date-utilities 0.0.4

mod utilities;

use utilities::Template;

/// represents times after 1970. second precision
pub struct Instant {
    /// without `utc_offset` applied
    utc_secs: u64,
    utc_offset: i32,
}

impl Instant {
    pub fn now_utc() -> Self {
        use std::time::SystemTime;

        let time = SystemTime::now();
        let since = time.duration_since(SystemTime::UNIX_EPOCH).unwrap();
        let utc_secs = since.as_secs();
        Self::from_utc_secs(utc_secs)
    }

    pub fn now_local() -> Self {
        use std::time::SystemTime;

        let time = SystemTime::now();
        let since = time.duration_since(SystemTime::UNIX_EPOCH).unwrap();
        let utc_secs = since.as_secs();
        let utc_offset = system_utc_offset_seconds();
        Self {
            utc_secs,
            utc_offset,
        }
    }

    pub fn from_utc_secs(utc_secs: u64) -> Self {
        Self {
            utc_secs,
            utc_offset: 0,
        }
    }

    // TODO std gate && Result
    pub fn from_system_time(time: std::time::SystemTime) -> Self {
        let secs = time
            .duration_since(std::time::SystemTime::UNIX_EPOCH)
            .unwrap()
            .as_secs();
        Self::from_utc_secs(secs)
    }

    pub fn format(&self, template: &str) -> String {
        let template = Template::new(template, '%');
        let secs = self.seconds();

        let day_of_week_str = self.day_of_week_str();

        let (day_of_year, offset_year) = self.day_of_year_and_offset_year();

        let year = BASE_YEAR + offset_year;

        let date_prefixes = if is_leap_year(year) {
            LEAP_YEAR_MONTHS_PREFIX_SUM
        } else {
            NON_LEAP_YEAR_MONTHS_PREFIX_SUM
        };

        let result = date_prefixes
            .iter()
            .enumerate()
            .rev()
            .find(|(_, (_, _, acc))| *acc <= day_of_year);

        let Some((month, (month_name, _, day_sum))) = result else {
            panic!("bad day of year {day_of_year}");
        };

        let date = day_of_year - day_sum + 1; // days are one indexed
        let month = month + 1;

        let week = self.week_of_year();

        // {
        //     let first_day_of_year = (total_days - day_of_year + 3) % 7;
        //     let weeks = (day_of_year + first_day_of_year) / 7 + 1; // weeks are one indexed
        //     let first_day_of_year = DAYS[first_day_of_year as usize];
        // }

        template.interpolate(|item| {
            use std::borrow::Cow;

            fn hour_zero_to_twelve(i: u64) -> u64 {
                if i == 0 { 12 } else { i }
            }

            match item {
                "second" => Cow::Owned(format!("{second:02}", second = secs % 60)),
                "minute" => Cow::Owned(format!("{minute:02}", minute = (secs / MINUTE) % 60)),
                "hour" | "hour24" => Cow::Owned(format!("{hour:02}", hour = (secs / HOUR) % 24)),
                "hour12" => Cow::Owned(format!(
                    "{hour:02}",
                    hour = hour_zero_to_twelve((secs / HOUR) % 12)
                )),
                // TODO
                "week" => Cow::Owned(week.to_string()),
                "week_day" => Cow::Borrowed(day_of_week_str),
                "week_day_short" => Cow::Borrowed(&day_of_week_str[..3]),
                "date_suffix" => Cow::Borrowed(number_index_suffix(date as usize)),
                "date" => Cow::Owned(format!("{date:02}")),
                "month_name" => Cow::Borrowed(month_name),
                "month_name_short" => Cow::Borrowed(&month_name[..3]),
                "month" => Cow::Owned(format!("{month:02}")),
                "full_year" => Cow::Owned(format!("{year}", year = year % 100)),
                "year" => Cow::Owned(format!("{year}")),
                "offset" => {
                    /// I think this is correct
                    fn offset(prefix: char, utc_offset: u64) -> String {
                        let hour = utc_offset / HOUR;
                        let minute = (utc_offset / MINUTE) % 60;
                        format!("{prefix}{hour:02}{minute:02}")
                    }

                    if self.utc_offset < 0 {
                        Cow::Owned(offset('-', -self.utc_offset as u64))
                    } else {
                        Cow::Owned(offset('+', self.utc_offset as u64))
                    }
                }
                name => {
                    panic!("unknown interpolation {name}");
                }
            }
        })
    }

