# -*- coding: utf-8 -*-
# input-remapper - GUI for device specific keyboard mappings
# Copyright (C) 2025 sezanzeb <b8x45ygc9@mozmail.com>
#
# This file is part of input-remapper.
#
# input-remapper is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# input-remapper is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with input-remapper.  If not, see <https://www.gnu.org/licenses/>.

"""Abstractions to detect the currently focused window across compositors.

Focus detection is implemented as a registry of backends. To add support for a
new compositor, implement a new ``FocusBackend`` and append its class to
``focus_backend_classes`` (ordered by priority). ``select_backend`` returns the
first backend that reports itself as available, so the most specific backend
for the current session wins.
"""

from __future__ import annotations

from typing import List, Type

from inputremapper.focus.backends.hyprland import HyprlandFocusBackend
from inputremapper.focus.backends.null import NullBackend
from inputremapper.focus.backends.sway import SwayFocusBackend
from inputremapper.focus.backends.wlr_foreign_toplevel import (
    WlrForeignToplevelBackend,
)
from inputremapper.focus.backends.xorg import XorgFocusBackend
from inputremapper.focus.focus_backend import FocusBackend, FocusEvent
from inputremapper.logging.logger import logger

# Re-exported for convenience / backwards compatible imports.
__all__ = [
    "FocusEvent",
    "FocusBackend",
    "focus_backend_classes",
    "select_backend",
]


# Ordered by priority. The first one that reports is_available() wins.
# SWAYSOCK -> HYPRLAND_INSTANCE_SIGNATURE -> wlr-foreign-toplevel -> DISPLAY -> Null
focus_backend_classes: List[Type[FocusBackend]] = [
    SwayFocusBackend,
    HyprlandFocusBackend,
    WlrForeignToplevelBackend,
    XorgFocusBackend,
    NullBackend,
]


def select_backend() -> FocusBackend:
    """Instantiate the first available focus backend by priority."""
    for backend_class in focus_backend_classes:
        try:
            available = backend_class.is_available()
        except Exception as error:  # pragma: no cover - defensive
            logger.debug(
                "Backend %s failed its availability check: %s",
                backend_class.__name__,
                error,
            )
            available = False

        if available:
            logger.info("Using focus backend %s", backend_class.name)
            return backend_class()

    # NullBackend.is_available() always returns True, so this is unreachable
    # as long as it stays in the registry.
    logger.warning("No focus backend available, falling back to NullBackend")
    return NullBackend()