A git hook for annotating a git commit message with info about an associated Trello card.

prepare-commit-msg

#!/usr/bin/python
"""
This is a prepare-commit-msg hook for use with git-flow and Trello

Copy this file to $GITREPOSITORY/.git/hooks/prepare-commit-msg

It will prepend [<card id>] to your commit message, and append a
link to the Trello card at the end of the commit message

Assumes you name your feature branches card-id/name.

For example: A1b2C56xQ/my-cool-feature

This would start the commit message with:

[A1b2C56xQ]

And end the commit message with:

https://trello.com/c/A1b2C56xQ


"""
import subprocess
import sys


def get_card_id():
    """Return the card id number associated with the current feature branch"""
    branchname = subprocess.check_output(["/usr/bin/git", "symbolic-ref",
                                          "HEAD"])
    # This looks like: refs/heads/feature/A1b2C56xQ/my-cool-feature
    args = branchname.split('/')
    if len(args) != 5:
        raise ValueError("Not in feature branch format")
    if args[2] != 'feature':
        raise ValueError("Not a feature branch")
    story = branchname.split('/')[3]
    return story


def prepend_commit_msg(text):
    """Prepend the commit message with `text`"""
    msgfile = sys.argv[1]

    with open(msgfile) as f:
        contents = f.read()

    with open(msgfile, 'w') as f:
        # Don't append if it's already there
        if not contents.startswith(text):
            f.write(text)
        f.write(contents)


def append_commit_msg(text):
    """Prepend the commit message with `text`"""

    msgfile = sys.argv[1]

    with open(msgfile) as f:
        contents = f.read()

    # Strip out all lines that start with "#"
    message = '\n'.join(x for x in contents.split('\n')
                                if not x.startswith('#'))

    with open(msgfile, 'a') as f:
        # Don't append if the text is already in the commit message
        if text not in message:
            f.write(text)


def get_trello_link(card_id):
    return "https://trello.com/c/%s" % card_id


def main():
    # Fail silently
    try:
        card_id = get_card_id()
        header = "[{}] ".format(card_id)
        link = get_trello_link(card_id)
        prepend_commit_msg(header)
        footer = "\n{}".format(link)
        append_commit_msg(footer)

    except Exception as e:
        # Fail silently
        pass

if __name__ == '__main__':
    main()