extern crate chrono;
use chrono::{NaiveDate, Datelike};

fn get_months(start_date_opt: Option<NaiveDate>, end_date_opt: Option<NaiveDate>) -> i64 {
    let mut days_in_month = vec![31,28,31,30,31,30,31,31,30,31,30,31];
    if start_date_opt.is_none() || end_date_opt.is_none() {
        return 0;
    } else {
        if start_date_opt.unwrap() > end_date_opt.unwrap() {
            return 0;
        }
        let start_date_year = start_date_opt.unwrap().year();
        if is_leap_year(start_date_year) {
            days_in_month[1] = 29;
        }
        let end_date_year = end_date_opt.unwrap().year();
        let start_date_month = start_date_opt.unwrap().month();
        let end_date_month = end_date_opt.unwrap().month();
        let start_date_day = start_date_opt.unwrap().day();
        let end_date_day = end_date_opt.unwrap().day();
        let mut no_years = end_date_year - start_date_year;
        let mut no_months = 0;
        if end_date_month < start_date_month {
            no_years -= 1;
            no_months += (12 - start_date_month) + end_date_month;
        } else {
            no_months += end_date_month - start_date_month;
        }
        if end_date_day < start_date_day {
            no_months -= 1;
        }
        if end_date_day > start_date_day && start_date_day != days_in_month[(start_date_month - 1) as usize] {
            no_months += 1;
        }
        (no_years * 12) as i64 + no_months as i64
    }
}

fn is_leap_year(year: i32) -> bool {
    return (year % 4 == 0) && (year % 100 != 0 || year % 400 == 0);
}

fn main() {
    let st_date = Some(NaiveDate::from_ymd(2019, 2, 27));
    let end_date = Some(NaiveDate::from_ymd(2019, 3, 31));
    println!("{}", get_months(st_date, end_date));
}