feat: ordinal utility

src/lib.rs

@@ -1,2 +1,3 @@
 pub mod macros;
 pub mod time;
+pub mod util;

src/util.rs

@@ -0,0 +1,50 @@
+/// Returns the number with its ordinal suffix (1st, 2nd, 3rd, etc.)
+///
+/// # Examples
+///
+/// ```
+/// use diaryrs::util::ordinal;
+///
+/// assert_eq!(ordinal(1), "1st");
+/// // Accounts for teens properly: 11th, 12th, 13th etc.
+/// assert_eq!(ordinal(12), "12th");
+/// assert_eq!(ordinal(21), "21st");
+/// assert_eq!(ordinal(22), "22nd");
+/// // Works with larger teens as well
+/// assert_eq!(ordinal(112), "112th");
+/// ```
+pub fn ordinal(n: u32) -> String {
+    // Teens are a special case
+    if n % 100 >= 11 && n % 100 <= 13 {
+        return format!("{}th", n);
+    }
+
+    let suffix = match n % 10 {
+        1 => "st",
+        2 => "nd",
+        3 => "rd",
+        _ => "th",
+    };
+    format!("{}{}", n, suffix)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_ordinal() {
+        assert_eq!(ordinal(1), "1st");
+        assert_eq!(ordinal(2), "2nd");
+        assert_eq!(ordinal(3), "3rd");
+        assert_eq!(ordinal(4), "4th");
+        assert_eq!(ordinal(11), "11th");
+        assert_eq!(ordinal(12), "12th");
+        assert_eq!(ordinal(13), "13th");
+        assert_eq!(ordinal(21), "21st");
+        assert_eq!(ordinal(22), "22nd");
+        assert_eq!(ordinal(23), "23rd");
+        assert_eq!(ordinal(24), "24th");
+        assert_eq!(ordinal(112), "112th");
+    }
+}