Added a SectionNumber newtype to represent section numbering ("1.2.3")

src/loader/summary.rs

@@ -1,9 +1,64 @@
 use std::error::Error;
+use std::fmt::{self, Formatter, Display};
+use std::ops::{Deref, DerefMut};
 use pulldown_cmark;
 
-/// The parsed `SUMMARY.md`, specifying how the book should be laid out.
-pub struct Summary;
 
+/// The parsed `SUMMARY.md`, specifying how the book should be laid out.
+pub struct Summary {
+    title: Option<String>,
+}
+
+/// Parse the text from a `SUMMARY.md` file into a sort of "recipe" to be
+/// used when loading a book from disk.
 pub fn parse_summary(summary: &str) -> Result<Summary, Box<Error>> {
     unimplemented!()
 }
+
+/// A section number like "1.2.3", basically just a newtype'd `Vec<u32>`.
+#[derive(Debug, PartialEq, Clone, Default)]
+struct SectionNumber(Vec<u32>);
+
+impl Display for SectionNumber {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        let dotted_number: String = self.0.iter().map(|i| format!("{}", i))
+        .collect::<Vec<String>>()
+        .join(".");
+
+        write!(f, "{}", dotted_number)
+    }
+}
+
+impl Deref for SectionNumber {
+    type Target = Vec<u32>;
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl DerefMut for SectionNumber {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn section_number_has_correct_dotted_representation() {
+        let inputs = vec![
+            (vec![0], "0"),
+            (vec![1, 3], "1.3"),
+            (vec![1, 2, 3], "1.2.3"),
+        ];
+
+        for (input, should_be) in inputs {
+            let section_number = SectionNumber(input);
+            let string_repr = format!("{}", section_number);
+
+            assert_eq!(string_repr, should_be);
+        }
+    }
+}