Add utility code to get max UID

Other changes:
- Introduce logging
- Introduce .env config parameters
  - LDAP_SEARCH_BASE: The base used in the LDAP search to find uid
  - IPV6_WORK_USER_GROUP: The LDAP group to which the newly added
      user should belong to

ipv6work/settings.py

@@ -12,9 +12,12 @@ https://docs.djangoproject.com/en/2.1/ref/settings/
 
 import os
 import ldap
+import logging
 from decouple import config, Csv
 from django_auth_ldap.config import LDAPSearch, LDAPSearchUnion
 
+logger = logging.getLogger(__name__)
+
 # Build paths inside the project like this: os.path.join(BASE_DIR, ...)
 BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
 
@@ -207,6 +210,44 @@ LOGGING = {
     },
 }
 
+LDAP_SEARCH_BASE=config(
+    'LDAP_SEARCH_BASE',
+    default='ou=users,dc=ungleich,dc=ch'
+)
+
+LDAP_MAX_UID_PATH = os.path.join(
+    os.path.abspath(os.path.dirname(__file__)),
+    'ldap_max_uid_file'
+)
+
+IPV6_WORK_USER_GROUP = config('IPV6_WORK_USER_GROUP', cast=int)
+
+
+def set_max_uid(max_uid):
+    """
+    a utility function to save max_uid value to a file
+
+    :param max_uid: an integer representing the max uid
+    :return:
+    """
+    with open(LDAP_MAX_UID_PATH, 'w+') as handler:
+        handler.write(max_uid)
+
+
+def get_max_uid():
+    """
+    A utility function to read the max uid value that was previously set
+
+    :return: An integer representing the max uid value that was previously set
+    """
+    try:
+        with open(LDAP_MAX_UID_PATH, 'r+') as handler:
+            return int(handler.read())
+    except FileNotFoundError as fnfe:
+        logger.error("File not found : " + str(fnfe))
+        ret = config('DEFAULT_START_UID', cast=int, default=10000)
+        logger.error("So, returing UID={}".format(ret))
+
 if config('ENABLE_DEBUG_LOG', cast=bool, default=False):
     loggers_dict = {}
     LOGGING['handlers']['file'] = {