuration for use
+    in the templating of the Terraform configuration.
+    """
+
+    def create_missing(self) -> None:
         bridgeconfs: Iterable[BridgeConf] = BridgeConf.query.filter(
             BridgeConf.provider == self.provider,
             BridgeConf.destroyed == None
@@ -35,7 +46,7 @@ class BridgeAutomation(TerraformAutomation):
                         break
         db.session.commit()
 
-    def destroy_expired(self):
+    def destroy_expired(self) -> None:
         cutoff = datetime.datetime.utcnow() - datetime.timedelta(days=0)
         bridges = [b for b in Bridge.query.filter(
             Bridge.destroyed == None,
@@ -48,8 +59,9 @@ class BridgeAutomation(TerraformAutomation):
     def tf_prehook(self) -> Optional[Any]:
         self.create_missing()
         self.destroy_expired()
+        return None
 
-    def tf_generate(self):
+    def tf_generate(self) -> None:
         self.tf_write(
             self.template,
             groups=Group.query.all(),