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"""

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    Generating zone serials.

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"""

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import datetime

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import logging; log = logging.getLogger('pvl.dns.serial')

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# date fmt to use in serial

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DATE_FMT = '%Y%m%d'

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DATE_LEN = 8

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SERIAL_FMT = "{date:8}{count:02}"

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SERIAL_LEN = 10

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def format_serial (date, count) :

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    """

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        Format serial as string.

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        >>> format_serial(datetime.date(2013, 9, 10), 0)

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        '2013091000'

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        >>> format_serial(datetime.date(2013, 9, 10), 1)

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        '2013091001'

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    """

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    assert 0 <= count <= 99

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    return SERIAL_FMT.format(date=date.strftime(DATE_FMT), count=count)

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def next_serial (date, count) :

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    """

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        Return serial with next count.

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        >>> next_serial(datetime.date(2013, 9, 10), 1)

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        '2013091002'

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        >>> next_serial(datetime.date(2013, 9, 10), 99)

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        '2013091100'

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    """

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    # check

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    if count < 99 :

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        return format_serial(date, count + 1)

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    else:

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        serial = str(int(format_serial(date, count)) + 1)

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        log.warn("Serial count rollover: %s, %s; fallback -> %s", date, count, serial)

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        return serial

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def update_serial (serial, today=None) :

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    """

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        Parse given serial number (string), returning an updated serial, based on date.

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        Raises ValueError on invalid (non-numeric) serial.

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        >>> print update_serial('', today=datetime.date(2013, 9, 10))

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        2013091001

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        >>> print update_serial('13', today=datetime.date(2013, 9, 10))

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        14

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        >>> print update_serial('2013083501', today=datetime.date(2013, 9, 10))

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        2013083502

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        >>> print update_serial('2013083102', today=datetime.date(2013, 9, 10))

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        2013091001

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        >>> print update_serial('2013091002', today=datetime.date(2013, 9, 10))

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        2013091003

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        >>> print update_serial('2013091102', today=datetime.date(2013, 9, 10))

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        2013091103

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    """

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    if not today:

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        today = datetime.date.today()

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    # handle

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    if not serial :

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        # fresh

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        log.info("Setting initial serial: %s01", today)

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        return format_serial(today, 1)

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    elif len(serial) != SERIAL_LEN :

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        log.warn("Invalid serial format: %s", serial)

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        value = int(serial)

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        serial = str(value + 1)

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        log.info("Incrementing serial: %d -> %s", value, serial)

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        return serial

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    else :

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        # parse

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        value = int(serial)

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        try :

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            date = datetime.datetime.strptime(serial[:DATE_LEN], DATE_FMT).date()

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            count = int(serial[DATE_LEN:])

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        except ValueError, e :

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            # invalid date/count format?

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            log.warn("Unable to parse serial: %s: %s", serial, e)

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            serial = str(value + 1)

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            log.info("Incrementing serial: %d -> %s", value, serial)

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            return serial

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        log.debug("old serial=%s, value=%d, date=%s, count=%s", serial, value, date, count)

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    # update

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    if date < today :

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        log.info("Updating to today: %s -> %s", date, today)

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        # update date

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        return format_serial(today, 1)

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    elif date == today :

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        # keep date, update count

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        log.info("Updating today's count: %s, %s", date, count)

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        # handle count rollover

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        return next_serial(date, count)

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    elif date > today :

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        # keep, update count

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        serial = next_serial(date, count)

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        log.warn("Serial in future; incrementing count: %s, %s -> %s", date, count, serial)

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        return serial

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    else :

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        raise Exception("Impossible serial: %s:%s", date, count)