leap-seconds 0.1.0

//! This crate provides a means of accessing current leap second data.
//!
//! This is achieved through a parser that can read and provide access to the data in a
//! `leap-seconds.list` file. A copy of this file can be obtained from various sources. To name a
//! few:
//!  - IERS: <https://hpiers.obspm.fr/iers/bul/bulc/ntp/leap-seconds.list>
//!  - TZDB (from IANA): <https://data.iana.org/time-zones/tzdb/leap-seconds.list>
//!  - TZDB (from GitHub): <https://raw.githubusercontent.com/eggert/tz/main/leap-seconds.list>
//!  - Meinberg: <https://www.meinberg.de/download/ntp/leap-seconds.list>
//!
//! It is recommended that you get the file from the [IERS] as they are responsible for announcing
//! leap seconds. Consequently, they will most likely provide the most up to date version of the
//! file.
//!
//! You do not need to have any knowledge of the structure or contents of the `leap-seconds.list`
//! file in order to use this crate. However, if you want to know more about `leap-seconds.list`,
//! here's an article from Meinberg on the matter:
//!
//! <https://kb.meinbergglobal.com/kb/time_sync/ntp/configuration/ntp_leap_second_file> (last
//! accessed 2022-11-26)
//!
//! # Quickstart
//!
//! [reqwest] is used in this example, but any other HTTP library or a local file will work just as
//! well.
//!
//! ```
//! use leap_seconds::LeapSecondsList;
//! use std::io::BufReader;
//!
//! // ======= fetching & parsing the file ======= //
//!
//! // get the file from the IERS
//! let file = reqwest::blocking::get("https://hpiers.obspm.fr/iers/bul/bulc/ntp/leap-seconds.list")
//!         .unwrap();
//! // parse the file
//! let leap_seconds_list = LeapSecondsList::new(BufReader::new(file)).unwrap();
//!
//! // make sure the file is up to date
//! // you should always do this unless you don't mind working with outdated data
//! assert!(!leap_seconds_list.is_expired());
//!
//! // ======= some things that are possible ======= //
//!
//! // get the next leap second that will be introduced
//! let next_leap_second = leap_seconds_list.next_leap_second();
//!
//! // get an ordered slice of all future leap seconds currently announced
//! let future_leap_seconds = leap_seconds_list.planned_leap_seconds();
//!
//! // get an ordered slice of all leap seconds that have been introduced since 1970
//! let all_leap_seconds = leap_seconds_list.leap_seconds();
//!
//! // get the last time the `leap-seconds.list` file was updated
//! let last_update = leap_seconds_list.last_update();
//! ```
//!
//! [IERS]: https://www.iers.org
//! [reqwest]: https://crates.io/crates/reqwest

#![deny(clippy::all)]
#![warn(clippy::pedantic)]
#![warn(clippy::cargo)]
#![warn(missing_docs)]

use {
    core::fmt::{self, Display},
    sha1::{Digest, Sha1},
    std::{io::BufRead, time::SystemTime},
};

pub use errors::*;

pub mod errors;

const SECONDS_PER_MINUTE: u8 = 60;
const MINUTES_PER_HOUR: u8 = 60;
const HOURS_PER_DAY: u8 = 24;

const SECONDS_PER_HOUR: u64 = (MINUTES_PER_HOUR as u64) * (SECONDS_PER_MINUTE as u64);
const SECONDS_PER_DAY: u64 = (HOURS_PER_DAY as u64) * SECONDS_PER_HOUR;

const JANUARY: u8 = 1;
const FEBRUARY: u8 = 2;
const MARCH: u8 = 3;
const APRIL: u8 = 4;
const MAY: u8 = 5;
const JUNE: u8 = 6;
const JULY: u8 = 7;
const AUGUST: u8 = 8;
const SEPTEMBER: u8 = 9;
const OCTOBER: u8 = 10;
const NOVEMBER: u8 = 11;
const DECEMBER: u8 = 12;

const DAYS_PER_ERA: u64 = 365 * 400 + 100 - 4 + 1;
const DAYS_BETWEEN_1900_01_01_AND_0000_03_01: u64 =
    1900 * 365 + (1900 / 400) - (1900 / 100) + (1900 / 4) - 31 - 28;

#[allow(clippy::identity_op)]
const DAYS_BETWEEN_1900_01_01_AND_1970_01_01: u64 = 70 * 365 + (70 / 400) - (70 / 100) + (70 / 4);
const SECONDS_BETWEEN_1900_01_01_AND_1970_01_01: u64 =
    DAYS_BETWEEN_1900_01_01_AND_1970_01_01 * SECONDS_PER_DAY;

