# ext/declarative/api.py
# Copyright (C) 2005-2020 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
"""Public API functions and helpers for declarative."""
from __future__ import absolute_import

import re
import weakref

from . import attributes
from . import clsregistry
from . import exc as orm_exc
from . import interfaces
from .base import _inspect_mapped_class
from .decl_base import _add_attribute
from .decl_base import _as_declarative
from .decl_base import _declarative_constructor
from .decl_base import _DeferredMapperConfig
from .decl_base import _del_attribute
from .decl_base import _mapper
from .descriptor_props import SynonymProperty as _orm_synonym
from .. import inspection
from .. import util
from ..sql.schema import MetaData
from ..util import hybridmethod
from ..util import hybridproperty

if util.TYPE_CHECKING:
    from .mapper import Mapper


def has_inherited_table(cls):
    """Given a class, return True if any of the classes it inherits from has a
    mapped table, otherwise return False.

    This is used in declarative mixins to build attributes that behave
    differently for the base class vs. a subclass in an inheritance
    hierarchy.

    .. seealso::

        :ref:`decl_mixin_inheritance`

    """
    for class_ in cls.__mro__[1:]:
        if getattr(class_, "__table__", None) is not None:
            return True
    return False


class DeclarativeMeta(type):
    def __init__(cls, classname, bases, dict_, **kw):
        if not cls.__dict__.get("__abstract__", False):
            _as_declarative(cls.registry, cls, cls.__dict__)
        type.__init__(cls, classname, bases, dict_)

    def __setattr__(cls, key, value):
        _add_attribute(cls, key, value)

    def __delattr__(cls, key):
        _del_attribute(cls, key)


def synonym_for(name, map_column=False):
    """Decorator that produces an :func:`_orm.synonym`
    attribute in conjunction with a Python descriptor.

    The function being decorated is passed to :func:`_orm.synonym` as the
    :paramref:`.orm.synonym.descriptor` parameter::

        class MyClass(Base):
            __tablename__ = 'my_table'

            id = Column(Integer, primary_key=True)
            _job_status = Column("job_status", String(50))

            @synonym_for("job_status")
            @property
            def job_status(self):
                return "Status: %s" % self._job_status

    The :ref:`hybrid properties <mapper_hybrids>` feature of SQLAlchemy
    is typically preferred instead of synonyms, which is a more legacy
    feature.

    .. seealso::

        :ref:`synonyms` - Overview of synonyms

        :func:`_orm.synonym` - the mapper-level function

        :ref:`mapper_hybrids` - The Hybrid Attribute extension provides an
        updated approach to augmenting attribute behavior more flexibly than
        can be achieved with synonyms.

    """

    def decorate(fn):
        return _orm_synonym(name, map_column=map_column, descriptor=fn)

    return decorate


class declared_attr(interfaces._MappedAttribute, property):
    """Mark a class-level method as representing the definition of
    a mapped property or special declarative member name.

    @declared_attr turns the attribute into a scalar-like
    property that can be invoked from the uninstantiated class.
    Declarative treats attributes specifically marked with
    @declared_attr as returning a construct that is specific
    to mapping or declarative table configuration.  The name
    of the attribute is that of what the non-dynamic version
    of the attribute would be.

    @declared_attr is more often than not applicable to mixins,
    to define relationships that are to be applied to different
    implementors of the class::

        class ProvidesUser(object):
            "A mixin that adds a 'user' relationship to classes."

            @declared_attr
            def user(self):
                return relationship("User")

    It also can be applied to mapped classes, such as to provide
    a "polymorphic" scheme for inheritance::

        class Employee(Base):
            id = Column(Integer, primary_key=True)
            type = Column(String(50), nullable=False)

            @declared_attr
            def __tablename__(cls):
                return cls.__name__.lower()

            @declared_attr
            def __mapper_args__(cls):
                if cls.__name__ == 'Employee':
                    return {
                            "polymorphic_on":cls.type,
                            "polymorphic_identity":"Employee"
                    }
                else:
                    return {"polymorphic_identity":cls.__name__}

