open Utilities.Result

module Error = struct
  open Condition

  let unqualified_name name =
    condition "unqualified-name" "A relation must be named as multigroup:relation"
      ("name" |=| Value.String name)
end

let page_limit = 16

let relation_path branch name =
  match String.index_opt name ':' with
  | Some i when i > 0 && i < String.length name - 1 ->
      Ok
        (String.concat "\\"
           [ branch;
             "multigroup";
             String.sub name 0 i;
             "relation";
             String.sub name (i + 1) (String.length name - i - 1) ] )
  | _ -> Error (Error.unqualified_name name)

let rec compile branch = function
  | Ast.Base name -> relation_path branch name |> Result.map (fun path -> RNT.Base path)
  | Ast.Project (attributes, query) ->
      compile branch query |> Result.map (fun plan -> RNT.Project (plan, attributes))

let execute (ctx : Sublanguage_context.t) query =
  let* plan = compile (ctx.session#path ^ "\\branch") query in
  let* relation = RNT.execute ctx.kernel plan in
  Fun.protect
    ~finally:(fun () -> RNT.release relation)
    (fun () ->
      let* cursor = RNT.enumerate relation in
      Fun.protect
        ~finally:(fun () -> RNT.release cursor)
        (fun () ->
          let* {RNT.tuples; exhausted} = RNT.fetch cursor page_limit in
          Ok (Sublanguage_types.Cursor {rows= tuples; has_more= not exhausted}) ) )