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Diffstat (limited to 'rustversion/src/time.rs')
-rw-r--r-- | rustversion/src/time.rs | 44 |
1 files changed, 44 insertions, 0 deletions
diff --git a/rustversion/src/time.rs b/rustversion/src/time.rs new file mode 100644 index 0000000..1e6dd90 --- /dev/null +++ b/rustversion/src/time.rs @@ -0,0 +1,44 @@ +use crate::date::Date; +use std::time::{SystemTime, UNIX_EPOCH}; + +// Timestamp of 2016-03-01 00:00:00 in UTC. +const BASE: u64 = 1456790400; +const BASE_YEAR: u16 = 2016; +const BASE_MONTH: u8 = 3; + +// Days between leap days. +const CYCLE: u64 = 365 * 4 + 1; + +const DAYS_BY_MONTH: [u8; 12] = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]; + +pub fn today() -> Date { + let default = Date { + year: 2019, + month: 1, + day: 1, + }; + try_today().unwrap_or(default) +} + +fn try_today() -> Option<Date> { + let now = SystemTime::now(); + let since_epoch = now.duration_since(UNIX_EPOCH).ok()?; + let secs = since_epoch.as_secs(); + + let approx_days = secs.checked_sub(BASE)? / 60 / 60 / 24; + let cycle = approx_days / CYCLE; + let mut rem = approx_days % CYCLE; + + let mut year = BASE_YEAR + cycle as u16 * 4; + let mut month = BASE_MONTH; + loop { + let days_in_month = DAYS_BY_MONTH[month as usize - 1]; + if rem < days_in_month as u64 { + let day = rem as u8 + 1; + return Some(Date { year, month, day }); + } + rem -= days_in_month as u64; + year += (month == 12) as u16; + month = month % 12 + 1; + } +} |