type 'a cube_type =
| U16 : int16_cube cube_type
| F64 : float64_cube cube_type
(* with sexp *)

let cube_type_of_sexp : type a . Sexp.t -> a cube_type = function
  | Sexp.Atom "U16" -> U16
  | Sexp.Atom "F64" -> F64

let map_cube ?(mode=`Read) cube_type { frames; rows; cols } path =
  let open Unix in
  let flags, shared =
    match mode with
    | `Read -> [O_RDONLY], false
    | `Write -> [O_RDWR], true
    | `Create -> [O_RDWR;O_CREAT;O_TRUNC], true
  in
  let fd = Unix.openfile path flags 0o644 in
  let get : type a . a cube_type -> a = function
    | U16 -> Array3.map_file fd ~pos:0L int16_unsigned fortran_layout shared cols rows frames
    | F64 -> Array3.map_file fd ~pos:0L float64 fortran_layout shared cols rows frames
  in
  get cube_type