# orm/base.py
# Copyright (C) 2005-2018 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

"""Constants and rudimental functions used throughout the ORM.

"""

from .. import util, inspection, exc as sa_exc
from ..sql import expression
from . import exc
import operator

PASSIVE_NO_RESULT = util.symbol(
    'PASSIVE_NO_RESULT',
    """Symbol returned by a loader callable or other attribute/history
    retrieval operation when a value could not be determined, based
    on loader callable flags.
    """
)

ATTR_WAS_SET = util.symbol(
    'ATTR_WAS_SET',
    """Symbol returned by a loader callable to indicate the
    retrieved value, or values, were assigned to their attributes
    on the target object.
    """
)

ATTR_EMPTY = util.symbol(
    'ATTR_EMPTY',
    """Symbol used internally to indicate an attribute had no callable."""
)

NO_VALUE = util.symbol(
    'NO_VALUE',
    """Symbol which may be placed as the 'previous' value of an attribute,
    indicating no value was loaded for an attribute when it was modified,
    and flags indicated we were not to load it.
    """
)

NEVER_SET = util.symbol(
    'NEVER_SET',
    """Symbol which may be placed as the 'previous' value of an attribute
    indicating that the attribute had not been assigned to previously.
    """
)

NO_CHANGE = util.symbol(
    "NO_CHANGE",
    """No callables or SQL should be emitted on attribute access
    and no state should change
    """, canonical=0
)

CALLABLES_OK = util.symbol(
    "CALLABLES_OK",
    """Loader callables can be fired off if a value
    is not present.
    """, canonical=1
)

SQL_OK = util.symbol(
    "SQL_OK",
    """Loader callables can emit SQL at least on scalar value attributes.""",
    canonical=2
)

RELATED_OBJECT_OK = util.symbol(
    "RELATED_OBJECT_OK",
    """Callables can use SQL to load related objects as well
    as scalar value attributes.
    """, canonical=4
)

INIT_OK = util.symbol(
    "INIT_OK",
    """Attributes should be initialized with a blank
    value (None or an empty collection) upon get, if no other
    value can be obtained.
    """, canonical=8
)

NON_PERSISTENT_OK = util.symbol(
    "NON_PERSISTENT_OK",
    """Callables can be emitted if the parent is not persistent.""",
    canonical=16
)

LOAD_AGAINST_COMMITTED = util.symbol(
    "LOAD_AGAINST_COMMITTED",
    """Callables should use committed values as primary/foreign keys during a
    load.
    """, canonical=32
)

NO_AUTOFLUSH = util.symbol(
    "NO_AUTOFLUSH",
    """Loader callables should disable autoflush.""",
    canonical=64
)

# pre-packaged sets of flags used as inputs
PASSIVE_OFF = util.symbol(
    "PASSIVE_OFF",
    "Callables can be emitted in all cases.",
    canonical=(RELATED_OBJECT_OK | NON_PERSISTENT_OK |
               INIT_OK | CALLABLES_OK | SQL_OK)
)
PASSIVE_RETURN_NEVER_SET = util.symbol(
    "PASSIVE_RETURN_NEVER_SET",
    """PASSIVE_OFF ^ INIT_OK""",
    canonical=PASSIVE_OFF ^ INIT_OK
)
PASSIVE_NO_INITIALIZE = util.symbol(
    "PASSIVE_NO_INITIALIZE",
    "PASSIVE_RETURN_NEVER_SET ^ CALLABLES_OK",
    canonical=PASSIVE_RETURN_NEVER_SET ^ CALLABLES_OK
)
PASSIVE_NO_FETCH = util.symbol(
    "PASSIVE_NO_FETCH",
    "PASSIVE_OFF ^ SQL_OK",
    canonical=PASSIVE_OFF ^ SQL_OK
)
PASSIVE_NO_FETCH_RELATED = util.symbol(
    "PASSIVE_NO_FETCH_RELATED",
    "PASSIVE_OFF ^ RELATED_OBJECT_OK",
    canonical=PASSIVE_OFF ^ RELATED_OBJECT_OK
)
PASSIVE_ONLY_PERSISTENT = util.symbol(
    "PASSIVE_ONLY_PERSISTENT",
    "PASSIVE_OFF ^ NON_PERSISTENT_OK",
    canonical=PASSIVE_OFF ^ NON_PERSISTENT_OK
)

DEFAULT_MANAGER_ATTR = '_sa_class_manager'
DEFAULT_STATE_ATTR = '_sa_instance_state'
_INSTRUMENTOR = ('mapper', 'instrumentor')

EXT_CONTINUE = util.symbol('EXT_CONTINUE')
EXT_STOP = util.symbol('EXT_STOP')

ONETOMANY = util.symbol(
    'ONETOMANY',
    """Indicates the one-to-many direction for a :func:`.relationship`.

