From cf2673d4d4bc8d6b96f4488847d8c2b3c3545010 Mon Sep 17 00:00:00 2001
From: Botahamec <botahamec@outlook.com>
Date: Mon, 21 Mar 2022 22:00:30 -0400
Subject: Add seconds or nanoseconds to DateTime

---
 src/datetime.rs | 32 +++++++++++++++++++++++++++++++-
 src/month.rs    |  2 +-
 src/tai.rs      |  6 +++---
 src/timezone.rs |  8 ++++----
 4 files changed, 39 insertions(+), 9 deletions(-)

diff --git a/src/datetime.rs b/src/datetime.rs
index 9332de1..49506e3 100644
--- a/src/datetime.rs
+++ b/src/datetime.rs
@@ -30,6 +30,16 @@ impl<Tz: TimeZone> DateTime<Tz> {
 		}
 	}
 
+	pub fn from_local(local_datetime: NaiveDateTime, timezone: Tz) -> Result<Self, Tz::Err> {
+		let offset = timezone.offset_from_local_naive(local_datetime)?;
+		// TODO overflow
+		let utc_datetime = local_datetime
+			.add_seconds_overflowing(-offset.seconds_ahead() as i64)
+			.0;
+
+		Ok(Self::from_utc(utc_datetime, timezone))
+	}
+
 	pub fn offset(&self) -> UtcOffset {
 		let utc = self.as_utc();
 		self.timezone.utc_offset(utc)
@@ -69,6 +79,26 @@ impl<Tz: TimeZone> DateTime<Tz> {
 	pub fn tai_timestamp(&self) -> UnixTimestamp {
 		self.as_tai().to_naive_overflowing().0.timestamp()
 	}
+
+	#[must_use]
+	pub fn add_seconds_overflowing(self, seconds: i64) -> (Self, bool) {
+		let (tai_timestamp, overflow) = self.tai_timestamp().add_seconds_overflowing(seconds);
+		let tai_naive_dt = NaiveDateTime::from_timestamp(tai_timestamp);
+		let tai_dt = DateTime::from_local(tai_naive_dt, Tai).unwrap();
+
+		(tai_dt.into_timezone(self.timezone), overflow)
+	}
+
+	#[must_use]
+	pub fn add_nanoseconds_overflowing(self, nanoseconds: i64) -> (Self, bool) {
+		let (tai_timestamp, overflow) = self
+			.tai_timestamp()
+			.add_nanoseconds_overflowing(nanoseconds);
+		let tai_naive_dt = NaiveDateTime::from_timestamp(tai_timestamp);
+		let tai_dt = DateTime::from_local(tai_naive_dt, Tai).unwrap();
+
+		(tai_dt.into_timezone(self.timezone), overflow)
+	}
 }
 
 impl NaiveDateTime {
@@ -285,7 +315,7 @@ impl<Tz: TimeZone, Other: TimeZone> PartialEq<DateTime<Other>> for DateTime<Tz>
 }
 
 impl<Tz: TimeZone> Hash for DateTime<Tz> {
-	fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
+	fn hash<H: core::hash::Hasher>(&self, state: &mut H) {
 		self.utc_datetime.hash(state);
 	}
 }
diff --git a/src/month.rs b/src/month.rs
index 1419717..faf891d 100644
--- a/src/month.rs
+++ b/src/month.rs
@@ -405,7 +405,7 @@ impl Month {
 		let zero_indexed_month = zero_indexed_num % 12;
 		let month = match Self::from_u8((zero_indexed_month as u8) + 1) {
 			Some(month) => month,
-			None => unsafe { std::hint::unreachable_unchecked() },
+			None => unsafe { core::hint::unreachable_unchecked() },
 		};
 
 		(month, wraps)
diff --git a/src/tai.rs b/src/tai.rs
index 8dd91d2..015e70e 100644
--- a/src/tai.rs
+++ b/src/tai.rs
@@ -83,7 +83,7 @@ impl TimeZone for Tai {
 	}
 
 	// TODO optimize
-	fn offset_from_local_time(&self, date_time: NaiveDateTime) -> Result<UtcOffset, Self::Err> {
+	fn offset_from_local_naive(&self, date_time: NaiveDateTime) -> Result<UtcOffset, Self::Err> {
 		// TAI times cannot have leap seconds
 		if date_time.second() == 60 {
 			return Err(UnexpectedLeapSecond {
@@ -120,7 +120,7 @@ mod tests {
 	#[test]
 	fn test_conversion_no_leap_seconds() {
 		let offset = unsafe {
-			Tai.offset_from_local_time(NaiveDateTime::new(
+			Tai.offset_from_local_naive(NaiveDateTime::new(
 				Date::from_ymd_unchecked(2000.into(), Month::January, 1),
 				Time::from_hms_unchecked(0, 0, 0),
 			))
@@ -134,7 +134,7 @@ mod tests {
 	fn test_conversion_one_leap_second() {
 		add_leap_second(unsafe { Date::from_ymd_unchecked(2000.into(), Month::January, 1) });
 		let offset = unsafe {
-			Tai.offset_from_local_time(NaiveDateTime::new(
+			Tai.offset_from_local_naive(NaiveDateTime::new(
 				Date::from_ymd_unchecked(2000.into(), Month::January, 2),
 				Time::from_hms_unchecked(0, 0, 0),
 			))
diff --git a/src/timezone.rs b/src/timezone.rs
index f0096c6..eb539fb 100644
--- a/src/timezone.rs
+++ b/src/timezone.rs
@@ -5,7 +5,7 @@ use core::fmt::Display;
 /// A type that can be used to represent a `TimeZone`
 pub trait TimeZone: Sized + Eq + Display {
 	/// The error to return in case of a failure to convert the local time to UTC
-	type Err;
+	type Err: core::fmt::Debug;
 
 	/// Given the time in the UTC timezone, determine the `UtcOffset`
 	fn utc_offset(&self, date_time: DateTime<Utc>) -> UtcOffset;
@@ -16,7 +16,7 @@ pub trait TimeZone: Sized + Eq + Display {
 	///
 	/// This returns an Err if the given `NaiveDateTime` cannot exist in this timezone.
 	/// For example, the time may have been skipped because of daylight savings time.
-	fn offset_from_local_time(&self, date_time: NaiveDateTime) -> Result<UtcOffset, Self::Err>;
+	fn offset_from_local_naive(&self, date_time: NaiveDateTime) -> Result<UtcOffset, Self::Err>;
 }
 
 #[derive(Copy, Clone, Eq, PartialEq, Hash, Debug)]
@@ -30,7 +30,7 @@ impl TimeZone for Utc {
 		UtcOffset::UTC
 	}
 
-	fn offset_from_local_time(&self, _: NaiveDateTime) -> Result<UtcOffset, Self::Err> {
+	fn offset_from_local_naive(&self, _: NaiveDateTime) -> Result<UtcOffset, Self::Err> {
 		Ok(UtcOffset::UTC)
 	}
 }
@@ -121,7 +121,7 @@ impl TimeZone for UtcOffset {
 		*self
 	}
 
-	fn offset_from_local_time(&self, _: NaiveDateTime) -> Result<UtcOffset, Self::Err> {
+	fn offset_from_local_naive(&self, _: NaiveDateTime) -> Result<UtcOffset, Self::Err> {
 		Ok(*self)
 	}
 }
-- 
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