import logging
from multiprocessing import Process, Pipe

class SubprocessOperatorMixin:
    timer = None
    log = logging.getLogger("%s.SubprocessOperatorMixin" % __name__)

    # run once in invoke
    def setup(self):
        pass
    # run on receipt of data from subprocess
    def handle_response(self, resp):
        pass

    def __init__(self):
        self.pipe = Pipe()
        self.subprocess = None

    def execute(self, context):
        return self.invoke(context, None)

    def invoke(self, context, event):
        self.subprocess.start()
        # we have to explicitly close the end of the pipe we are NOT using,
        # otherwise no exception will be generated when the other process closes its end.
        self.pipe[1].close()

        wm = context.window_manager
        wm.modal_handler_add(self)
        self.timer = wm.event_timer_add(.01, context.window)

        self.setup()

        return {'RUNNING_MODAL'}

    def modal(self, context, event):
        self.log.debug("polling")
        try:
            if self.pipe[0].poll():
                newdata = self.pipe[0].recv()
            else:
                newdata = None
        except EOFError:
            self.log.debug("done polling")
            return {'FINISHED'}

        if newdata is not None:
            self.handle_response(newdata)
        return {'PASS_THROUGH'}