Add update_commit_msg

Update hooks file

Update description

Simplify approach

Remove redundant statement

Add test

Add more tests

Updates lints

Use io.open instead

Update setup.py

Remove unused import

Rename update-commit-msg to prepend-ticket-number-to-commit-msg

pre_commit_hooks/prepend_ticket_number_to_commit_msg.py

@@ -0,0 +1,63 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+from __future__ import absolute_import
+from __future__ import unicode_literals
+
+import argparse
+import io
+import re
+import subprocess
+import sys
+
+import six
+
+
+def update_commit_message(filename, regex):
+    with io.open(filename, 'r+') as fd:
+        contents = fd.readlines()
+        commit_msg = contents[0]
+        # Check if we can grab ticket info from branch name.
+        branch = get_branch_name()
+        if all([
+            not re.search(regex, commit_msg),
+            re.search(regex, branch),
+        ]):
+            ticket = branch.split(six.text_type('_'))[0]
+            new_commit_msg = '{} {}'.format(ticket, commit_msg)
+            fd.seek(0)
+            fd.write(
+                six.text_type(
+                    new_commit_msg,
+                ),
+            )
+            fd.truncate()
+
+
+def get_branch_name():
+    # Only git support for right now.
+    return subprocess.check_output(
+        [
+            'git',
+            'rev-parse',
+            '--abbrev-ref',
+            'HEAD',
+        ],
+    ).decode('UTF-8')
+
+
+def main(argv=None):
+    """This hook saves developers time by prepending ticket numbers to commit-msgs.
+    For this to work the following two conditions must be met:
+        - The ticket format regex specified must match.
+        - The branch name format must be <ticket number>_<rest of the branch name>
+    """
+    parser = argparse.ArgumentParser()
+    parser.add_argument('filenames', nargs='+')
+    parser.add_argument('--regex')
+    args = parser.parse_args(argv)
+    regex = args.regex or '[A-Z]+-\d+'  # noqa
+    update_commit_message(args.filenames[0], regex)
+
+
+if __name__ == '__main__':
+    sys.exit(main())