Create 'v2' get notification route

The new 'v2' API wants to return less data than the previous one,
which was sending back tons of fields the clients never used.

This new route returns only useful information, with the JSON
response dict being built up in the model's `.serialize()` method.

Note that writing the test for this was a bit painful because of
having to treat loads of keys differently. Hopefully we think this
is a good way to write this test, because if we don't, we should
start thinking of a better way to check the values are what we
expect.

app/models.py

@@ -1,5 +1,6 @@
 import uuid
 import datetime
+from flask import url_for
 
 from sqlalchemy.dialects.postgresql import (
     UUID,
@@ -22,7 +23,8 @@ from app.authentication.utils import get_secret
 from app import (
     db,
     encryption,
-    DATETIME_FORMAT)
+    DATETIME_FORMAT
+)
 
 from app.history_meta import Versioned
 
@@ -281,6 +283,10 @@ class Template(db.Model):
     created_by = db.relationship('User')
     version = db.Column(db.Integer, default=1, nullable=False)
 
+    def get_link(self):
+        # TODO: use "/v2/" route once available
+        return url_for("template.get_template_by_id_and_service_id", service_id=self.service_id, template_id=self.id)
+
 
 class TemplateHistory(db.Model):
     __tablename__ = 'templates_history'
@@ -553,6 +559,49 @@ class Notification(db.Model):
 
         return provider_rate.rate * self.billable_units
 
+    def completed_at(self):
+        if self.status in [
+            NOTIFICATION_DELIVERED,
+            NOTIFICATION_FAILED,
+            NOTIFICATION_TECHNICAL_FAILURE,
+            NOTIFICATION_TEMPORARY_FAILURE,
+            NOTIFICATION_PERMANENT_FAILURE
+        ]:
+            return self.updated_at.strftime(DATETIME_FORMAT)
+
+        return None
+
+    def serialize(self):
+
+        template_dict = {
+            'version': self.template.version,
+            'id': self.template.id,
+            'uri': self.template.get_link()
+        }
+
+        serialized = {
+            "id": self.id,
+            "reference": self.client_reference,
+            "email_address": self.to if self.notification_type == EMAIL_TYPE else None,
+            "phone_number": self.to if self.notification_type == SMS_TYPE else None,
+            "line_1": None,
+            "line_2": None,
+            "line_3": None,
+            "line_4": None,
+            "line_5": None,
+            "line_6": None,
+            "postcode": None,
+            "cost": self.cost(),
+            "type": self.notification_type,
+            "status": self.status,
+            "template": template_dict,
+            "created_at": self.created_at.strftime(DATETIME_FORMAT),
+            "sent_at": self.sent_at.strftime(DATETIME_FORMAT) if self.sent_at else None,
+            "completed_at": self.completed_at()
+        }
+
+        return serialized
+
 
 class NotificationHistory(db.Model):
     __tablename__ = 'notification_history'