from contextlib import suppress
from os import open as osopen
from os import write, close, O_WRONLY, O_NONBLOCK
from threading import Thread

from .terminate_process_on_failure import terminate_process_on_failure


class PipeReaderThread(Thread):
    eof = b''
    stop_sequence = b'stop_reading\n'

    def __init__(self, pipe_path, stop_event, message_handler):
        super().__init__(daemon=True)
        self._message_handler = message_handler
        self._pipe_path = pipe_path
        self._stop_event = stop_event

    @terminate_process_on_failure
    def run(self):
        with self._open() as pipe:
            while True:
                message = pipe.readline()
                if message == self.stop_sequence:
                    self._stop_event.set()
                    break
                if message == self.eof:
                    self._open().close()
                    continue
                self._message_handler(message[:-1])

    def _open(self):
        return open(self._pipe_path, 'rb')

    def stop(self):
        while self.is_alive():
            self._unblock()
        self.join()

    def _unblock(self):
        with suppress(OSError):
            fd = osopen(self._pipe_path, O_WRONLY | O_NONBLOCK)
            write(fd, self.stop_sequence)
            close(fd)