    """

    def __init__(self, fget, cascading=False):
        super(declared_attr, self).__init__(fget)
        self.__doc__ = fget.__doc__
        self._cascading = cascading

    def __get__(desc, self, cls):
        # the declared_attr needs to make use of a cache that exists
        # for the span of the declarative scan_attributes() phase.
        # to achieve this we look at the class manager that's configured.
        manager = attributes.manager_of_class(cls)
        if manager is None:
            if not re.match(r"^__.+__$", desc.fget.__name__):
                # if there is no manager at all, then this class hasn't been
                # run through declarative or mapper() at all, emit a warning.
                util.warn(
                    "Unmanaged access of declarative attribute %s from "
                    "non-mapped class %s" % (desc.fget.__name__, cls.__name__)
                )
            return desc.fget(cls)
        elif manager.is_mapped:
            # the class is mapped, which means we're outside of the declarative
            # scan setup, just run the function.
            return desc.fget(cls)

        # here, we are inside of the declarative scan.  use the registry
        # that is tracking the values of these attributes.
        declarative_scan = manager.declarative_scan
        reg = declarative_scan.declared_attr_reg

        if desc in reg:
            return reg[desc]
        else:
            reg[desc] = obj = desc.fget(cls)
            return obj

    @hybridmethod
    def _stateful(cls, **kw):
        return _stateful_declared_attr(**kw)

    @hybridproperty
    def cascading(cls):
        """Mark a :class:`.declared_attr` as cascading.

        This is a special-use modifier which indicates that a column
        or MapperProperty-based declared attribute should be configured
        distinctly per mapped subclass, within a mapped-inheritance scenario.

        .. warning::

            The :attr:`.declared_attr.cascading` modifier has several
            limitations:

            * The flag **only** applies to the use of :class:`.declared_attr`
              on declarative mixin classes and ``__abstract__`` classes; it
              currently has no effect when used on a mapped class directly.

            * The flag **only** applies to normally-named attributes, e.g.
              not any special underscore attributes such as ``__tablename__``.
              On these attributes it has **no** effect.

            * The flag currently **does not allow further overrides** down
              the class hierarchy; if a subclass tries to override the
              attribute, a warning is emitted and the overridden attribute
              is skipped.  This is a limitation that it is hoped will be
              resolved at some point.

        Below, both MyClass as well as MySubClass will have a distinct
        ``id`` Column object established::

            class HasIdMixin(object):
                @declared_attr.cascading
                def id(cls):
                    if has_inherited_table(cls):
                        return Column(
                            ForeignKey('myclass.id'), primary_key=True
                        )
                    else:
                        return Column(Integer, primary_key=True)

            class MyClass(HasIdMixin, Base):
                __tablename__ = 'myclass'
                # ...

            class MySubClass(MyClass):
                ""
                # ...

        The behavior of the above configuration is that ``MySubClass``
        will refer to both its own ``id`` column as well as that of
        ``MyClass`` underneath the attribute named ``some_id``.

        .. seealso::

            :ref:`declarative_inheritance`

            :ref:`mixin_inheritance_columns`


        """
        return cls._stateful(cascading=True)


class _stateful_declared_attr(declared_attr):
    def __init__(self, **kw):
        self.kw = kw

    def _stateful(self, **kw):
        new_kw = self.kw.copy()
        new_kw.update(kw)
        return _stateful_declared_attr(**new_kw)

    def __call__(self, fn):
        return declared_attr(fn, **self.kw)


def declarative_base(
    bind=None,
    metadata=None,
    mapper=None,
    cls=object,
    name="Base",
    constructor=_declarative_constructor,
    class_registry=None,
    metaclass=DeclarativeMeta,
):
    r"""Construct a base class for declarative class definitions.

    The new base class will be given a metaclass that produces
    appropriate :class:`~sqlalchemy.schema.Table` objects and makes
    the appropriate :func:`~sqlalchemy.orm.mapper` calls based on the
    information provided declaratively in the class and any subclasses
    of the class.

    The :func:`_orm.declarative_base` function is a shorthand version
    of using the :meth:`_orm.registry.generate_base`
    method.  That is, the following::

        from sqlalchemy.orm import declarative_base

        Base = declarative_base()

    Is equvialent to::

        from sqlalchemy.orm import registry

        mapper_registry = registry()
        Base = mapper_registry.generate_base()

    See the docstring for :class:`_orm.registry`
    and :meth:`_orm.registry.generate_base`
    for more details.

