Fix for bug in before epoch dates (#146)

* Fix for bug in before epoch dates

* Remove commented test

src/structure/tfc/datetime.rs

@@ -11,10 +11,8 @@ pub fn datetime_to_parts(datetime: &NaiveDateTime) -> (bool, Integer, u32) {
     let mut seconds = Integer::from(datetime.timestamp());
     let is_neg = seconds < 0;
     let mut nanos = datetime.timestamp_subsec_nanos();
-    if is_neg {
-        if nanos != 0 {
-            seconds += 1;
-        }
+    if is_neg && nanos != 0 {
+        seconds += 1;
         nanos = 1_000_000_000 - nanos;
     }
     (is_neg, seconds, nanos)
@@ -31,7 +29,6 @@ pub fn datetime_to_storage(datetime: &NaiveDateTime) -> Vec<u8> {
     } else {
         Some(format!("{nanos:09}"))
     };
-
     integer_and_fraction_to_storage(is_neg, seconds, fraction.as_ref().map(|b| b.as_ref()))
 }
 
@@ -42,11 +39,7 @@ pub fn storage_to_datetime<B: Buf>(bytes: &mut B) -> NaiveDateTime {
         .to_i64()
         .expect("This is a surprisingly large number of seconds!");
     if fraction.is_empty() {
-        if is_pos {
-            NaiveDateTime::from_timestamp_opt(seconds, 0).unwrap()
-        } else {
-            NaiveDateTime::from_timestamp_opt(-seconds, 0).unwrap()
-        }
+        NaiveDateTime::from_timestamp_opt(seconds, 0).unwrap()
     } else {
         let zeros = "0".repeat(9 - fraction.len());
         let fraction = format!("{fraction}{zeros}");
@@ -113,4 +106,44 @@ mod tests {
         let dt_storage = storage_to_datetime(&mut storage.as_slice());
         assert_eq!(dt, dt_storage)
     }
+
+    #[test]
+    fn no_time_ns() {
+        let year: i32 = 1959;
+        let month: u32 = 10;
+        let day: u32 = 11;
+        let hour: u32 = 0;
+        let minute: u32 = 0;
+        let second: u32 = 0;
+        let nano: u32 = 0;
+        let dt = NaiveDate::from_ymd_opt(year, month, day)
+            .unwrap()
+            .and_hms_nano_opt(hour, minute, second, nano)
+            .unwrap();
+        let result = datetime_to_parts(&dt);
+        assert_eq!((true, Integer::from(-322704000), 0_u32), result);
+        let storage = datetime_to_storage(&dt);
+        let dt_storage = storage_to_datetime(&mut storage.as_slice());
+        assert_eq!(dt, dt_storage)
+    }
+
+    #[test]
+    fn a_bit_of_ns() {
+        let year: i32 = 1959;
+        let month: u32 = 10;
+        let day: u32 = 11;
+        let hour: u32 = 0;
+        let minute: u32 = 0;
+        let second: u32 = 0;
+        let nano: u32 = 3;
+        let dt = NaiveDate::from_ymd_opt(year, month, day)
+            .unwrap()
+            .and_hms_nano_opt(hour, minute, second, nano)
+            .unwrap();
+        let result = datetime_to_parts(&dt);
+        assert_eq!((true, Integer::from(-322703999), 999999997_u32), result);
+        let storage = datetime_to_storage(&dt);
+        let dt_storage = storage_to_datetime(&mut storage.as_slice());
+        assert_eq!(dt, dt_storage)
+    }
 }