How to use the pibooth.hookimpl function in pibooth

    @pibooth.hookimpl
    def state_wait_do(self, cfg, app, events):
        if app.find_print_event(events) and app.previous_picture_file and app.printer.is_installed():

            if app.count.remaining_duplicates < 0:
                LOGGER.warning("Too many duplicates sent to the printer (%s max)",
                               cfg.getint('PRINTER', 'max_duplicates'))
                return

            elif not app.printer.is_available():
                LOGGER.warning("Maximum number of printed pages reached (%s/%s max)", app.count.printed,
                               cfg.getint('PRINTER', 'max_pages'))
                return

            with timeit("Send final picture to printer"):
                app.printer.print_file(app.previous_picture_file,
                                       cfg.getint('PRINTER', 'pictures_per_page'))

    @pibooth.hookimpl
    def state_preview_do(self, cfg, app):
        pygame.event.pump()  # Before blocking actions
        if cfg.getboolean('WINDOW', 'preview_countdown'):
            app.camera.preview_countdown(cfg.getint('WINDOW', 'preview_delay'))
        else:
            app.camera.preview_wait(cfg.getint('WINDOW', 'preview_delay'))

    @pibooth.hookimpl
    def pibooth_cleanup(self, app):
        app.camera.quit()

    @pibooth.hookimpl
    def state_chosen_enter(self, app, win):
        with timeit("Show picture choice ({} captures selected)".format(app.capture_nbr)):
            win.show_choice(app.capture_choices, selected=app.capture_nbr)
        self.layout_timer.start()

    @pibooth.hookimpl
    def state_processing_exit(self, cfg, app):
        app.count.remaining_duplicates = cfg.getint('PRINTER', 'max_duplicates')
        # Do it here because 'print' state can be skipped

    @pibooth.hookimpl
    def state_capture_do(self, cfg, app, win):
        effects = cfg.gettyped('PICTURE', 'captures_effects')
        if not isinstance(effects, (list, tuple)):
            # Same effect for all captures
            effect = effects
        elif len(effects) >= app.capture_nbr:
            # Take the effect corresponding to the current capture
            effect = effects[self.count]
        else:
            # Not possible
            raise ValueError("Not enough effects defined for {} captures {}".format(
                app.capture_nbr, effects))

        with timeit("Take a capture"):
            if cfg.getboolean('WINDOW', 'flash'):
                with win.flash(2):  # Manage the window here, have no choice

    @pibooth.hookimpl
    def state_preview_enter(self, cfg, app, win):
        LOGGER.info("Show preview before next capture")
        if not app.capture_nbr:
            app.capture_nbr = app.capture_choices[0]
        if not app.capture_date:
            app.capture_date = time.strftime("%Y-%m-%d-%H-%M-%S")
        app.camera.preview(win)

    @pibooth.hookimpl
    def state_print_validate(self, app, win, events):
        printed = app.find_print_event(events)
        forgotten = app.find_capture_event(events)
        if self.print_view_timer.is_timeout() or printed or forgotten:
            if printed:
                win.set_print_number(len(app.printer.get_all_tasks()), not app.printer.is_available())
            return 'finish'

    @pibooth.hookimpl
    def state_wait_do(self, cfg, app):
        if cfg.getfloat('WINDOW', 'final_image_delay') > 0 and self.picture_destroy_timer.is_timeout()\
                and app.previous_picture_file:
            self._reset_vars(app)

    @pibooth.hookimpl
    def state_choose_enter(self, app):
        app.leds.blink(on_time=self.blink_time, off_time=self.blink_time)