# orm/identity.py
# Copyright (C) 2005-2015 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php

import weakref
from . import attributes
from .. import util


class IdentityMap(dict):

    def __init__(self):
        self._modified = set()
        self._wr = weakref.ref(self)

    def replace(self, state):
        raise NotImplementedError()

    def add(self, state):
        raise NotImplementedError()

    def update(self, dict):
        raise NotImplementedError("IdentityMap uses add() to insert data")

    def clear(self):
        raise NotImplementedError("IdentityMap uses remove() to remove data")

    def _manage_incoming_state(self, state):
        state._instance_dict = self._wr

        if state.modified:
            self._modified.add(state)

    def _manage_removed_state(self, state):
        del state._instance_dict
        self._modified.discard(state)

    def _dirty_states(self):
        return self._modified

    def check_modified(self):
        """return True if any InstanceStates present have been marked
        as 'modified'.

        """
        return bool(self._modified)

    def has_key(self, key):
        return key in self

    def popitem(self):
        raise NotImplementedError("IdentityMap uses remove() to remove data")

    def pop(self, key, *args):
        raise NotImplementedError("IdentityMap uses remove() to remove data")

    def setdefault(self, key, default=None):
        raise NotImplementedError("IdentityMap uses add() to insert data")

    def copy(self):
        raise NotImplementedError()

    def __setitem__(self, key, value):
        raise NotImplementedError("IdentityMap uses add() to insert data")

    def __delitem__(self, key):
        raise NotImplementedError("IdentityMap uses remove() to remove data")


class WeakInstanceDict(IdentityMap):

    def __init__(self):
        IdentityMap.__init__(self)

    def __getitem__(self, key):
        state = dict.__getitem__(self, key)
        o = state.obj()
        if o is None:
            raise KeyError(key)
        return o

    def __contains__(self, key):
        try:
            if dict.__contains__(self, key):
                state = dict.__getitem__(self, key)
                o = state.obj()
            else:
                return False
        except KeyError:
            return False
        else:
            return o is not None

    def contains_state(self, state):
        return dict.get(self, state.key) is state

    def replace(self, state):
        if dict.__contains__(self, state.key):
            existing = dict.__getitem__(self, state.key)
            if existing is not state:
                self._manage_removed_state(existing)
            else:
                return

        dict.__setitem__(self, state.key, state)
        self._manage_incoming_state(state)

    def add(self, state):
        key = state.key
        # inline of self.__contains__
        if dict.__contains__(self, key):
            try:
                existing_state = dict.__getitem__(self, key)
                if existing_state is not state:
                    o = existing_state.obj()
                    if o is not None:
                        raise AssertionError(
                            "A conflicting state is already "
                            "present in the identity map for key %r"
                            % (key, ))
                else:
                    return
            except KeyError:
                pass
        dict.__setitem__(self, key, state)
        self._manage_incoming_state(state)

    def get(self, key, default=None):
        state = dict.get(self, key, default)
        if state is default:
            return default
        o = state.obj()
        if o is None:
            return default
        return o

    def _items(self):
        values = self.all_states()
        result = []
        for state in values:
            value = state.obj()
            if value is not None:
                result.append((state.key, value))
        return result

    def _values(self):
        values = self.all_states()
        result = []
        for state in values:
            value = state.obj()
            if value is not None:
                result.append(value)

        return result

    if util.py2k:
        items = _items
        values = _values

        def iteritems(self):
            return iter(self.items())

        def itervalues(self):
            return iter(self.values())
    else:
        def items(self):
            return iter(self._items())

        def values(self):
            return iter(self._values())

    def all_states(self):
        if util.py2k:
            return dict.values(self)
        else:
            return list(dict.values(self))

    def discard(self, state):
        st = dict.get(self, state.key, None)
        if st is state:
            dict.pop(self, state.key, None)
            self._manage_removed_state(state)

    def prune(self):
        return 0


class StrongInstanceDict(IdentityMap):
    """A 'strong-referencing' version of the identity map.

    .. deprecated:: this object is present in order to fulfill
       the ``weak_identity_map=False`` option of the Session.
       This option is present to allow compatibility with older applications,
       but it is recommended that strong references to objects
       be maintained by the calling application
       externally to the :class:`.Session` itself, to the degree
       that is needed by the application.

    """

    def all_states(self):
        return [attributes.instance_state(o) for o in self.values()]

    def contains_state(self, state):
        return (
            state.key in self and
            attributes.instance_state(self[state.key]) is state)

    def replace(self, state):
        if dict.__contains__(self, state.key):
            existing = dict.__getitem__(self, state.key)
            existing = attributes.instance_state(existing)
            if existing is not state:
                self._manage_removed_state(existing)
            else:
                return

        dict.__setitem__(self, state.key, state.obj())
        self._manage_incoming_state(state)

    def add(self, state):
        if state.key in self:
            if attributes.instance_state(
                dict.__getitem__(
                    self,
                    state.key)) is not state:
                raise AssertionError('A conflicting state is already '
                                     'present in the identity map for key %r'
                                     % (state.key, ))
        else:
            dict.__setitem__(self, state.key, state.obj())
            self._manage_incoming_state(state)

    def discard(self, state):
        obj = dict.get(self, state.key, None)
        if obj is not None:
            st = attributes.instance_state(obj)
            if st is state:
                dict.pop(self, state.key, None)
                self._manage_removed_state(state)

    def prune(self):
        """prune unreferenced, non-dirty states."""

        ref_count = len(self)
        dirty = [s.obj() for s in self.all_states() if s.modified]

        # work around http://bugs.python.org/issue6149
        keepers = weakref.WeakValueDictionary()
        keepers.update(self)

        dict.clear(self)
        dict.update(self, keepers)
        self.modified = bool(dirty)
        return ref_count - len(self)