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//! A parser implementation for durations as defined in RFC5545.
//!
//! These are mostly used for alarms, to indicate their time relative to the time of an event or
//! todo.
//!
//! For convenience, [`Rfc5545Duration`](crate::Rfc5545Duration) implements [`Add`](core::ops::Add)
//! for [`icalendar::DatePerhapsTime`], [`chrono::DateTime`] and
//! [`chrono::naive::NaiveDateTime`].
//!
//! ## Example
//!
//! ```
//! use chrono::TimeZone;
//! use chrono::Utc;
//!
//! let duration = icalendar_duration::parse("PT24H")?;
//! let dt = Utc.ymd(2022, 9, 1).and_hms(22, 9, 14);
//!
//! assert_eq!(dt + duration, Utc.ymd(2022, 9, 2).and_hms(22, 9, 14));
//! # Ok::<(), Box<dyn std::error::Error>>(())
//! ```
use std::fmt::Display;
use std::ops::{Add, MulAssign, Neg, Sub};
use chrono::{DateTime, Duration, NaiveDateTime, TimeZone};
use icalendar::{CalendarDateTime, DatePerhapsTime};
mod parser;
pub use parser::parse;
/// The sign for a duration (which can be negative or positive).
///
/// The default is positive, as the absence of an explicit sign implies positive.
#[derive(Default, PartialEq, Eq, Debug)]
pub enum Sign {
#[default]
Positive,
Negative,
}
/// Converts a "+" or "-" into a `Sign`.
///
/// # Quirks
///
/// Will return `Sign:Positive` for invalid input.
impl From<Option<char>> for Sign {
fn from(value: Option<char>) -> Self {
if Some('-') == value {
Sign::Negative
} else {
Sign::Positive
}
}
}
impl Display for Sign {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
let sign = match self {
Sign::Positive => "+",
Sign::Negative => "-",
};
write!(f, "{}", sign)
}
}
impl Neg for Sign {
type Output = Sign;
fn neg(self) -> Self::Output {
match self {
Sign::Positive => Sign::Negative,
Sign::Negative => Sign::Positive,
}
}
}
/// The Duration specified in RFC554.
///
/// This has a few quirks that ultimately, make it incompatible with the Duration classes from both
/// Chrono and the stdlib. The main difference is how DST transition and leap seconds are handled.
///
/// From Section 3.3.6:
///
/// > The duration of a week or a day depends on its position in the calendar. In the case of
/// > discontinuities in the time scale, such as the change from standard time to daylight time and
/// > back, the computation of the exact duration requires the subtraction or addition of the
/// > change of duration of the discontinuity. Leap seconds MUST NOT be considered when computing
/// > an exact duration. When computing an exact duration, the greatest order time components MUST
/// > be added first, that is, the number of days MUST be added first, followed by the number of
/// > hours, number of minutes, and number of seconds.
///
/// This will usually behave rather intuitively for users. For an event that occurs at 16:00hs on
/// the Monday after daylight saving, an alarm set 1 day before will trigger at 16hs, even though
/// this is technically 25 (or 23) hours before the event.
///
/// # Caveats
///
/// The specification indicates that numerical values are "one or more digits". Technically,
/// setting an alarm one million years before an event is perfectly valid. However, modelling this
/// would require arbitrary precision numbers or using absurdly large sized integers. These
/// scenarios are valid but unrealistic, and are deliberately not supported in the interest of
/// better performance. Any `1*DIGIT` is restricted to an [u16].
///
/// Parsing and re-encoding a duration will sometimes yield different results. In particular the
/// `+` sign is always dropped (it is the implicit default) and units with value `0` are dropped.
/// E.g.: `-P0DT1H` will become `-PT1H`, and `+PT1H` will become `PT1H`. These are equivalent.
///
/// # See also
///
/// [`icalendar_duration::parse`](crate::parse).
#[derive(Default, PartialEq, Eq, Debug)]
pub struct Rfc5545Duration {
sign: Sign,
weeks: i64,
days: i64,
hours: i64,
minutes: i64,
seconds: i64,
}
impl Display for Rfc5545Duration {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
// XXX: Modeling an absent sign is required to avoid altering explicit "PLUS".
if self.sign == Sign::Negative {
write!(f, "-")?;
}
write!(f, "P")?;
if self.weeks > 0 {
write!(f, "{}W", self.weeks)?;
}
if self.days > 0 {
write!(f, "{}D", self.days)?;
}
if self.hours > 0 || self.minutes > 0 || self.seconds > 0 {
write!(f, "T")?;
if self.hours > 0 {
write!(f, "{}H", self.hours)?;
}
if self.minutes > 0 {
write!(f, "{}M", self.minutes)?;
}
if self.seconds > 0 {
write!(f, "{}S", self.seconds)?;
}
}
Ok(())
}
}
impl MulAssign<Sign> for Rfc5545Duration {
#[inline]
fn mul_assign(&mut self, rhs: Sign) {
self.sign = rhs;
}
}
impl Rfc5545Duration {
/// Return this duration in seconds.
