# orm/state.py
# Copyright (C) 2005-2014 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

"""Defines instrumentation of instances.

This module is usually not directly visible to user applications, but
defines a large part of the ORM's interactivity.

"""

import weakref
from .. import util
from . import exc as orm_exc, interfaces
from .path_registry import PathRegistry
from .base import PASSIVE_NO_RESULT, SQL_OK, NEVER_SET, ATTR_WAS_SET, \
    NO_VALUE, PASSIVE_NO_INITIALIZE, INIT_OK, PASSIVE_OFF
from . import base


class InstanceState(interfaces._InspectionAttr):
    """tracks state information at the instance level.

    The :class:`.InstanceState` is a key object used by the
    SQLAlchemy ORM in order to track the state of an object;
    it is created the moment an object is instantiated, typically
    as a result of :term:`instrumentation` which SQLAlchemy applies
    to the ``__init__()`` method of the class.

    :class:`.InstanceState` is also a semi-public object,
    available for runtime inspection as to the state of a
    mapped instance, including information such as its current
    status within a particular :class:`.Session` and details
    about data on individual attributes.  The public API
    in order to acquire a :class:`.InstanceState` object
    is to use the :func:`.inspect` system::

        >>> from sqlalchemy import inspect
        >>> insp = inspect(some_mapped_object)

    .. seealso::

        :ref:`core_inspection_toplevel`

    """

    session_id = None
    key = None
    runid = None
    load_options = util.EMPTY_SET
    load_path = ()
    insert_order = None
    _strong_obj = None
    modified = False
    expired = False
    deleted = False
    _load_pending = False

    is_instance = True

    def __init__(self, obj, manager):
        self.class_ = obj.__class__
        self.manager = manager
        self.obj = weakref.ref(obj, self._cleanup)
        self.callables = {}
        self.committed_state = {}

    @util.memoized_property
    def attrs(self):
        """Return a namespace representing each attribute on
        the mapped object, including its current value
        and history.

        The returned object is an instance of :class:`.AttributeState`.
        This object allows inspection of the current data
        within an attribute as well as attribute history
        since the last flush.

        """
        return util.ImmutableProperties(
            dict(
                (key, AttributeState(self, key))
                for key in self.manager
            )
        )

    @property
    def transient(self):
        """Return true if the object is :term:`transient`.

        .. seealso::

            :ref:`session_object_states`

        """
        return self.key is None and \
            not self._attached

    @property
    def pending(self):
        """Return true if the object is :term:`pending`.


        .. seealso::

            :ref:`session_object_states`

        """
        return self.key is None and \
            self._attached

    @property
    def persistent(self):
        """Return true if the object is :term:`persistent`.

        .. seealso::

            :ref:`session_object_states`

            """
        return self.key is not None and \
            self._attached

    @property
    def detached(self):
        """Return true if the object is :term:`detached`.

        .. seealso::

            :ref:`session_object_states`

        """
        return self.key is not None and \
            not self._attached

    @property
    @util.dependencies("sqlalchemy.orm.session")
    def _attached(self, sessionlib):
        return self.session_id is not None and \
            self.session_id in sessionlib._sessions

    @property
    @util.dependencies("sqlalchemy.orm.session")
    def session(self, sessionlib):
        """Return the owning :class:`.Session` for this instance,
        or ``None`` if none available."""
        return sessionlib._state_session(self)

    @property
    def object(self):
        """Return the mapped object represented by this
        :class:`.InstanceState`."""
        return self.obj()

    @property
    def identity(self):
        """Return the mapped identity of the mapped object.
        This is the primary key identity as persisted by the ORM
        which can always be passed directly to
        :meth:`.Query.get`.

        Returns ``None`` if the object has no primary key identity.

        .. note::
            An object which is transient or pending
            does **not** have a mapped identity until it is flushed,
            even if its attributes include primary key values.

        """
        if self.key is None:
            return None
        else:
            return self.key[1]

    @property
    def identity_key(self):
        """Return the identity key for the mapped object.

        This is the key used to locate the object within
        the :attr:`.Session.identity_map` mapping.   It contains
        the identity as returned by :attr:`.identity` within it.


