Go back to template after editing contact details

Users who go to edit the contact details for a letter from the template
page get very confused when they click save and are dumped on the
settings page. It doesn’t match the way editing other parts of
letter works, and you can’t see an accurate preview of the changes from
the settings page.

So this commit changes the flow to go from the _edit contact details_
page back to the _view template_ page when the user has got there by
clicking the blue _Edit_ button on the _view template_ page.

app/main/views/service_settings.py

@@ -275,6 +275,10 @@ def service_set_letter_contact_block(service_id):
             current_service['id'],
             letter_contact_block=form.letter_contact_block.data.replace('\r', '') or None
         )
+        if request.args.get('from_template'):
+            return redirect(
+                url_for('.view_template', service_id=service_id, template_id=request.args.get('from_template'))
+            )
         return redirect(url_for('.service_settings', service_id=service_id))
     return render_template(
         'views/service-settings/set-letter-contact-block.html',

app/templates/views/templates/_template.html

@@ -35,7 +35,7 @@
 <div class="column-whole template-container">
   {% if current_user.has_permissions(permissions=['manage_templates'], admin_override=True) and template.template_type == 'letter' %}
     <a href="{{ url_for(".edit_service_template", service_id=current_service.id, template_id=template.id) }}" class="edit-template-link-letter-body">Edit</a>
-    <a href="{{ url_for(".service_set_letter_contact_block", service_id=current_service.id) }}" class="edit-template-link-letter-contact">Edit</a>
+    <a href="{{ url_for(".service_set_letter_contact_block", service_id=current_service.id, from_template=template.id) }}" class="edit-template-link-letter-contact">Edit</a>
     <a href="#" class="edit-template-link-letter-address">Edit</a>
   {% endif %}
   {{ template|string }}

tests/app/main/views/test_service_settings.py

@@ -1,6 +1,7 @@
 from unittest.mock import call, ANY, Mock
 
 import pytest
+import uuid
 from flask import url_for
 from bs4 import BeautifulSoup
 from werkzeug.exceptions import InternalServerError
@@ -619,6 +620,30 @@ def test_set_letter_contact_block_saves(
     mock_update_service.assert_called_once_with(service_one['id'], letter_contact_block='foo bar baz waz')
 
 
+def test_set_letter_contact_block_redirects_to_template(
+    logged_in_client,
+    service_one,
+    mock_update_service,
+):
+    service_one['can_send_letters'] = True
+    fake_template_id = uuid.uuid4()
+    response = logged_in_client.post(
+        url_for(
+            'main.service_set_letter_contact_block',
+            service_id=service_one['id'],
+            from_template=fake_template_id,
+        ),
+        data={'letter_contact_block': ''},
+    )
+    assert response.status_code == 302
+    assert response.location == url_for(
+        'main.view_template',
+        service_id=service_one['id'],
+        template_id=fake_template_id,
+        _external=True,
+    )
+
+
 def test_set_letter_contact_block_has_max_10_lines(
     logged_in_client,
     service_one,