module Ics = Colitur_render.Emit_ics

let out_2027 () = Ics.year (Test_view.view_of 2027)

let lines s =
  String.split_on_char '\n' s
  |> List.map (fun l -> if l <> "" && l.[String.length l - 1] = '\r' then String.sub l 0 (String.length l - 1) else l)
  |> List.filter (fun l -> l <> "")

let count_prefix p ls =
  List.length (List.filter (fun l -> String.length l >= String.length p && String.sub l 0 (String.length p) = p) ls)

let test_envelope () =
  let ls = lines (out_2027 ()) in
  Alcotest.(check string) "first line" "BEGIN:VCALENDAR" (List.hd ls);
  Alcotest.(check string) "last line" "END:VCALENDAR" (List.nth ls (List.length ls - 1));
  Alcotest.(check int) "version" 1 (count_prefix "VERSION:2.0" ls);
  Alcotest.(check int) "prodid" 1 (count_prefix "PRODID:" ls);
  Alcotest.(check int) "365 events" 365 (count_prefix "BEGIN:VEVENT" ls)

(* RFC 5545 section 3.6.1: for an all-day event DTEND is EXCLUSIVE. Getting
   this wrong shows every event a day short in every client. *)
let test_dtend_is_exclusive () =
  let ls = lines (out_2027 ()) in
  let starts = List.filter_map (fun l ->
      if count_prefix "DTSTART;VALUE=DATE:" [l] = 1 then
        Some (String.sub l (String.length "DTSTART;VALUE=DATE:") 8) else None) ls in
  let ends = List.filter_map (fun l ->
      if count_prefix "DTEND;VALUE=DATE:" [l] = 1 then
        Some (String.sub l (String.length "DTEND;VALUE=DATE:") 8) else None) ls in
  Alcotest.(check int) "same count" (List.length starts) (List.length ends);
  Alcotest.(check string) "1 Jan starts" "20270101" (List.hd starts);
  Alcotest.(check string) "1 Jan ends on the 2nd" "20270102" (List.hd ends);
  Alcotest.(check string) "31 Dec ends on 1 Jan next" "20280101"
    (List.nth ends (List.length ends - 1))

let test_uids_unique_and_shaped () =
  let ls = lines (out_2027 ()) in
  let uids = List.filter_map (fun l ->
      if count_prefix "UID:" [l] = 1 then Some (String.sub l 4 (String.length l - 4)) else None) ls in
  Alcotest.(check int) "365 uids" 365 (List.length uids);
  let sorted = List.sort_uniq String.compare uids in
  Alcotest.(check int) "all unique" 365 (List.length sorted);
  Alcotest.(check string) "shape" "20270101-ef@colitur" (List.hd uids)

(* The rule that punishes silently, months later, in someone else's phone:
   regenerating a feed must not duplicate every event. *)
let test_output_is_byte_stable_across_runs () =
  Alcotest.(check string) "two runs identical" (out_2027 ()) (out_2027 ())

let test_every_line_folded_and_crlf () =
  let raw = out_2027 () in
  List.iter
    (fun l ->
      if String.length l > 75 then Alcotest.failf "line of %d octets: %s" (String.length l) l)
    (lines raw);
  (* Every physical line ends CRLF (RFC 5545 section 3.1). *)
  let n = String.length raw in
  let rec check i =
    if i >= n then ()
    else if raw.[i] = '\n' then (
      if i = 0 || raw.[i - 1] <> '\r' then Alcotest.failf "bare LF at offset %d" i;
      check (i + 1))
    else check (i + 1)
  in
  check 0

let test_no_rrule () =
  Alcotest.(check int) "no RRULE" 0 (count_prefix "RRULE" (lines (out_2027 ())))

let test_text_escaped () =
  let ls = lines (Ics.year (Test_view.view_of 2035)) in
  (* 2035-04-03 is St Joseph, whose English name contains a comma. *)
  let joseph = List.find (fun l -> count_prefix "SUMMARY:St. Joseph" [l] = 1) ls in
  Alcotest.(check bool) "comma escaped" true
    (let re = "\\," in
     let n = String.length re in
     let rec f i = i + n <= String.length joseph && (String.sub joseph i n = re || f (i + 1)) in
     f 0)

