(** Alcotest tests for the Wire_diff library. *)

module D = Wire_diff.Diff

let pad wire_size buf =
  if String.length buf >= wire_size then String.sub buf 0 wire_size
  else
    let b = Bytes.make wire_size '\000' in
    Bytes.blit_string buf 0 b 0 (String.length buf);
    Bytes.to_string b

let check_result name = function
  | D.Match | D.Both_failed -> ()
  | D.Value_mismatch msg -> Alcotest.failf "%s: value mismatch: %s" name msg
  | D.Only_c_ok msg -> Alcotest.failf "%s: only C succeeded: %s" name msg
  | D.Only_ocaml_ok msg ->
      Alcotest.failf "%s: only OCaml succeeded: %s" name msg

(* Roundtrip a simple struct through the OCaml codec *)
let test_roundtrip_struct () =
  let s =
    Wire.struct_ "Simple"
      [ Wire.field "a" Wire.uint8; Wire.field "b" Wire.uint16 ]
  in
  let buf = "\x01\x02\x03" in
  match D.roundtrip_struct s buf with
  | Ok out -> Alcotest.(check string) "roundtrip" buf out
  | Error e -> Alcotest.failf "roundtrip failed: %a" Wire.pp_parse_error e

(* Schema with no C implementation — Both_failed is acceptable *)
let test_schema_read_no_c () =
  let wire_size = 3 in
  let buf = pad wire_size "\xff\xff\xff" in
  let s =
    Wire.Codec.(
      record "NoCTest" (fun a b -> (a, b))
      |+ field "a" Wire.uint8 fst |+ field "b" Wire.uint16 snd |> seal)
  in
  let schema =
    D.schema ~name:"NoCTest" ~codec:s
      ~c_read:(fun _ -> None)
      ~c_write:(fun _ -> None)
      ~equal:(fun (a1, b1) (a2, b2) -> a1 = a2 && b1 = b2)
  in
  check_result "no_c read" (D.read schema buf)

let suite =
  ( "diff",
    [
      Alcotest.test_case "roundtrip_struct" `Quick test_roundtrip_struct;
      Alcotest.test_case "schema read (no C)" `Quick test_schema_read_no_c;
    ] )