    .. versionchanged:: 1.4  The :func:`_orm.declarative_base`
       function is now a specialization of the more generic
       :class:`_orm.registry` class.  The function also moves to the
       ``sqlalchemy.orm`` package from the ``declarative.ext`` package.


    :param bind: An optional
      :class:`~sqlalchemy.engine.Connectable`, will be assigned
      the ``bind`` attribute on the :class:`~sqlalchemy.schema.MetaData`
      instance.

      .. deprecated:: 1.4  The "bind" argument to declarative_base is
         deprecated and will be removed in SQLAlchemy 2.0.

    :param metadata:
      An optional :class:`~sqlalchemy.schema.MetaData` instance.  All
      :class:`~sqlalchemy.schema.Table` objects implicitly declared by
      subclasses of the base will share this MetaData.  A MetaData instance
      will be created if none is provided.  The
      :class:`~sqlalchemy.schema.MetaData` instance will be available via the
      ``metadata`` attribute of the generated declarative base class.

    :param mapper:
      An optional callable, defaults to :func:`~sqlalchemy.orm.mapper`. Will
      be used to map subclasses to their Tables.

    :param cls:
      Defaults to :class:`object`. A type to use as the base for the generated
      declarative base class. May be a class or tuple of classes.

    :param name:
      Defaults to ``Base``.  The display name for the generated
      class.  Customizing this is not required, but can improve clarity in
      tracebacks and debugging.

    :param constructor:
      Specify the implementation for the ``__init__`` function on a mapped
      class that has no ``__init__`` of its own.  Defaults to an
      implementation that assigns \**kwargs for declared
      fields and relationships to an instance.  If ``None`` is supplied,
      no __init__ will be provided and construction will fall back to
      cls.__init__ by way of the normal Python semantics.

    :param class_registry: optional dictionary that will serve as the
      registry of class names-> mapped classes when string names
      are used to identify classes inside of :func:`_orm.relationship`
      and others.  Allows two or more declarative base classes
      to share the same registry of class names for simplified
      inter-base relationships.

    :param metaclass:
      Defaults to :class:`.DeclarativeMeta`.  A metaclass or __metaclass__
      compatible callable to use as the meta type of the generated
      declarative base class.

    .. seealso::

        :class:`_orm.registry`

    """

    if bind is not None:
        # util.deprecated_params does not work
        util.warn_deprecated_20(
            "The ``bind`` argument to declarative_base is "
            "deprecated and will be removed in SQLAlchemy 2.0.",
        )

    return registry(
        _bind=bind,
        metadata=metadata,
        class_registry=class_registry,
        constructor=constructor,
    ).generate_base(
        mapper=mapper,
        cls=cls,
        name=name,
        metaclass=metaclass,
    )


class registry(object):
    """Generalized registry for mapping classes.

    The :class:`_orm.registry` serves as the basis for maintaining a collection
    of mappings, and provides configurational hooks used to map classes.

    The three general kinds of mappings supported are Declarative Base,
    Declarative Decorator, and Imperative Mapping.   All of these mapping
    styles may be used interchangeably:

    * :meth:`_orm.registry.generate_base` returns a new declarative base
      class, and is the underlying implementation of the
      :func:`_orm.declarative_base` function.

    * :meth:`_orm.registry.mapped` provides a class decorator that will
      apply declarative mapping to a class without the use of a declarative
      base class.

    * :meth:`_orm.registry.map_imperatively` will produce a
      :class:`_orm.Mapper` for a class without scanning the class for
      declarative class attributes. This method suits the use case historically
      provided by the
      :func:`_orm.mapper` classical mapping function.

    .. versionadded:: 1.4

    .. seealso::

        :ref:`orm_mapping_classes_toplevel` - overview of class mapping
        styles.

    """

    def __init__(
        self,
        metadata=None,
        class_registry=None,
        constructor=_declarative_constructor,
        _bind=None,
    ):
        r"""Construct a new :class:`_orm.registry`

        :param metadata:
          An optional :class:`_schema.MetaData` instance.  All
          :class:`_schema.Table` objects generated using declarative
          table mapping will make use of this :class:`_schema.MetaData`
          collection.  If this argument is left at its default of ``None``,
          a blank :class:`_schema.MetaData` collection is created.

