middleware: New middleware to check need for setup

- Call the setup helper to check if a installation or update of a module
  is required.

- Show installation and progress using the setup view.

plinth/__main__.py

@@ -256,6 +256,7 @@ def configure_django():
             'django.middleware.clickjacking.XFrameOptionsMiddleware',
             'stronghold.middleware.LoginRequiredMiddleware',
             'plinth.modules.first_boot.middleware.FirstBootMiddleware',
+            'plinth.middleware.SetupMiddleware',
         ),
         ROOT_URLCONF='plinth.urls',
         SECURE_PROXY_SSL_HEADER=secure_proxy_ssl_header,

plinth/middleware.py

@@ -0,0 +1,75 @@
+#
+# This file is part of Plinth.
+#
+# 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/>.
+#
+
+"""
+Django middleware to show pre-setup message and setup progress.
+"""
+
+from django.contrib import messages
+from django.core.urlresolvers import resolve
+from django.utils.translation import ugettext_lazy as _
+import logging
+
+import plinth
+from plinth.package import PackageException
+from . import views
+
+
+logger = logging.getLogger(__name__)
+
+
+class SetupMiddleware(object):
+    """Show setup page or progress if setup is neccessary or running."""
+
+    @staticmethod
+    def process_request(request):
+        """Handle a request as Django middleware request handler."""
+        # Perform a URL resolution. This is slightly inefficient as
+        # Django will do this resolution again.
+        resolver_match = resolve(request.path_info)
+        if not resolver_match.namespaces or not len(resolver_match.namespaces):
+            # Requested URL does not belong to any application
+            return
+
+        module_name = resolver_match.namespaces[0]
+        module = plinth.module_loader.loaded_modules[module_name]
+
+        # Collect errors from any previous operations and show them
+        if module.setup_helper.is_finished:
+            exception = module.setup_helper.collect_result()
+            if not exception:
+                messages.success(request, _('Application installed.'))
+            else:
+                if isinstance(exception, PackageException):
+                    error_string = getattr(exception, 'error_string',
+                                           str(exception))
+                    error_details = getattr(exception, 'error_details', '')
+                    message = _('Error installing application: {string} '
+                                '{details}').format(
+                        string=error_string, details=error_details)
+                else:
+                    message = _('Error installing application: {error}') \
+                        .format(error=exception)
+
+                messages.error(request, message)
+
+        # Check if application is up-to-date
+        if module.setup_helper.get_state() == 'up-to-date':
+            return
+
+        view = views.SetupView.as_view()
+        return view(request, setup_helper=module.setup_helper)