/// A date.
///
/// Is limited to years `>= 0`.
#[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
pub struct Date {
    year: u64,
    month: u8,
    day: u8,
}

impl Date {
    /// Creates a new [`Date`].
    ///
    /// ```
    /// # use leap_seconds::{Date, InvalidDate};
    /// #
    /// let _ = Date::new(2003, 03, 30)?;
    /// #
    /// # Ok::<(), InvalidDate>(())
    /// ```
    ///
    /// # Errors
    ///
    /// Fails if the given date is invalid.
    ///
    /// ```
    /// # use leap_seconds::Date;
    /// #
    /// // The year 7_777_777 is not a leap year
    /// let error = Date::new(7_777_777, 2, 29);
    /// assert!(error.is_err());
    /// ```
    pub const fn new(year: u64, month: u8, day: u8) -> Result<Self, InvalidDate> {
        if month > 12 || month < 1 {
            Err(InvalidDate::MonthOutOfRange(month))
        } else if day < 1 || day > days_in_month(month, year) {
            Err(InvalidDate::DayOutOfRange(day))
        } else {
            Ok(Date { year, month, day })
        }
    }

    /// Gets the day of this [`Date`].
    ///
    /// ```
    /// # use leap_seconds::{Date, InvalidDate};
    /// #
    /// let date = Date::new(1977, 5, 25)?;
    /// assert_eq!(date.day(), 25);
    /// #
    /// # Ok::<(), InvalidDate>(())
    /// ```
    #[must_use]
    pub const fn day(self) -> u8 {
        self.day
    }

    /// Gets the month of this [`Date`].
    ///
    /// ```
    /// # use leap_seconds::{Date, InvalidDate};
    /// #
    /// let date = Date::new(1980, 5, 21)?;
    /// assert_eq!(date.month(), 5);
    /// #
    /// # Ok::<(), InvalidDate>(())
    /// ```
    #[must_use]
    pub const fn month(self) -> u8 {
        self.month
    }

    /// Gets the year of this [`Date`].
    ///
    /// ```
    /// # use leap_seconds::{Date, InvalidDate};
    /// #
    /// let date = Date::new(1983, 5, 25)?;
    /// assert_eq!(date.year(), 1983);
    /// #
    /// # Ok::<(), InvalidDate>(())
    /// ```
    #[must_use]
    pub const fn year(self) -> u64 {
        self.year
    }

    const fn days_since_1900(self) -> u64 {
        // Credits to Howard Hinnant for the algorithm:
        // https://howardhinnant.github.io/date_algorithms.html (last accessed 2022-11-24)

        let month = self.month as u64;
        let day = self.day as u64;

        let year = self.year - (month <= 2) as u64;
        let era = year / 400;
        let year_of_era = year - era * 400; // [0, 399]
        let day_of_year = (153 * ((month + 9) % 12) + 2) / 5 + day - 1; // [0, 365]
        let day_of_era = year_of_era * 365 + year_of_era / 4 - year_of_era / 100 + day_of_year; // [0, 146096]

        era * DAYS_PER_ERA + day_of_era - DAYS_BETWEEN_1900_01_01_AND_0000_03_01
    }
}

/// A time.
#[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
pub struct Time {
    hours: u8,
    minutes: u8,
    seconds: u8,
}

impl Time {
    /// Create a new [`Time`].
    ///
    /// ```
    /// # use leap_seconds::{InvalidTime, Time};
    /// #
    /// // 15:03:42
    /// let _ = Time::new(15, 3, 42)?;
    /// #
    /// # Ok::<(), InvalidTime>(())
    /// ```
    ///
    /// # Errors
    ///
    /// Fails if the given time is invalid.
    ///
    /// ```
    /// # use leap_seconds::Time;
    /// #
    /// let error = Time::new(23, 60, 15);
    /// assert!(error.is_err());
    /// ```
    pub fn new(hours: u8, minutes: u8, seconds: u8) -> Result<Self, InvalidTime> {
        if hours >= HOURS_PER_DAY {
            Err(InvalidTime::HoursOutOfRange(hours))
        } else if minutes >= MINUTES_PER_HOUR {
            Err(InvalidTime::MinutesOutOfRange(minutes))
        } else if seconds >= SECONDS_PER_MINUTE {
            Err(InvalidTime::SecondsOutOfRange(seconds))
        } else {
            Ok(Time {
                hours,
                minutes,
                seconds,
            })
        }
    }

    /// Gets the hours of this [`Time`].
    ///
    /// ```
    /// # use leap_seconds::{InvalidTime, Time};
    /// #
    /// let time = Time::new(13, 17, 29)?;
    /// assert_eq!(time.hours(), 13);
    /// #
    /// # Ok::<(), InvalidTime>(())
    /// ```
    #[must_use]
    pub const fn hours(self) -> u8 {
        self.hours
    }

    /// Gets the minutes of this [`Time`].
    ///
    /// ```
    /// # use leap_seconds::{InvalidTime, Time};
    /// #
    /// let time = Time::new(13, 17, 29)?;
    /// assert_eq!(time.minutes(), 17);
    /// #
    /// # Ok::<(), InvalidTime>(())
    /// ```
    #[must_use]
    pub const fn minutes(self) -> u8 {
        self.minutes
    }

