Added the changelog URL (#5)

...so users can get a clickable link to see the list of changes between the revisions.

This approach makes a few assumptions:

- The repo is hosted on GitHub.
- The repo has a remote named `origin`, which points to the GitHub repo.

src/main.rs

@@ -16,7 +16,9 @@ impl Changelog {
         let lines = Changelog::get_lines_from(&output);
         let mut lines_iterator = lines.iter();
 
-        print!("## {}\n\n", self.to_revision);
+        println!("## {}", self.to_revision);
+        print!("[Full Changelog](https://github.com/{}/compare/{}...{})\n\n",
+               self.get_repo_slug(), self.from_revision, self.to_revision);
 
         loop {
             match lines_iterator.next() {
@@ -49,6 +51,35 @@ impl Changelog {
                 .split('\n')
                 .collect()
     }
+
+    fn get_repo_slug(&self) -> String {
+        let output = Command::new("git")
+                .arg("remote")
+                .arg("get-url")
+                .arg("origin")
+                .current_dir(&self.repository_path)
+                .output()
+                .unwrap_or_else(|e| panic!("Failed to run 'git log' with error: {}", e));
+
+        let url = String::from_utf8_lossy(&output.stdout).into_owned();
+
+        // The command output contains a trailing newline that we want to get rid of.
+        let trimmed_url = url.trim();
+
+        self.get_repo_slug_from(trimmed_url)
+    }
+
+    fn get_repo_slug_from(&self, url: &str) -> String {
+        // This very simplistic and stupid algorithm works for repos of these forms:
+        // https://github.com/dekellum/fishwife.git
+        // [email protected]:chaos4ever/chaos.git
+        let mangled_url = url.replace(":", "/").replace(".git", "");
+        let mut url_parts: Vec<_> = mangled_url.split('/').collect();
+        let repo_name = url_parts.pop().unwrap();
+        let org_name = url_parts.pop().unwrap();
+
+        format!("{}/{}", org_name, repo_name)
+    }
 }
 
 fn main() {