# Copyright 2013 OpenStack Foundation
# Copyright 2013 IBM Corp.
#
# 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.


class Hints(object):
    """Encapsulate driver hints for listing entities.

    Hints are modifiers that affect the return of entities from a
    list_<entities> operation.  They are typically passed to a driver to give
    direction as to what filtering, pagination or list limiting actions are
    being requested.

    It is optional for a driver to action some or all of the list hints,
    but any filters that it does satisfy must be marked as such by calling
    removing the filter from the list.

    A Hint object contains filters, which is a list of dicts that can be
    accessed publicly. Also it contains a dict called limit, which will
    indicate the amount of data we want to limit our listing to.

    If the filter is discovered to never match, then `cannot_match` can be set
    to indicate that there will not be any matches and the backend work can be
    short-circuited.

    Each filter term consists of:

    * ``name``: the name of the attribute being matched
    * ``value``: the value against which it is being matched
    * ``comparator``: the operation, which can be one of ``equals``,
                      ``startswith`` or ``endswith``
    * ``case_sensitive``: whether any comparison should take account of
                          case
    * ``type``: will always be 'filter'

    """
    def __init__(self):
        self.limit = None
        self.filters = list()
        self.cannot_match = False

    def add_filter(self, name, value, comparator='equals',
                   case_sensitive=False):
        """Adds a filter to the filters list, which is publicly accessible."""
        self.filters.append({'name': name, 'value': value,
                             'comparator': comparator,
                             'case_sensitive': case_sensitive,
                             'type': 'filter'})

    def get_exact_filter_by_name(self, name):
        """Return a filter key and value if exact filter exists for name."""
        for entry in self.filters:
            if (entry['type'] == 'filter' and entry['name'] == name and
                    entry['comparator'] == 'equals'):
                return entry

    def set_limit(self, limit, truncated=False):
        """Set a limit to indicate the list should be truncated."""
        self.limit = {'limit': limit, 'type': 'limit', 'truncated': truncated}