    /// Gets the seconds of this [`Time`].
    ///
    /// ```
    /// # use leap_seconds::{InvalidTime, Time};
    /// #
    /// let time = Time::new(13, 17, 29)?;
    /// assert_eq!(time.seconds(), 29);
    /// #
    /// # Ok::<(), InvalidTime>(())
    /// ```
    #[must_use]
    pub const fn seconds(self) -> u8 {
        self.seconds
    }

    const fn total_seconds(self) -> u64 {
        (self.hours as u64) * SECONDS_PER_HOUR
            + (self.minutes as u64) * (SECONDS_PER_MINUTE as u64)
            + (self.seconds as u64)
    }
}

/// A [`Date`] and a [`Time`].
///
/// That's literally what it is, nothing more to see here.
#[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
pub struct DateTime {
    /// The [`Date`] of the [`DateTime`].
    pub date: Date,
    /// The [`Time`] of the [`DateTime`].
    pub time: Time,
}

impl From<Timestamp> for DateTime {
    fn from(timestamp: Timestamp) -> Self {
        timestamp.date_time()
    }
}

const fn is_leap_year(year: u64) -> bool {
    (year % 4 == 0) && ((year % 100 != 0) || (year % 400 == 0))
}

const fn days_in_month(month: u8, year: u64) -> u8 {
    match month {
        JANUARY | MARCH | MAY | JULY | AUGUST | OCTOBER | DECEMBER => 31,
        APRIL | JUNE | SEPTEMBER | NOVEMBER => 30,
        FEBRUARY => {
            if is_leap_year(year) {
                29
            } else {
                28
            }
        }
        // This should be unreachable!, but unreachable! is not yet const, so this is the best I
        // can do right now.
        _ => panic!("invalid month"),
    }
}

/// A date and time represented as seconds since 1900-01-01 00:00:00.
///
/// [`Timestamp`] is a simple wrapper around a [`u64`] with a couple of convenience functions.
#[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
pub struct Timestamp {
    value: u64,
}

impl Timestamp {
    /// The maximum [`DateTime`] that can be represented as [`Timestamp`].
    ///
    /// ```
    /// # use std::error::Error;
    /// use leap_seconds::{Date, DateTime, Time, Timestamp};
    ///
    /// let alt_max_1 = DateTime {
    ///     date: Date::new(584_554_051_153, 11, 9)?,
    ///     time: Time::new(7, 0, 15)?,
    /// };
    ///
    /// let alt_max_2 = Timestamp::from_u64(u64::MAX).date_time();
    ///
    /// assert_eq!(Timestamp::MAX_REPRESENTABLE_DATE_TIME, alt_max_1);
    /// assert_eq!(Timestamp::MAX_REPRESENTABLE_DATE_TIME, alt_max_2);
    /// #
    /// # Ok::<(), Box<dyn Error>>(())
    /// ```
    pub const MAX_REPRESENTABLE_DATE_TIME: DateTime = Self::from_u64(u64::MAX).date_time();

    /// The minimum [`DateTime`] that can be represented as [`Timestamp`].
    ///
    /// ```
    /// # use std::error::Error;
    /// use leap_seconds::{Date, DateTime, Time, Timestamp};
    ///
    /// let alt_min_1 = DateTime {
    ///     date: Date::new(1900, 1, 1)?,
    ///     time: Time::new(0, 0, 0)?,
    /// };
    ///
    /// let alt_min_2 = Timestamp::from_u64(0).date_time();
    ///
    /// assert_eq!(Timestamp::MIN_REPRESENTABLE_DATE_TIME, alt_min_1);
    /// assert_eq!(Timestamp::MIN_REPRESENTABLE_DATE_TIME, alt_min_2);
    /// #
    /// # Ok::<(), Box<dyn Error>>(())
    /// ```
    pub const MIN_REPRESENTABLE_DATE_TIME: DateTime = Self::from_u64(0).date_time();

    /// Creates a new [`Timestamp`] from a [`DateTime`].
    ///
    /// # Errors
    ///
    /// Fails if the [`DateTime`] is not representable as a [`Timestamp`].
    ///
    /// ```
    /// use leap_seconds::{Date, DateTime, Time, Timestamp};
    ///
    /// let error = Timestamp::from_date_time(DateTime {
    ///     date: Date::new(1899, 1, 1).expect("valid date"),
    ///     time: Time::new(12, 0, 0).expect("valid time"),
    /// });
    ///
    /// assert!(error.is_err());
    /// ```
    pub fn from_date_time(date_time: DateTime) -> Result<Self, DateTimeNotRepresentable> {
        if (date_time >= Self::MIN_REPRESENTABLE_DATE_TIME)
            && (date_time <= Self::MAX_REPRESENTABLE_DATE_TIME)
        {
            Ok(Timestamp::from_u64(
                date_time.date.days_since_1900() * SECONDS_PER_DAY + date_time.time.total_seconds(),
            ))
        } else {
            Err(DateTimeNotRepresentable { date_time })
        }
    }

    /// Creates a new [`Timestamp`] from a [`u64`].
    #[must_use]
    pub const fn from_u64(value: u64) -> Self {
        Self { value }
    }

    /// Returns the current time.
    #[must_use]
    pub fn now() -> Self {
        let secs_since_unix_epoch = SystemTime::now()
            .duration_since(SystemTime::UNIX_EPOCH)
            .expect("now is later than the unix epoch")
            .as_secs();
        let secs_since_1900_01_01 =
            secs_since_unix_epoch + SECONDS_BETWEEN_1900_01_01_AND_1970_01_01;

