import re
import sys

_URL_PLACEHOLDER_PATTERN = re.compile('<(.*?)>')


def get_pipe(name):
    """通过 mod.ClassName 导入自定义的PipeHandler"""
    module_name, obj_name = name.rsplit('.', 1)
    __import__(module_name)
    module = sys.modules[module_name]
    obj = getattr(module, obj_name)
    return obj


def extract_placeholders(url):
    """
    >>> res = extract_placeholders("/<service_name>/resource/<resource_id>/submit/")
    >>> assert set(res) == {"service_name", "resource_id"}
    :param url: request url name
    :return: list of placeholder name
    """
    return _URL_PLACEHOLDER_PATTERN.findall(url)


def replace_placeholder(url, placeholder_name, value):
    return url.replace('<{}>'.format(placeholder_name), str(value))