Add SMTPService and Email helper

* Email helper class that wraps EmailMessage

* SMTPService class that creates connection to
  SMTP server using config options in services.smtp

* send method on SMTPService that takes Email as
  an arg to send an email using the SMTP connection

Signed-off-by: joseph-sentry <[email protected]>

conftest.py

@@ -134,6 +134,12 @@ def mock_configuration(mocker):
                 "verify_ssl": False,
             },
             "redis_url": "redis://redis:@localhost:6379/",
+            "smtp": {
+                "host": "testserver",
+                "port": 12345,
+                "username": None,
+                "password": None,
+            },
         },
         "setup": {
             "codecov_url": "https://codecov.io",

helpers/email.py

@@ -0,0 +1,13 @@
+from email.message import EmailMessage
+
+
+class Email:
+    def __init__(
+        self, to_addr=None, from_addr=None, subject=None, text=None, html=None
+    ):
+        self.message = EmailMessage()
+        self.message["To"] = to_addr
+        self.message["From"] = from_addr
+        self.message["Subject"] = subject
+        self.message.set_content(text)
+        self.message.add_alternative(html, "text/html")

services/smtp.py

@@ -0,0 +1,44 @@
+import smtplib
+import ssl
+from functools import cached_property
+
+from shared.config import get_config
+
+from helpers.email import Email
+
+_smtp_service = None
+
+
+def get_smtp_service():
+    if len(get_config("services", "smtp", default={})) == 0:
+        return None
+    return _get_cached_smtp_service()
+
+
+def _get_cached_smtp_service():
+    global _smtp_service
+    if _smtp_service is None:
+        _smtp_service = SMTPService()
+    return _smtp_service
+
+
+class SMTPService:
+    def __init__(self):
+        self.host = get_config("services", "smtp", "host", default="mailhog")
+        self.port = get_config("services", "smtp", "port", default=1025)
+        self.username = get_config("services", "smtp", "username", default=None)
+        self.password = get_config("services", "smtp", "password", default=None)
+        self.ssl_context = ssl.create_default_context()
+
+        self._conn = smtplib.SMTP(
+            host=self.host,
+            port=self.port,
+        )
+        self._conn.starttls(context=self.ssl_context)
+        if self.username and self.password:
+            self._conn.login(self.username, self.password)
+
+    def send(self, email: Email):
+        return self._conn.send_message(
+            email.message,
+        )

services/tests/test_smtp.py

@@ -0,0 +1,26 @@
+from ssl import create_default_context
+from unittest.mock import MagicMock, call
+
+from services.smtp import get_smtp_service
+
+
+class TestStorage(object):
+    def test_correct_init(self, mocker, mock_configuration):
+        mocker.patch("smtplib.SMTP")
+        m = mocker.patch("ssl.create_default_context", return_value=MagicMock())
+        service = get_smtp_service()
+        service._conn.starttls.assert_called_with(context=m.return_value)
+
+    def test_idempotent_service(self, mocker, mock_configuration):
+        mocker.patch("smtplib.SMTP")
+        first = get_smtp_service()
+        second = get_smtp_service()
+        assert id(first) == id(second)
+
+    def test_idempotent_connection(self, mocker, mock_configuration):
+        mocker.patch("smtplib.SMTP")
+        first = get_smtp_service()
+        first_conn = first._conn
+        second = get_smtp_service()
+        second_conn = second._conn
+        assert id(first_conn) == id(second_conn)