Config.hs: Add a function to lookup group

Like in the python code, this is a bit more complex since groups are
indexed by UUID, so we must fallback to lookup via the name (slow; but
the number of groups should be small).

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Agata Murawska <agatamurawska@google.com>

htools/Ganeti/Config.hs

@@ -31,6 +31,7 @@ module Ganeti.Config
     , getInstancesIpByLink
     , getNode
     , getInstance
+    , getGroup
     , getInstPrimaryNode
     , getInstMinorsForNode
     , buildLinkIpInstnameMap
@@ -132,6 +133,18 @@ getInstance :: ConfigData -> String -> Result Instance
 getInstance cfg name =
   getItem "Instance" name (fromContainer $ configInstances cfg)
 
+-- | Looks up a node group. This is more tricky than for
+-- node/instances since the groups map is indexed by uuid, not name.
+getGroup :: ConfigData -> String -> Result NodeGroup
+getGroup cfg name =
+  let groups = fromContainer (configNodegroups cfg)
+  in case getItem "NodeGroup" name groups of
+       -- if not found by uuid, we need to look it up by name, slow
+       Ok grp -> Ok grp
+       Bad _ -> let by_name = M.mapKeys
+                              (\k -> groupName ((M.!) groups k )) groups
+                in getItem "NodeGroup" name by_name
+
 -- | Looks up an instance's primary node.
 getInstPrimaryNode :: ConfigData -> String -> Result Node
 getInstPrimaryNode cfg name =