Limit allowable child types based on parent.

[ChrisNelsonPE]

This feature is ported from ChildTickets plugin.

diff --git a/tracsubtickets/api.py b/tracsubtickets/api.py
index 71f2d67..9ad2674 100644
--- a/tracsubtickets/api.py
+++ b/tracsubtickets/api.py
@@ -181,6 +181,19 @@ class SubTicketsSystem(Component):
                         errors += _check_parents(x, all_parents)
                 return errors
 
+            def _check_types(ticket, parent):
+                if not self.config.getbool('subtickets', 
+                                           '%s.allow_child_tickets' % 
+                                           parent['type']):
+                    yield None, "The parent ticket (#%s) has type '%s' which does not allow child tickets." % (parent.id, parent['type'])
+
+                # It is possible that the parent restricts the
+                # type of children it allows.
+                allowedtypes = self.config.getlist('subtickets', 
+                                                   '%s.restrict_child_types' % parent['type'])
+                if allowedtypes and ticket['type'] not in allowedtypes:
+                    yield None, "The parent ticket (#%s) has type '%s' which does not allow child type '%s'. Must be one of: %s." % (parent.id,parent['type'],ticket['type'],','.join(allowedtypes))
+
             for x in ids:
                 # check parent ticket state
                 parent = Ticket(self.env, x)
@@ -192,9 +205,14 @@ class SubTicketsSystem(Component):
                     for error in _check_parents(int(x), all_parents):
                         yield error
 
+                    # Check type
+                    for error in _check_types(ticket, parent):
+                        yield error
+
             ticket['parents'] = ', '.join(sorted(ids, key=lambda x: int(x)))
 
         except Exception, e:
             self.log.error(e)
             yield 'parents', 'Not a valid list of ticket IDs'
 
+