step fifty two: compute common ancestor of a commit

src/base.rs

@@ -301,6 +301,24 @@ pub fn merge(oid: String) {
     println!("Please commit");
 }
 
+pub fn get_merge_base(commit1: String, commit2: String) -> String {
+    let mut commit1_deq = VecDeque::new();
+    commit1_deq.push_front(commit1);
+
+    let mut commit2_deq = VecDeque::new();
+    commit2_deq.push_front(commit2);
+
+    let parents1 = iter_commits_and_parents(commit1_deq);
+
+    for oid in iter_commits_and_parents(commit2_deq) {
+        if parents1.contains(&oid) {
+            return oid;
+        }
+    }
+
+    return "".to_owned();
+}
+
 fn is_ignored(path: &String) -> bool {
     if path.contains(".rgit") {
         true

src/main.rs

@@ -86,6 +86,12 @@ fn main() {
                 .about("Merge changes of a different commit/branch")
                 .arg(Arg::with_name("commit").index(1).required(true)),
         )
+        .subcommand(
+            SubCommand::with_name("merge-base")
+                .about("Find the common ancestor between two commits")
+                .arg(Arg::with_name("commit1").index(1).required(true))
+                .arg(Arg::with_name("commit2").index(2).required(true)),
+        )
         .get_matches();
 
     match matches.subcommand_name() {
@@ -105,6 +111,7 @@ fn main() {
         Some("show") => show(matches),
         Some("diff") => difference(matches),
         Some("merge") => merge(matches),
+        Some("merge-base") => merge_base(matches),
         _ => println!("unknown sub command"),
     }
 }
@@ -326,6 +333,14 @@ fn merge(matches: ArgMatches) {
     }
 }
 
+fn merge_base(matches: ArgMatches) {
+    if let Some(cmd_matches) = matches.subcommand_matches("merge-base") {
+        let commit1 = base::get_oid(cmd_matches.value_of("commit1").unwrap().to_owned());
+        let commit2 = base::get_oid(cmd_matches.value_of("commit2").unwrap().to_owned());
+        println!("{}", base::get_merge_base(commit1, commit2));
+    }
+}
+
 fn print_commit(oid: String, commit: &base::Commit, mut refs: HashMap<String, Vec<String>>) {
     let ref_str = if refs.contains_key(&oid) {
         refs.get_mut(&oid).unwrap().join(", ")