path: root/lib/dml/executor.ml

module Make (NT : Nt.S) = struct
  module DrlExec = Drl.Executor.Make (NT)

  module Error = struct
    open Condition

    (* TODO: more structure *)
    let parse_error msg = condition "parse-error" msg empty

    let relation_not_found name =
      condition "relation-not-found" "Relation not found" ("name" |=| of_string name)

    let multigroup_not_found name =
      condition "multigroup-not-found" "Multigroup not found" ("name" |=| of_string name)
  end

  let ( let* ) = Result.bind
  let parse_fqn (s : string) : (Qualified_name.t, Condition.t) result = Qualified_name.try_parse s

  let lookup_mg (ctx : Sublanguage_context.t) (mg_name : string) :
      (Management.Multigroup.multigroup, Condition.t) result =
    match ctx.branch#mg_of mg_name with
    | Some mg -> Ok mg
    | None -> Error (Error.multigroup_not_found mg_name)

  let get_rel (ctx : Sublanguage_context.t) (fqn : Qualified_name.t) =
    let* mg = lookup_mg ctx fqn.mg in
    match NT.get_relation mg fqn.name with
    | Some r -> Ok r
    | None -> Error (Error.relation_not_found (Qualified_name.to_string fqn))

  let retarget target (t : Tuple.materialized) = {t with Tuple.relation= target}

  let build_tuple ~relation (attributes : Ast.attr_value list) : Tuple.materialized =
    let attr_map =
      List.fold_left
        (fun acc (name, value) ->
          Tuple.AttributeMap.add name {Attribute.value= Drl.Ast.value_to_abstract value} acc )
        Tuple.AttributeMap.empty attributes
    in
    {Tuple.relation; attributes= attr_map}

  (* Drain all tuples from a DRL query using ctx.resolve for path resolution.
     Cross-multigroup reads work transparently here. *)
  let drain_query (ctx : Sublanguage_context.t) query =
    let* plan = DrlExec.compile ctx query in
    let* stream = NT.execute_query plan ~rel_name:"dml_drain" in
    let rec drain acc =
      match NT.stream_next stream with
      | Error _ -> List.rev acc
      | Ok None -> List.rev acc
      | Ok (Some t) -> drain (t :: acc)
    in
    let tuples = drain [] in
    ignore (NT.stream_close stream);
    Ok tuples

  (* Stored-relation paths referenced by a query, for ephemeral dependency
     pinning. A qualified leaf resolves through ctx; an unqualified one is a
     previously Defined session ephemeral (views compose). *)
  let rec base_dep_paths (ctx : Sublanguage_context.t) (q : Drl.Ast.query) : string list =
    match q with
    | Drl.Ast.Base name -> (
      match Qualified_name.try_parse name with
      | Ok fqn -> [ctx.resolve fqn]
      | Error _ -> [Sublanguage_context.ephemeral_path ctx name] )
    | Drl.Ast.Const _ -> []
    | Drl.Ast.Select (a, b)
     |Drl.Ast.Join (_, a, b)
     |Drl.Ast.Cartesian (a, b)
     |Drl.Ast.Union (a, b)
     |Drl.Ast.Diff (a, b) ->
        base_dep_paths ctx a @ base_dep_paths ctx b
    | Drl.Ast.Project (_, s) | Drl.Ast.Rename (_, s) | Drl.Ast.Take (_, s) -> base_dep_paths ctx s

  (* Schema of a query result, walked structurally from the base relations'
     schemas. Mirrors the operator semantics in docs/relational-algebra.org. *)
  let rec infer_schema (ctx : Sublanguage_context.t) (q : Drl.Ast.query) :
      (Schema.t, Condition.t) result =
    match q with
    | Drl.Ast.Base name -> (
      match Qualified_name.try_parse name with
      | Error _ ->
          (* Session ephemeral: RNT owns its schema; nothing to derive
                on the OCaml-side, so treated as contributing no attributes. *)
          Ok []
      | Ok fqn ->
          let* rel = get_rel ctx fqn in
          Ok rel#schema )
    | Drl.Ast.Const attrs -> Ok (List.map (fun (n, _) -> n, "abstract") attrs)
    | Drl.Ast.Select (_, src) -> infer_schema ctx src
    | Drl.Ast.Join (_, l, r) | Drl.Ast.Cartesian (l, r) ->
        let* ls = infer_schema ctx l in
        let* rs = infer_schema ctx r in
        Ok (ls @ List.filter (fun (n, _) -> not (List.mem_assoc n ls)) rs)
    | Drl.Ast.Project (attrs, src) ->
        let* s = infer_schema ctx src in
        Ok (List.filter (fun (n, _) -> List.mem n attrs) s)
    | Drl.Ast.Rename (renames, src) ->
        let* s = infer_schema ctx src in
        Ok
          (List.map
             (fun (n, d) -> match List.assoc_opt n renames with Some n' -> n', d | None -> n, d)
             s )
    | Drl.Ast.Union (l, _) | Drl.Ast.Diff (l, _) -> infer_schema ctx l
    | Drl.Ast.Take (_, src) -> infer_schema ctx src

  let attr_val_eq a b = Stdlib.( = ) a.Attribute.value b.Attribute.value

  let tuple_matches_pred common (target_t : Tuple.materialized) (pred_t : Tuple.materialized) =
    List.for_all
      (fun attr ->
        match
          ( Tuple.AttributeMap.find_opt attr target_t.Tuple.attributes,
            Tuple.AttributeMap.find_opt attr pred_t.Tuple.attributes )
        with
        | Some a, Some b -> attr_val_eq a b
        | _ -> false )
      common

  let semijoin common target_tuples pred_tuples =
    List.filter (fun t -> List.exists (tuple_matches_pred common t) pred_tuples) target_tuples

