Add a new Chapter struct for the new Book struct

src/book/chapter.rs

@@ -0,0 +1,52 @@
+use book::metadata::BookMetadata;
+
+use std::path;
+
+/// The Chapter struct holds the title of the chapter as written in the SUMMARY.md file,
+/// the location of the markdown file containing the content and eventually sub-chapters
+pub struct Chapter {
+    title: String,
+    file: path::PathBuf,
+
+    sub_chapters: Vec<Chapter>,
+}
+
+
+impl Chapter {
+    /// Creates a new chapter with the given title and source file and no sub-chapters
+    pub fn new(title: &str, file: &path::Path) -> Self {
+        Chapter {
+            title: title.to_owned(),
+            file: file.to_owned(),
+
+            sub_chapters: Vec::new(),
+        }
+    }
+
+    /// This function takes a slice `&[x,y,z]` and returns the corresponding sub-chapter if it exists.
+    ///
+    /// For example: `chapter.get_sub_chapter(&[1,3])` will return the third sub-chapter of the first sub-chapter.
+    pub fn get_sub_chapter(&self, section: &[usize]) -> Option<&Chapter> {
+        match section.len() {
+            0 => None,
+            1 => self.sub_chapters.get(section[0]),
+            _ => {
+                // The lengt of the slice is more than one, this means that we want a sub-chapter of a sub-chapter
+                // We call `get_sub_chapter` recursively until we are deep enough and return the asked sub-chapter
+                self.sub_chapters
+                    .get(section[0])
+                    .and_then(|ch| ch.get_sub_chapter(&section[1..]))
+            },
+        }
+    }
+
+    pub fn title(&self) -> &str {
+        &self.title
+    }
+    pub fn file(&self) -> &path::Path {
+        &self.file
+    }
+    pub fn sub_chapters(&self) -> &[Chapter] {
+        &self.sub_chapters
+    }
+}