module D = Colitur_kernel.Date
module C = Colitur_kernel.Computus

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

let test_gregorian_known () =
  let cases = [ (2024, 3, 31); (2025, 4, 20); (2026, 4, 5); (2027, 3, 28); (2000, 4, 23); (1583, 4, 10) ] in
  List.iter
    (fun (y, m, d) ->
      Alcotest.(check (triple int int int)) (Printf.sprintf "Gregorian Easter %d" y)
        (y, m, d) (ymd (C.gregorian_easter y)))
    cases

let test_julian_known () =
  (* Orthodox (Julian) Easter, expressed as the equivalent Gregorian date *)
  let cases = [ (2023, 4, 16); (2024, 5, 5) ] in
  List.iter
    (fun (y, m, d) ->
      Alcotest.(check (triple int int int)) (Printf.sprintf "Julian Easter %d" y)
        (y, m, d) (ymd (C.julian_easter y)))
    cases

let test_gregorian_invariants_exhaustive () =
  (* the confidence-to-9999 guarantee: EVERY year's Easter is a Sunday in
     [Mar 22, Apr 25] inclusive. *)
  for y = 1583 to 9999 do
    let e = C.gregorian_easter y in
    Alcotest.(check bool) (Printf.sprintf "%d Easter is Sunday" y) true (D.weekday e = D.Sun);
    let _, m, d = ymd e in
    let ok = (m = 3 && d >= 22) || (m = 4 && d <= 25) in
    Alcotest.(check bool) (Printf.sprintf "%d Easter in [Mar22,Apr25]" y) true ok
  done

let suite =
  ( "Computus",
    [ Alcotest.test_case "Gregorian known dates" `Quick test_gregorian_known;
      Alcotest.test_case "Julian known dates" `Quick test_julian_known;
      Alcotest.test_case "Gregorian invariants 1583..9999" `Slow test_gregorian_invariants_exhaustive ] )