Add indentor.rs

src/indentor.rs

@@ -0,0 +1,62 @@
+const ADDITIONAL_INDENT: usize = 4;
+
+#[derive(Debug)]
+pub struct Indentor {
+    indent_str: Vec<u8>,
+    buf: Vec<u8>,
+}
+
+impl Indentor {
+    /// Constructs an indentor
+    ///
+    /// The length of `indent_str` must be `> 0`
+    pub fn new(indent_str: impl AsRef<[u8]>) -> Self {
+        assert!(!indent_str.as_ref().is_empty());
+
+        Self {
+            indent_str: indent_str.as_ref().to_vec(),
+            buf: indent_str.as_ref().repeat(ADDITIONAL_INDENT),
+        }
+    }
+
+    /// Return a `&[u8]` of the `indent_str` repeated `level` times
+    ///
+    /// Will update internal buffer if required
+    pub fn get_indent(&mut self, level: usize) -> &[u8] {
+        let levels_cached = self.levels_cached();
+
+        if level > levels_cached {
+            self.buf.append(
+                &mut self
+                    .indent_str
+                    .repeat(level - levels_cached + ADDITIONAL_INDENT),
+            );
+        }
+
+        &self.buf[0..(level * self.indent_str.len())]
+    }
+
+    /// Gets the number of indent levels cached
+    fn levels_cached(&self) -> usize {
+        self.buf.len() / self.indent_str.len()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_indentor() {
+        let mut i = Indentor::new("\t");
+
+        assert_eq!(i.get_indent(1), b"\t");
+
+        assert_eq!(i.buf.len(), ADDITIONAL_INDENT);
+
+        assert_eq!(i.get_indent(100), b"\t".repeat(100));
+
+        assert!(i.buf.len() >= 100);
+        assert!(i.buf.len() <= 100 + ADDITIONAL_INDENT);
+    }
+}