# Copyright (C) 2009 Raymond Hettinger

#                          *** MIT License ***
# Permission is hereby granted, free of charge, to any person obtaining a copy of
# this software and associated documentation files (the "Software"), to deal in
# the Software without restriction, including without limitation the rights to
# use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
# of the Software, and to permit persons to whom the Software is furnished to do
# so, subject to the following conditions:

# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

# {{{ http://code.activestate.com/recipes/576694/ (r7)

import collections

KEY, PREV, NEXT = list(range(3))


class OrderedSet(collections.abc.MutableSet):

    def __init__(self, iterable=None):
        self.end = end = []
        end += [None, end, end]         # sentinel node for doubly linked list
        self.map = {}                   # key --> [key, prev, next]
        if iterable is not None:
            self |= iterable

    def __len__(self):
        return len(self.map)

    def __contains__(self, key):
        return key in self.map

    def add(self, key):
        if key not in self.map:
            end = self.end
            curr = end[PREV]
            curr[NEXT] = end[PREV] = self.map[key] = [key, curr, end]

    def discard(self, key):
        if key in self.map:
            key, prev, next_ = self.map.pop(key)
            prev[NEXT] = next_
            next_[PREV] = prev

    def __iter__(self):
        end = self.end
        curr = end[NEXT]
        while curr is not end:
            yield curr[KEY]
            curr = curr[NEXT]

    def __reversed__(self):
        end = self.end
        curr = end[PREV]
        while curr is not end:
            yield curr[KEY]
            curr = curr[PREV]

    def pop(self):
        last = True
        if not self:
            raise KeyError('set is empty')
        key = next(reversed(self)) if last else next(iter(self))
        self.discard(key)
        return key

    def intersection(self, other):
        # return set with all objects in self that are in other
        return OrderedSet([x for x in self if x in other])

    def __repr__(self):
        if not self:
            return '%s()' % (self.__class__.__name__,)
        return '%s(%r)' % (self.__class__.__name__, list(self))

    def __eq__(self, other):
        if isinstance(other, OrderedSet):
            return len(self) == len(other) and list(self) == list(other)
        return set(self) == set(other)

    def __del__(self):
        self.clear()                    # remove circular references


oset = OrderedSet

if __name__ == '__main__':
    print(OrderedSet('abracadaba'))
    print(OrderedSet('simsalabim'))

# end of http://code.activestate.com/recipes/576694/ }}}