        Timestamp::from_u64(secs_since_1900_01_01)
    }

    /// Gets the integer representation of this [`Timestamp`].
    #[must_use]
    pub const fn as_u64(self) -> u64 {
        self.value
    }

    /// Gets the date and time of this [`Timestamp`].
    #[must_use]
    pub const fn date_time(self) -> DateTime {
        DateTime {
            date: self.date(),
            time: self.time(),
        }
    }

    /// Gets the time of this [`Timestamp`].
    #[must_use]
    pub const fn time(self) -> Time {
        Time {
            hours: self.hours(),
            minutes: self.minutes(),
            seconds: self.seconds(),
        }
    }

    /// Gets the date of this [`Timestamp`].
    #[must_use]
    pub const fn date(self) -> Date {
        // Credits to Howard Hinnant for the algorithm:
        // https://howardhinnant.github.io/date_algorithms.html (last accessed 2022-11-24)

        let days_since_1900_01_01 = self.total_days();
        let days_since_0000_03_01 = days_since_1900_01_01 + DAYS_BETWEEN_1900_01_01_AND_0000_03_01;
        let era = days_since_0000_03_01 / DAYS_PER_ERA;
        let day_of_era = days_since_0000_03_01 % DAYS_PER_ERA; // [0, 146096]
        let year_of_era =
            (day_of_era - day_of_era / 1460 + day_of_era / 36524 - day_of_era / 146_096) / 365; // [0, 399]
        let year = year_of_era + era * 400;
        let day_of_year = day_of_era - (365 * year_of_era + year_of_era / 4 - year_of_era / 100); // [0, 365]

        let mp = (5 * day_of_year + 2) / 153; // [0, 11]
        #[allow(clippy::cast_possible_truncation)]
        let day = (day_of_year - (153 * mp + 2) / 5 + 1) as u8; // [1, 31]
        let month = ((mp + 2) % 12) as u8 + 1; // [1, 12]
        let year = year + (month <= 2) as u64;

        Date { year, month, day }
    }

    const fn hours(self) -> u8 {
        #[allow(clippy::cast_possible_truncation)]
        {
            (self.total_hours() % (HOURS_PER_DAY as u64)) as u8
        }
    }

    const fn minutes(self) -> u8 {
        #[allow(clippy::cast_possible_truncation)]
        {
            (self.total_minutes() % (MINUTES_PER_HOUR as u64)) as u8
        }
    }

    const fn seconds(self) -> u8 {
        #[allow(clippy::cast_possible_truncation)]
        {
            (self.total_seconds() % (SECONDS_PER_MINUTE as u64)) as u8
        }
    }

    const fn total_seconds(self) -> u64 {
        self.value
    }

    const fn total_minutes(self) -> u64 {
        self.value / (SECONDS_PER_MINUTE as u64)
    }

    const fn total_hours(self) -> u64 {
        self.value / SECONDS_PER_HOUR
    }

    const fn total_days(self) -> u64 {
        self.value / SECONDS_PER_DAY
    }
}

impl Display for Timestamp {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", self.value)
    }
}

impl From<u64> for Timestamp {
    fn from(timestamp: u64) -> Timestamp {
        Self::from_u64(timestamp)
    }
}

impl From<Timestamp> for u64 {
    fn from(timestamp: Timestamp) -> u64 {
        timestamp.as_u64()
    }
}

impl TryFrom<DateTime> for Timestamp {
    type Error = DateTimeNotRepresentable;
    fn try_from(date_time: DateTime) -> Result<Self, Self::Error> {
        Self::from_date_time(date_time)
    }
}

/// A leap second as read from a `leap-seconds.list` file.
///
/// Consists of...
///  - ... a [`Timestamp`] of the date the leap second is introduced. The leap second is added to
///    (or removed from) the end of the previous day.
///
///    Here is some more information on leap seconds: <https://en.wikipedia.org/wiki/leap_second>.
///
///  - ... a [`u16`] indicating the updated time difference (in seconds) between
///    [UTC] and [TAI].
///
/// [UTC]: https://en.wikipedia.org/wiki/Coordinated_Universal_Time
/// [TAI]: https://en.wikipedia.org/wiki/International_Atomic_Time
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct LeapSecond {
    timestamp: Timestamp,
    tai_diff: u16,
}

impl LeapSecond {
    /// Gets the [`Timestamp`] of the date this leap second was introduced.
    #[must_use]
    pub const fn timestamp(self) -> Timestamp {
        self.timestamp
    }

    /// Gets the difference between [UTC] and [TAI] as of the introduction of this leap second.
    ///
    /// [UTC]: https://en.wikipedia.org/wiki/Coordinated_Universal_Time
    /// [TAI]: https://en.wikipedia.org/wiki/International_Atomic_Time
    #[must_use]
    pub const fn tai_diff(self) -> u16 {
        self.tai_diff
    }
}

