Add tests for negative timestamps / DateTime before Unix Epoch

src/datetime.rs

@@ -74,7 +74,7 @@ impl DateTime {
             let mut month = Some(Month::December);
             while month.is_some() {
                 let m = month.unwrap();
-                if seconds < -m.seconds(year) {
+                if -seconds < m.seconds(year) {
                     break;
                 }
                 seconds += m.seconds(year);
@@ -87,16 +87,17 @@ impl DateTime {
                 day -= 1;
             }
             let mut hour: i8 = 23;
-            while hour >= 0 && seconds < -SECONDS_PER_HOUR {
+            while hour > 0 && seconds < -SECONDS_PER_HOUR {
                 seconds += SECONDS_PER_HOUR;
                 hour -= 1;
             }
             let hour = hour.try_into().unwrap();
             let mut minute: i8 = 60;
-            while minute >= 0 && seconds < -60 {
+            while minute > 0 && seconds < -60 {
                 seconds += 60;
                 minute -= 1;
             }
+            minute -= 1;
             let minute = minute.try_into().unwrap();
             let second: u8 = (seconds + 60).try_into().unwrap();
             Self {
@@ -150,8 +151,9 @@ impl DateTime {
 
     pub fn weekday(&self) -> Weekday {
         let ts = self.timestamp_naive();
-        let days = ts / SECONDS_PER_DAY;
+        let mut days = ts / SECONDS_PER_DAY;
-        let rem = days % 7;
+        if ts < 0 { days -= 1 }
+        let rem = days.rem_euclid(7);
         rem.try_into().unwrap()
     }
 
@@ -230,6 +232,28 @@ mod tests {
             },
         };
         assert_eq!(dt.weekday(), Weekday::Saturday);
+        dt = DateTime {
+            year: Year::new(1965),
+            month: Month::February,
+            day: 9,
+            hour: 4,
+            minute: 4,
+            second: 37,
+            zone: TimeZone::Utc,
+        };
+        assert_eq!(dt.weekday(), Weekday::Tuesday);
+        dt.day -= 1;
+        assert_eq!(dt.weekday(), Weekday::Monday);
+        dt.day -= 1;
+        assert_eq!(dt.weekday(), Weekday::Sunday);
+        dt.day -= 1;
+        assert_eq!(dt.weekday(), Weekday::Saturday);
+        dt.day -= 1;
+        assert_eq!(dt.weekday(), Weekday::Friday);
+        dt.day -= 1;
+        assert_eq!(dt.weekday(), Weekday::Thursday);
+        dt.day -= 1;
+        assert_eq!(dt.weekday(), Weekday::Wednesday);
     }
 
     #[test]
@@ -271,6 +295,22 @@ mod tests {
         assert_eq!(dt, DateTime::from_timestamp(ts));
     }
 
+    #[test]
+    fn ts_negative() {
+        let ts: i64 = -154382123;
+        let dt = DateTime {
+            year: Year::new(1965),
+            month: Month::February,
+            day: 9,
+            hour: 4,
+            minute: 4,
+            second: 37,
+            zone: TimeZone::Utc,
+        };
+        assert_eq!(dt.timestamp(), ts);
+        assert_eq!(dt, DateTime::from_timestamp(ts));
+    }
+
     #[test]
     fn fmt() {
         let mut dt = DateTime::from_timestamp(1706571482);