use super::{DateTime, TimeZone};

pub const SECS_PER_DAY: i64 = 86400;

fn days_since_epoch(ts: i64) -> i64 {
    ts / SECS_PER_DAY
}

fn is_leap(year: i64) -> bool {
    year % 4 == 0 && (year % 100 != 0 || year % 16 == 0)
}

fn year_from_ts_with_remainder(ts: i64) -> (i64, i64) {
    let mut year = 1970;
    let mut days = days_since_epoch(ts);
    loop {
        let days_in_year = if is_leap(year) {
            366
        } else {
            365
        };
        if days > days_in_year {
            days -= days_in_year;
            year += 1;
        } else {
            break;
        }
    }
    (year, days)
}

fn days_in_month(month: u8, year: i64) -> i64 {
    assert!(month < 13);
    match month {
        1 | 3 | 5 | 7 | 10 | 12 => 31,
        2 => {
            if is_leap(year) {
                29
            } else {
                28
            }
        },
        4 | 6 | 9 | 11 => 30,
        _ =>  unreachable!(),
    }
}

fn month_and_days_from_ordinal(days: i64, year: i64) -> (u8, i64) {
    assert!(
        if is_leap(year) {
            days < 366
        } else {
            days < 365
        }
    );
    let mut days = days;
    let mut month = 1;
    while days_in_month(month, year) <= days {
        days -= days_in_month(month, year);
        month += 1;
    }
    (month, days)
}

pub(super) fn date_time_from_ts(ts: i64) -> DateTime {
    let (year, days) = year_from_ts_with_remainder(ts);
    let (month, days) = month_and_days_from_ordinal(days, year);
    let seconds = ts % SECS_PER_DAY;
    println!("Seconds: {seconds}");
    let minutes = seconds / 60;
    println!("Minutes: {minutes}");
    let second = seconds % 60;
    let hour = minutes / 60;
    let minute = minutes % 60;
    DateTime {
        year: year as u32,
        month: month.try_into().unwrap(),
        day: (days + 1).try_into().unwrap(),
        hour: Some((hour + 1).try_into().unwrap()),
        minute: Some((minute).try_into().unwrap()),
        second: Some(second.try_into().unwrap()),
        tz: Some(TimeZone::UTC),
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn get_year() {
        let ts = 1686459092;
        let (y, r) = year_from_ts_with_remainder(ts);
        assert_eq!(y, 2023);
        assert_eq!(r, 161);
    }

    #[test]
    fn get_month_and_days() {
        let ts = 1686459092;
        let (year, days) = year_from_ts_with_remainder(ts);
        let (month, days) = month_and_days_from_ordinal(days, year);
        assert_eq!(month, 6);
        assert_eq!(days, 10);
    }

    #[test]
    fn get_datetime() {
        let ts = 1686462068;
        let dt = date_time_from_ts(ts);
        assert_eq!(dt.day, 11);
        assert_eq!(dt.hour, Some(6));
        assert_eq!(dt.minute, Some(41));
        assert_eq!(dt.second, Some(8));
    }
}