# orm/interfaces.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

"""

Contains various base classes used throughout the ORM.

Defines some key base classes prominent within the internals,
as well as the now-deprecated ORM extension classes.

Other than the deprecated extensions, this module and the
classes within are mostly private, though some attributes
are exposed when inspecting mappings.

"""

from __future__ import absolute_import

from .. import util
from ..sql import operators
from .base import (ONETOMANY, MANYTOONE, MANYTOMANY,
                   EXT_CONTINUE, EXT_STOP, NOT_EXTENSION)
from .base import InspectionAttr, InspectionAttrInfo, _MappedAttribute
import collections
from .. import inspect
from . import path_registry

# imported later
MapperExtension = SessionExtension = AttributeExtension = None

__all__ = (
    'AttributeExtension',
    'EXT_CONTINUE',
    'EXT_STOP',
    'ONETOMANY',
    'MANYTOMANY',
    'MANYTOONE',
    'NOT_EXTENSION',
    'LoaderStrategy',
    'MapperExtension',
    'MapperOption',
    'MapperProperty',
    'PropComparator',
    'SessionExtension',
    'StrategizedProperty',
)


class MapperProperty(_MappedAttribute, InspectionAttr, util.MemoizedSlots):
    """Represent a particular class attribute mapped by :class:`.Mapper`.

    The most common occurrences of :class:`.MapperProperty` are the
    mapped :class:`.Column`, which is represented in a mapping as
    an instance of :class:`.ColumnProperty`,
    and a reference to another class produced by :func:`.relationship`,
    represented in the mapping as an instance of
    :class:`.RelationshipProperty`.

    """

    __slots__ = (
        '_configure_started', '_configure_finished', 'parent', 'key',
        'info'
    )

    cascade = frozenset()
    """The set of 'cascade' attribute names.

    This collection is checked before the 'cascade_iterator' method is called.

    The collection typically only applies to a RelationshipProperty.

    """

    is_property = True
    """Part of the InspectionAttr interface; states this object is a
    mapper property.

    """

    def _memoized_attr_info(self):
        """Info dictionary associated with the object, allowing user-defined
        data to be associated with this :class:`.InspectionAttr`.

        The dictionary is generated when first accessed.  Alternatively,
        it can be specified as a constructor argument to the
        :func:`.column_property`, :func:`.relationship`, or :func:`.composite`
        functions.

        .. versionadded:: 0.8  Added support for .info to all
           :class:`.MapperProperty` subclasses.

        .. versionchanged:: 1.0.0 :attr:`.MapperProperty.info` is also
           available on extension types via the
           :attr:`.InspectionAttrInfo.info` attribute, so that it can apply
           to a wider variety of ORM and extension constructs.

        .. seealso::

            :attr:`.QueryableAttribute.info`

            :attr:`.SchemaItem.info`

        """
        return {}

    def setup(self, context, entity, path, adapter, **kwargs):
        """Called by Query for the purposes of constructing a SQL statement.

        Each MapperProperty associated with the target mapper processes the
        statement referenced by the query context, adding columns and/or
        criterion as appropriate.

        """

    def create_row_processor(self, context, path,
                             mapper, result, adapter, populators):
        """Produce row processing functions and append to the given
        set of populators lists.

        """

    def cascade_iterator(self, type_, state, visited_instances=None,
                         halt_on=None):
        """Iterate through instances related to the given instance for
        a particular 'cascade', starting with this MapperProperty.

        Return an iterator3-tuples (instance, mapper, state).

        Note that the 'cascade' collection on this MapperProperty is
        checked first for the given type before cascade_iterator is called.

        This method typically only applies to RelationshipProperty.

        """

        return iter(())

    def set_parent(self, parent, init):
        """Set the parent mapper that references this MapperProperty.

        This method is overridden by some subclasses to perform extra
        setup when the mapper is first known.

        """
        self.parent = parent

    def instrument_class(self, mapper):
        """Hook called by the Mapper to the property to initiate
        instrumentation of the class attribute managed by this
        MapperProperty.

        The MapperProperty here will typically call out to the
        attributes module to set up an InstrumentedAttribute.

        This step is the first of two steps to set up an InstrumentedAttribute,
        and is called early in the mapper setup process.

        The second step is typically the init_class_attribute step,
        called from StrategizedProperty via the post_instrument_class()
        hook.  This step assigns additional state to the InstrumentedAttribute
        (specifically the "impl") which has been determined after the
        MapperProperty has determined what kind of persistence
        management it needs to do (e.g. scalar, object, collection, etc).

        """

    def __init__(self):
        self._configure_started = False
        self._configure_finished = False

    def init(self):
        """Called after all mappers are created to assemble
        relationships between mappers and perform other post-mapper-creation
        initialization steps.

        """
        self._configure_started = True
        self.do_init()
        self._configure_finished = True

    @property
    def class_attribute(self):
        """Return the class-bound descriptor corresponding to this
        :class:`.MapperProperty`.

