step sixteen: set parent to HEAD

src/base.rs

@@ -64,6 +64,11 @@ pub fn read_tree(oid: String) {
 
 pub fn commit(message: &str) -> String {
     let mut commit = format!("tree {}\n", write_tree(".".to_owned()));
+
+    if let Ok(head) = data::get_head() {
+        commit += format!("parent {}\n", head).as_str();
+    }
+
     commit += "\n";
     commit += format!("{}\n", message).as_str();
 

src/data.rs

@@ -45,3 +45,8 @@ pub fn get_object(hash: String, expected: String) -> String {
 pub fn set_head(oid: String) {
     fs::write(format!("{}/HEAD", RGIT_DIR), oid).expect("Failed to updated HEAD");
 }
+
+pub fn get_head() -> Result<String, Box<dyn std::error::Error + 'static>> {
+    let oid = fs::read_to_string(format!("{}/HEAD", RGIT_DIR))?;
+    return Ok(oid);
+}