#!/usr/bin/env python3

"""
Perform a git rebase operation, restoring original tags

Copyleft 2017 by Ignacio Nunez Hernanz <nacho _a_t_ ownyourbits _d_o_t_ com>
GPL licensed (see LICENSE file in repository root).
Use at your own risk!

Details:
    A new bash shell will be spawned in the case of interactive rebasing.
    Tags will be restored upon exiting that shell.

Usage
    git-rebasetags <rebase args>

More at https://ownyourbits.com/2017/08/14/rebasing-in-git-without-losing-tabs
"""

import sys
import pty
import os
from subprocess import run, PIPE

# Save tag-comment information
TAGS = run(['git', 'show-ref', '--tags'], stdout=PIPE).stdout.decode('utf-8').splitlines()

TAGHASHES = {}
for line in TAGS:
    tag    = line.split()[1].split('/')[2]
    commit = line.split()[0]
    TAGHASHES[tag] = commit

TAGCOMMENTS = {}
for tag, commit in TAGHASHES.items():
    OUT = run(['git', '--no-pager', 'show', '-s', '--format=%s', commit], stdout=PIPE)
    TAGCOMMENTS[tag] = OUT.stdout.decode('utf-8').rstrip()

# Interactive rebase
pty.spawn(['/bin/bash', '-c', 'git rebase ' + ' '.join(sys.argv[1:])])
pty.spawn(['/bin/bash', '-c', 'reset'])

while True:
    if os.path.exists('.git/rebase-merge'):
        print('\nRebase in progress. Type \'git rebase --abort\' to cancel. Type \'exit\' when you are done')
        pty.spawn('/bin/bash')
    else:
        break

# Restore tags after rebase, matching comments
print('Restoring tags...')

OUT = run(['git', 'log', '--no-decorate', '--oneline'], stdout=PIPE).stdout.decode('utf-8').splitlines()

count = 0
for line in OUT:
    for tag, comment in TAGCOMMENTS.items():
        if comment == ' '.join(line.split()[1:]):
            commit = line.split()[0]
            print('tag ' + tag + ' -> ' + commit)
            run(['git', 'tag', '-d', tag], stdout=PIPE, stderr=PIPE)
            run(['git', 'tag', tag, commit])
            count += 1

if count < len(TAGS):
    print('WARNING: ' + str(len(TAGS) - count) + 'tags without a match')

# License
#
# This script is free software; you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This script is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this script; if not, write to the
# Free Software Foundation, Inc., 59 Temple Place, Suite 330,
# Boston, MA  02111-1307  USA