open! Base

type t = Temperature of float
       
let temperature f = Temperature f

let value (Temperature f) = f

let parse s =
  let re = Str.regexp " t=\\([0-9]+\\)" in
  try
    if (Str.search_forward re s 0) > 0   
    then Some (Float.of_string (Str.matched_group 1 s) /. 1000.0)
    else None
  with Stdlib.Not_found -> None

let%test_unit "parse temperature" = 
  [%test_eq: float option] (parse "brol\nmore junk text t=18241") (Some 18.241)  


let read_temperature file_name =
  let open Lwt.Infix in
  Lwt_io.with_file ~mode:Lwt_io.Input file_name (fun ic ->
      Lwt_io.read ic >>= (fun s ->
        parse s |> Option.map ~f:temperature |> Lwt.return 
      )
    ) 

let write_test_file file_name =
  Lwt_io.with_file ~mode:Lwt_io.Output file_name (fun oc ->
      Lwt_io.write_line oc "brol\nmore junk text t=18241"
    )

let%test "read temperature from file" = 
  let open Lwt.Infix in
  let file_name = "test_temperature.txt" in
  let aux = write_test_file file_name 
    >>= fun () -> (read_temperature file_name) 
    >>= function 
    | Some (Temperature t) -> Lwt.return Float.(t = 18.241)
    | _ -> Lwt.return false
  in Lwt_main.run aux