add truncation wrappers

Author: Juliette Cordor

src/lib.rs

@@ -41,3 +41,108 @@ cfg_if::cfg_if! {
         pub mod root;
     }
 }
+
+/// Truncation helpers for truncating strings when formatting
+pub mod truncate {
+    use std::fmt;
+
+    #[derive(Debug)]
+    #[must_use]
+    /// A wrapper that truncates its contents when used.
+    ///
+    /// This should be used through the [`fmt::Display`] trait,
+    /// in [`println!`] and other formatting circumstances
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// # use quork::truncate::Truncate;
+    /// let name = Truncate::new("Juliette Cordor", 8);
+    ///
+    /// assert_eq!(name.to_string(), "Juliette")
+    /// ```
+    pub struct Truncate<T> {
+        length: usize,
+        data: T,
+        suffix: Option<String>,
+    }
+
+    impl<T> Truncate<T> {
+        /// Construct a new [`Truncate`] from the provided data and length
+        pub fn new(data: T, length: usize) -> Self {
+            Self {
+                length,
+                data,
+                suffix: None,
+            }
+        }
+
+        /// Add a suffix to the provided [`Truncate`], to print after the truncation
+        ///
+        /// # Examples
+        ///
+        /// ```rust
+        /// # use quork::truncate::Truncate;
+        /// let mut name = Truncate::new("Juliette Cordor", 8).with_suffix("...");
+        ///
+        /// assert_eq!(name.to_string(), "Juliette...")
+        /// ```
+        pub fn with_suffix(self, suffix: impl fmt::Display) -> Self {
+            Self {
+                suffix: Some(suffix.to_string()),
+                ..self
+            }
+        }
+    }
+
+    impl<T: fmt::Display> fmt::Display for Truncate<T> {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            use fmt::Write;
+            let mut truncator = TruncatedFormatter::new(f, self.length);
+
+            write!(truncator, "{}", self.data)?;
+
+            if let Some(ref suffix) = self.suffix {
+                write!(f, "{suffix}")?;
+            }
+
+            Ok(())
+        }
+    }
+
+    #[derive(Debug)]
+    #[must_use]
+    /// A wrapper over a writer that truncates the output to a certain length
+    ///
+    /// Primarily intended to be used through the [`Truncate`] struct
+    pub struct TruncatedFormatter<'a, T> {
+        remaining: usize,
+        writer: &'a mut T,
+    }
+
+    impl<'a, T> TruncatedFormatter<'a, T> {
+        /// Construct a new [`TruncatedFormatter`] from the provided writer and length
+        pub fn new(writer: &'a mut T, length: usize) -> Self {
+            Self {
+                remaining: length,
+                writer,
+            }
+        }
+    }
+
+    impl<'a, T> fmt::Write for TruncatedFormatter<'a, T>
+    where
+        T: fmt::Write,
+    {
+        fn write_str(&mut self, s: &str) -> fmt::Result {
+            if self.remaining < s.len() {
+                self.writer.write_str(&s[0..self.remaining])?;
+                self.remaining = 0;
+                Ok(())
+            } else {
+                self.remaining -= s.len();
+                self.writer.write_str(s)
+            }
+        }
+    }
+}