#!/usr/bin/python
import subprocess, sys

class GitError(EnvironmentError):
    def __init__(self, err, out, returncode):
        EnvironmentError.__init__(self, err)
        self.stdout = out
        self.returncode = returncode

def _git(*args, **kw):
    p = subprocess.Popen(('git',) + args, **kw)
    out, err = p.communicate()
    if p.returncode:
        raise GitError(err, out, p.returncode)
    return out

def git(*args, **kw):
    out = _git(stdout=subprocess.PIPE, stderr=subprocess.PIPE, *args, **kw)
    return out.strip()

def main():
    try:
        src, dst = git('rev-parse', '--symbolic-full-name',
                       'HEAD', '@{u}').splitlines()
        assert src[:11] == 'refs/heads/' and dst[:13] == 'refs/remotes/'
        src = src[11:]
        dst = dst[13:]
        remote, dst = dst.split('/', 1)
        push_args = 'push', '--porcelain', remote, '%s:%s' % (src, dst)
        try:
            print git(*push_args)
        except GitError, e:
            # first check why we could not push
            status = [x for x in e.stdout.splitlines() if x[:1] == '!']
            if (len(status) !=  1 or
                status[0].split()[2:] != ['[rejected]', '(non-fast-forward)']):
                raise
            _git('fetch')
            if not int(git('rev-list', '--count', '..@{u}')):
                raise
            # try to update our working copy
            try:
                git('rebase', '@{u}')
            except GitError:
                # XXX: how to know how it failed ?
                sys.stderr.write('Rebasing failed. Aborting...\n')
                _git('rebase', '--abort')
                return 1
            # retry to push everything
            _git(*push_args)
    except GitError, e:
        err = str(e)
        if err:
            sys.stderr.write(err)
        return e.returncode

if __name__ == "__main__":
    sys.exit(main())