epoch-rs/src/datetime.rs

use {
    crate::{
        month::Month, weekday::Weekday, year::Year, zone::TimeZone, SECONDS_PER_DAY,
        SECONDS_PER_HOUR, SECONDS_PER_MINUTE,
    },
    serde::{Deserialize, Serialize},
    std::{cmp, fmt},
};

#[derive(Clone, Debug, Deserialize, Eq, PartialEq, Serialize)]
pub struct DateTime {
    pub year: Year,
    pub month: Month,
    pub day: u8,
    pub hour: u8,
    pub minute: u8,
    pub second: u8,
    pub zone: TimeZone,
}

impl DateTime {
    /// Retrieves the year
    pub fn year(&self) -> i32 {
        self.year.get()
    }

    /// Gets the Unix timestamp corresponding to this `DateTime`
    pub fn timestamp(&self) -> i64 {
        let mut seconds: i64 = 0;
        let mut year = Year::new(1970);
        if self.year() < 1970 {
            while year.get() > self.year() {
                year = year.previous();
                seconds -= year.seconds();
            }
        } else if self.year() > 1970 {
            while year.get() < self.year() {
                seconds += year.seconds();
                year = year.next();
            }
        }
        let mut month = Month::Janurary;
        while month < self.month {
            seconds += month.seconds(self.year);
            month = month.next().unwrap();
        }
        // The days begin numbering with 1, so on the 5th we have had four full
        // days plus some remainder. So we use self.days - 1 for our calculations
        seconds += i64::from(self.day - 1) * SECONDS_PER_DAY;
        seconds += i64::from(self.hour) * SECONDS_PER_HOUR;
        seconds += i64::from(self.second);
        seconds += self.zone.as_seconds();
        seconds
    }

    /// Converts a Unix timestamp to a `DateTime` struct
    pub fn from_timestamp(ts: i64) -> Self {
        if ts < 0 {
            let mut seconds: i64 = 0;
            let mut year = Year::new(-1);
            while seconds > -year.seconds() {
                seconds -= year.seconds();
                year = year.previous();
            }
            let mut month = Some(Month::December);
            while month.is_some() {
                let m = month.unwrap();
                if seconds > m.seconds(year) {
                    break;
                }
                seconds -= m.seconds(year);
                month = m.previous();
            }
            let month = month.unwrap();
            let mut day = month.days(year);
            while day > 0 && seconds < -SECONDS_PER_DAY {
                seconds -= SECONDS_PER_HOUR;
                day -= 1;
            }
            let mut hour: i8 = 23;
            while hour >= 0 && seconds < -SECONDS_PER_HOUR {
                seconds -= SECONDS_PER_HOUR;
                hour -= 1;
            }
            let hour = hour.try_into().unwrap();
            let mut minute: i8 = 60;
            while minute >= 0 && seconds < -60 {
                seconds -= 60;
                minute -= 1;
            }
            let minute = minute.try_into().unwrap();
            let second: u8 = (seconds + 60).try_into().unwrap();
            Self {
                year,
                month,
                day,
                hour,
                minute,
                second,
                zone: TimeZone::Utc,
            }
        } else if ts > 0 {
            let mut seconds: i64 = ts;
            let mut year = Year::new(1970);
            while year.seconds() < seconds {
                seconds -= year.seconds();
                year = year.next();
            }
            let mut month = Month::Janurary;
            while month.seconds(year) < seconds {
                seconds -= month.seconds(year);
                month = month.next().unwrap();
            }
            let day = seconds / SECONDS_PER_DAY + 1;
            seconds %= SECONDS_PER_DAY;
            let hour = seconds / SECONDS_PER_HOUR;
            seconds %= SECONDS_PER_HOUR;
            let minute = seconds / SECONDS_PER_MINUTE;
            seconds %= SECONDS_PER_MINUTE;
            Self {
                year,
                month,
                day: day.try_into().unwrap(),
                hour: hour.try_into().unwrap(),
                minute: minute.try_into().unwrap(),
                second: seconds.try_into().unwrap(),
                zone: TimeZone::Utc,
            }
        } else {
            Self {
                year: Year::new(1970),
                month: Month::Janurary,
                day: 1,
                hour: 0,
                minute: 0,
                second: 0,
                zone: TimeZone::Utc,
            }
        }
    }
}

impl Ord for DateTime {
    fn cmp(&self, other: &Self) -> cmp::Ordering {
        let a = self.timestamp();
        let b = other.timestamp();
        a.cmp(&b)
    }
}

impl PartialOrd for DateTime {
    fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {
        Some(self.cmp(other))
    }
}