from typing import Set
import re


def parse_story_from_pr_body(body: str) -> Set[str]:
    """
    parse keyword (Fixes [ch-xxx]) from pr_body

    :param body: the body of pull request
    :return: stories set
    """
    candidates = []
    stories: Set[str] = set()
    regexp = re.compile(r"Fixes \[ch-\d+\]")

    if regexp.search(body):
        print("matched")
        candidates = re.findall(regexp, body)
        print(candidates)

    if not candidates:
        print("no matching stories")
        return stories

    for candidate in candidates:
        stories.add(candidate[10:-1])

    return stories