module D = Colitur_kernel.Date

let mk y m d =
  match D.make ~year:y ~month:m ~day:d with
  | Ok t -> t
  | Error e -> Alcotest.failf "make %04d-%02d-%02d: %s" y m d e

let wd_str = function
  | D.Sun -> "Sun" | D.Mon -> "Mon" | D.Tue -> "Tue" | D.Wed -> "Wed"
  | D.Thu -> "Thu" | D.Fri -> "Fri" | D.Sat -> "Sat"

let ymd d = (D.year d, D.month d, D.day d)

let test_weekday () =
  Alcotest.(check string) "1970-01-01 is Thursday" "Thu" (wd_str (D.weekday (mk 1970 1 1)));
  Alcotest.(check string) "2026-07-31 is Friday" "Fri" (wd_str (D.weekday (mk 2026 7 31)))

let test_roundtrip () =
  let d = mk 2026 7 31 in
  Alcotest.(check int) "of_rata(to_rata d) = d" 0 (D.compare (D.of_rata (D.to_rata d)) d)

let test_add_days () =
  Alcotest.(check (triple int int int)) "2024-02-28 +1 = 2024-02-29"
    (2024, 2, 29) (ymd (D.add_days (mk 2024 2 28) 1));
  Alcotest.(check (triple int int int)) "2023-02-28 +1 = 2023-03-01"
    (2023, 3, 1) (ymd (D.add_days (mk 2023 2 28) 1))

let test_make_reject () =
  Alcotest.(check bool) "reject 2026-02-30" true (Result.is_error (D.make ~year:2026 ~month:2 ~day:30));
  Alcotest.(check bool) "reject year 1000" true (Result.is_error (D.make ~year:1000 ~month:1 ~day:1))

(* ---- properties (year-independent, the confidence-to-9999 core) ---- *)

let arb_date =
  let open QCheck in
  map
    (fun (y, off) ->
      let jan1 = match D.make ~year:y ~month:1 ~day:1 with Ok t -> t | Error e -> failwith e in
      D.of_rata (D.to_rata jan1 + off))
    (pair (int_range 1583 9999) (int_range 0 364))

let prop_roundtrip =
  QCheck.Test.make ~name:"of_rata . to_rata = id" arb_date
    (fun d -> D.compare (D.of_rata (D.to_rata d)) d = 0)

let prop_add_inverse =
  QCheck.Test.make ~name:"add_days n then -n = id"
    QCheck.(pair arb_date (int_range (-4000) 4000))
    (fun (d, n) -> D.compare (D.add_days (D.add_days d n) (-n)) d = 0)

let prop_weekday_cycle =
  QCheck.Test.make ~name:"weekday(add_days d 7) = weekday d" arb_date
    (fun d -> D.weekday (D.add_days d 7) = D.weekday d)

let test_iso8601 () =
  Alcotest.(check string) "to_iso8601" "2026-04-05" (D.to_iso8601 (mk 2026 4 5));
  (match D.of_iso8601 "2026-04-05" with
   | Ok d -> Alcotest.(check int) "of_iso8601 roundtrip" 0 (D.compare d (mk 2026 4 5))
   | Error e -> Alcotest.failf "of_iso8601: %s" e);
  Alcotest.(check bool) "reject garbage" true (Result.is_error (D.of_iso8601 "nope"));
  Alcotest.(check bool) "reject 2026-02-30" true (Result.is_error (D.of_iso8601 "2026-02-30"))

let test_date_sexp () =
  let d = mk 2026 4 5 in
  Alcotest.(check string) "sexp_of_t" "2026-04-05" (Sexplib.Sexp.to_string (D.sexp_of_t d));
  Alcotest.(check int) "t_of_sexp roundtrip" 0
    (D.compare (D.t_of_sexp (D.sexp_of_t d)) d);
  Alcotest.(check string) "weekday_to_string" "sunday" (D.weekday_to_string (D.weekday d))

let suite =
  ( "Date",
    [ Alcotest.test_case "weekday" `Quick test_weekday;
      Alcotest.test_case "roundtrip" `Quick test_roundtrip;
      Alcotest.test_case "add_days boundaries" `Quick test_add_days;
      Alcotest.test_case "make rejects invalid" `Quick test_make_reject;
      Alcotest.test_case "iso8601" `Quick test_iso8601;
      Alcotest.test_case "sexp" `Quick test_date_sexp ]
    @ List.map QCheck_alcotest.to_alcotest
        [ prop_roundtrip; prop_add_inverse; prop_weekday_cycle ] )