automatically-write-ticket-number-in-commit.sh

#!/usr/bin/env python3
#
# Extract the ticket's id from the branch name and add it
# to the commit message. Adapted from:
# https://andy-carter.com/blog/automating-git-commit-messages-with-git-hooks
# Parameters are explained here:
# https://git-scm.com/docs/githooks#_prepare_commit_msg

import re
import sys
from subprocess import check_output
from typing import Optional


def extract_issue_from_branch_name() -> Optional[str]:
    branch = check_output(['git', 'rev-parse', '--abbrev-ref', 'HEAD'], text=True).strip()
    match = re.match('(feature|bugfix|hotfix)/(\\w+-\\d+)', branch)
    if match:
        return match.group(2)
    else:
        return None


def conform_to_commit_template(commit_msg_filepath: str, issue_id: str):
    with open(commit_msg_filepath, 'r') as fh:
        commit_msg = fh.readlines()

    # no modification if a line starts with the id (no position check)
    if any(line.startswith(issue_id) for line in commit_msg):
        return

    # Add the issue id below the possibly existing commit message, 
    # but above the generated comment block listing the changes.
    last_content_line_index = -1
    for index, line in enumerate(commit_msg):
        if line.strip() and not line.startswith('#'):
            last_content_line_index = index

    if last_content_line_index == -1:
        commit_msg.insert(0, '\n')
        last_content_line_index = 0

    commit_msg.insert(last_content_line_index + 1, '\n')
    commit_msg.insert(last_content_line_index + 2, issue_id + '\n')

    # delete extra blank lines after the issue id
    extra_blank_lines = 0
    index_after_id = last_content_line_index + 3
    for i in range(index_after_id, len(commit_msg)):
        if not commit_msg[i].strip():
            extra_blank_lines += 1

    if extra_blank_lines > 0:
        del commit_msg[index_after_id:index_after_id + extra_blank_lines]

    # override the whole file
    with open(commit_msg_filepath, 'w') as fh:
        fh.writelines(commit_msg)


msg_filepath = sys.argv[1]
issue = extract_issue_from_branch_name()
if issue:
    conform_to_commit_template(msg_filepath, issue)