let test_dtstamp_is_a_parameter () =
  let a = Ics.year ~dtstamp:"20200101T000000Z" (Test_view.view_of 2027) in
  let b = Ics.year ~dtstamp:"20210101T000000Z" (Test_view.view_of 2027) in
  Alcotest.(check bool) "differs with the parameter" true (a <> b);
  (* DTSTAMP is a per-VEVENT property (RFC 5545 section 3.8.7.2), not a
     calendar-level one -- every one of the 365 events carries the same
     default value, not just one line in the whole feed. *)
  Alcotest.(check int) "default is deterministic" 365
    (count_prefix "DTSTAMP:20270101T000000Z" (lines (out_2027 ())))

(* F1 (fix round 1, 2026-08-19): 9999 is the domain's own last civil year.
   Its last VEVENT's successor date (10000-01-01) falls outside the
   1583..9999 domain [Date.make] enforces (date.mli) -- [Date.add_days] is
   itself unbounded, and [to_iso8601] pads but never truncates, so the naive
   successor string would be 9 digits, not 8. RFC 5545 section 3.6.1 makes a
   DATE-valued DTSTART with neither DTEND nor DURATION mean exactly one day,
   so [dtend_of] omits the DTEND line entirely for that one event rather than
   emit it malformed. *)
let out_9999 () = Ics.year (Test_view.view_of 9999)

let test_dtend_omitted_at_domain_end () =
  let ls = Array.of_list (lines (out_9999 ())) in
  let n = Array.length ls in
  let idx = ref (-1) in
  Array.iteri (fun i l -> if l = "DTSTART;VALUE=DATE:99991231" then idx := i) ls;
  if !idx < 0 then Alcotest.fail "DTSTART;VALUE=DATE:99991231 not found";
  let next_line = if !idx + 1 < n then ls.(!idx + 1) else "" in
  Alcotest.(check bool) "no DTEND line follows DTSTART 99991231" true
    (count_prefix "DTEND;VALUE=DATE:" [ next_line ] = 0);
  Alcotest.(check bool) "SUMMARY follows DTSTART directly instead" true
    (count_prefix "SUMMARY:" [ next_line ] = 1)

(* The general form of F1's bug class: every DTEND value anywhere in the
   feed must be an 8-digit YYYYMMDD, never 9 (a future domain-boundary
   regression anywhere else in 1583..9999 would show up here too). *)
let test_all_9999_dtends_are_eight_digits () =
  let ls = lines (out_9999 ()) in
  let prefix = "DTEND;VALUE=DATE:" in
  let ends =
    List.filter_map
      (fun l ->
        if count_prefix prefix [ l ] = 1 then
          Some (String.sub l (String.length prefix) (String.length l - String.length prefix))
        else None)
      ls
  in
  Alcotest.(check bool) "at least one DTEND present in 9999" true (List.length ends > 0);
  List.iter
    (fun v -> if String.length v <> 8 then Alcotest.failf "DTEND value %S is %d digits, not 8" v (String.length v))
    ends

let suite =
  ( "Emit/ics",
    [ Alcotest.test_case "envelope" `Quick test_envelope;
      Alcotest.test_case "DTEND exclusive" `Quick test_dtend_is_exclusive;
      Alcotest.test_case "uids unique and shaped" `Quick test_uids_unique_and_shaped;
      Alcotest.test_case "byte-stable across runs" `Quick test_output_is_byte_stable_across_runs;
      Alcotest.test_case "folded and CRLF" `Quick test_every_line_folded_and_crlf;
      Alcotest.test_case "no RRULE" `Quick test_no_rrule;
      Alcotest.test_case "text escaped" `Quick test_text_escaped;
      Alcotest.test_case "DTSTAMP is a parameter" `Quick test_dtstamp_is_a_parameter;
      Alcotest.test_case "DTEND omitted at domain end" `Quick test_dtend_omitted_at_domain_end;
      Alcotest.test_case "all 9999 DTENDs are eight digits" `Quick test_all_9999_dtends_are_eight_digits ] )