"""Provide a simple user friendly API to PyTensor-managed memory."""

import copy
from contextlib import contextmanager
from functools import singledispatch
from typing import TYPE_CHECKING

from pytensor.graph.basic import Variable
from pytensor.graph.utils import add_tag_trace
from pytensor.link.basic import Container
from pytensor.link.c.type import generic


if TYPE_CHECKING:
    from pytensor.graph.type import Type


__SHARED_CONTEXT__: list[Variable] | None = None


@contextmanager
def collect_new_shareds():
    r"""Return all the `SharedVariable`\s created within this context manager."""
    global __SHARED_CONTEXT__
    old_context = __SHARED_CONTEXT__
    context = []
    try:
        __SHARED_CONTEXT__ = context
        yield context
    finally:
        __SHARED_CONTEXT__ = old_context


class SharedVariable(Variable):
    """Variable that is shared between compiled functions."""

    def __init__(
        self,
        type: "Type",
        value,
        strict: bool,
        allow_downcast=None,
        container: Container | None = None,
        name: str | None = None,
    ):
        r"""
        Parameters
        ----------
        type
            The `Type` for this variable (see `Variable`).
        value
            A value to associate with this variable (a new container will be
            created).
        strict
            ``True`` means that values assigned to this variable will not be
            cast or copied, so they must have the correct `Type`\s.
        allow_downcast
            Only applies if `strict` is ``False``.
            ``True`` means that the assigned value can lose precision when cast
            during assignment. ``None`` means that only down-casting of a Python
            float to a scalar ``floatX`` is allowed.
        container
            The container to use for this variable. Illegal to pass this as well as
            a value.
        name
            The name for this variable (see `Variable`).

        """
        super().__init__(type=type, owner=None, index=None, name=name)

        if container is not None:
            self.container = container
            if (value is not None) or (strict is not None):
                raise TypeError(
                    "value and strict are ignored if you pass a container here"
                )
        else:
            self.container = Container(
                self,
                storage=[
                    type.filter(value, strict=strict, allow_downcast=allow_downcast)
                ],
                readonly=False,
                strict=strict,
                allow_downcast=allow_downcast,
            )

        global __SHARED_CONTEXT__

        if isinstance(__SHARED_CONTEXT__, list):
            __SHARED_CONTEXT__.append(self)

        self._default_update: Variable | None = None

    def get_value(self, borrow=False, return_internal_type=False):
        """
        Get the non-symbolic value associated with this SharedVariable.

        Parameters
        ----------
        borrow : bool
            True to permit returning of an object aliased to internal memory.
        return_internal_type : bool
            True to permit the returning of an arbitrary type object used
            internally to store the shared variable.

        Only with borrow=False and return_internal_type=True does this function
        guarantee that you actually get the internal object.
        But in that case, you may get different return types when using
        different compute devices.

        """
        if borrow:
            return self.container.value
        else:
            return copy.deepcopy(self.container.value)

    def set_value(self, new_value, borrow=False):
        """
        Set the non-symbolic value associated with this SharedVariable.

        Parameters
        ----------
        borrow : bool
            True to use the new_value directly, potentially creating problems
            related to aliased memory.

        Changes to this value will be visible to all functions using
        this SharedVariable.
        """
        if borrow:
            self.container.value = new_value
        else:
            self.container.value = copy.deepcopy(new_value)

    def get_test_value(self):
        return self.get_value(borrow=True, return_internal_type=True)

    def clone(self, **kwargs):
        name = kwargs.get("name", self.name)
        cp = self.__class__(
            name=name,
            type=self.type,
            value=None,
            strict=None,
            container=self.container,
        )
        cp.tag = copy.copy(self.tag)
        return cp

    @property
    def default_update(self) -> Variable | None:
        """A default update expression for this `Variable`.

        If this value is non-``None``, its value will be used as the `update`
        (see `pytensor.function`) for this `Variable` when no updates are
        provided through `pytensor.function` and `no_default_updates` isn't
        enabled.
        """
        return self._default_update

    @default_update.setter
    def default_update(self, value):
        if value is not None:
            self._default_update = self.type.filter_variable(value, allow_convert=True)
        else:
            self._default_update = value


def shared(value, name=None, strict=False, allow_downcast=None, **kwargs):
    r"""Create a `SharedVariable` initialized with a copy or reference of `value`.

    This function iterates over constructor functions to find a
    suitable `SharedVariable` subclass.  The suitable one is the first
    constructor that accept the given value.  See the documentation of
    :func:`shared_constructor` for the definition of a constructor
    function.

    This function is meant as a convenient default.  If you want to use a
    specific constructor, consider calling it directly.

    `pytensor.shared` is a shortcut to this function.

    Notes
    -----
    By passing kwargs, you effectively limit the set of potential constructors
    to those that can accept those kwargs.

    Some shared variable have `borrow` as a kwarg.

    `SharedVariable`\s of `TensorType` have `broadcastable` as a kwarg. As shared
    variable shapes can change, all dimensions default to not being
    broadcastable, even if `value` has a shape of 1 along some dimension.
    This parameter allows one to create for example a row or column tensor.

    """

    if isinstance(value, Variable):
        raise TypeError("Shared variable values can not be symbolic.")

    try:
        var = shared_constructor(
            value,
            name=name,
            strict=strict,
            allow_downcast=allow_downcast,
            **kwargs,
        )
        add_tag_trace(var)
        return var
    except MemoryError as e:
        e.args = (*e.args, "Consider using `pytensor.shared(..., borrow=True)`")
        raise


@singledispatch
def shared_constructor(value, name=None, strict=False, allow_downcast=None, **kwargs):
    return SharedVariable(
        type=generic,
        value=value,
        strict=strict,
        allow_downcast=allow_downcast,
        name=name,
    )
