import signal
import socket
from PyQt5.QtNetwork import QAbstractSocket


def setup(app):
    app.signalwatchdog = SignalWatchdog() # need to store to keep socket pair alive
    signal.signal(signal.SIGINT, make_quit_handler(app))


def make_quit_handler(app):
    def handler(*args):
        print() # make ^C appear on its own line
        app.quit()
    return handler



class SignalWatchdog(QAbstractSocket):

    def __init__(self):
        """
        Propagates system signals from Python to QEventLoop
        adapted from https://stackoverflow.com/a/65802260/655404
        """
        super().__init__(QAbstractSocket.SctpSocket, None)

        self.writer, self.reader = writer, reader = socket.socketpair()
        writer.setblocking(False)

        fd_writer = writer.fileno()
        fd_reader = reader.fileno()

        signal.set_wakeup_fd(fd_writer) # Python hook
        self.setSocketDescriptor(fd_reader) # Qt hook

        self.readyRead.connect(lambda: None) # dummy function call that lets the Python interpreter run