///
/// Care should be taken not to use this on timezone-aware datetimes, since the results would
/// not be correct.
fn absolute_seconds(&self) -> i64 {
self.days
.saturating_mul(24)
.saturating_add(self.hours)
.saturating_mul(60)
.saturating_add(self.minutes)
.saturating_mul(60)
.saturating_add(self.seconds)
}
}
/// Changes the sign from positive to negative and vice versa.
///
/// Usage of this function is discouraged, since it creates a copy of the entire struct.
impl Neg for Rfc5545Duration {
type Output = Rfc5545Duration;
fn neg(self) -> Self::Output {
Self::Output {
sign: -self.sign,
..self
}
}
}
/// Adds a duration to [`DatePerhapsTime`].
///
/// A [`DatePerhapsTime::Date`] is equivalent to one with time `00:00:00`. From rfc5545,
/// section-3.8.6.3:
///
/// > Alarms specified in an event or to-do that is defined in terms of a DATE value
/// > type will be triggered relative to 00:00:00 of the user's configured time zone
/// > on the specified date, or relative to 00:00:00 UTC on the specified date if no
/// > configured time zone can be found for the user.
impl Add<Rfc5545Duration> for DatePerhapsTime {
type Output = CalendarDateTime;
fn add(self, rhs: Rfc5545Duration) -> Self::Output {
match self {
DatePerhapsTime::DateTime(CalendarDateTime::Floating(naive)) => {
CalendarDateTime::Floating(naive + rhs)
}
DatePerhapsTime::DateTime(CalendarDateTime::Utc(aware)) => {
CalendarDateTime::Utc(aware + rhs)
}
DatePerhapsTime::DateTime(CalendarDateTime::WithTimezone {
date_time: naive,
tzid,
}) => CalendarDateTime::WithTimezone {
date_time: naive + rhs,
tzid,
},
DatePerhapsTime::Date(date) => CalendarDateTime::Floating(date.and_hms(0, 0, 0) + rhs),
}
}
}
impl<Tz: TimeZone> Add<Rfc5545Duration> for DateTime<Tz> {
type Output = DateTime<Tz>;
/// # Panics
///
/// Panics if the resulting time does not exist in the datetime's timezone.
fn add(self, rhs: Rfc5545Duration) -> Self::Output {
// Converting to naive AND THEN operating on that makes sure we ignore any DST transition,
// leap seconds and other discontinuities.
let result = self.naive_local() + rhs;
self.timezone()
.from_local_datetime(&result)
.earliest()
.unwrap()
}
}
impl Add<Rfc5545Duration> for NaiveDateTime {
type Output = NaiveDateTime;
fn add(self, rhs: Rfc5545Duration) -> Self::Output {
// Converting to naive AND THEN operating on that makes sure we ignore any DST transition,
// leap seconds and other discontinuities.
match rhs.sign {
Sign::Positive => self + Duration::seconds(rhs.absolute_seconds()),
Sign::Negative => self - Duration::seconds(rhs.absolute_seconds()),
}
}
}
impl<Tz: TimeZone> Sub<Rfc5545Duration> for DateTime<Tz> {
type Output = DateTime<Tz>;
fn sub(self, rhs: Rfc5545Duration) -> Self::Output {
let result = self.naive_local() - rhs;
self.timezone()
.from_local_datetime(&result)
.earliest()
.unwrap()
}
}
impl Sub<Rfc5545Duration> for NaiveDateTime {
type Output = NaiveDateTime;
fn sub(self, rhs: Rfc5545Duration) -> Self::Output {
// Converting to naive AND THEN operating on that makes sure we ignore any DST transition,
// leap seconds and other discontinuities.
//
// See [`Rfc5545Duration`]
//
// # Panics
//
// Panics if the resulting time does not exist in the given timezone.
match rhs.sign {
Sign::Positive => self - Duration::seconds(rhs.absolute_seconds()),
Sign::Negative => self + Duration::seconds(rhs.absolute_seconds()),
}
}
}