        :param constructor:
          Specify the implementation for the ``__init__`` function on a mapped
          class that has no ``__init__`` of its own.  Defaults to an
          implementation that assigns \**kwargs for declared
          fields and relationships to an instance.  If ``None`` is supplied,
          no __init__ will be provided and construction will fall back to
          cls.__init__ by way of the normal Python semantics.

        :param class_registry: optional dictionary that will serve as the
          registry of class names-> mapped classes when string names
          are used to identify classes inside of :func:`_orm.relationship`
          and others.  Allows two or more declarative base classes
          to share the same registry of class names for simplified
          inter-base relationships.

        """
        lcl_metadata = metadata or MetaData()
        if _bind:
            lcl_metadata.bind = _bind

        if class_registry is None:
            class_registry = weakref.WeakValueDictionary()

        self._class_registry = class_registry
        self.metadata = lcl_metadata
        self.constructor = constructor

    def _dispose_cls(self, cls):
        clsregistry.remove_class(cls.__name__, cls, self._class_registry)

    def generate_base(
        self,
        mapper=None,
        cls=object,
        name="Base",
        metaclass=DeclarativeMeta,
    ):
        """Generate a declarative base class.

        Classes that inherit from the returned class object will be
        automatically mapped using declarative mapping.

        E.g.::

            from sqlalchemy.orm import registry

            mapper_registry = registry()

            Base = mapper_registry.generate_base()

            class MyClass(Base):
                __tablename__ = "my_table"
                id = Column(Integer, primary_key=True)

        The :meth:`_orm.registry.generate_base` method provides the
        implementation for the :func:`_orm.declarative_base` function, which
        creates the :class:`_orm.registry` and base class all at once.


        See the section :ref:`orm_declarative_mapping` for background and
        examples.

        :param mapper:
          An optional callable, defaults to :func:`~sqlalchemy.orm.mapper`.
          This function is used to generate new :class:`_orm.Mapper` objects.

        :param cls:
          Defaults to :class:`object`. A type to use as the base for the
          generated declarative base class. May be a class or tuple of classes.

        :param name:
          Defaults to ``Base``.  The display name for the generated
          class.  Customizing this is not required, but can improve clarity in
          tracebacks and debugging.

        :param metaclass:
          Defaults to :class:`.DeclarativeMeta`.  A metaclass or __metaclass__
          compatible callable to use as the meta type of the generated
          declarative base class.

        .. seealso::

            :ref:`orm_declarative_mapping`

            :func:`_orm.declarative_base`

        """
        metadata = self.metadata

        bases = not isinstance(cls, tuple) and (cls,) or cls

        class_dict = dict(registry=self, metadata=metadata)
        if isinstance(cls, type):
            class_dict["__doc__"] = cls.__doc__

        if self.constructor:
            class_dict["__init__"] = self.constructor

        class_dict["__abstract__"] = True
        if mapper:
            class_dict["__mapper_cls__"] = mapper

        return metaclass(name, bases, class_dict)

    def mapped(self, cls):
        """Class decorator that will apply the Declarative mapping process
        to a given class.

        E.g.::

            from sqlalchemy.orm import registry

            mapper_registry = registry()

            @mapper_registry.mapped
            class Foo:
                __tablename__ = 'some_table'

                id = Column(Integer, primary_key=True)
                name = Column(String)

        See the section :ref:`orm_declarative_mapping` for complete
        details and examples.

        :param cls: class to be mapped.

        :return: the class that was passed.

        .. seealso::

            :ref:`orm_declarative_mapping`

            :meth:`_orm.registry.generate_base` - generates a base class
            that will apply Declarative mapping to subclasses automatically
            using a Python metaclass.

        """
        _as_declarative(self, cls, cls.__dict__)
        return cls

    def as_declarative_base(self, **kw):
        """
        Class decorator which will invoke
        :meth:`_orm.registry.generate_base`
        for a given base class.

        E.g.::

            from sqlalchemy.orm import registry

            mapper_registry = registry()

            @mapper_registry.as_declarative_base()
            class Base(object):
                @declared_attr
                def __tablename__(cls):
                    return cls.__name__.lower()
                id = Column(Integer, primary_key=True)

            class MyMappedClass(Base):
                # ...

        All keyword arguments passed to
        :meth:`_orm.registry.as_declarative_base` are passed
        along to :meth:`_orm.registry.generate_base`.

