from contextvars import ContextVar
from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from flet.controls.page import Page


class Context:
    """
    Manages the context for Flet controls, including page reference
    and auto-update behavior.

    Context instance is accessed via [`ft.context`][flet.context].
    """

    @property
    def page(self) -> "Page":
        """
        Returns the current [`Page`][flet.Page] associated with the context.

        For example:

        ```python
        # take page width anywhere in the app
        width = ft.context.page.width
        ```

        Returns:
            The current page.

        Raises:
            AssertionError: if property is called outside of Flet app.
        """
        page = _context_page.get()
        assert page, "The context is not associated with any page."
        return page

    def enable_auto_update(self):
        """
        Enables auto-update behavior for the current context.

        For example:

        ```python
        import flet as ft

        # disable auto-update globally for the app
        ft.context.disable_auto_update()


        def main(page: ft.Page):
            # enable auto-update just inside main
            ft.context.enable_auto_update()

            page.controls.append(ft.Text("Hello, world!"))
            # page.update() - we don't need to call it explicitly


        ft.run(main)
        ```
        """
        _update_behavior_context_var.get()._auto_update_enabled = True

    def disable_auto_update(self):
        """
        Disables auto-update behavior for the current context.

        For example:

        ```python
        import flet as ft


        def main(page: ft.Page):
            def button_click():
                ft.context.disable_auto_update()
                b.content = "Button clicked!"
                # update just the button
                b.update()

                page.controls.append(ft.Text("This won't appear"))
                # no page.update() will be called here

            page.controls.append(b := ft.Button("Action!", on_click=button_click))
            # page.update() - auto-update is enabled by default


        ft.run(main)
        ```
        """
        _update_behavior_context_var.get()._auto_update_enabled = False

    def auto_update_enabled(self) -> bool:
        """
        Returns whether auto-update is enabled in the current context.

        Returns:
            `True` if auto-update is enabled, `False` otherwise.
        """
        return _update_behavior_context_var.get()._auto_update_enabled

    def reset_auto_update(self):
        """
        Copies the parent auto-update state into the current context.
        """
        current = _update_behavior_context_var.get()
        new = UpdateBehavior()
        new._auto_update_enabled = current._auto_update_enabled
        _update_behavior_context_var.set(new)


class UpdateBehavior:
    """
    Internal class used by the Context API to manage auto-update behavior.

    An instance of UpdateBehavior is stored in a context variable and tracks
    whether automatic updates are enabled for the current context. The Context
    class interacts with UpdateBehavior to enable, disable, and query the
    auto-update state.
    """

    _auto_update_enabled: bool = True


_context_page = ContextVar("flet_session_page", default=None)

_update_behavior_context_var = ContextVar("update_behavior", default=UpdateBehavior())  # noqa: B039

context = Context()