import re
import os

def _unidiff_output(expected, actual):
    """
    Helper function. Returns a string containing the unified diff of two multiline strings.
    """

    import difflib
    expected=expected.splitlines(1)
    actual=actual.splitlines(1)

    diff=difflib.unified_diff(expected, actual)

    return ''.join(diff)

def return_nix_libraries_list(nix_file_path):
    original_content = ""

    with open(nix_file_path,'r') as nix_file:
        nix_file_content = nix_file.read()
        #print(nix_file_content)
        derivations_list = re.findall(re.compile('\s+pname = "(.*?)";\s+version = "(.*?)";\s+sha256 = "(.*?)";(\s+revision = "(.*?)";)*', re.MULTILINE), nix_file_content)

        for derivation in derivations_list:

            pname = derivation[0]
            version = derivation[1]
            sha256 = derivation[2]
            revision = derivation[4]

            original_content += pname + ', ' + version + ', ' + sha256 + ', ' + revision + os.linesep
            #print(pname + ', ' + version + ', ' + sha256 + ', ' + revision)

    return original_content

# _unidiff_output(return_nix_libraries_list('path_to_default.nix'), return_nix_libraries_list('path_to_default.nix'))