        """

        def decorate(cls):
            kw["cls"] = cls
            kw["name"] = cls.__name__
            return self.generate_base(**kw)

        return decorate

    def map_declaratively(self, cls):
        # type: (type) -> Mapper
        """Map a class declaratively.

        In this form of mapping, the class is scanned for mapping information,
        including for columns to be associaed with a table, and/or an
        actual table object.

        Returns the :class:`_orm.Mapper` object.

        E.g.::

            from sqlalchemy.orm import registry

            mapper_registry = registry()

            class Foo:
                __tablename__ = 'some_table'

                id = Column(Integer, primary_key=True)
                name = Column(String)

            mapper = mapper_registry.map_declaratively(Foo)

        This function is more conveniently invoked indirectly via either the
        :meth:`_orm.registry.mapped` class decorator or by subclassing a
        declarative metaclass generated from
        :meth:`_orm.registry.generate_base`.

        See the section :ref:`orm_declarative_mapping` for complete
        details and examples.

        :param cls: class to be mapped.

        :return: a :class:`_orm.Mapper` object.

        .. seealso::

            :ref:`orm_declarative_mapping`

            :meth:`_orm.registry.mapped` - more common decorator interface
            to this function.

            :meth:`_orm.registry.map_imperatively`

        """
        return _as_declarative(self, cls, cls.__dict__)

    def map_imperatively(self, class_, local_table=None, **kw):
        r"""Map a class imperatively.

        In this form of mapping, the class is not scanned for any mapping
        information.  Instead, all mapping constructs are passed as
        arguments.

        This method is intended to be fully equivalent to the classic
        SQLAlchemy :func:`_orm.mapper` function, except that it's in terms of
        a particular registry.

        E.g.::

            from sqlalchemy.orm import registry

            mapper_registry = registry()

            my_table = Table(
                "my_table",
                mapper_registry.metadata,
                Column('id', Integer, primary_key=True)
            )

            class MyClass:
                pass

            mapper_registry.map_imperatively(MyClass, my_table)

        See the section :ref:`orm_imperative_mapping` for complete background
        and usage examples.

        :param class\_: The class to be mapped.  Corresponds to the
         :paramref:`_orm.mapper.class_` parameter.

        :param local_table: the :class:`_schema.Table` or other
         :class:`_sql.FromClause` object that is the subject of the mapping.
         Corresponds to the
         :paramref:`_orm.mapper.local_table` parameter.

        :param \**kw: all other keyword arguments are passed to the
         :func:`_orm.mapper` function directly.

        .. seealso::

            :ref:`orm_imperative_mapping`

            :ref:`orm_declarative_mapping`

        """
        return _mapper(self, class_, local_table, kw)


@util.deprecated_params(
    bind=(
        "2.0",
        "The ``bind`` argument to as_declarative is "
        "deprecated and will be removed in SQLAlchemy 2.0.",
    )
)
def as_declarative(**kw):
    """
    Class decorator which will adapt a given class into a
    :func:`_orm.declarative_base`.

    This function makes use of the :meth:`_orm.registry.as_declarative_base`
    method, by first creating a :class:`_orm.registry` automatically
    and then invoking the decorator.

    E.g.::

        from sqlalchemy.orm import as_declarative

        @as_declarative()
        class Base(object):
            @declared_attr
            def __tablename__(cls):
                return cls.__name__.lower()
            id = Column(Integer, primary_key=True)

        class MyMappedClass(Base):
            # ...

    .. seealso::

        :meth:`_orm.registry.as_declarative_base`

    """
    bind, metadata, class_registry = (
        kw.pop("bind", None),
        kw.pop("metadata", None),
        kw.pop("class_registry", None),
    )

    return registry(
        _bind=bind, metadata=metadata, class_registry=class_registry
    ).as_declarative_base(**kw)


@inspection._inspects(DeclarativeMeta)
def _inspect_decl_meta(cls):
    mp = _inspect_mapped_class(cls)
    if mp is None:
        if _DeferredMapperConfig.has_cls(cls):
            _DeferredMapperConfig.raise_unmapped_for_cls(cls)
            raise orm_exc.UnmappedClassError(
                cls,
                msg="Class %s has a deferred mapping on it.  It is not yet "
                "usable as a mapped class." % orm_exc._safe_cls_name(cls),
            )
    return mp