Updater: Add a utility to auto-update

In the process of updating zygrader to a package, it will be nice to automatically
update if new versions exists. This provides the ability to do so.

__main__.py

@@ -8,6 +8,7 @@
 from zygrader import config
 from zygrader.data import lock
 from zygrader import logger
+from zygrader import updater
 
 def lock_cleanup():
     lock.unlock_all_labs_by_grader(getpass.getuser())
@@ -47,6 +48,14 @@ def sigtstp_handler(signum, frame):
 # Set a short ESC key delay (curses environment variable)
 os.environ.setdefault('ESCDELAY', '25')
 
+# Check for updates
+latest_version = updater.get_latest_version()
+if latest_version != config.g_data.VERSION:
+    updater.update_zygrader(latest_version)
+
+    # update_zygrader will update then fork a new zygrader process
+    sys.exit()
+
 zygrader.start()
 
 logger.log("zygrader exited normally")

zygrader/config/g_data.py

@@ -3,7 +3,7 @@
 
 from .. import data
 
-# Only change these if you know what you are doing!
+# Zygrader version
 VERSION = 3.5
 
 # TODO: save this in configuration

zygrader/updater.py

@@ -0,0 +1,39 @@
+"""Updater: To auto-update zygrader during runtime"""
+import requests
+import subprocess
+import sys
+
+from . import config
+
+REPO_NAME = "natecraddock/zygrader"
+API_URL = f"https://api.github.com/repos/{REPO_NAME}/tags"
+INSTALL_URL = f"https://github.com/{REPO_NAME}/tarball/master"
+
+def get_latest_version():
+    """Check the zygrader git repo tags for a new version"""
+    r = requests.get(API_URL)
+    if not r.ok:
+        return config.g_data.VERSION
+
+    latest = float(r.json()[0]["name"])
+    if latest > config.g_data.VERSION:
+        return latest
+
+    return config.g_data.VERSION
+
+def update_zygrader(latest_version):
+    """Download zygrader from the git repository and update it"""
+    print()
+    print(f"Updating zygrader [{config.g_data.VERSION} -> {latest_version}]")
+    print()
+
+    # Install the new version of zygrader
+    try:
+        subprocess.check_call([sys.executable, "-m", "pip", "install", "--upgrade", INSTALL_URL])
+    except subprocess.CalledProcessError:
+        print("Failed to update zygrader. Exiting")
+        print()
+        return
+
+    # zygrader updated properly, fork and run zygrader again
+    # TODO: Update here once zygrader is a package