diff --git a/joint_teapot/git.py b/joint_teapot/git.py
index 9dd439a..d85606b 100644
--- a/joint_teapot/git.py
+++ b/joint_teapot/git.py
@@ -1,5 +1,31 @@
+import os
+
 import git
 
+from joint_teapot.config import settings
+
 
 class Git:
-    ...
+    def __init__(self, org_name: str = settings.org_name, repos_dir: str = ""):
+        self.org_name = org_name
+        if not os.path.isdir(repos_dir):
+            raise Exception(f"{repos_dir} does not exist! Create it first.")
+        self.repos_dir = repos_dir
+
+    def __get_repo(self, repo_name: str) -> git.Repo:
+        repo_dir = os.path.join(self.repos_dir, repo_name)
+        if os.path.exists(repo_dir):
+            return git.Repo(repo_dir)
+        return git.Repo.clone_from(
+            f"https://focs.ji.sjtu.edu.cn/git/{self.org_name}/{repo_name}",
+            repo_dir,
+            branch="master",
+        )
+
+    def repo_checkout_to_tag(self, repo_name: str, tag_name: str) -> str:
+        repo = self.__get_repo(repo_name)
+        repo.git.fetch("--tags", "--all", "-f")
+        repo.git.reset("--hard", f"origin/master")
+        repo.git.clean("-d", "-f", "-x")
+        repo.git.checkout(f"tags/{tag_name}")
+        return os.path.join(self.repos_dir, repo_name)
diff --git a/joint_teapot/gitea.py b/joint_teapot/gitea.py
index c0de92f..1d00830 100644
--- a/joint_teapot/gitea.py
+++ b/joint_teapot/gitea.py
@@ -68,9 +68,13 @@ class Gitea:
         repo_name_convertor: Callable[
             [User], Optional[str]
         ] = default_repo_name_convertor,
-    ) -> None:
+    ) -> List[str]:
+        repo_names = []
         for student in students:
             repo_name = repo_name_convertor(student)
+            if repo_name is None:
+                continue
+            repo_names.append(repo_name)
             repo: Dict[str, Any] = self.organization_api.create_org_repo(
                 self.org_name,
                 body={
@@ -87,6 +91,7 @@ class Gitea:
                 repo["name"],
                 self.__get_username_by_student_id(student.sis_login_id),
             )
+        return repo_names
 
     def create_teams_and_repos_by_canvas_groups(
         self,
@@ -95,13 +100,15 @@ class Gitea:
         team_name_convertor: Callable[[str], Optional[str]] = lambda name: name,
         repo_name_convertor: Callable[[str], Optional[str]] = lambda name: name,
         permission: PermissionEnum = PermissionEnum.write,
-    ) -> None:
+    ) -> List[str]:
+        repo_names = []
         group: Group
         for group in groups:
             team_name = team_name_convertor(group.name)
             repo_name = repo_name_convertor(group.name)
             if team_name is None or repo_name is None:
                 continue
+            repo_names.append(repo_name)
             team: Dict[str, Any] = self.organization_api.org_create_team(
                 self.org_name,
                 body={
@@ -145,6 +152,7 @@ class Gitea:
                 self.organization_api.org_add_team_member(
                     team["id"], self.__get_username_by_student_id(student.sis_login_id)
                 )
+        return repo_names
 
     def get_public_key_of_students(
         self, students: PaginatedList