open Remind_sync
open Utils

type week_first_day = [ `Sunday | `Monday ] [@@deriving show]

type simple_weekly = {
  count_or_until : Icalendar.count_or_until option;
  interval : int option;  (** Optional interval for weekly recurrence, default is 1 *)
  byday : Icalendar.weekday list;
  week_start : week_first_day option;  (** First day of the week for weekly recurrence *)
}
[@@deriving show]
(** A simple weekly REM command *)

type rem = {
  original_uuid : string;  (** Original UID from the iCalendar event *)
  summary : string;  (** Summary or title of the reminder *)
  date : Timedesc.Date.t;  (** Date specification (day, month, year) *)
  end_date : Timedesc.Date.t option;  (** Optional end date for a date range *)
  time : Timedesc.Time.t option;  (** Optional time specification (hour, minute) *)
  duration : Timedesc.Span.t option;  (** Optional duration for timed events *)
  yearly : (int * int) option;  (** Optional simple yearly recurrence (month, day) *)
  weekly : simple_weekly option;  (** Optional simple weekly recurrence *)
  recurring : Icalendar.event list;
      (** List of events that are part of the same recurring series: these are only the overrides, not the master event
      *)
  exdate : Icalendar.date_or_datetime list;  (** List of excluded dates for recurring events *)
}
[@@deriving show]
(** A complete REM command *)

let empty =
  {
    original_uuid = "";
    summary = "";
    date = Timedesc.Date.Ymd.make_exn ~year:1970 ~month:1 ~day:1;
    end_date = None;
    time = None;
    duration = None;
    yearly = None;
    weekly = None;
    recurring = [];
    exdate = [];
  }

let render_yearly month day summary =
  let month_str = month_of_int month |> string_of_month in
  spf "REM %s %d MSG %s\n" month_str day summary

let render_weekly rem weekly =
  let b = Buffer.create 256 in
  List.iter
    begin fun weekday ->
      Buffer.add_string b "REM ";
      Buffer.add_string b (spf "INFO \"UID: %s\" " rem.original_uuid);
      Buffer.add_string b (spf "%s " (string_of_weekday weekday));
      Buffer.add_string b (Timedesc.Date.to_rfc3339 rem.date);
      Buffer.add_string b " ";
      (match weekly.interval with
      | Some interval -> Buffer.add_string b (spf "*%d " (interval * 7))
      | None -> Buffer.add_string b "*7 ");

      (match weekly.count_or_until with
      | Some (`Count count) -> begin
          (* We must compute the until date based on the count and the interval *)
          let wd = Timedesc.Date.weekday rem.date in
          let wd_int = Timedesc.Utils.tm_int_of_weekday wd in
          let day_to_subtract =
            match weekly.week_start with
            | Some `Sunday -> wd_int
            | Some `Monday -> wd_int - 1
            | None -> wd_int (* Default to Sunday if not specified *)
          in
          let interval = Option.value ~default:1 weekly.interval in
          let until_date = Timedesc.Date.add ~days:((count * 7 * interval) - day_to_subtract) rem.date in
          Buffer.add_string b "UNTIL ";
          Buffer.add_string b (Timedesc.Date.to_rfc3339 until_date);
          Buffer.add_string b " "
        end
      | Some (`Until until_date) -> begin
          Buffer.add_string b "UNTIL ";
          let ts = timedesc_of_utc_or_timestamp_local until_date in
          Buffer.add_string b (Timedesc.Date.to_rfc3339 (Timedesc.date ts));
          Buffer.add_string b " "
        end
      | None -> ());

      (match rem.time with
      | Some time ->
          Buffer.add_string b " AT ";
          Buffer.add_string b (string_of_time time)
      | None -> ());

      (match rem.duration with
      | Some duration ->
          Buffer.add_string b " DURATION ";
          Buffer.add_string b (string_of_span duration);
          Buffer.add_string b ""
      | None -> ());

      Buffer.add_string b " MSG ";
      Buffer.add_string b rem.summary;
      Buffer.add_string b "\n"
    end
    weekly.byday;
  Buffer.contents b

let string_of_rem rem =
  match rem.weekly with
  | Some weekly -> render_weekly rem weekly
  | None ->
      begin match rem.yearly with
      | Some (month, day) -> render_yearly month day rem.summary
      | None -> begin
          let b = Buffer.create 256 in
          Buffer.add_string b "REM ";
          Buffer.add_string b (spf "INFO \"UID: %s\" " rem.original_uuid);
          Buffer.add_string b (Timedesc.Date.to_rfc3339 rem.date);
          (match rem.time with
          | Some time ->
              Buffer.add_string b " AT ";
              Buffer.add_string b (string_of_time time)
          | None -> ());
          (match rem.duration with
          | Some duration ->
              Buffer.add_string b " DURATION ";
              Buffer.add_string b (string_of_span duration);
              Buffer.add_string b ""
          | None -> ());
          (match rem.end_date with
          | Some end_date ->
              Buffer.add_string b " THROUGH ";
              Buffer.add_string b (Timedesc.Date.to_rfc3339 end_date)
          | None -> ());
          Buffer.add_string b " MSG ";
          Buffer.add_string b rem.summary;
          Buffer.add_string b "\n";
          Buffer.contents b
        end
      end