#[derive(Clone, Debug)]
struct Line {
    content: String,
    number: usize,
}

impl Line {
    fn kind(&self) -> LineType {
        if self.content.starts_with('#') {
            match self.content[1..].chars().next() {
                Some('$') => LineType::LastUpdate,
                Some('@') => LineType::ExpirationDate,
                Some('h') => LineType::Hash,
                _ => LineType::Comment,
            }
        } else {
            LineType::LeapSecond
        }
    }
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
enum LineType {
    Comment,
    LastUpdate,
    ExpirationDate,
    LeapSecond,
    Hash,
}

#[derive(Clone, Copy, Debug)]
struct LineBorrow<'a> {
    content: &'a str,
    number: usize,
}

fn extract_content(line: &Line) -> LineBorrow<'_> {
    LineBorrow {
        content: line.content[2..].trim(),
        number: line.number,
    }
}

fn parse_timestamp(timestamp: LineBorrow<'_>) -> Result<Timestamp, ParseLineError> {
    let timestamp = timestamp
        .content
        .parse::<u64>()
        .map_err(|_| ParseLineError {
            cause: ParseLineErrorKind::InvalidTimestamp,
            line: timestamp.content.to_owned(),
            line_number: timestamp.number,
        })?;

    Ok(Timestamp::from_u64(timestamp))
}

/// A SHA-1 hash.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Sha1Hash {
    bytes: [u8; 20],
}

impl Sha1Hash {
    const fn from_bytes(array: [u8; 20]) -> Self {
        Self { bytes: array }
    }

    /// Converts a [`Sha1Hash`] to a byte array.
    #[must_use]
    pub const fn as_bytes(&self) -> &[u8; 20] {
        &self.bytes
    }

    /// Converts a [`Sha1Hash`] to a byte array.
    #[must_use]
    pub const fn into_bytes(self) -> [u8; 20] {
        self.bytes
    }
}

impl From<Sha1Hash> for [u8; 20] {
    fn from(hash: Sha1Hash) -> Self {
        hash.into_bytes()
    }
}

impl Display for Sha1Hash {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let to_string = self
            .bytes
            .iter()
            .map(|byte| format!("{byte:0>2x}"))
            .collect::<String>();
        write!(f, "{to_string}")
    }
}

fn parse_hash(hash: LineBorrow) -> Result<Sha1Hash, ParseLineError> {
    let hash_vec = hash
        .content
        .split_ascii_whitespace()
        .map(|word| {
            u32::from_str_radix(word, 16).map_err(|_| ParseLineError {
                cause: ParseLineErrorKind::InvalidHash,
                line: hash.content.to_owned(),
                line_number: hash.number,
            })
        })
        .collect::<Result<Vec<_>, _>>()?
        .into_iter()
        .flat_map(u32::to_be_bytes)
        .collect::<Vec<_>>();

    let hash = TryInto::<[u8; 20]>::try_into(hash_vec).map_err(|_| ParseLineError {
        cause: ParseLineErrorKind::InvalidHash,
        line: hash.content.to_owned(),
        line_number: hash.number,
    })?;

    Ok(Sha1Hash::from_bytes(hash))
}

fn parse_leap_second_lines(
    lines: &[Line],
) -> Result<Vec<(LineBorrow<'_>, LineBorrow<'_>)>, ParseLineError> {
    lines
        .iter()
        .map(|line| {
            let mut leap_second = line.content.as_str();
            if let Some(start_of_comment) = leap_second.find('#') {
                leap_second = &leap_second[..start_of_comment];
            }
            let leap_second = leap_second.trim();

            let leap_second = leap_second
                .split(|c: char| c.is_ascii_whitespace())
                .filter(|s| !s.is_empty())
                .collect::<Vec<_>>();

            if leap_second.len() == 2 {
                Ok((
                    LineBorrow {
                        content: leap_second[0],
                        number: line.number,
                    },
                    LineBorrow {
                        content: leap_second[1],
                        number: line.number,
                    },
                ))
            } else {
                Err(ParseLineError {
                    cause: ParseLineErrorKind::InvalidLeapSecondLine,
                    line: line.content.clone(),
                    line_number: line.number,
                })
            }
        })
        .collect::<Result<Vec<_>, _>>()
}

fn calculate_hash<'a>(
    last_update: LineBorrow<'a>,
    expiration_date: LineBorrow<'a>,
    leap_seconds: &'a [(LineBorrow<'a>, LineBorrow<'a>)],
) -> Sha1Hash {
    let mut hasher = Sha1::new();

    hasher.update(last_update.content.as_bytes());
    hasher.update(expiration_date.content.as_bytes());

    for chunk in leap_seconds.iter().flat_map(|(s1, s2)| [s1, s2]) {
        hasher.update(chunk.content.as_bytes());
    }

