[WIP] OCaml Date implementation

date.ml

open Unix

type date = {
  year : int;
  month : int;
  day : int;
}

exception InvalidDate of string

let is_leap_year year =
  year mod 4 = 0 && (year mod 100 <> 0 || year mod 400 = 0)

let days_in_year year =
  if is_leap_year year then 366 else 365

let days_in_month year month =
  match month with
  | 1 | 3 | 5 | 7 | 8 | 10 | 12 -> 31
  | 4 | 6 | 9 | 11 -> 30
  | 2 -> if is_leap_year year then 29 else 28
  | _ -> 0

let is_valid_date { year; month; day } =
  month >= 1 && month <= 12 && day >= 1 && (days_in_month year day) > 0

let create year month day =
  let date = { year; month; day } in
  match is_valid_date date with
  | true -> date
  | _ -> raise (InvalidDate "Invalid date")

let today () =
  let tm = Unix.localtime (Unix.time ()) in
  create (tm.tm_year + 1900) (tm.tm_mon + 1) tm.tm_mday