URI shortcut for upcoming category event

- This resolves indico#3388.

indico/modules/categories/blueprint.py

@@ -22,11 +22,11 @@
 from indico.modules.categories.controllers.admin import RHManageUpcomingEvents
 from indico.modules.categories.controllers.display import (RHCategoryCalendarView, RHCategoryIcon, RHCategoryInfo,
                                                            RHCategoryLogo, RHCategoryOverview, RHCategorySearch,
-                                                           RHCategoryStatistics, RHDisplayCategory, RHEventList,
-                                                           RHExportCategoryAtom, RHExportCategoryICAL,
-                                                           RHReachableCategoriesInfo, RHShowFutureEventsInCategory,
-                                                           RHShowPastEventsInCategory, RHSubcatInfo,
-                                                           RHXMLExportCategoryInfo)
+                                                           RHCategoryStatistics, RHCategoryUpcomingEvent,
+                                                           RHDisplayCategory, RHEventList, RHExportCategoryAtom,
+                                                           RHExportCategoryICAL, RHReachableCategoriesInfo,
+                                                           RHShowFutureEventsInCategory, RHShowPastEventsInCategory,
+                                                           RHSubcatInfo, RHXMLExportCategoryInfo)
 from indico.modules.categories.controllers.management import (RHCreateCategory, RHDeleteCategory, RHDeleteEvents,
                                                               RHDeleteSubcategories, RHManageCategoryContent,
                                                               RHManageCategoryIcon, RHManageCategoryLogo,
@@ -46,6 +46,9 @@ def _redirect_event_creation(category_id, event_type):
 _bp = IndicoBlueprint('categories', __name__, template_folder='templates', virtual_template_folder='categories',
                       url_prefix='/category/<int:category_id>')
 
+# Upcoming event of the category
+_bp.add_url_rule('/upcoming', 'category_upcoming', RHCategoryUpcomingEvent, methods=('GET',))
+
 # Category management
 _bp.add_url_rule('/manage/', 'manage_content', RHManageCategoryContent)
 _bp.add_url_rule('/manage/delete', 'delete', RHDeleteCategory, methods=('POST',))

indico/modules/categories/controllers/display.py

@@ -26,13 +26,14 @@
 
 import dateutil
 from dateutil.relativedelta import relativedelta
-from flask import Response, jsonify, request, session
+from flask import Response, flash, jsonify, redirect, request, session
 from pytz import utc
 from sqlalchemy.orm import joinedload, load_only, subqueryload, undefer, undefer_group
 from werkzeug.exceptions import BadRequest, NotFound
 
 from indico.core.db import db
 from indico.core.db.sqlalchemy.colors import ColorTuple
+from indico.core.db.sqlalchemy.util.queries import get_n_matching
 from indico.modules.categories.controllers.base import RHDisplayCategoryBase
 from indico.modules.categories.legacy import XMLCategorySerializer
 from indico.modules.categories.models.categories import Category
@@ -670,3 +671,27 @@ def _get_event_data(self, event_query):
     def _render_ongoing_events(self, ongoing_events):
         template = get_template_module('categories/display/_calendar_ongoing_events.html')
         return template.render_ongoing_events(ongoing_events, self.category.display_tzinfo)
+
+
+class RHCategoryUpcomingEvent(RHDisplayCategoryBase):
+    """Redirect to the upcoming event of a category."""
+
+    def _process(self):
+        event_id = self._get_upcoming_event()
+        if event_id:
+            resp = redirect(url_for('events.display', confId=event_id))
+        else:
+            flash(_('There are no upcoming events for this category'))
+            resp = redirect(url_for('categories.display', category_id=self.category.id))
+        return resp
+
+    def _get_upcoming_event(self):
+        query = (Event.query
+                 .filter(Event.is_visible_in(self.category),
+                         Event.start_dt > now_utc())
+                 .options(load_only('id', 'start_dt'))
+                 .order_by(Event.start_dt)
+                 .order_by(Event.id))  # in case two events start exactly at the same time
+        res = get_n_matching(query, 1, lambda event: event.can_access(session.user))
+        if res:
+            return res[0].id