        """
        # TODO: just change .key to .identity_key across
        # the board ?  probably
        return self.key

    @util.memoized_property
    def parents(self):
        return {}

    @util.memoized_property
    def _pending_mutations(self):
        return {}

    @util.memoized_property
    def mapper(self):
        """Return the :class:`.Mapper` used for this mapepd object."""
        return self.manager.mapper

    @property
    def has_identity(self):
        """Return ``True`` if this object has an identity key.

        This should always have the same value as the
        expression ``state.persistent or state.detached``.

        """
        return bool(self.key)

    def _detach(self):
        self.session_id = self._strong_obj = None

    def _dispose(self):
        self._detach()
        del self.obj

    def _cleanup(self, ref):
        instance_dict = self._instance_dict()
        if instance_dict:
            instance_dict.discard(self)

        self.callables = {}
        self.session_id = self._strong_obj = None
        del self.obj

    def obj(self):
        return None

    @property
    def dict(self):
        """Return the instance dict used by the object.

        Under normal circumstances, this is always synonymous
        with the ``__dict__`` attribute of the mapped object,
        unless an alternative instrumentation system has been
        configured.

        In the case that the actual object has been garbage
        collected, this accessor returns a blank dictionary.

        """
        o = self.obj()
        if o is not None:
            return base.instance_dict(o)
        else:
            return {}

    def _initialize_instance(*mixed, **kwargs):
        self, instance, args = mixed[0], mixed[1], mixed[2:]
        manager = self.manager

        manager.dispatch.init(self, args, kwargs)

        try:
            return manager.original_init(*mixed[1:], **kwargs)
        except:
            manager.dispatch.init_failure(self, args, kwargs)
            raise

    def get_history(self, key, passive):
        return self.manager[key].impl.get_history(self, self.dict, passive)

    def get_impl(self, key):
        return self.manager[key].impl

    def _get_pending_mutation(self, key):
        if key not in self._pending_mutations:
            self._pending_mutations[key] = PendingCollection()
        return self._pending_mutations[key]

    def __getstate__(self):
        state_dict = {'instance': self.obj()}
        state_dict.update(
            (k, self.__dict__[k]) for k in (
                'committed_state', '_pending_mutations', 'modified',
                'expired', 'callables', 'key', 'parents', 'load_options',
                'class_',
            ) if k in self.__dict__
        )
        if self.load_path:
            state_dict['load_path'] = self.load_path.serialize()

        state_dict['manager'] = self.manager._serialize(self, state_dict)

        return state_dict

    def __setstate__(self, state_dict):
        inst = state_dict['instance']
        if inst is not None:
            self.obj = weakref.ref(inst, self._cleanup)
            self.class_ = inst.__class__
        else:
            # None being possible here generally new as of 0.7.4
            # due to storage of state in "parents".  "class_"
            # also new.
            self.obj = None
            self.class_ = state_dict['class_']

        self.committed_state = state_dict.get('committed_state', {})
        self._pending_mutations = state_dict.get('_pending_mutations', {})
        self.parents = state_dict.get('parents', {})
        self.modified = state_dict.get('modified', False)
        self.expired = state_dict.get('expired', False)
        self.callables = state_dict.get('callables', {})

        self.__dict__.update([
            (k, state_dict[k]) for k in (
                'key', 'load_options',
            ) if k in state_dict
        ])

        if 'load_path' in state_dict:
            self.load_path = PathRegistry.\
                deserialize(state_dict['load_path'])

        state_dict['manager'](self, inst, state_dict)

    def _initialize(self, key):
        """Set this attribute to an empty value or collection,
           based on the AttributeImpl in use."""

        self.manager.get_impl(key).initialize(self, self.dict)

    def _reset(self, dict_, key):
        """Remove the given attribute and any
           callables associated with it."""

        old = dict_.pop(key, None)
        if old is not None and self.manager[key].impl.collection:
            self.manager[key].impl._invalidate_collection(old)
        self.callables.pop(key, None)

    def _expire_attribute_pre_commit(self, dict_, key):
        """a fast expire that can be called by column loaders during a load.

        The additional bookkeeping is finished up in commit_all().

        Should only be called for scalar attributes.

        This method is actually called a lot with joined-table
        loading, when the second table isn't present in the result.

