metadata: add helper lib for common queries

pkg/arvo/lib/metadata.hoon

@@ -0,0 +1,54 @@
+::  metadata: helpers for getting data from the metadata-store
+::
+/-  *metadata-store
+::
+|_  =bowl:gall
+++  app-paths-from-group
+  |=  [=app-name =group-path]
+  ^-  (list app-path)
+  %+  murn
+    %~  tap  in
+    =-  (~(gut by -) group-path ~)
+    .^  (jug ^group-path resource)
+      %gy
+      (scot %p our.bowl)
+      %metadata-store
+      (scot %da now.bowl)
+      /group-indices
+    ==
+  |=  =resource
+  ^-  (unit app-path)
+  ?.  =(app-name.resource app-name)  ~
+  `app-path.resource
+::
+++  groups-from-resource
+  |=  =resource
+  ^-  (list group-path)
+  =;  resources
+    %~  tap  in
+    %+  ~(gut by resources)
+      resource
+    *(set group-path)
+  .^  (jug ^resource group-path)
+    %gy
+    (scot %p our.bowl)
+    %metadata-store
+    (scot %da now.bowl)
+    /resource-indices
+  ==
+::
+++  check-resource-permissions
+  |=  [=ship =resource]
+  ^-  ?
+  %+  lien  (groups-from-resource resource)
+  |=  =group-path
+  .^  ?
+    %gx
+    (scot %p our.bowl)
+    %permission-store
+    (scot %da now.bowl)
+    %permitted
+    (scot %p ship)
+    (snoc group-path %noun)
+  ==
+--