Paginate the function to get all complaints

The DAO function to get all complaints has been paginated and the
endpoint which uses it has been updated to take a page number as a query
parameter.

tests/app/complaint/test_complaint_rest.py

@@ -8,7 +8,7 @@ from tests import create_authorization_header
 from tests.app.db import create_complaint, create_service, create_template, create_notification
 
 
-def test_get_all_complaints_returns_list_for_multiple_services_and_complaints(client, notify_db_session):
+def test_get_all_complaints_returns_complaints_for_multiple_services(client, notify_db_session):
     service = create_service(service_name='service1')
     template = create_template(service=service)
     notification = create_notification(template=template)
@@ -18,14 +18,33 @@ def test_get_all_complaints_returns_list_for_multiple_services_and_complaints(cl
     response = client.get('/complaint', headers=[create_authorization_header()])
 
     assert response.status_code == 200
-    assert json.loads(response.get_data(as_text=True)) == [complaint_2.serialize(), complaint_1.serialize()]
+    assert json.loads(response.get_data(as_text=True))['complaints'] == [
+        complaint_2.serialize(), complaint_1.serialize()]
 
 
-def test_get_all_complaints_returns_empty_list(client):
+def test_get_all_complaints_returns_empty_complaints_list(client):
     response = client.get('/complaint', headers=[create_authorization_header()])
 
     assert response.status_code == 200
-    assert json.loads(response.get_data(as_text=True)) == []
+    assert json.loads(response.get_data(as_text=True))['complaints'] == []
+
+
+def test_get_all_complaints_returns_pagination_links(mocker, client, notify_db_session):
+    mocker.patch.dict('app.dao.complaint_dao.current_app.config', {'PAGE_SIZE': 1})
+    service_1 = create_service(service_name='service1')
+    service_2 = create_service(service_name='service2')
+
+    create_complaint()
+    create_complaint(service=service_1)
+    create_complaint(service=service_2)
+
+    response = client.get(url_for('complaint.get_all_complaints', page=2), headers=[create_authorization_header()])
+
+    assert response.status_code == 200
+    assert json.loads(response.get_data(as_text=True))['links'] == {
+        'last': '/complaint?page=3',
+        'next': '/complaint?page=3',
+        'prev': '/complaint?page=1'}
 
 
 def test_get_complaint_with_start_and_end_date_passes_these_to_dao_function(mocker, client):

tests/app/dao/test_complaint_dao.py

@@ -2,11 +2,40 @@ import uuid
 
 from datetime import datetime, timedelta
 
-from app.dao.complaint_dao import save_complaint, fetch_complaints_by_service, fetch_count_of_complaints
+from app.dao.complaint_dao import (
+    fetch_complaints_by_service,
+    fetch_count_of_complaints,
+    fetch_paginated_complaints,
+    save_complaint,
+)
 from app.models import Complaint
 from tests.app.db import create_service, create_template, create_notification, create_complaint
 
 
+def test_fetch_paginated_complaints(mocker, sample_email_notification):
+    mocker.patch.dict('app.dao.complaint_dao.current_app.config', {'PAGE_SIZE': 2})
+    create_complaint(service=sample_email_notification.service,
+                     notification=sample_email_notification,
+                     created_at=datetime(2018, 1, 1))
+    create_complaint(service=sample_email_notification.service,
+                     notification=sample_email_notification,
+                     created_at=datetime(2018, 1, 2))
+    create_complaint(service=sample_email_notification.service,
+                     notification=sample_email_notification,
+                     created_at=datetime(2018, 1, 3))
+
+    res = fetch_paginated_complaints(page=1)
+
+    assert len(res.items) == 2
+    assert res.items[0].created_at == datetime(2018, 1, 3)
+    assert res.items[1].created_at == datetime(2018, 1, 2)
+
+    res = fetch_paginated_complaints(page=2)
+
+    assert len(res.items) == 1
+    assert res.items[0].created_at == datetime(2018, 1, 1)
+
+
 def test_fetch_complaint_by_service_returns_one(sample_service, sample_email_notification):
     complaint = Complaint(notification_id=sample_email_notification.id,
                           service_id=sample_service.id,