    This symbol is typically used by the internals but may be exposed within
    certain API features.

    """)

MANYTOONE = util.symbol(
    'MANYTOONE',
    """Indicates the many-to-one direction for a :func:`.relationship`.

    This symbol is typically used by the internals but may be exposed within
    certain API features.

    """)

MANYTOMANY = util.symbol(
    'MANYTOMANY',
    """Indicates the many-to-many direction for a :func:`.relationship`.

    This symbol is typically used by the internals but may be exposed within
    certain API features.

    """)

NOT_EXTENSION = util.symbol(
    'NOT_EXTENSION',
    """Symbol indicating an :class:`InspectionAttr` that's
    not part of sqlalchemy.ext.

    Is assigned to the :attr:`.InspectionAttr.extension_type`
    attibute.

    """)

_never_set = frozenset([NEVER_SET])

_none_set = frozenset([None, NEVER_SET, PASSIVE_NO_RESULT])

_SET_DEFERRED_EXPIRED = util.symbol("SET_DEFERRED_EXPIRED")

_DEFER_FOR_STATE = util.symbol("DEFER_FOR_STATE")


def _generative(*assertions):
    """Mark a method as generative, e.g. method-chained."""

    @util.decorator
    def generate(fn, *args, **kw):
        self = args[0]._clone()
        for assertion in assertions:
            assertion(self, fn.__name__)
        fn(self, *args[1:], **kw)
        return self
    return generate


# these can be replaced by sqlalchemy.ext.instrumentation
# if augmented class instrumentation is enabled.
def manager_of_class(cls):
    return cls.__dict__.get(DEFAULT_MANAGER_ATTR, None)

instance_state = operator.attrgetter(DEFAULT_STATE_ATTR)

instance_dict = operator.attrgetter('__dict__')


def instance_str(instance):
    """Return a string describing an instance."""

    return state_str(instance_state(instance))


def state_str(state):
    """Return a string describing an instance via its InstanceState."""

    if state is None:
        return "None"
    else:
        return '<%s at 0x%x>' % (state.class_.__name__, id(state.obj()))


def state_class_str(state):
    """Return a string describing an instance's class via its
    InstanceState.
    """

    if state is None:
        return "None"
    else:
        return '<%s>' % (state.class_.__name__, )


def attribute_str(instance, attribute):
    return instance_str(instance) + "." + attribute


def state_attribute_str(state, attribute):
    return state_str(state) + "." + attribute


def object_mapper(instance):
    """Given an object, return the primary Mapper associated with the object
    instance.

    Raises :class:`sqlalchemy.orm.exc.UnmappedInstanceError`
    if no mapping is configured.

    This function is available via the inspection system as::

        inspect(instance).mapper

    Using the inspection system will raise
    :class:`sqlalchemy.exc.NoInspectionAvailable` if the instance is
    not part of a mapping.

    """
    return object_state(instance).mapper


def object_state(instance):
    """Given an object, return the :class:`.InstanceState`
    associated with the object.

    Raises :class:`sqlalchemy.orm.exc.UnmappedInstanceError`
    if no mapping is configured.

    Equivalent functionality is available via the :func:`.inspect`
    function as::

        inspect(instance)

    Using the inspection system will raise
    :class:`sqlalchemy.exc.NoInspectionAvailable` if the instance is
    not part of a mapping.

    """
    state = _inspect_mapped_object(instance)
    if state is None:
        raise exc.UnmappedInstanceError(instance)
    else:
        return state


@inspection._inspects(object)
def _inspect_mapped_object(instance):
    try:
        return instance_state(instance)
        # TODO: whats the py-2/3 syntax to catch two
        # different kinds of exceptions at once ?
    except exc.UnmappedClassError:
        return None
    except exc.NO_STATE:
        return None


def _class_to_mapper(class_or_mapper):
    insp = inspection.inspect(class_or_mapper, False)
    if insp is not None:
        return insp.mapper
    else:
        raise exc.UnmappedClassError(class_or_mapper)


def _mapper_or_none(entity):
    """Return the :class:`.Mapper` for the given class or None if the
    class is not mapped.
    """

    insp = inspection.inspect(entity, False)
    if insp is not None:
        return insp.mapper
    else:
        return None


def _is_mapped_class(entity):
    """Return True if the given object is a mapped class,
    :class:`.Mapper`, or :class:`.AliasedClass`.
    """

    insp = inspection.inspect(entity, False)
    return insp is not None and \
        not insp.is_clause_element and \
        (
            insp.is_mapper or insp.is_aliased_class
        )


def _attr_as_key(attr):
    if hasattr(attr, 'key'):
        return attr.key
    else:
        return expression._column_as_key(attr)


def _orm_columns(entity):