import logging
import os
import subprocess


class DiffException(Exception):
    pass

def diff_strings(output: str, expected_output: str) -> str:

    mdiff_path = "frontend_tests/zjsunit/mdiff.js"
    if not os.path.isfile(mdiff_path):  # nocoverage
        msg = "Cannot find mdiff for Markdown diff rendering"
        logging.error(msg)
        raise DiffException(msg)

    command = ['node', mdiff_path, output, expected_output]
    diff = subprocess.check_output(command, universal_newlines=True)
    return diff