    /// with `utc_offset` applied
    pub fn seconds(&self) -> u64 {
        // we branch to prevent truncation
        if self.utc_offset > 0 {
            self.utc_secs + self.utc_offset as u64
        } else {
            self.utc_secs - self.utc_offset as u64
        }
    }

    /// `month` and `day` are one indexed
    pub fn new(year: u64, month: u64, day: u64, hour: u64, minute: u64, second: u64) -> Self {
        let date_prefixes = if is_leap_year(year) {
            LEAP_YEAR_MONTHS_PREFIX_SUM
        } else {
            NON_LEAP_YEAR_MONTHS_PREFIX_SUM
        };

        let year = year - BASE_YEAR;

        let leap_years = (BASE_YEAR..)
            .take(year as usize)
            .filter(|year| is_leap_year(*year))
            .count() as u64;
        let year = year * NON_LEAP_YEAR + leap_years * DAY;

        let days = (day - 1 + date_prefixes[month as usize - 1].2) * DAY;
        Self::from_utc_secs(year + days + hour * HOUR + minute * MINUTE + second)
    }

    /// *nth month year*
    /// TODO errors
    pub fn parse_english<S: AsRef<str>>(
        mut words: impl Iterator<Item = S>,
    ) -> Result<Self, &'static str> {
        let Some(mut date) = words.next() else {
            return Err("no date");
        };

        if let Some((day, month_and_year)) = date.as_ref().split_once('/') {
            let (month, year) = month_and_year.split_once('/').unwrap();

            let day = str::parse::<u64>(day).unwrap();
            let month = str::parse::<u64>(month).unwrap();
            let year = str::parse::<u64>(year).unwrap();

            let year = if year < 100 { year + 2000 } else { year };

            let next = words.next();
            let (hour, minute, second) = if let Some(next) = next
                && let Some(triple) = parse_time(next.as_ref())
            {
                triple
            } else {
                (12, 0, 0)
            };

            Ok(Instant::new(year, month, day, hour, minute, second))
        } else if let Some((hour, minute, second)) = parse_time(date.as_ref()) {
            Ok(Instant::now_local().set_time(hour, minute, second))
        } else {
            if date.as_ref().eq_ignore_ascii_case("the") {
                if let Some(next) = words.next() {
                    date = next;
                } else {
                    return Err("nothing after the");
                }
            }

            let Some(mut month) = words.next() else {
                return Err("no month");
            };

            if month.as_ref().eq_ignore_ascii_case("of") {
                if let Some(next) = words.next() {
                    month = next;
                } else {
                    return Err("nothing after of");
                }
            }

            let year = words.next();

            //

            let year = if let Some(year) = year {
                let Ok(year) = year.as_ref().parse() else {
                    return Err("invalid year");
                };
                if year < 100 { year + 2000 } else { year }
            } else {
                Instant::now_local().year()
            };

            //

            let month = month.as_ref();

            let months = if is_leap_year(year) {
                LEAP_YEAR_MONTHS_PREFIX_SUM
            } else {
                NON_LEAP_YEAR_MONTHS_PREFIX_SUM
            };

            let month = if month.len() == 3 {
                months
                    .iter()
                    .position(|(name, ..)| name[..3].eq_ignore_ascii_case(month))
            } else {
                months
                    .iter()
                    .position(|(name, ..)| name.eq_ignore_ascii_case(month))
            };

            let month = if let Some(month) = month {
                month + 1
            } else {
                return Err("cannot find month");
            };

            //
            let date = {
                let date = date.as_ref();
                let suffixed = date.ends_with("st")
                    || date.ends_with("nd")
                    || date.ends_with("rd")
                    || date.ends_with("th");
                if suffixed {
                    &date[..(date.len() - 2)]
                } else {
                    date
                }
            };

            let Ok(day) = date.parse() else {
                return Err("invalid date");
            };

            let (hour, minute, seconds) = if let Some(other) = words.next() {
                if let Some(triple) = parse_time(other.as_ref()) {
                    triple
                } else {
                    return Err("invalid time");
                }
            } else {
                (12, 0, 0)
            };

