"""Background Loop for running a monitor process

Uses a daemon thread, so no delays in exiting.
Don't use this for things that involve writing data, as weird things
may happen if the daemon dies while writing.

Pass in an a function to call as "action"

This does what I need it for at the moment, for other uses one might
need to extend the action call to pass on parameters or *args, **kwargs.
"""
import time
import threading


class BackgroundLoop:
    def __init__(self, interval=45, action=None):
        """
        Don't forget to .start() the loop after init.

        :param interval: time to sleep in seconds
        :param action: function to run at interval
        """
        self.interval = interval
        self.action = action
        self.thread = None

    def _loop(self):
        while self.should_continue:
            self.action()
            time.sleep(self.interval)

    def start(self):
        """Start monitor execution."""
        self.should_continue = True
        self.thread = threading.Thread(target=self._loop, daemon=True)
        self.thread.start()

    def stop(self):
        """Stop monitor execution."""
        self.should_continue = False


if __name__ == '__main__':
    def do_the_thing():
        """Test things."""
        print('hello world')

    loop = BackgroundLoop(interval=5, action=do_the_thing)
    loop.start()