warn users on debian if they are running with a non-default user

bin/kalite

@@ -28,6 +28,13 @@ import subprocess
 from distutils import spawn
 import warnings
 
+
+# Python 2+3 definition
+try:
+    input = raw_input  # @ReservedAssignment
+except NameError:
+    pass
+
 kalite_path = None
 
 # Ensure that PATH is set because distutils.find_executable fails on
@@ -78,6 +85,30 @@ if not os.path.exists(kalite_path):
 # Converts to normal string for Windows users, where it gets turned into a unicode string and errors out in subprocess
 env['KALITE_DIR'] = str(kalite_path)
 
+# TODO(benjaoming): Delegate responsibility to the .deb package
+# This always evaluates to False on Windows, so no problem with the
+# system-specific path
+if os.name == "posix" and os.path.isfile("/etc/ka-lite/username"):
+    username = open("/etc/ka-lite/username", "r").read()
+    username = username.split("\n")[0] if username else None
+    if username and username != os.environ["USER"]:
+        default_home = os.environ.get("KALITE_HOME", os.path.expanduser("~/.kalite"))
+        if not os.path.exists(default_home) or not os.listdir(default_home):
+            sys.stderr.write((
+                "You are not running kalite as the default user {0}. "
+                "This is recommended unless you want to re-create the database "
+                "and start storing new videos/exercises etc. for a different "
+                "user account\n\n"
+            ).format(username))
+            sys.stderr.write((
+                "To run the command as the default user, run this instead:\n\n"
+                "    sudo su {user} -s /bin/sh -c {command}\n\n"
+            ).format(user=username, command=" ".join(sys.argv)))
+            cont = input("Do you wish to continue? [y/N] ")
+            if not cont.lower() == "y":
+                sys.exit(0)
+
+
 if 'KALITE_PYTHON' in os.environ:
     python_executable = os.environ['KALITE_PYTHON']
     if not spawn.find_executable(python_executable):