Fixes Negative numbers for @ not being recognized

This commit resolves #40.
Adds new file and functions parse_timestamp.
Adds tests for handling negative numbers.

Author: philolo1

Cargo.lock

@@ -10,3 +10,4 @@ readme = "README.md"
 [dependencies]
 regex = "1.9"
 chrono = { version="0.4", default-features=false, features=["std", "alloc", "clock"] }
+nom = "7.1.3"

Cargo.toml

@@ -14,10 +14,12 @@ use std::fmt::{self, Display};
 
 // Expose parse_datetime
 mod parse_relative_time;
+mod parse_timestamp;
 
 use chrono::{DateTime, FixedOffset, Local, LocalResult, NaiveDateTime, TimeZone};
 
 use parse_relative_time::parse_relative_time;
+use parse_timestamp::parse_timestamp;
 
 #[derive(Debug, PartialEq)]
 pub enum ParseDateTimeError {
@@ -169,9 +171,9 @@ pub fn parse_datetime_at_date<S: AsRef<str> + Clone>(
     }
 
     // Parse epoch seconds
-    if s.as_ref().bytes().next() == Some(b'@') {
-        if let Ok(parsed) = NaiveDateTime::parse_from_str(&s.as_ref()[1..], "%s") {
-            if let Ok(dt) = naive_dt_to_fixed_offset(date, parsed) {
+    if let Ok(timestamp) = parse_timestamp(s.as_ref()) {
+        if let Some(timestamp_date) = NaiveDateTime::from_timestamp_opt(timestamp, 0) {
+            if let Ok(dt) = naive_dt_to_fixed_offset(date, timestamp_date) {
                 return Ok(dt);
             }
         }
@@ -359,15 +361,21 @@ mod tests {
         use chrono::{TimeZone, Utc};
 
         #[test]
-        fn test_positive_offsets() {
+        fn test_positive_and_negative_offsets() {
             let offsets: Vec<i64> = vec![
                 0, 1, 2, 10, 100, 150, 2000, 1234400000, 1334400000, 1692582913, 2092582910,
             ];
 
             for offset in offsets {
+                // positive offset
                 let time = Utc.timestamp_opt(offset, 0).unwrap();
                 let dt = parse_datetime(format!("@{}", offset));
                 assert_eq!(dt.unwrap(), time);
+
+                // negative offset
+                let time = Utc.timestamp_opt(-offset, 0).unwrap();
+                let dt = parse_datetime(format!("@-{}", offset));
+                assert_eq!(dt.unwrap(), time);
             }
         }
     }

src/lib.rs

@@ -1,3 +1,5 @@
+// For the full copyright and license information, please view the LICENSE
+// file that was distributed with this source code.
 use crate::ParseDateTimeError;
 use chrono::{Duration, Local, NaiveDate, Utc};
 use regex::Regex;

src/parse_relative_time.rs

@@ -0,0 +1,111 @@
+// For the full copyright and license information, please view the LICENSE
+// file that was distributed with this source code.
+use core::fmt;
+use std::error::Error;
+use std::fmt::Display;
+use std::num::ParseIntError;
+
+use nom::branch::alt;
+use nom::character::complete::{char, digit1};
+use nom::combinator::all_consuming;
+use nom::multi::fold_many0;
+use nom::sequence::preceded;
+use nom::sequence::tuple;
+use nom::{self, IResult};
+
+#[derive(Debug, PartialEq)]
+pub enum ParseTimestampError {
+    InvalidNumber(ParseIntError),
+    InvalidInput,
+}
+
+impl Display for ParseTimestampError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::InvalidInput => {
+                write!(f, "Invalid input string: cannot be parsed as a timestamp")
+            }
+            Self::InvalidNumber(err) => {
+                write!(f, "Invalid timestamp number: {err}")
+            }
+        }
+    }
+}
+
+impl Error for ParseTimestampError {}
+
+// TODO is this necessary
+impl From<ParseIntError> for ParseTimestampError {
+    fn from(err: ParseIntError) -> Self {
+        Self::InvalidNumber(err)
+    }
+}
+
+type NomError<'a> = nom::Err<nom::error::Error<&'a str>>;
+
+impl<'a> From<NomError<'a>> for ParseTimestampError {
+    fn from(_err: NomError<'a>) -> Self {
+        Self::InvalidInput
+    }
+}
+
+pub(crate) fn parse_timestamp(s: &str) -> Result<i64, ParseTimestampError> {
+    let s = s.trim().to_lowercase();
+    let s = s.as_str();
+
+    let res: IResult<&str, (char, &str)> = all_consuming(preceded(
+        char('@'),
+        tuple((
+            // Note: to stay compatible with gnu date this code allows
+            // multiple + and - and only considers the last one
+            fold_many0(
+                // parse either + or -
+                alt((char('+'), char('-'))),
+                // start with a +
+                || '+',
+                // whatever we get (+ or -), update the accumulator to that value
+                |_, c| c,
+            ),
+            digit1,
+        )),
+    ))(s);
+
+    let (_, (sign, number_str)) = res?;
+
+    let mut number = number_str.parse::<i64>()?;
+
+    if sign == '-' {
+        number *= -1;
+    }
+
+    Ok(number)
+}
+
+#[cfg(test)]
+mod tests {
+
+    use crate::parse_timestamp::parse_timestamp;
+
+    #[test]
+    fn test_valid_timestamp() {
+        assert_eq!(parse_timestamp("@1234"), Ok(1234));
+        assert_eq!(parse_timestamp("@99999"), Ok(99999));
+        assert_eq!(parse_timestamp("@-4"), Ok(-4));
+        assert_eq!(parse_timestamp("@-99999"), Ok(-99999));
+        assert_eq!(parse_timestamp("@+4"), Ok(4));
+        assert_eq!(parse_timestamp("@0"), Ok(0));
+
+        // gnu date acceppts numbers signs and uses the last sign
+        assert_eq!(parse_timestamp("@---+12"), Ok(12));
+        assert_eq!(parse_timestamp("@+++-12"), Ok(-12));
+        assert_eq!(parse_timestamp("@+----+12"), Ok(12));
+        assert_eq!(parse_timestamp("@++++-123"), Ok(-123));
+    }
+
+    #[test]
+    fn test_invalid_timestamp() {
+        assert!(parse_timestamp("@").is_err());
+        assert!(parse_timestamp("@+--+").is_err());
+        assert!(parse_timestamp("@+1ab2").is_err());
+    }
+}