Support weekdays in parse_datetime

This commit resolves issue uutils#23.

Adds parse_weekday function that uses chrono weekday parser with a map for edge cases.
Adds tests cases to make sure it works correctly.
Use nom for parsing.

Cargo.toml

@@ -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"

src/lib.rs

@@ -15,7 +15,12 @@ use std::fmt::{self, Display};
 // Expose parse_datetime
 mod parse_relative_time;
 
-use chrono::{DateTime, FixedOffset, Local, LocalResult, NaiveDateTime, TimeZone};
+mod parse_weekday;
+
+use chrono::{
+    DateTime, Datelike, Duration, FixedOffset, Local, LocalResult, NaiveDateTime, TimeZone,
+    Timelike,
+};
 
 use parse_relative_time::parse_relative_time;
 
@@ -168,6 +173,27 @@ pub fn parse_datetime_at_date<S: AsRef<str> + Clone>(
         }
     }
 
+    // parse weekday
+    if let Some(weekday) = parse_weekday::parse_weekday(s.as_ref()) {
+        let mut beginning_of_day = date
+            .with_hour(0)
+            .unwrap()
+            .with_minute(0)
+            .unwrap()
+            .with_second(0)
+            .unwrap()
+            .with_nanosecond(0)
+            .unwrap();
+
+        while beginning_of_day.weekday() != weekday {
+            beginning_of_day += Duration::days(1);
+        }
+
+        let dt = DateTime::<FixedOffset>::from(beginning_of_day);
+
+        return Ok(dt);
+    }
+
     // Parse epoch seconds
     if s.as_ref().bytes().next() == Some(b'@') {
         if let Ok(parsed) = NaiveDateTime::parse_from_str(&s.as_ref()[1..], "%s") {
@@ -353,6 +379,56 @@ mod tests {
         }
     }
 
+    #[cfg(test)]
+    mod weekday {
+        use chrono::{DateTime, Local, TimeZone};
+
+        use crate::parse_datetime_at_date;
+
+        fn get_formatted_date(date: DateTime<Local>, weekday: &str) -> String {
+            let result = parse_datetime_at_date(date, weekday).unwrap();
+
+            return result.format("%F %T %f").to_string();
+        }
+        #[test]
+        fn test_weekday() {
+            // add some constant hours and minutes and seconds to check its reset
+            let date = Local.with_ymd_and_hms(2023, 02, 28, 10, 12, 3).unwrap();
+
+            // 2023-2-28 is tuesday
+            assert_eq!(
+                get_formatted_date(date, "tuesday"),
+                "2023-02-28 00:00:00 000000000"
+            );
+
+            // 2023-3-01 is wednesday
+            assert_eq!(
+                get_formatted_date(date, "wed"),
+                "2023-03-01 00:00:00 000000000"
+            );
+
+            assert_eq!(
+                get_formatted_date(date, "thu"),
+                "2023-03-02 00:00:00 000000000"
+            );
+
+            assert_eq!(
+                get_formatted_date(date, "fri"),
+                "2023-03-03 00:00:00 000000000"
+            );
+
+            assert_eq!(
+                get_formatted_date(date, "sat"),
+                "2023-03-04 00:00:00 000000000"
+            );
+
+            assert_eq!(
+                get_formatted_date(date, "sun"),
+                "2023-03-05 00:00:00 000000000"
+            );
+        }
+    }
+
     #[cfg(test)]
     mod timestamp {
         use crate::parse_datetime;

src/parse_weekday.rs

@@ -0,0 +1,96 @@
+use chrono::Weekday;
+use nom::branch::alt;
+use nom::bytes::complete::tag;
+use nom::combinator::value;
+use nom::{self, IResult};
+
+pub(crate) fn parse_weekday(s: &str) -> Option<Weekday> {
+    let s = s.trim().to_lowercase();
+    let s = s.as_str();
+
+    let parse_result: IResult<&str, Weekday> = nom::combinator::all_consuming(alt((
+        value(Weekday::Mon, alt((tag("monday"), tag("mon")))),
+        value(Weekday::Tue, alt((tag("tuesday"), tag("tues"), tag("tue")))),
+        value(
+            Weekday::Wed,
+            alt((tag("wednesday"), tag("wednes"), tag("wed"))),
+        ),
+        value(
+            Weekday::Thu,
+            alt((tag("thursday"), tag("thurs"), tag("thur"), tag("thu"))),
+        ),
+        value(Weekday::Fri, alt((tag("friday"), tag("fri")))),
+        value(Weekday::Sat, alt((tag("saturday"), tag("sat")))),
+        value(Weekday::Sun, alt((tag("sunday"), tag("sun")))),
+    )))(s);
+
+    match parse_result {
+        Ok((_, weekday)) => Some(weekday),
+        Err(_) => None,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+
+    use chrono::Weekday::*;
+
+    use crate::parse_weekday::parse_weekday;
+
+    #[test]
+    fn test_valid_weekdays() {
+        let days = [
+            ("mon", Mon),
+            ("monday", Mon),
+            ("tue", Tue),
+            ("tues", Tue),
+            ("tuesday", Tue),
+            ("wed", Wed),
+            ("wednes", Wed),
+            ("wednesday", Wed),
+            ("thu", Thu),
+            ("thursday", Thu),
+            ("fri", Fri),
+            ("friday", Fri),
+            ("sat", Sat),
+            ("saturday", Sat),
+            ("sun", Sun),
+            ("sunday", Sun),
+        ];
+
+        for (name, weekday) in days {
+            assert_eq!(parse_weekday(name), Some(weekday));
+            assert_eq!(parse_weekday(&format!(" {}", name)), Some(weekday));
+            assert_eq!(parse_weekday(&format!(" {} ", name)), Some(weekday));
+            assert_eq!(parse_weekday(&format!("{} ", name)), Some(weekday));
+
+            let (left, right) = name.split_at(1);
+            let (test_str1, test_str2) = (
+                format!("{}{}", left.to_uppercase(), right.to_lowercase()),
+                format!("{}{}", left.to_lowercase(), right.to_uppercase()),
+            );
+
+            assert_eq!(parse_weekday(&test_str1), Some(weekday));
+            assert_eq!(parse_weekday(&test_str2), Some(weekday));
+        }
+    }
+
+    #[test]
+    fn test_invalid_weekdays() {
+        let days = [
+            "mond",
+            "tuesda",
+            "we",
+            "th",
+            "fr",
+            "sa",
+            "su",
+            "garbageday",
+            "tomorrow",
+            "yesterday",
+        ];
+        for day in days {
+            assert!(parse_weekday(day).is_none());
+        }
+    }
+}