Move "merge 2 people" logic into People Handler

view now delegates to handler, which lives in the rattail package

tailbone/views/people.py

@@ -85,16 +85,13 @@ class PersonView(MasterView):
     ]
 
     mergeable = True
-    merge_additive_fields = [
-        'usernames',
-        'member_uuids',
-    ]
-    merge_fields = merge_additive_fields + [
-        'uuid',
-        'first_name',
-        'last_name',
-        'display_name',
-    ]
+
+    def __init__(self, request):
+        super(PersonView, self).__init__(request)
+
+        # always get a reference to the People Handler
+        app = self.get_rattail_app()
+        self.handler = app.get_people_handler()
 
     def configure_grid(self, g):
         super(PersonView, self).configure_grid(g)
@@ -190,9 +187,7 @@ class PersonView(MasterView):
                 names[key] = None
 
         # do explicit name update w/ common handler logic
-        app = self.get_rattail_app()
-        handler = app.get_people_handler()
-        handler.update_names(person, **names)
+        self.handler.update_names(person, **names)
 
         return person
 
@@ -365,33 +360,30 @@ class PersonView(MasterView):
             (model.VendorContact, 'person_uuid'),
         ]
 
+    def get_merge_fields(self):
+        fields = self.handler.get_merge_preview_fields()
+        return [field['name'] for field in fields]
+
+    def get_merge_additive_fields(self):
+        fields = self.handler.get_merge_preview_fields()
+        return [field['name'] for field in fields
+                if field.get('additive')]
+
+    def get_merge_coalesce_fields(self):
+        fields = self.handler.get_merge_preview_fields()
+        return [field['name'] for field in fields
+                if field.get('coalesce')]
+
     def get_merge_data(self, person):
-        return {
-            'uuid': person.uuid,
-            'first_name': person.first_name,
-            'last_name': person.last_name,
-            'display_name': person.display_name,
-            'usernames': [u.username for u in person.users],
-            'member_uuids': [m.uuid for m in person.members],
-        }
+        return self.handler.get_merge_preview_data(person)
+
+    def validate_merge(self, removing, keeping):
+        reason = self.handler.why_not_merge(removing, keeping)
+        if reason:
+            raise Exception(reason)
 
     def merge_objects(self, removing, keeping):
-        """
-        Execute a merge operation on the two given person records.
-        """
-        # move Member records to final Person
-        for member in list(removing.members):
-            removing.members.remove(member)
-            keeping.members.append(member)
-
-        # move User records to final Person
-        for user in list(removing.users):
-            removing.users.remove(user)
-            keeping.users.append(user)
-
-        # delete unwanted Person
-        self.Session.delete(removing)
-        self.Session.flush()
+        self.handler.perform_merge(removing, keeping)
 
     def view_profile(self):
         """