upgrades: Show notification when FreedomBox is updated

- Don't not show notification on first install/run.

- Shows notification when upgrading or downgrading.

- This also serves as an example of how to show more specific notifications when
  upgraded to a newer version. Closes: 1637.

Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

plinth/modules/upgrades/__init__.py

@@ -19,7 +19,9 @@ FreedomBox app for upgrades.
 """
 
 from django.utils.translation import ugettext_lazy as _
+from django.utils.translation import ugettext_noop
 
+import plinth
 from plinth import actions
 from plinth import app as app_module
 from plinth import menu
@@ -55,6 +57,37 @@ class UpgradesApp(app_module.App):
                               'upgrades:index', parent_url_name='system')
         self.add(menu_item)
 
+        self._show_new_release_notification()
+
+    def _show_new_release_notification(self):
+        """When upgraded to new release, show a notification."""
+        from plinth.notification import Notification
+        try:
+            note = Notification.get('upgrades-new-release')
+            if note.data['version'] == plinth.__version__:
+                # User already has notification for update to this version. It
+                # may be dismissed or not yet dismissed
+                return
+
+            # User currently has a notification for an older version, update.
+            dismiss = False
+        except KeyError:
+            # Don't show notification for the first version user runs, create
+            # but don't show it.
+            dismiss = True
+
+        data = {
+            'version': plinth.__version__,
+            'app_name': 'Update',
+            'app_icon': 'fa-refresh'
+        }
+        title = ugettext_noop('FreedomBox Updated')
+        note = Notification.update_or_create(
+            id='upgrades-new-release', app_id='upgrades', severity='info',
+            title=title, body_template='upgrades-new-release.html', data=data,
+            group='admin')
+        note.dismiss(should_dismiss=dismiss)
+
 
 def init():
     """Initialize the module."""

plinth/modules/upgrades/templates/upgrades-new-release.html

@@ -0,0 +1,39 @@
+{% comment %}
+#
+# This file is part of FreedomBox.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+{% endcomment %}
+
+{% load i18n %}
+{% load static %}
+
+<div class="notification-title">
+  {% blocktrans %}{{box_name}} Updated{% endblocktrans %}
+</div>
+
+<p>
+  {% blocktrans trimmed with url="https://discuss.freedombox.org/c/announcements/7" %}
+    {{ box_name }} has been updated to version {{ version }}. See the
+    <a href="{{ url }}">release announcement</a>.
+  {% endblocktrans %}
+</p>
+
+<p>
+  <a href="{% url 'notification_dismiss' id='upgrades-new-release' %}?next={{ request.path|iriencode }}"
+     role="button" class="btn btn-default">
+    {% trans "Dismiss" %}
+  </a>
+</p>