            Ok(Self::new(year, month as u64, day, hour, minute, seconds))
        }
    }

    /// Returns the [`Duration`] between dates. If other
    pub fn difference(&self, other: Instant) -> Result<Duration, Duration> {
        let difference = self.seconds().checked_sub(other.seconds());
        match difference {
            Some(secs) => Ok(Duration { secs }),
            None => Err(Duration {
                secs: other.seconds() - self.seconds(),
            }),
        }
    }

    #[must_use]
    pub fn set_time(mut self, hours: u64, minutes: u64, seconds: u64) -> Self {
        // reset
        self.utc_secs -= self.utc_secs % DAY;
        self.utc_secs -= self.utc_secs % HOUR;
        self.utc_secs -= self.utc_secs % MINUTE;

        // set new
        self.utc_secs += hours * HOUR;
        self.utc_secs += minutes * MINUTE;
        self.utc_secs += seconds;
        self
    }

    #[must_use]
    pub fn year(&self) -> u64 {
        // This will overcount
        let non_leap_years = self.seconds() / NON_LEAP_YEAR;
        let accounting_for_leap_years =
            (self.seconds() - DAY * leap_years_since(non_leap_years)) / NON_LEAP_YEAR;
        BASE_YEAR + accounting_for_leap_years
    }

    #[must_use]
    pub fn day_of_week(&self) -> u8 {
        ((self.seconds() / DAY + 3) % 7) as u8
    }

    #[must_use]
    pub fn day_of_week_str(&self) -> &str {
        DAYS[self.day_of_week() as usize]
    }

    /// 1 indexed
    #[must_use]
    pub fn week_of_year(&self) -> u64 {
        let (day_of_year, _) = self.day_of_year_and_offset_year();
        let offset = Self::utc_start_of_year(self.year()).day_of_week() as u64;
        ((day_of_year + offset) / 7) + 1
    }

    fn day_of_year_and_offset_year(&self) -> (u64, u64) {
        let secs = self.seconds();

        let offset_year = secs / NON_LEAP_YEAR;
        let day_of_year = (secs / DAY) % 365;

        let leap_years = leap_years_since(offset_year);

        if leap_years > day_of_year {
            let year = offset_year - 1;
            let day = (count_of_days_in_year(BASE_YEAR + year) + day_of_year) - leap_years;
            (day, year)
        } else {
            (day_of_year - leap_years, offset_year)
        }
    }

    pub fn month(&self) -> (&'static str, u64, u64) {
        let (day_of_year, offset_year) = self.day_of_year_and_offset_year();

        let year = BASE_YEAR + offset_year;
        let date_prefixes = if is_leap_year(year) {
            LEAP_YEAR_MONTHS_PREFIX_SUM
        } else {
            NON_LEAP_YEAR_MONTHS_PREFIX_SUM
        };

        let result = date_prefixes
            .iter()
            .enumerate()
            .rev()
            .find(|(_, (_, _, acc))| *acc <= day_of_year);

        let Some((month, (month_name, _, day_sum))) = result else {
            panic!("bad day of year {day_of_year}");
        };

        let date = day_of_year - day_sum + 1; // days are one indexed
        (month_name, month as u64, date)
    }

    // pub fn month_str() -> &str {}

    /// TODO utc vs local etc
    #[must_use]
    pub fn utc_start_of_year(year: u64) -> Self {
        let year = year - BASE_YEAR;
        Self {
            utc_secs: year * NON_LEAP_YEAR + leap_years_since(year) * DAY,
            utc_offset: 0,
        }
    }
}

fn parse_time(on: &str) -> Option<(u64, u64, u64)> {
    if let Some((hour, minute_and_seconds)) = on.split_once(':') {
        let hour = str::parse::<u64>(hour).unwrap();
        if let Some((minute, second)) = minute_and_seconds.split_once(':') {
            let minute = str::parse::<u64>(minute).unwrap();
            let second = str::parse::<u64>(second).unwrap();
            Some((hour, minute, second))
        } else {
            let minute = minute_and_seconds;
            let minute = str::parse::<u64>(minute).unwrap();
            Some((hour, minute, 0))
        }
    } else {
        None
    }
}

pub struct Month {
    pub name: &'static str,
    pub days: u8,
}

/// From offset year
pub struct Year(u32);

impl Year {
    pub fn new(year: u32) -> Self {
        Self(year)
    }
    pub fn months(&self) -> impl Iterator<Item = Month> {
        let months = if is_leap_year(self.0 as u64) {
            LEAP_YEAR_MONTHS_PREFIX_SUM
        } else {
            NON_LEAP_YEAR_MONTHS_PREFIX_SUM
        };

        months.iter().map(|(name, days, _)| Month {
            name,
            days: *days as u8,
        })
    }
}

