step nineteen: checkout, read tree and move HEAD

src/base.rs

@@ -109,6 +109,12 @@ pub fn get_commit(oid: String) -> Commit {
     };
 }
 
+pub fn checkout(oid: String) {
+    let commit = get_commit(oid.clone());
+    read_tree(commit.tree);
+    data::set_head(oid);
+}
+
 fn is_ignored(path: &String) -> bool {
     if path.contains(".rgit") {
         true

src/main.rs

@@ -43,6 +43,11 @@ fn main() {
                 .about("List all commits")
                 .arg(Arg::with_name("oid").index(1).required(false)),
         )
+        .subcommand(
+            SubCommand::with_name("checkout")
+                .about("Move the current content and HEAD to given commit")
+                .arg(Arg::with_name("oid").index(1).required(true)),
+        )
         .get_matches();
 
     match matches.subcommand_name() {
@@ -53,6 +58,7 @@ fn main() {
         Some("read-tree") => read_tree(matches),
         Some("commit") => commit(matches),
         Some("log") => log_commits(matches),
+        Some("checkout") => checkout(matches),
         _ => println!("unknown sub command"),
     }
 }
@@ -126,3 +132,10 @@ fn log_commits(matches: ArgMatches) {
         }
     }
 }
+
+fn checkout(matches: ArgMatches) {
+    if let Some(cmd_matches) = matches.subcommand_matches("checkout") {
+        let oid = cmd_matches.value_of("oid").unwrap().to_owned();
+        base::checkout(oid);
+    }
+}