    Sha1Hash::from_bytes(hasher.finalize().into())
}

fn parse_tai_diff(tai_diff: LineBorrow<'_>) -> Result<u16, ParseLineError> {
    tai_diff.content.parse::<u16>().map_err(|_| ParseLineError {
        cause: ParseLineErrorKind::InvalidTaiDiff,
        line: tai_diff.content.to_owned(),
        line_number: tai_diff.number,
    })
}

fn parse_leap_seconds<'a>(
    leap_second_lines: &[(LineBorrow<'a>, LineBorrow<'a>)],
) -> Result<Vec<LeapSecond>, ParseLineError> {
    let mut leap_seconds = leap_second_lines
        .iter()
        .map(|(timestamp, tai_diff)| {
            Ok(LeapSecond {
                timestamp: parse_timestamp(*timestamp)?,
                tai_diff: parse_tai_diff(*tai_diff)?,
            })
        })
        .collect::<Result<Vec<_>, _>>()?;

    leap_seconds.sort_by(|t1, t2| t1.timestamp.cmp(&t2.timestamp));

    Ok(leap_seconds)
}

fn set_option(
    option: &Option<Line>,
    to: Line,
    data_component: DataComponent,
) -> Result<Line, ParseFileError> {
    if let Some(line) = option {
        Err(ParseFileError::DuplicateData {
            data_component,
            line1: line.number,
            line2: to.number,
        })
    } else {
        Ok(to)
    }
}

fn extract_content_lines<R: BufRead>(file: R) -> Result<ContentLines, ParseFileError> {
    let mut last_update = None;
    let mut expiration_date = None;
    let mut leap_seconds = Vec::new();
    let mut hash = None;

    let lines = file
        .lines()
        .enumerate()
        .map(|(number, line)| line.map(|content| Line { content, number }));

    for line in lines {
        let line = line?;
        match line.kind() {
            LineType::Comment => continue,
            LineType::LeapSecond => leap_seconds.push(line),
            LineType::LastUpdate => {
                last_update = Some(set_option(&last_update, line, DataComponent::LastUpdate)?);
            }
            LineType::ExpirationDate => {
                expiration_date = Some(set_option(
                    &expiration_date,
                    line,
                    DataComponent::ExpirationDate,
                )?);
            }
            LineType::Hash => {
                hash = Some(set_option(&hash, line, DataComponent::Hash)?);
            }
        }
    }

    let last_update =
        last_update.ok_or_else(|| ParseFileError::MissingData(DataComponent::LastUpdate))?;
    let expiration_date = expiration_date
        .ok_or_else(|| ParseFileError::MissingData(DataComponent::ExpirationDate))?;
    let hash = hash.ok_or_else(|| ParseFileError::MissingData(DataComponent::Hash))?;

    Ok(ContentLines {
        last_update,
        expiration_date,
        hash,
        leap_seconds,
    })
}

#[derive(Clone, Debug)]
struct ContentLines {
    last_update: Line,
    expiration_date: Line,
    hash: Line,
    leap_seconds: Vec<Line>,
}

impl ContentLines {
    fn last_update(&self) -> LineBorrow<'_> {
        extract_content(&self.last_update)
    }

    fn expiration_date(&self) -> LineBorrow<'_> {
        extract_content(&self.expiration_date)
    }

    fn hash(&self) -> LineBorrow<'_> {
        extract_content(&self.hash)
    }
}

/// Provides access to the data in `leap-seconds.list`.
///
/// **IMPORTANT:** If you don't want to use outdated data, check [`LeapSecondsList::is_expired()`] before using a
/// [`LeapSecondsList`].
///
/// For examples see the [crate-level documentation](crate).
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct LeapSecondsList {
    last_update: Timestamp,
    expiration_date: Timestamp,
    leap_seconds: Vec<LeapSecond>,
}

impl LeapSecondsList {
    /// Parse a `leap-seconds.list` file.
    ///
    /// # Errors
    ///
    /// If the given `leap-seconds.list` could not be parsed successfully.
    ///
    /// See [`ParseFileError`] for more information on what each error variant means.
    pub fn new<R: BufRead>(file: R) -> Result<Self, ParseFileError> {
        let content_lines = extract_content_lines(file)?;

        let last_update = content_lines.last_update();
        let expiration_date = content_lines.expiration_date();
        let hash = content_lines.hash();

        let leap_second_lines = parse_leap_second_lines(&content_lines.leap_seconds)?;

        let calculated_hash = calculate_hash(last_update, expiration_date, &leap_second_lines);

        let last_update = parse_timestamp(last_update)?;
        let expiration_date = parse_timestamp(expiration_date)?;
        let hash_from_file = parse_hash(hash)?;

        let leap_seconds = parse_leap_seconds(&leap_second_lines)?;

        if calculated_hash != hash_from_file {
            return Err(ParseFileError::InvalidHash {
                calculated: calculated_hash,
                found: hash_from_file,
            });
        }

        Ok(LeapSecondsList {
            last_update,
            expiration_date,
            leap_seconds,
        })
    }

    /// Returns whether this [`LeapSecondsList`] is expired.
    #[must_use]
    pub fn is_expired(&self) -> bool {
        self.expiration_date() <= Timestamp::now()
    }

    /// Gets the last time the file was updated.
    #[must_use]
    pub const fn last_update(&self) -> Timestamp {
        self.last_update
    }

    /// Gets the expiration date of the file.
    #[must_use]
    pub const fn expiration_date(&self) -> Timestamp {
        self.expiration_date
    }