#[derive(Clone, Copy)]
pub struct Duration {
    pub(crate) secs: u64,
}

impl Duration {
    #[must_use]
    pub const fn from_secs(secs: u64) -> Self {
        Self { secs }
    }

    #[must_use]
    pub const fn from_seconds(secs: u64) -> Self {
        Self { secs }
    }

    #[must_use]
    pub const fn from_minutes(minutes: u64) -> Self {
        Self {
            secs: minutes * MINUTE,
        }
    }

    #[must_use]
    pub const fn from_hours(hours: u64) -> Self {
        Self { secs: hours * HOUR }
    }

    #[must_use]
    pub const fn from_days(days: u64) -> Self {
        Self { secs: days * DAY }
    }

    #[must_use]
    pub const fn from_weeks(weeks: u64) -> Self {
        Self { secs: weeks * WEEK }
    }

    #[must_use]
    pub fn format(&self) -> String {
        fn format_(secs: u64, precision: usize, buf: &mut String) {
            use std::fmt::Write;

            if secs == 0 {
                return;
            }

            if !buf.is_empty() {
                if precision > 1 {
                    buf.push_str(", ");
                } else if precision == 1 {
                    buf.push_str(" and ");
                } else if precision == 0 {
                    return;
                }
            }

            if secs < MINUTE {
                write!(buf, "{secs} seconds").unwrap();
            } else if secs < HOUR {
                let mins = secs / MINUTE;
                write!(buf, "{mins} minutes").unwrap();
                format_(secs % MINUTE, precision - 1, buf);
            } else if secs < DAY {
                let hours = secs / HOUR;
                write!(buf, "{hours} hours").unwrap();
                format_(secs % HOUR, precision - 1, buf);
            } else if secs < WEEK {
                let days = secs / DAY;
                write!(buf, "{days} days").unwrap();
                format_(secs % DAY, precision - 1, buf);
            } else if secs < NON_LEAP_YEAR {
                let weeks = secs / WEEK;
                write!(buf, "{weeks} weeks").unwrap();
                format_(secs % WEEK, precision - 1, buf);
            } else {
                const MONTH: u64 = DAY * 30;
                let months = secs / MONTH;
                write!(buf, "{months} months").unwrap();
                // format!("{years} years", years = self.secs / NON_LEAP_YEAR)
            }
        }

        let precision = 2;
        let mut buf = String::new();

        format_(self.secs, precision, &mut buf);

        buf
    }
}

impl std::ops::Add<Duration> for Instant {
    type Output = Self;

    fn add(mut self, duration: Duration) -> Self::Output {
        self.utc_secs += duration.secs;
        self
    }
}

impl std::ops::AddAssign<Duration> for Instant {
    fn add_assign(&mut self, duration: Duration) {
        self.utc_secs += duration.secs;
    }
}

impl std::ops::Sub<Duration> for Instant {
    type Output = Self;

    fn sub(mut self, duration: Duration) -> Self::Output {
        self.utc_secs -= duration.secs;
        self
    }
}

impl std::ops::SubAssign<Duration> for Instant {
    fn sub_assign(&mut self, duration: Duration) {
        self.utc_secs -= duration.secs;
    }
}

pub const MINUTE: u64 = 60;
pub const HOUR: u64 = 60 * MINUTE;
pub const DAY: u64 = 24 * HOUR;
pub const WEEK: u64 = 7 * DAY;

const NON_LEAP_YEAR: u64 = 365 * DAY;
// const LEAP_YEAR: u64 = 364 * DAY;

const BASE_YEAR: u64 = 1970;

