add skeleton

services.py

@@ -0,0 +1,21 @@
+class InvoiceService:
+    def create_invoice(self) -> str:
+        return "invoice created by service"
+
+
+class EmailService:
+    def send(self, receiver, invoice) -> None:
+        print(f'e-mail service is sending "{invoice}" to "{receiver}"')
+
+
+class BusinessLogic:
+    def __init__(self, invoice: InvoiceService, email: EmailService) -> None:
+        self.email_service = email
+        self.invoice_service = invoice
+
+    def send(self, email_address) -> None:
+        print('create invoice')
+        invoice = self.invoice_service.create_invoice()
+        print(f'sending invoice "{invoice}" to "{email_address}"')
+        self.email_service.send(email_address, invoice)
+        print('wat fott is is fott')