events preview displayed in the agenda

Closes #3881

tabellio/agenda/event.py

@@ -101,6 +101,16 @@ class BaseEvent(Item):
             return 'today'
         return ''
 
+    def preview(self):
+        n = 3
+
+        def nth_position(string, sub, n, pos = 0):
+            if n:
+                sliced_from = string.find(sub) + len(sub)
+                return pos + nth_position(string[sliced_from:],
+                                          sub, n-1, sliced_from)
+            return pos
+        return self.text.output[:nth_position(self.text.output, '</p>', n)]
 
 class Event(BaseEvent):
     implements(IEvent)

tabellio/agenda/folder_templates/view.pt

@@ -126,6 +126,7 @@
                                class string:d-${event/start/year}-${event/start/month}-${event/start/day}">
              <h3><span tal:content="event/longdatetime"/> <span tal:content="event/title"/></h3>
              <p tal:condition="event/place" class="place" tal:content="event/place"></p>
+             <span tal:condition="event/text" class="preview" tal:content="structure event/preview"></span>
              <a href="#" class="event-details" tal:attributes="href event/absolute_url">Détail de l'événement</a>
              <span class="closediv"/>
           </div>