/*
1	January	  31
2	February  28 (29 in leap years)
3	March	  31
4	April	  30
5	May	      31
6	June	  30
7	July      31
8	August    31
9	September 30
10	October	  31
11	November  30
12	December  31
*/
const NON_LEAP_YEAR_MONTHS_PREFIX_SUM: &[(&str, u64, u64)] = &[
    ("January", 31, 0),
    ("February", 28, 31),
    ("March", 31, 59),
    ("April", 30, 90),
    ("May", 31, 120),
    ("June", 30, 151),
    ("July", 31, 181),
    ("August", 31, 212),
    ("September", 30, 243),
    ("October", 31, 273),
    ("November", 30, 304),
    ("December", 31, 334),
];

const LEAP_YEAR_MONTHS_PREFIX_SUM: &[(&str, u64, u64)] = &[
    ("January", 31, 0),
    ("February", 29, 31),
    ("March", 31, 60),
    ("April", 30, 91),
    ("May", 31, 121),
    ("June", 30, 152),
    ("July", 31, 182),
    ("August", 31, 213),
    ("September", 30, 244),
    ("October", 31, 274),
    ("November", 30, 305),
    ("December", 31, 335),
];

const DAYS: &[&str] = &[
    "Monday",
    "Tuesday",
    "Wednesday",
    "Thursday",
    "Friday",
    "Saturday",
    "Sunday",
];

pub fn count_of_days_in_year(year: u64) -> u64 {
    365 + is_leap_year(year) as u64
}

fn is_leap_year(year: u64) -> bool {
    year.is_multiple_of(4) && (!year.is_multiple_of(100) || year.is_multiple_of(400))
}

fn leap_years_since(offset_year: u64) -> u64 {
    (BASE_YEAR..)
        .take(offset_year as usize)
        .filter(|year| is_leap_year(*year))
        .count() as u64
}

fn number_index_suffix(item: usize) -> &'static str {
    match item % 10 {
        1 => "st",
        2 => "nd",
        3 => "rd",
        _ => "th",
    }
}

#[allow(non_snake_case)]
pub mod FORMATS {
    /// 🇬🇧
    pub const DATE_MONTH_YEAR: &str = "%date/%month/%year";
    /// 🇺🇸
    pub const MONTH_DATE_YEAR: &str = "%month/%date/%year";

    pub const DATE_NAME_MONTH_YEAR: &str = "%week_day %date%date_suffix %month_name %year";
    pub const TIME_DATE_NAME_MONTH_YEAR: &str =
        "%hour:%minute %week_day %date%date_suffix %month_name %year";
    pub const ENGLISH: &str = "%week_day the %date%date_suffix of %month_name %year";

    pub const TIME: &str = "%hour:%minute";
    pub const TIME_WITH_SECONDS: &str = "%hour:%minute:%second";

    pub const WEEK: &str = "%week";

    pub const FULL_MINIMAL: &str = "%hour:%minute:%second %date/%month/%year";

    /// TODO
    pub const FULL: &str = "%hour:%minute:%second %date/%month/%year";

    pub const ISO_8601: &str = "%year-%month-%dateT%hour:%minute:%second";
    // Thu, 07 Apr 2005 22:13:13 +0200
    pub const RFC_2822: &str = "%year-%month-%dateT%hour:%minute:%second";
}

#[cfg(unix)]
fn system_utc_offset_seconds() -> i32 {
    use std::mem::MaybeUninit;

    unsafe {
        let mut now: libc::time_t = 0;
        libc::time(&raw mut now);

        let mut tm = MaybeUninit::<libc::tm>::uninit();
        libc::localtime_r(&raw const now, tm.as_mut_ptr());

        let tm = tm.assume_init();
        i32::try_from(tm.tm_gmtoff).unwrap()
    }
}

#[cfg(windows)]
fn system_utc_offset_seconds() -> i32 {
    use std::mem::MaybeUninit;
    use winapi::um::timezoneapi::GetTimeZoneInformation;
    use winapi::um::timezoneapi::TIME_ZONE_INFORMATION;

    unsafe {
        let mut tzi = MaybeUninit::<TIME_ZONE_INFORMATION>::uninit();
        let state = GetTimeZoneInformation(tzi.as_mut_ptr());
        let tzi = tzi.assume_init();

        let mut bias = tzi.Bias;

        match state {
            winapi::um::timezoneapi::TIME_ZONE_ID_DAYLIGHT => {
                bias += tzi.DaylightBias;
            }
            winapi::um::timezoneapi::TIME_ZONE_ID_STANDARD => {
                bias += tzi.StandardBias;
            }
            _ => {}
        }

        // Windows bias is minutes *west* of UTC
        -bias * 60
    }
}