--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/pvl/dns/serial.py	Thu May 16 01:14:35 2013 +0300
@@ -0,0 +1,105 @@
+"""
+    Generating zone serials.
+"""
+
+import datetime
+
+import logging; log = logging.getLogger('pvl.dns.serial')
+
+# date fmt to use in serial
+DATE_FMT = '%Y%m%d'
+DATE_LEN = 8
+
+SERIAL_FMT = "{date:8}{count:02}"
+SERIAL_LEN = 10
+
+def format_serial (date, count) :
+    return SERIAL_FMT.format(date=date.strftime(DATE_FMT), count=count)
+
+def next_count (value, date, count) :
+    """
+        Return serial with next count.
+    """
+
+    count += 1
+
+    # check
+    if count > 99 :
+        serial = str(value + 1)
+
+        log.warn("Serial count rollover: %s, %s; fallback -> %s", date, count, serial)
+
+        return serial
+
+    return format_serial(date, count)
+
+def update_serial (serial) :
+    """
+        Parse given serial number (string), returning an updated serial, based on date.
+    """
+    
+    today = datetime.date.today()
+
+    # handle
+    if not serial :
+        # fresh
+        log.info("Setting initial serial: %s01", today)
+        
+        return format_serial(today, 1)
+
+    elif len(serial) != SERIAL_LEN :
+        log.warn("Invalid serial format: %s", serial)
+        
+        value = int(serial)
+        serial = str(value + 1)
+
+        log.info("Incrementing serial: %d -> %s", value, serial)
+
+        return serial
+
+    else :
+        # parse
+        value = int(serial)
+
+        try :
+            date = datetime.datetime.strptime(serial[:DATE_LEN], DATE_FMT).date()
+            count = int(serial[DATE_LEN:])
+
+        except ValueError, e :
+            # invalid date/count format?
+            log.warn("Unable to parse serial: %s: %s", serial, e)
+
+            serial = str(value + 1)
+
+            log.info("Incrementing serial: %d -> %s", value, serial)
+
+            return serial
+            
+        log.debug("old serial=%s, value=%d, date=%s, count=%s", serial, value, date, count)
+        
+    # update
+    if date < today :
+        log.info("Updating to today: %s -> %s", date, today)
+
+        # update date
+        return format_serial(today, 1)
+
+    elif date == today :
+        # keep date, update count
+        log.info("Updating today's count: %s, %s", date, count)
+        
+        # handle count rollover
+        return next_count(value, date, count)
+
+    elif date > today :
+        # keep, update count
+        serial = next_count(value, date, count)
+
+        log.warn("Serial in future; incrementing count: %s, %s -> %s", date, count, serial)
+
+        return serial
+
+    else :
+        raise Exception("Invalid serial: %s:%s", old_date, old_count)
+    
+