counter.py

# Copyright 2010-present Basho Technologies, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import six

from riak.datatypes.datatype import Datatype
from riak.datatypes import TYPES


class Counter(Datatype):
    """
    A convergent datatype that represents a counter which can be
    incremented or decremented. This type can stand on its own or be
    embedded within a :class:`~riak.datatypes.Map`.
    """

    type_name = 'counter'
    _type_error_msg = "Counters can only be integers"

    def _post_init(self):
        self._increment = 0

    def _default_value(self):
        return 0

    @Datatype.modified.getter
    def modified(self):
        """
        Whether this counter has staged increments.
        """
        return self._increment != 0

    def to_op(self):
        """
        Extracts the mutation operation from the counter
        :rtype: int, None
        """
        if not self._increment == 0:
            return ('increment', self._increment)

    def increment(self, amount=1):
        """
        Increments the counter by one or the given amount.

        :param amount: the amount to increment the counter
        :type amount: int
        """
        self._raise_if_badtype(amount)
        self._increment += amount

    def decrement(self, amount=1):
        """
        Decrements the counter by one or the given amount.

        :param amount: the amount to decrement the counter
        :type amount: int
        """
        self._raise_if_badtype(amount)
        self._increment -= amount

    def _check_type(self, new_value):
        return isinstance(new_value, six.integer_types)


TYPES['counter'] = Counter