        This is basically a ``getattr()`` call::

            return getattr(self.parent.class_, self.key)

        I.e. if this :class:`.MapperProperty` were named ``addresses``,
        and the class to which it is mapped is ``User``, this sequence
        is possible::

            >>> from sqlalchemy import inspect
            >>> mapper = inspect(User)
            >>> addresses_property = mapper.attrs.addresses
            >>> addresses_property.class_attribute is User.addresses
            True
            >>> User.addresses.property is addresses_property
            True


        """

        return getattr(self.parent.class_, self.key)

    def do_init(self):
        """Perform subclass-specific initialization post-mapper-creation
        steps.

        This is a template method called by the ``MapperProperty``
        object's init() method.

        """

    def post_instrument_class(self, mapper):
        """Perform instrumentation adjustments that need to occur
        after init() has completed.

        The given Mapper is the Mapper invoking the operation, which
        may not be the same Mapper as self.parent in an inheritance
        scenario; however, Mapper will always at least be a sub-mapper of
        self.parent.

        This method is typically used by StrategizedProperty, which delegates
        it to LoaderStrategy.init_class_attribute() to perform final setup
        on the class-bound InstrumentedAttribute.

        """

    def merge(self, session, source_state, source_dict, dest_state,
              dest_dict, load, _recursive, _resolve_conflict_map):
        """Merge the attribute represented by this ``MapperProperty``
        from source to destination object.

        """

    def __repr__(self):
        return '<%s at 0x%x; %s>' % (
            self.__class__.__name__,
            id(self), getattr(self, 'key', 'no key'))


class PropComparator(operators.ColumnOperators):
    r"""Defines SQL operators for :class:`.MapperProperty` objects.

    SQLAlchemy allows for operators to
    be redefined at both the Core and ORM level.  :class:`.PropComparator`
    is the base class of operator redefinition for ORM-level operations,
    including those of :class:`.ColumnProperty`,
    :class:`.RelationshipProperty`, and :class:`.CompositeProperty`.

    .. note:: With the advent of Hybrid properties introduced in SQLAlchemy
       0.7, as well as Core-level operator redefinition in
       SQLAlchemy 0.8, the use case for user-defined :class:`.PropComparator`
       instances is extremely rare.  See :ref:`hybrids_toplevel` as well
       as :ref:`types_operators`.

    User-defined subclasses of :class:`.PropComparator` may be created. The
    built-in Python comparison and math operator methods, such as
    :meth:`.operators.ColumnOperators.__eq__`,
    :meth:`.operators.ColumnOperators.__lt__`, and
    :meth:`.operators.ColumnOperators.__add__`, can be overridden to provide
    new operator behavior. The custom :class:`.PropComparator` is passed to
    the :class:`.MapperProperty` instance via the ``comparator_factory``
    argument. In each case,
    the appropriate subclass of :class:`.PropComparator` should be used::

        # definition of custom PropComparator subclasses

        from sqlalchemy.orm.properties import \
                                ColumnProperty,\
                                CompositeProperty,\
                                RelationshipProperty

        class MyColumnComparator(ColumnProperty.Comparator):
            def __eq__(self, other):
                return self.__clause_element__() == other

        class MyRelationshipComparator(RelationshipProperty.Comparator):
            def any(self, expression):
                "define the 'any' operation"
                # ...

        class MyCompositeComparator(CompositeProperty.Comparator):
            def __gt__(self, other):
                "redefine the 'greater than' operation"

                return sql.and_(*[a>b for a, b in
                                  zip(self.__clause_element__().clauses,
                                      other.__composite_values__())])


        # application of custom PropComparator subclasses

        from sqlalchemy.orm import column_property, relationship, composite
        from sqlalchemy import Column, String

        class SomeMappedClass(Base):
            some_column = column_property(Column("some_column", String),
                                comparator_factory=MyColumnComparator)

            some_relationship = relationship(SomeOtherClass,
                                comparator_factory=MyRelationshipComparator)

            some_composite = composite(
                    Column("a", String), Column("b", String),
                    comparator_factory=MyCompositeComparator
                )

    Note that for column-level operator redefinition, it's usually
    simpler to define the operators at the Core level, using the
    :attr:`.TypeEngine.comparator_factory` attribute.  See
    :ref:`types_operators` for more detail.

    See also:

    :class:`.ColumnProperty.Comparator`

    :class:`.RelationshipProperty.Comparator`

    :class:`.CompositeProperty.Comparator`

    :class:`.ColumnOperators`

    :ref:`types_operators`

    :attr:`.TypeEngine.comparator_factory`

    """

    __slots__ = 'prop', 'property', '_parententity', '_adapt_to_entity'

    def __init__(self, prop, parentmapper, adapt_to_entity=None):
        self.prop = self.property = prop
        self._parententity = adapt_to_entity or parentmapper
        self._adapt_to_entity = adapt_to_entity

    def __clause_element__(self):
        raise NotImplementedError("%r" % self)