        """
        dict_.pop(key, None)
        self.callables[key] = self

    @classmethod
    def _row_processor(cls, manager, fn, key):
        impl = manager[key].impl
        if impl.collection:
            def _set_callable(state, dict_, row):
                old = dict_.pop(key, None)
                if old is not None:
                    impl._invalidate_collection(old)
                state.callables[key] = fn
        else:
            def _set_callable(state, dict_, row):
                state.callables[key] = fn
        return _set_callable

    def _expire(self, dict_, modified_set):
        self.expired = True
        if self.modified:
            modified_set.discard(self)

        self.modified = False
        self._strong_obj = None

        self.committed_state.clear()

        InstanceState._pending_mutations._reset(self)

        # clear out 'parents' collection.  not
        # entirely clear how we can best determine
        # which to remove, or not.
        InstanceState.parents._reset(self)

        for key in self.manager:
            impl = self.manager[key].impl
            if impl.accepts_scalar_loader and \
                    (impl.expire_missing or key in dict_):
                self.callables[key] = self
            old = dict_.pop(key, None)
            if impl.collection and old is not None:
                impl._invalidate_collection(old)

        self.manager.dispatch.expire(self, None)

    def _expire_attributes(self, dict_, attribute_names):
        pending = self.__dict__.get('_pending_mutations', None)

        for key in attribute_names:
            impl = self.manager[key].impl
            if impl.accepts_scalar_loader:
                self.callables[key] = self
            old = dict_.pop(key, None)
            if impl.collection and old is not None:
                impl._invalidate_collection(old)

            self.committed_state.pop(key, None)
            if pending:
                pending.pop(key, None)

        self.manager.dispatch.expire(self, attribute_names)

    def __call__(self, state, passive):
        """__call__ allows the InstanceState to act as a deferred
        callable for loading expired attributes, which is also
        serializable (picklable).

        """

        if not passive & SQL_OK:
            return PASSIVE_NO_RESULT

        toload = self.expired_attributes.\
            intersection(self.unmodified)

        self.manager.deferred_scalar_loader(self, toload)

        # if the loader failed, or this
        # instance state didn't have an identity,
        # the attributes still might be in the callables
        # dict.  ensure they are removed.
        for k in toload.intersection(self.callables):
            del self.callables[k]

        return ATTR_WAS_SET

    @property
    def unmodified(self):
        """Return the set of keys which have no uncommitted changes"""

        return set(self.manager).difference(self.committed_state)

    def unmodified_intersection(self, keys):
        """Return self.unmodified.intersection(keys)."""

        return set(keys).intersection(self.manager).\
            difference(self.committed_state)

    @property
    def unloaded(self):
        """Return the set of keys which do not have a loaded value.

        This includes expired attributes and any other attribute that
        was never populated or modified.

        """
        return set(self.manager).\
            difference(self.committed_state).\
            difference(self.dict)

    @property
    def _unloaded_non_object(self):
        return self.unloaded.intersection(
            attr for attr in self.manager
            if self.manager[attr].impl.accepts_scalar_loader
        )

    @property
    def expired_attributes(self):
        """Return the set of keys which are 'expired' to be loaded by
           the manager's deferred scalar loader, assuming no pending
           changes.

           see also the ``unmodified`` collection which is intersected
           against this set when a refresh operation occurs.

        """
        return set([k for k, v in self.callables.items() if v is self])

    def _instance_dict(self):
        return None

    def _modified_event(
            self, dict_, attr, previous, collection=False, force=False):
        if not attr.send_modified_events:
            return
        if attr.key not in self.committed_state or force:
            if collection:
                if previous is NEVER_SET:
                    if attr.key in dict_:
                        previous = dict_[attr.key]

                if previous not in (None, NO_VALUE, NEVER_SET):
                    previous = attr.copy(previous)

            self.committed_state[attr.key] = previous

        # assert self._strong_obj is None or self.modified

        if (self.session_id and self._strong_obj is None) \
                or not self.modified:
            instance_dict = self._instance_dict()
            if instance_dict:
                instance_dict._modified.add(self)

            # only create _strong_obj link if attached
            # to a session

            inst = self.obj()
            if self.session_id:
                self._strong_obj = inst

            if inst is None:
                raise orm_exc.ObjectDereferencedError(
                    "Can't emit change event for attribute '%s' - "
                    "parent object of type %s has been garbage "
                    "collected."
                    % (
                        self.manager[attr.key],
                        base.state_class_str(self)
                    ))
            self.modified = True

    def _commit(self, dict_, keys):
        """Commit attributes.