    /// Gets the leap second list from the file, ordered by introduction timestamp.
    #[must_use]
    pub fn leap_seconds(&self) -> &[LeapSecond] {
        &self.leap_seconds
    }

    /// Gets the leap second list from the file, ordered by introduction timestamp.
    #[must_use]
    pub fn into_leap_seconds(self) -> Vec<LeapSecond> {
        self.leap_seconds
    }

    /// Gets all the leap seconds introduced after a given [`Timestamp`].
    #[must_use]
    pub fn leap_seconds_after(&self, timestamp: Timestamp) -> &[LeapSecond] {
        // this is possible because the self.leap_seconds is sorted by timestamp
        let start_index = self
            .leap_seconds()
            .iter()
            .enumerate()
            .find(|(_, leap_second)| leap_second.timestamp() > timestamp)
            .map_or_else(|| self.leap_seconds().len(), |(index, _)| index);

        &self.leap_seconds()[start_index..]
    }

    /// Gets all the leap seconds that are planned in the future.
    #[must_use]
    pub fn planned_leap_seconds(&self) -> &[LeapSecond] {
        self.leap_seconds_after(Timestamp::now())
    }

    /// Gets the next [`LeapSecond`] after a given [`Timestamp`].
    ///
    /// Returns [`None`] if the list doesn't contain any leap seconds after the [`Timestamp`].
    #[must_use]
    pub fn next_leap_second_after(&self, timestamp: Timestamp) -> Option<LeapSecond> {
        // this is possible because the self.leap_seconds is sorted by timestamp
        self.leap_seconds_after(timestamp).first().copied()
    }

    /// Gets the next [`LeapSecond`] that will be introduced.
    ///
    /// Returns [`None`] if a next leap second been announced.
    ///
    /// Equivalent to calling [`LeapSecondsList::next_leap_second_after()`] with
    /// [`Timestamp::now()`].
    #[must_use]
    pub fn next_leap_second(&self) -> Option<LeapSecond> {
        self.next_leap_second_after(Timestamp::now())
    }
}

#[cfg(test)]
mod proptests;

#[cfg(test)]
mod tests {
    mod crate_doc_file_sources {
        use {
            crate::{LeapSecond, LeapSecondsList, Timestamp},
            std::io::BufReader,
        };

        #[test]
        fn iers() {
            test_source("https://hpiers.obspm.fr/iers/bul/bulc/ntp/leap-seconds.list")
        }

        #[test]
        fn tzdb_iana() {
            test_source("https://data.iana.org/time-zones/tzdb/leap-seconds.list")
        }

        #[test]
        fn tzdb_github() {
            test_source("https://raw.githubusercontent.com/eggert/tz/main/leap-seconds.list")
        }

        #[test]
        fn meinberg() {
            test_source("https://www.meinberg.de/download/ntp/leap-seconds.list")
        }

        fn test_source(url: &str) {
            let file = reqwest::blocking::get(url).unwrap();
            let leap_seconds_list =
                LeapSecondsList::new(BufReader::new(file)).expect("parsing should be successful");

            // file shouldn't be expired
            assert!(!leap_seconds_list.is_expired());

            // expiration date will always be >= the expiration date at the time of writing
            let min_expiration_date = Timestamp::from_u64(3896899200);
            assert!(leap_seconds_list.expiration_date() >= min_expiration_date);

            // last update will always be >= the expiration date at the time of writing
            let min_last_update = Timestamp::from_u64(3676924800);
            assert!(leap_seconds_list.last_update() >= min_last_update);

            // first leap second will always be the same
            let first_leap_second = &leap_seconds_list.leap_seconds()[0];
            let expected_timestamp = Timestamp::from_u64(2272060800);
            let expected_tai_diff = 10;
            assert_eq!(first_leap_second.timestamp(), expected_timestamp);
            assert_eq!(first_leap_second.tai_diff(), expected_tai_diff);

            // next leap second
            let expected = Some(LeapSecond {
                timestamp: Timestamp::from_u64(2950473600),
                tai_diff: 28,
            });
            let actual = leap_seconds_list.next_leap_second_after(Timestamp::from_u64(2918937600));
            assert_eq!(actual, expected);

            // there should be no leap seconds after the last one
            let last_leap_second = leap_seconds_list
                .leap_seconds()
                .last()
                .expect("list contains at least 1 element");
            assert!(leap_seconds_list
                .leap_seconds_after(last_leap_second.timestamp())
                .is_empty());
        }
    }

    mod timestamp {
        use {
            crate::{Date, DateTime, Time, Timestamp},
            chrono::{offset::Utc, Datelike, Timelike},
        };

        #[test]
        fn now() {
            let expected = {
                let now = Utc::now();
                let date = now.date_naive();
                let time = now.time();

