(* Low-level ctypes bindings to RNT_C_API.h.
   This module is internal to Nt — never import it anywhere else. *)

open Ctypes
open Foreign

let fn name typ = foreign name typ

(* Runtime ----------------------------------------------------------------- *)
let rnt_init =
  fn "rnt_init" (string @-> string @-> returning int)

(* Auth -------------------------------------------------------------------- *)
let rnt_firewall =
  fn "rnt_firewall" (string @-> ptr (ptr char) @-> returning int)

(* Session lifecycle ------------------------------------------------------- *)
let rnt_session_open =
  fn "rnt_session_open" (ptr void @-> ptr (ptr char) @-> returning int)

let rnt_session_close =
  fn "rnt_session_close" (string @-> returning int)

let rnt_session_set_branch =
  fn "rnt_session_set_branch"
    (string @-> string @-> string @-> returning int)

(* Handle lifecycle -------------------------------------------------------- *)
let rnt_open_handle =
  fn "rnt_open_handle" (string @-> ptr void @-> returning (ptr void))

let rnt_close_handle =
  fn "rnt_close_handle" (ptr void @-> returning int)

(* Branch hash-pointer ----------------------------------------------------- *)
let rnt_branch_target =
  fn "rnt_branch_target"
    (ptr void @-> ptr (ptr char) @-> returning int)

let rnt_branch_advance =
  fn "rnt_branch_advance" (string @-> string @-> returning int)

(* Object registration ----------------------------------------------------- *)
let rnt_register_relation =
  fn "rnt_register_relation" (string @-> returning int)

let rnt_register_branch =
  fn "rnt_register_branch" (string @-> string @-> returning int)

(* Branch / snapshot relation enumeration ----------------------------------- *)
let rnt_list_relations =
  fn "rnt_list_relations" (string @-> ptr (ptr char) @-> returning int)

let rnt_list_branch_multigroups =
  fn "rnt_list_branch_multigroups" (string @-> ptr (ptr char) @-> returning int)

let rnt_list_snapshot_relations =
  fn "rnt_list_snapshot_relations" (string @-> ptr (ptr char) @-> returning int)

(* Tuple storage ----------------------------------------------------------- *)
let rnt_link_tuple =
  fn "rnt_link_tuple"
    (string @-> string @-> ptr (ptr char) @-> returning int)

let rnt_unlink_tuple =
  fn "rnt_unlink_tuple" (string @-> string @-> returning int)

let rnt_clear_relation =
  fn "rnt_clear_relation" (string @-> returning int)

let rnt_relation_root =
  fn "rnt_relation_root"
    (string @-> ptr (ptr char) @-> returning int)

(* Cursor and VM ----------------------------------------------------------- *)
let rnt_cursor_open =
  fn "rnt_cursor_open" (ptr void @-> returning (ptr void))

let rnt_cursor_next =
  fn "rnt_cursor_next" (ptr void @-> ptr (ptr char) @-> returning int)

let rnt_cursor_close =
  fn "rnt_cursor_close" (ptr void @-> returning int)

(* VM plan builder --------------------------------------------------------- *)

type operation = Scan | Join | Take | Project

let int_of_operation = function
  | Scan -> 1 | Join -> 2 | Take -> 3 | Project -> 4

let operation_of_int = function
  | 1 -> Scan | 2 -> Join | 3 -> Take | 4 -> Project
  | _ -> failwith "Bad operation" (* FIXME *)

let operation = view ~read:operation_of_int ~write:int_of_operation int

type plan_args_scan
let plan_args_scan : plan_args_scan structure typ = structure "plan_args_scan"
let pas_relation_path = field plan_args_scan "pas_relation_path" string
let () = seal plan_args_scan

type plan_args_join
let plan_args_join : plan_args_join structure typ = structure "plan_args_join"
let paj_left = field plan_args_join "paj_left" (ptr void)
let paj_right = field plan_args_join "paj_right" (ptr void)
let () = seal plan_args_join

type plan_args_take
let plan_args_take : plan_args_take structure typ = structure "plan_args_take"
let pat_source = field plan_args_take "pat_source" (ptr void)
let pat_limit = field plan_args_take "pat_limit" size_t
let () = seal plan_args_take

type plan_args_project
let plan_args_project : plan_args_project structure typ = structure "plan_args_project"
let pap_source = field plan_args_project "pap_source" (ptr void)
let pap_attrs = field plan_args_project "pap_attrs" (ptr (ptr char))
let () = seal plan_args_project

type plan_action
let plan_action : plan_action structure typ = structure "plan_action"
let pa_operation = field plan_action "pa_operation" operation
let pa_scan = field plan_action "pa_scan" plan_args_scan
let pa_join = field plan_action "pa_join" plan_args_join
let pa_take = field plan_action "pa_take" plan_args_take
let pa_project = field plan_action "pa_project" plan_args_project
let () = seal plan_action

let rnt_plan_assemble = fn "rnt_plan_assemble" (plan_action @-> returning (ptr void))

let ( &-> ) = getf

let rnt_plan_scan str =
  let plan = make plan_action in
  setf plan pa_operation Scan;
  setf (plan &-> pa_scan) pas_relation_path str;
  rnt_plan_assemble plan

let rnt_plan_join left right =
  let plan = make plan_action in
  setf plan pa_operation Join;
  setf (plan &-> pa_join) paj_left left;
  setf (plan &-> pa_join) paj_right right;
  rnt_plan_assemble plan

let rnt_plan_take source limit =
  let plan = make plan_action in
  setf plan pa_operation Take;
  setf (plan &-> pa_take) pat_source source;
  setf (plan &-> pa_take) pat_limit limit;
  rnt_plan_assemble plan

let rnt_plan_free =
  fn "rnt_plan_free" (ptr void @-> returning void)

let rnt_vm_execute_plan =
  fn "rnt_vm_execute_plan" (ptr void @-> returning (ptr void))

let rnt_vm_cursor_next =
  fn "rnt_vm_cursor_next" (ptr void @-> ptr (ptr char) @-> returning int)

let rnt_vm_cursor_close =
  fn "rnt_vm_cursor_close" (ptr void @-> returning int)

(* Memory management ------------------------------------------------------- *)
let rnt_free_string =
  fn "rnt_free_string" (ptr char @-> returning void)

let rnt_free_bytes =
  fn "rnt_free_bytes" (ptr uint8_t @-> returning void)

(* --------------------------------------------------------------------------
   Helpers shared by Nt (not exported from the library module)
   -------------------------------------------------------------------------- *)

let null_char_ptr : char ptr = from_voidp char null

(* Reads a null-terminated C string from a char pointer, then frees it. *)
let consume_cstring (p : char ptr) : string =
  let n = ref 0 in
  while !@(p +@ !n) <> '\000' do incr n done;
  let s = string_from_ptr p ~length:!n in
  rnt_free_string p;
  s

(* Allocates a char* out-parameter, calls [f], returns the rc and string. *)
let with_out_string (f : char ptr ptr -> int) : int * string option =
  let pp = allocate (ptr char) null_char_ptr in
  let rc = f pp in
  let p  = !@ pp in
  if is_null p then (rc, None)
  else (rc, Some (consume_cstring p))

(* Converts a void* (returned from open_handle / cursor_open) to nativeint.
   Returns None when the pointer is NULL (failure). *)
let ptr_to_opt (p : unit ptr) : nativeint option =
  if is_null p then None
  else Some (raw_address_of_ptr p)

(* Converts a stored nativeint back to a void* for API calls. *)
let nint_to_ptr (n : nativeint) : unit ptr =
  ptr_of_raw_address n