gistfile1.txt

#!/home/szobov/.nix-profile/bin/python3
import re
import sys
from subprocess import check_output, CalledProcessError

JIRA_PROJECT_PREFIX = 'JIRA-'


def append_branch_number(prefix):
    """
    Add a substring with the task number to commit the message if necessary.
    Will added if:
    * Branch starts with a prefix
    * Constructed substring wasn't added previously.
    """
    commit_msg_filepath = sys.argv[1]

    try:
        branch = check_output(
            ['git', 'symbolic-ref', '--short', 'HEAD']).strip().decode('utf-8')
    except CalledProcessError:
        print('Can not get branch name. Probably, you are doing rabase.')
        return None

    result = re.match('(?P<number>[0-9]*)-', branch)
    if result is None:
        return None
    if not result.groupdict().get('number'):
        return None

    task_number = '{}{}'.format(
        JIRA_PROJECT_PREFIX, result.groupdict().get('number'))
    with open(commit_msg_filepath, 'r+') as f:
        content = f.read()
        if task_number in content.split('\n')[0]:
            return None
        f.seek(0, 0)
        f.write("[%s] %s" % (task_number, content))
        f.seek(len('[%s]' % (task_number, )), 0)


if __name__ == '__main__':
    append_branch_number(JIRA_PROJECT_PREFIX)