"""
novelWriter – Custom Object: Wheel Event Filter
===============================================

File History:
Created: 2023-08-31 [2.1rc1]

This file is a part of novelWriter
Copyright 2018–2023, Veronica Berglyd Olsen

This program 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.

This program 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 this program. If not, see <https://www.gnu.org/licenses/>.
"""
from __future__ import annotations

from PyQt5.QtGui import QWheelEvent
from PyQt5.QtCore import QEvent, QObject
from PyQt5.QtWidgets import QWidget


class WheelEventFilter(QObject):
    """Extensions: Wheel Event Filter

    An event filter that filters mouse wheel events for a widget and
    forward them to the root widget. This solves the lack of mouse wheel
    scrolling response in margins of widgets like the editor and viewer.

    Solves: https://github.com/vkbo/novelWriter/issues/1425
    Reference: https://stackoverflow.com/a/17739995/5825851
    """

    __slots__ = ("_parent", "_locked")

    def __init__(self, parent: QWidget) -> None:
        super().__init__(parent=parent)
        self._parent = parent
        self._locked = False
        return

    def eventFilter(self, object: QObject, event: QEvent) -> bool:
        """Filter events of type QWheelEvent and forward them to the
        parent widget's wheelEvent handler.
        """
        if self._locked:
            return False
        if isinstance(event, QWheelEvent):
            # Recursion protection may be redundant, but a comment on
            # StackOverflow points to Qt 5.12 as the change, and we
            # still support Qt 5.10
            self._locked = True
            self._parent.wheelEvent(event)
            self._locked = False
        return False

# END Class WheelEventFilter
