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use time::{
error::{Parse, TryFromParsed},
format_description::FormatItem,
macros::{format_description, offset, time},
Date, OffsetDateTime, PrimitiveDateTime, Time, UtcOffset, Weekday,
};
const FMT: &[FormatItem<'_>] = format_description!("[year]-[month]-[day] [hour]:[minute]");
const DATE: &[FormatItem<'_>] = format_description!("[year]-[month]-[day]");
const TIME: &[FormatItem<'_>] = format_description!("[hour]:[minute]");
#[allow(unused)]
const OFFSET: &[FormatItem<'_>] =
format_description!("[offset_hour sign:mandatory]:[offset_minute]");
const CST: UtcOffset = offset!(-06:00);
const CDT: UtcOffset = offset!(-05:00);
/// Offset for the united states in Central Time. Accounts for DST
/// DST starts the 2nd sunday in March and ends the 1st sunday in November.
/// https://www.nist.gov/pml/time-and-frequency-division/popular-links/daylight-saving-time-dst
fn us_dst_central_offset(datetime: PrimitiveDateTime) -> UtcOffset {
let second_sunday_march = {
let mut seen_sunday = false;
let mut curr = Date::from_calendar_date(datetime.year(), time::Month::March, 1).unwrap();
loop {
if curr.weekday() == Weekday::Sunday {
if seen_sunday {
break PrimitiveDateTime::new(curr, time!(02:00 AM));
} else {
seen_sunday = true;
}
}
curr = curr.next_day().unwrap();
}
};
let first_sunday_november = {
let mut curr = Date::from_calendar_date(datetime.year(), time::Month::November, 1).unwrap();
loop {
if curr.weekday() == Weekday::Sunday {
break PrimitiveDateTime::new(curr, time!(02:00 AM));
} else {
curr = curr.next_day().unwrap();
}
}
};
if datetime >= second_sunday_march && datetime < first_sunday_november {
CDT
} else {
CST
}
}
fn parse_offset(raw: &str) -> UtcOffset {
match raw.to_ascii_uppercase().as_str() {
"CST" => CST,
"CDT" => CDT,
_ => unimplemented!(),
}
}
fn parse_time(raw: &str) -> Result<Time, time::error::Parse> {
Time::parse(raw, TIME)
}
fn parse_date(raw: &str) -> Result<Date, time::error::Parse> {
Date::parse(raw, DATE)
}
/// Parses an OffsetDateTime from any of the following formats:
/// - date only: 2024-04-13
/// - date and time: 2024-04-13 2:56
/// - dat, time, and offset: 2024-04-13 2:56 CDT
///
/// If a time is not procided, noon (12:00) is assumed.
///
/// If an offset is not provided it will be assumed to be US Central Time and
/// it will correct for daylight savings.
pub fn parse(raw: &str) -> Result<OffsetDateTime, time::error::Parse> {
let mut splits = raw.trim().split(' ');
let date = match splits.next() {
None => return Err(Parse::TryFromParsed(TryFromParsed::InsufficientInformation)),
Some(raw) => parse_date(raw)?,
};
let time = match splits.next() {
None => time!(12:00:00),
Some(raw) => parse_time(raw)?,
};
let offset = match splits.next() {
None => us_dst_central_offset(PrimitiveDateTime::new(date, time)),
Some(raw) => parse_offset(raw),
};
Ok(OffsetDateTime::new_in_offset(date, time, offset))
}
#[cfg(test)]
mod test {
use time::{
macros::{datetime, offset},
OffsetDateTime, PrimitiveDateTime,
};
use crate::timeparse::{parse_offset, us_dst_central_offset, CDT, CST, FMT};
#[test]
fn calculates_cst_cdt_correctly() {
fn daylight(raw: &str) {
let date = PrimitiveDateTime::parse(raw, FMT).unwrap();
if us_dst_central_offset(date) != CDT {
panic!("CDT failed on {raw}")
}
}
fn standard(raw: &str) {
let date = PrimitiveDateTime::parse(raw, FMT).unwrap();
if us_dst_central_offset(date) != CST {
panic!("CST failed on {raw}")
}
}
// make sure CST and CDT are what we expect
assert_eq!(CST, offset!(-06:00));
assert_eq!(CDT, offset!(-05:00));
daylight("2024-04-13 02:56");
daylight("2024-03-10 14:00");
daylight("2024-03-10 02:00");
standard("2024-12-01 00:00");
standard("2024-11-03 14:00");
standard("2024-11-03 02:00");
// other years
daylight("2023-03-12 12:00"); // DST start Mar 12, end Nov 5
standard("2023-03-11 23:00");
standard("2023-11-05 12:00");
daylight("2023-11-04 23:00");
}
#[test]
fn paress_timezone_code() {
assert_eq!(parse_offset("CST"), CST);
assert_eq!(parse_offset("CDT"), CDT);
}
fn test_parse(raw: &str, expected: OffsetDateTime) {
assert_eq!(super::parse(raw).unwrap(), expected)
}
#[test]
fn parse_date_only() {
test_parse("2024-04-13", datetime!(2024-04-13 12:00 -05:00));
test_parse("2024-01-01", datetime!(2024-01-01 12:00 -06:00));
}
}
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