xmlrpc: Treat negative max_count as meaning "return last N results"

This is most useful when listing patches, as it lets you get the most
recent results instead of the oldest.

v2: Don't negative indexing on querysets, Django doesn't support that
    and was throwing an exception "Negative indexing is not supported."
    (Damien)

Signed-off-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>

patchwork/bin/pwclient

@@ -385,7 +385,12 @@ def main():
     filter_parser.add_argument(
         '-n', metavar='MAX#',
         type=int,
-        help='''Restrict number of results'''
+        help='''Return first N results'''
+    )
+    filter_parser.add_argument(
+        '-N', metavar='MAX#',
+        type=int,
+        help='''Return last N results'''
     )
     filter_parser.add_argument(
         '-m', metavar='MESSAGEID',
@@ -525,6 +530,12 @@ def main():
         except:
             action_parser.error("Invalid maximum count '%s'" % args.get('n'))
 
+    if args.get('N') != None:
+        try:
+            filt.add("max_count", 0 - args.get('N'))
+        except:
+            action_parser.error("Invalid maximum count '%s'" % args.get('N'))
+
     do_signoff = args.get('signoff')
 
     # grab settings from config files

patchwork/views/xmlrpc.py

@@ -371,6 +371,8 @@ def project_list(search_str=None, max_count=0):
 
         if max_count > 0:
             return map(project_to_dict, projects)[:max_count]
+        elif max_count < 0:
+            return map(project_to_dict, projects)[max_count:]
         else:
             return map(project_to_dict, projects)
     except Project.DoesNotExist:
@@ -423,6 +425,8 @@ def person_list(search_str=None, max_count=0):
 
         if max_count > 0:
             return map(person_to_dict, people)[:max_count]
+        elif max_count < 0:
+            return map(person_to_dict, people)[max_count:]
         else:
             return map(person_to_dict, people)
     except Person.DoesNotExist:
@@ -566,6 +570,10 @@ def patch_list(filt=None):
 
         if max_count > 0:
             return map(patch_to_dict, patches[:max_count])
+        elif max_count < 0:
+            results = map(patch_to_dict, patches.reverse()[:-max_count])
+            results.reverse()
+            return results
         else:
             return map(patch_to_dict, patches)
     except Patch.DoesNotExist:
@@ -759,6 +767,8 @@ def state_list(search_str=None, max_count=0):
 
         if max_count > 0:
             return map(state_to_dict, states)[:max_count]
+        elif max_count < 0:
+            return map(state_to_dict, states)[max_count:]
         else:
             return map(state_to_dict, states)
     except State.DoesNotExist: