1 files changed, 53 insertions, 0 deletions
diff --git a/lib/syntax/cte.ml b/lib/syntax/cte.ml
new file mode 100644
index 0000000..ff43d6d
--- /dev/null
+++ b/lib/syntax/cte.ml
@@ -0,0 +1,53 @@
+open StdLabels
+module Path = ImportDataTypes.Path
+module Expression = ImportExpression.T
+
+type t = {
+  filters : Path.t Expression.t list;
+  group : Path.t Expression.t option;
+}
+
+(** Ensure the group criteria in window functions match the global group by
+    criteria.
+
+    Traverse the configuration tree until finding a group window. *)
+
+(** Check if the expression contains a group function *)
+let matchWindowGroup : 'a ImportExpression.T.t -> bool =
+ fun expression ->
+  let exception Found in
+  let open ImportExpression.T in
+  let rec f = function
+    | Empty | Literal _ | Integer _ | Path _ -> ()
+    | Expr e -> f e
+    | Concat pp | Function' (_, pp) | Function (_, pp) | Nvl pp | Join (_, pp)
+      -> List.iter ~f pp
+    | Window (_, _, _) -> raise Found
+    | BOperator (_, arg1, arg2) ->
+        f arg1;
+        f arg2
+    | GEquality (_, arg1, args) ->
+        f arg1;
+        List.iter ~f args
+  in
+  try
+    f expression;
+    false
+  with
+  | Found -> true
+
+(** Transform a list of expression into a list of CTE to evaluate. *)
+let of_filters : Path.t Expression.t list -> t list =
+ fun filters ->
+  let last_group, prev =
+    List.fold_left filters
+      ~init:({ filters = []; group = None }, [])
+      ~f:(fun (cte, acc) expr ->
+        begin
+          if matchWindowGroup expr then
+            ( { filters = []; group = None },
+              { cte with group = Some expr } :: acc )
+          else ({ cte with filters = expr :: cte.filters }, acc)
+        end)
+  in
+  List.rev (last_group :: prev)