from __future__ import absolute_import

import collections

from .cache import Cache


class LRUCache(Cache):
  """Least Recently Used (LRU) cache implementation."""

  def __init__(self, maxsize, getsizeof=None):
    Cache.__init__(self, maxsize, getsizeof)
    self.__order = collections.OrderedDict()

  def __getitem__(self, key, cache_getitem=Cache.__getitem__):
    value = cache_getitem(self, key)
    self.__update(key)
    return value

  def __setitem__(self, key, value, cache_setitem=Cache.__setitem__):
    cache_setitem(self, key, value)
    self.__update(key)

  def __delitem__(self, key, cache_delitem=Cache.__delitem__):
    cache_delitem(self, key)
    del self.__order[key]

  def popitem(self):
    """Remove and return the `(key, value)` pair least recently used."""
    try:
      key = next(iter(self.__order))
    except StopIteration:
      raise KeyError('%s is empty' % self.__class__.__name__)
    else:
      return (key, self.pop(key))

  if hasattr(collections.OrderedDict, 'move_to_end'):

    def __update(self, key):
      try:
        self.__order.move_to_end(key)
      except KeyError:
        self.__order[key] = None
  else:

    def __update(self, key):
      try:
        self.__order[key] = self.__order.pop(key)
      except KeyError:
        self.__order[key] = None
