fix: support float timestamp values

Author: yuankunzhang

src/items/builder.rs

@@ -13,7 +13,7 @@ use super::{date, relative, time, weekday};
 #[derive(Debug, Default)]
 pub struct DateTimeBuilder {
     base: Option<DateTime<FixedOffset>>,
-    timestamp: Option<i32>,
+    timestamp: Option<f64>,
     date: Option<date::Date>,
     time: Option<time::Time>,
     weekday: Option<weekday::Weekday>,
@@ -35,7 +35,7 @@ impl DateTimeBuilder {
 
     /// Timestamp value is exclusive to other date/time components. Caller of
     /// the builder must ensure that it is not combined with other items.
-    pub(super) fn set_timestamp(mut self, ts: i32) -> Result<Self, &'static str> {
+    pub(super) fn set_timestamp(mut self, ts: f64) -> Result<Self, &'static str> {
         self.timestamp = Some(ts);
         Ok(self)
     }
@@ -117,10 +117,24 @@ impl DateTimeBuilder {
         )?;
 
         if let Some(ts) = self.timestamp {
-            dt = chrono::Utc
-                .timestamp_opt(ts.into(), 0)
-                .unwrap()
-                .with_timezone(&dt.timezone());
+            // TODO: How to make the fract -> nanosecond conversion more precise?
+            // Maybe considering using the
+            // [rust_decimal](https://crates.io/crates/rust_decimal) crate?
+            match chrono::Utc.timestamp_opt(ts as i64, (ts.fract() * 10f64.powi(9)).round() as u32)
+            {
+                chrono::MappedLocalTime::Single(t) => {
+                    // If the timestamp is valid, we can use it directly.
+                    dt = t.with_timezone(&dt.timezone());
+                }
+                chrono::MappedLocalTime::Ambiguous(earliest, _latest) => {
+                    // TODO: When there is a fold in the local time, which value
+                    // do we choose? For now, we use the earliest one.
+                    dt = earliest.with_timezone(&dt.timezone());
+                }
+                chrono::MappedLocalTime::None => {
+                    return None; // Invalid timestamp
+                }
+            }
         }
 
         if let Some(date::Date { year, month, day }) = self.date {

src/items/epoch.rs

@@ -3,9 +3,33 @@
 
 use winnow::{combinator::preceded, ModalResult, Parser};
 
-use super::primitive::{dec_int, s};
+use super::primitive::{float, s};
 
 /// Parse a timestamp in the form of `@1234567890`.
-pub fn parse(input: &mut &str) -> ModalResult<i32> {
-    s(preceded("@", dec_int)).parse_next(input)
+pub fn parse(input: &mut &str) -> ModalResult<f64> {
+    s(preceded("@", float)).parse_next(input)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::parse;
+
+    fn float_eq(a: f64, b: f64) -> bool {
+        (a - b).abs() < f64::EPSILON
+    }
+
+    #[test]
+    fn float() {
+        let mut input = "@1234567890";
+        assert!(float_eq(parse(&mut input).unwrap(), 1234567890.0));
+
+        let mut input = "@1234567890.12345";
+        assert!(float_eq(parse(&mut input).unwrap(), 1234567890.12345));
+
+        let mut input = "@1234567890,12345";
+        assert!(float_eq(parse(&mut input).unwrap(), 1234567890.12345));
+
+        let mut input = "@-1234567890.12345";
+        assert_eq!(parse(&mut input).unwrap(), -1234567890.12345);
+    }
 }

src/items/mod.rs

@@ -55,7 +55,7 @@ use crate::ParseDateTimeError;
 
 #[derive(PartialEq, Debug)]
 pub(crate) enum Item {
-    Timestamp(i32),
+    Timestamp(f64),
     Year(u32),
     DateTime(combined::DateTime),
     Date(date::Date),

src/items/primitive.rs

@@ -84,6 +84,7 @@ where
 ///
 /// Inputs like [+-]?0[0-9]* (e.g., `+012`) are therefore rejected. We provide a
 /// custom implementation to support such zero-prefixed integers.
+#[allow(unused)]
 pub(super) fn dec_int<'a, E>(input: &mut &'a str) -> winnow::Result<i32, E>
 where
     E: ParserError<&'a str>,