                DateTime {
                    date: Date::new(date.year() as u64, date.month() as u8, date.day() as u8)
                        .expect("chrono produces valid dates"),
                    time: Time::new(time.hour() as u8, time.minute() as u8, time.second() as u8)
                        .expect("chrono produces valid times"),
                }
            };
            let actual = Timestamp::now().date_time();

            assert_eq!(actual, expected);
        }

        #[test]
        fn from_and_to_date_time_0() {
            let timestamp = Timestamp::from_u64(0);
            let date_time = timestamp.date_time();
            let expected_date_time = DateTime {
                date: Date::new(1900, 1, 1).unwrap(),
                time: Time::new(0, 0, 0).unwrap(),
            };
            assert_eq!(date_time, expected_date_time);

            let timestamp_again =
                Timestamp::from_date_time(date_time).expect("should always be valid");
            assert_eq!(timestamp_again, timestamp);

            let date_time_again = timestamp_again.date_time();
            assert_eq!(date_time_again, date_time);
        }

        #[test]
        fn from_and_to_date_time_1889385054048000() {
            let timestamp = Timestamp::from_u64(1889385054048000);
            let date_time = timestamp.date_time();

            let timestamp_again =
                Timestamp::from_date_time(date_time).expect("should always be valid");
            assert_eq!(timestamp_again, timestamp);

            let date_time_again = timestamp_again.date_time();
            assert_eq!(date_time_again, date_time);
        }

        #[test]
        fn from_and_to_date_time_2004317826065173() {
            let timestamp = Timestamp::from_u64(2004317826065173);
            let date_time = timestamp.date_time();

            let timestamp_again =
                Timestamp::from_date_time(date_time).expect("should always be valid");
            assert_eq!(timestamp_again, timestamp);

            let date_time_again = timestamp_again.date_time();
            assert_eq!(date_time_again, date_time);
        }

        #[test]
        fn from_pre_1900_date_time() {
            let date_time = DateTime {
                date: Date::new(1899, 12, 31).unwrap(),
                time: Time::new(23, 59, 59).unwrap(),
            };

            let error = Timestamp::from_date_time(date_time);

            assert!(error.is_err());
        }

        #[test]
        fn from_and_as_u64() {
            let original = 123456780987654;
            let result = Timestamp::from_u64(original).as_u64();

            assert_eq!(result, original);
        }

        #[test]
        fn test_1900_01_01() {
            let expected = Timestamp::from_date_time(DateTime {
                date: Date::new(1900, 1, 1).unwrap(),
                time: Time::new(0, 0, 0).unwrap(),
            })
            .unwrap();
            let actual = Timestamp::from_u64(0);

            assert_eq!(actual, expected);
        }

        #[test]
        fn test_1901_01_07_19_45_33() {
            let year = 1 * 365 * 24 * 60 * 60;
            let day = 6 * 24 * 60 * 60;
            let hours = 19 * 60 * 60;
            let minutes = 45 * 60;
            let seconds = 33;

            let expected = Timestamp::from_date_time(DateTime {
                date: Date::new(1901, 1, 7).unwrap(),
                time: Time::new(19, 45, 33).unwrap(),
            })
            .unwrap();
            let actual = Timestamp::from_u64(year + day + hours + minutes + seconds);

            assert_eq!(actual, expected);
        }

        #[test]
        fn test_1904_02_29_23_59_59() {
            let year = 4 * 365 * 24 * 60 * 60;
            let month = 31 * 24 * 60 * 60;
            let day = 28 * 24 * 60 * 60;
            let hours = 23 * 60 * 60;
            let minutes = 59 * 60;
            let seconds = 59;

            let timestamp = Timestamp::from_u64(year + month + day + hours + minutes + seconds);
            let expected = Timestamp::from_date_time(DateTime {
                date: Date::new(1904, 2, 29).unwrap(),
                time: Time::new(23, 59, 59).unwrap(),
            })
            .unwrap();

            assert_eq!(timestamp, expected);

            let next_timestamp = Timestamp::from_u64(timestamp.as_u64() + 1);
            let next_expected = Timestamp::from_date_time(DateTime {
                date: Date::new(1904, 3, 1).unwrap(),
                time: Time::new(0, 0, 0).unwrap(),
            })
            .unwrap();

            assert_eq!(next_timestamp, next_expected);

            assert!(next_timestamp > timestamp);
        }

        #[test]
        fn test_2023_06_28() {
            let expected = Timestamp::from_date_time(DateTime {
                date: Date::new(2023, 6, 28).unwrap(),
                time: Time::new(0, 0, 0).unwrap(),
            })
            .unwrap();
            let actual = Timestamp::from_u64(3896899200);

            assert_eq!(actual, expected);
        }

        #[test]
        fn test_1985_07_01() {
            let expected = Timestamp::from_date_time(DateTime {
                date: Date::new(1985, 7, 1).unwrap(),
                time: Time::new(0, 0, 0).unwrap(),
            })
            .unwrap();
            let actual = Timestamp::from_u64(2698012800);

            assert_eq!(actual, expected);
        }

        #[test]
        fn test_2017_01_01() {
            let expected = Timestamp::from_date_time(DateTime {
                date: Date::new(2017, 1, 1).unwrap(),
                time: Time::new(0, 0, 0).unwrap(),
            })
            .unwrap();
            let actual = Timestamp::from_u64(3692217600);

            assert_eq!(actual, expected);
        }
    }
}