Convert DateTime to TAI timestamp

2 files changed, 31 insertions, 7 deletions

diff --git a/src/datetime.rs b/src/datetime.rs
index 931d023..a46d0b7 100644
--- a/src/datetime.rs
+++ b/src/datetime.rs
@@ -1,5 +1,6 @@
 use crate::{
 	date::{DayGreaterThanMaximumForMonthError, LeapDayNotInLeapYearError},
+	tai::Tai,
 	timezone::{Utc, UtcOffset},
 	Date, Month, Time, TimeZone, UnixTimestamp, Year,
 };
@@ -30,7 +31,7 @@ impl<Tz: TimeZone> DateTime<Tz> {
 	}
 
 	pub fn offset(&self) -> UtcOffset {
-		let utc = DateTime::<Utc>::from_utc(self.utc_datetime, Utc);
+		let utc = self.as_utc();
 		self.timezone.utc_offset(utc)
 	}
 
@@ -41,6 +42,29 @@ impl<Tz: TimeZone> DateTime<Tz> {
 	pub fn naive_utc(&self) -> NaiveDateTime {
 		self.utc_datetime
 	}
+
+	pub fn to_naive_overflowing(&self) -> (NaiveDateTime, bool) {
+		self.utc_datetime
+			.add_seconds_overflowing(self.offset().seconds_ahead().into())
+	}
+
+	pub fn as_utc(&self) -> DateTime<Utc> {
+		DateTime::<Utc>::from_utc(self.utc_datetime, Utc)
+	}
+
+	pub fn as_tai(&self) -> DateTime<Tai> {
+		DateTime::<Tai>::from_utc(self.utc_datetime, Tai)
+	}
+
+	pub fn unix_timestamp(&self) -> UnixTimestamp {
+		self.utc_datetime.timestamp()
+	}
+
+	// TODO rethink the name of UnixTimestamp
+	// TODO should this overflow?
+	pub fn tai_timestamp(&self) -> UnixTimestamp {
+		self.as_tai().to_naive_overflowing().0.timestamp()
+	}
 }
 
 impl NaiveDateTime {
diff --git a/src/timezone.rs b/src/timezone.rs
index 6f356ca..f0096c6 100644
--- a/src/timezone.rs
+++ b/src/timezone.rs
@@ -52,8 +52,8 @@ impl UtcOffset {
 	pub const UTC: Self = Self { offset_seconds: 0 };
 
 	/// Makes a new `UtcOffset` timezone with the given timezone difference.
-	/// A positive number is the Eastern hemisphere. A negative number is the
-	/// Western hemisphere.
+	/// A positive number is the Eastern hemisphere. A negative number behind
+	/// UTC, such as UTC-5.
 	#[must_use]
 	pub const fn from_seconds(seconds: i32) -> Self {
 		Self {
@@ -62,22 +62,22 @@ impl UtcOffset {
 	}
 
 	/// Makes a new `UtcOffset` timezone with the given timezone difference.
-	/// A positive number is the Eastern hemisphere. A negative number is the
-	/// Western hemisphere.
+	/// A positive number is the Eastern hemisphere. A negative number is
+	/// behind UTC, such as UTC-5.
 	#[must_use]
 	pub const fn from_hours(hours: i32) -> Self {
 		Self::from_seconds(hours * 3600)
 	}
 
 	/// The number of hours this timezone is ahead of UTC. This number is
-	/// negative if the timezone is in the Western hemisphere
+	/// negative if the timezone is behind UTC, such as UTC-5.
 	#[must_use]
 	pub fn hours_ahead(self) -> f32 {
 		self.offset_seconds as f32 / 3600.0
 	}
 
 	/// The number of seconds this timezone is ahead of UTC. This number is
-	/// negative if the timezone is in the Western hemisphere
+	/// negative if the timezone is behind UTC, such as UTC-5.
 	#[must_use]
 	pub const fn seconds_ahead(self) -> i32 {
 		self.offset_seconds