        This is used by a partial-attribute load operation to mark committed
        those attributes which were refreshed from the database.

        Attributes marked as "expired" can potentially remain "expired" after
        this step if a value was not populated in state.dict.

        """
        for key in keys:
            self.committed_state.pop(key, None)

        self.expired = False

        for key in set(self.callables).\
                intersection(keys).\
                intersection(dict_):
            del self.callables[key]

    def _commit_all(self, dict_, instance_dict=None):
        """commit all attributes unconditionally.

        This is used after a flush() or a full load/refresh
        to remove all pending state from the instance.

         - all attributes are marked as "committed"
         - the "strong dirty reference" is removed
         - the "modified" flag is set to False
         - any "expired" markers/callables for attributes loaded are removed.

        Attributes marked as "expired" can potentially remain
        "expired" after this step if a value was not populated in state.dict.

        """
        self._commit_all_states([(self, dict_)], instance_dict)

    @classmethod
    def _commit_all_states(self, iter, instance_dict=None):
        """Mass version of commit_all()."""

        for state, dict_ in iter:
            state.committed_state.clear()
            InstanceState._pending_mutations._reset(state)

            callables = state.callables
            for key in list(callables):
                if key in dict_ and callables[key] is state:
                    del callables[key]

            if instance_dict and state.modified:
                instance_dict._modified.discard(state)

            state.modified = state.expired = False
            state._strong_obj = None


class AttributeState(object):
    """Provide an inspection interface corresponding
    to a particular attribute on a particular mapped object.

    The :class:`.AttributeState` object is accessed
    via the :attr:`.InstanceState.attrs` collection
    of a particular :class:`.InstanceState`::

        from sqlalchemy import inspect

        insp = inspect(some_mapped_object)
        attr_state = insp.attrs.some_attribute

    """

    def __init__(self, state, key):
        self.state = state
        self.key = key

    @property
    def loaded_value(self):
        """The current value of this attribute as loaded from the database.

        If the value has not been loaded, or is otherwise not present
        in the object's dictionary, returns NO_VALUE.

        """
        return self.state.dict.get(self.key, NO_VALUE)

    @property
    def value(self):
        """Return the value of this attribute.

        This operation is equivalent to accessing the object's
        attribute directly or via ``getattr()``, and will fire
        off any pending loader callables if needed.

        """
        return self.state.manager[self.key].__get__(
            self.state.obj(), self.state.class_)

    @property
    def history(self):
        """Return the current pre-flush change history for
        this attribute, via the :class:`.History` interface.

        This method will **not** emit loader callables if the value of the
        attribute is unloaded.

        .. seealso::

            :meth:`.AttributeState.load_history` - retrieve history
            using loader callables if the value is not locally present.

            :func:`.attributes.get_history` - underlying function

        """
        return self.state.get_history(self.key,
                                      PASSIVE_NO_INITIALIZE)

    def load_history(self):
        """Return the current pre-flush change history for
        this attribute, via the :class:`.History` interface.

        This method **will** emit loader callables if the value of the
        attribute is unloaded.

        .. seealso::

            :attr:`.AttributeState.history`

            :func:`.attributes.get_history` - underlying function

        .. versionadded:: 0.9.0

        """
        return self.state.get_history(self.key,
                                      PASSIVE_OFF ^ INIT_OK)


class PendingCollection(object):
    """A writable placeholder for an unloaded collection.

    Stores items appended to and removed from a collection that has not yet
    been loaded. When the collection is loaded, the changes stored in
    PendingCollection are applied to it to produce the final result.

    """

    def __init__(self):
        self.deleted_items = util.IdentitySet()
        self.added_items = util.OrderedIdentitySet()

    def append(self, value):
        if value in self.deleted_items:
            self.deleted_items.remove(value)
        else:
            self.added_items.add(value)

    def remove(self, value):
        if value in self.added_items:
            self.added_items.remove(value)
        else:
            self.deleted_items.add(value)
