# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1441979373 -7200
# Node ID d3780420461dc68f0c13b0ba92681132ffbe19fc
# Parent  2e36f646bc59f50b014afaa493bec6ad77a66a81
Added support for testing whether a usable object can be handled.

diff -r 2e36f646bc59 -r d3780420461d imiptools/client.py
--- a/imiptools/client.py	Fri Sep 11 13:40:39 2015 +0200
+++ b/imiptools/client.py	Fri Sep 11 15:49:33 2015 +0200
@@ -268,6 +268,12 @@
         self.sequence = obj and self.obj.get_value("SEQUENCE")
         self.dtstamp = obj and self.obj.get_value("DTSTAMP")
 
+    def is_usable(self):
+
+        "Return whether the current object is usable."
+
+        return True
+
     # Object update methods.
 
     def update_recurrenceid(self):
@@ -286,7 +292,7 @@
 
         dtstamp = self.obj.get_utc_datetime("DTSTAMP")
         utcnow = to_timezone(datetime.utcnow(), "UTC")
-        self.dtstamp = format_datetime(dtstamp > utcnow and dtstamp or utcnow)
+        self.dtstamp = format_datetime(dtstamp and dtstamp > utcnow and dtstamp or utcnow)
         self.obj["DTSTAMP"] = [(self.dtstamp, {})]
 
     def set_sequence(self, increment=False):
diff -r 2e36f646bc59 -r d3780420461d imiptools/content.py
--- a/imiptools/content.py	Fri Sep 11 13:40:39 2015 +0200
+++ b/imiptools/content.py	Fri Sep 11 15:49:33 2015 +0200
@@ -69,7 +69,8 @@
                 # Dispatch to a handler and obtain any response.
 
                 handler.set_object(Object({name : item}))
-                methods[method](handler)()
+                if handler.is_usable():
+                    methods[method](handler)()
 
 # Handler registry.
 
diff -r 2e36f646bc59 -r d3780420461d imiptools/data.py
--- a/imiptools/data.py	Fri Sep 11 13:40:39 2015 +0200
+++ b/imiptools/data.py	Fri Sep 11 15:49:33 2015 +0200
@@ -648,6 +648,7 @@
     """
     Return the value provided by 'd' for 'name' as a datetime in the UTC zone
     or as a date, converting any date to a datetime if 'date_tzid' is specified.
+    If no datetime or date is available, None is returned.
     """
 
     t = get_datetime_item(d, name)
@@ -655,7 +656,7 @@
         return None
     else:
         dt, attr = t
-        return to_utc_datetime(dt, date_tzid)
+        return dt is not None and to_utc_datetime(dt, date_tzid) or None
 
 def get_datetime_item(d, name):
 
diff -r 2e36f646bc59 -r d3780420461d imiptools/handlers/common.py
--- a/imiptools/handlers/common.py	Fri Sep 11 13:40:39 2015 +0200
+++ b/imiptools/handlers/common.py	Fri Sep 11 15:49:33 2015 +0200
@@ -70,6 +70,12 @@
 
     "Common outgoing message handling functionality mix-in."
 
+    def is_usable(self):
+
+        "Return whether the current object is usable."
+
+        return self.obj and self.obj.get_value("DTSTART") 
+
     def update_event_in_freebusy(self, for_organiser=True):
 
         """