<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def runserver(ctx, conf, port, foreground):
 """Run the fnExchange server"""

    config = read_config(conf)

    debug = config['conf'].get('debug', False)
    click.echo('Debug mode {0}.'.format('on' if debug else 'off'))

    port = port or config['conf']['server']['port']

    app_settings = {
        'debug': debug,
        'auto_reload': config['conf']['server'].get('auto_reload', False),
    }
    handlers_settings = __create_handler_settings(config)

    if foreground:
        click.echo('Requested mode: foreground')
        start_app(port, app_settings, handlers_settings)
    else:
        click.echo('Requested mode: background')
        # subprocess.call([sys.executable, 'yourscript.py'], env=os.environ.copy())
        raise NotImplementedError