# coding: utf-8
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__authors__ = ["V. Valls"]
__license__ = "MIT"
__date__ = "16/10/2020"

import contextlib
from silx.gui import qt


class AbstractModel(qt.QObject):

    changed = qt.Signal()

    def __init__(self, parent=None):
        qt.QObject.__init__(self, parent)
        self.__isLocked = 0
        self.__wasChanged = False

    def isValid(self):
        return True

    def wasChanged(self):
        """Emit the change event in case of the model was not locked.

        :returns: True if the signal was emitted.
        """
        if self.__isLocked > 0:
            self.__wasChanged = True
            return False
        else:
            self.changed.emit()
            return True

    def isLocked(self):
        """Returns True if the events are locked.

        :rtype: bool
        """
        return self.__isLocked > 0

    @contextlib.contextmanager
    def lockContext(self):
        """Context manager to lock and unlock signals."""
        self.lockSignals()
        yield self
        self.unlockSignals()

    def lockSignals(self):
        """Lock the change events
        """
        self.__isLocked = self.__isLocked + 1

    def unlockSignals(self):
        """Unlock the change events

        :returns: False if the model is still locked, else True
        """
        assert self.__isLocked > 0
        self.__isLocked = self.__isLocked - 1
        if self.__isLocked == 0 and self.__wasChanged:
            self.__wasChanged = False
            self.wasChanged()
        return self.__isLocked == 0