  (* DML mutates tuples in a single mg per statement.  Returns a
     single-element transition delta keyed by that mg's name. *)
  let execute (ctx : Sublanguage_context.t) (stmt : Ast.statement) :
      (Sublanguage_types.transition_delta, Condition.t) result =
    let bh = ctx.write_handle in
    let branch_name = ctx.branch#name in
    let after fqn =
      Result.bind (lookup_mg ctx fqn.Qualified_name.mg) (fun mg -> Ok [fqn.Qualified_name.mg, mg])
    in
    match stmt with
    | Ast.InsertTuple {relation; attributes} ->
        let* fqn = parse_fqn relation in
        let* rel = get_rel ctx fqn in
        let tuple = build_tuple ~relation:rel#name attributes in
        let* _ = NT.create_tuple ~branch_name ~mg_name:fqn.mg ~rel_name:rel#name tuple in
        after fqn
    | Ast.InsertTuples {relation; tuples} ->
        let* fqn = parse_fqn relation in
        let* rel = get_rel ctx fqn in
        let tuple_list = List.map (build_tuple ~relation:rel#name) tuples in
        let* _ = NT.create_tuples ~branch_name ~mg_name:fqn.mg ~rel_name:rel#name tuple_list in
        after fqn
    | Ast.DeleteTuple {relation; attributes} ->
        let* fqn = parse_fqn relation in
        let* rel = get_rel ctx fqn in
        let tuple = build_tuple ~relation:rel#name attributes in
        let hash = Hashing.hash_tuple tuple in
        let* () = NT.retract_tuple ~branch_name ~mg_name:fqn.mg ~rel_name:rel#name hash in
        after fqn
    | Ast.Assign {target; body} ->
        let* fqn = parse_fqn target in
        let* mg = lookup_mg ctx fqn.mg in
        let* rel = get_rel ctx fqn in
        let* tuples = drain_query ctx body in
        let* _bh, new_mg =
          NT.clear_relation bh mg ~branch_name ~mg_name:fqn.mg (rel :> Relation.relation)
        in
        ctx.branch#set_mg ~name:fqn.mg new_mg;
        let* _ =
          NT.create_tuples ~branch_name ~mg_name:fqn.mg ~rel_name:rel#name
            (List.map (retarget rel#name) tuples)
        in
        Ok [fqn.mg, new_mg]
    | Ast.InsertFrom {target; source} ->
        let* fqn = parse_fqn target in
        let* rel = get_rel ctx fqn in
        let* tuples = drain_query ctx source in
        let* _ =
          NT.create_tuples ~branch_name ~mg_name:fqn.mg ~rel_name:rel#name
            (List.map (retarget rel#name) tuples)
        in
        after fqn
    | Ast.Define {target; body} ->
        let* () =
          if String.contains target ':' then
            Error
              (Error.parse_error ("Define target must be unqualified (session-scoped): " ^ target))
          else Ok ()
        in
        (* TODO: redefining an existing name isn't guarded. Right now we lean on
           Hashtbl.replace and whatever RNT does on collision. Pick replace or
           error and enforce it here. *)
        let* schema = infer_schema ctx body in
        (* TODO: every page drains the whole query and then filters down to the
           window, so paging costs O(total * pages) and reruns the VM plan each
           time. Push the offset/limit down or cache the result. *)
        let generator ~offset ~limit =
          match drain_query ctx body with
          | Error _ -> []
          | Ok tuples -> List.filteri (fun i _ -> i >= offset && i < offset + limit) tuples
        in
        let* _path =
          NT.register_ephemeral ~session:ctx.session_hash ~named:true ~name:target ~generator
            ~cardinality:Conventions.Cardinality.ConstrainedFinite
            ~identity:(Drl.Parser.to_string body) ~schema ~deps:(base_dep_paths ctx body)
        in
        Ok []
    | Ast.DropDefine {target} ->
        let* () = NT.drop_ephemeral ~session:ctx.session_hash ~name:target in
        Ok []
    | Ast.DeleteWhere {target; predicate} ->
        let* fqn = parse_fqn target in
        let* rel = get_rel ctx fqn in
        let* target_tuples = drain_query ctx (Drl.Ast.Base target) in
        let* pred_tuples = drain_query ctx predicate in
        let attr_names_of = function
          | [] -> []
          | t :: _ -> List.map fst (Tuple.AttributeMap.bindings t.Tuple.attributes)
        in
        let target_attrs = attr_names_of target_tuples in
        let pred_attrs = attr_names_of pred_tuples in
        let common = List.filter (fun n -> List.mem n pred_attrs) target_attrs in
        let to_delete = semijoin common target_tuples pred_tuples in
        let* () =
          List.fold_left
            (fun acc t ->
              let* () = acc in
              let hash = Hashing.hash_tuple (retarget rel#name t) in
              NT.retract_tuple ~branch_name ~mg_name:fqn.mg ~rel_name:rel#name hash )
            (Ok ()) to_delete
        in
        after fqn
end

module Memory = Make (Nt.Memory)