#!/usr/bin/env python
import sys
import argparse
from subprocess import check_call, call, check_output


def main():
    parser = argparse.ArgumentParser(
        description="Creates a PR for merging two branches")
    parser.add_argument("from_branch",
                        help="From branch (e.g 1.1)")
    parser.add_argument("to_branch",
                        help="To branch (e.g master)")
    parser.add_argument("--yes", action="store_true",
                        help="Assume yes. Warning: discards local changes.")
    parser.add_argument("--continue", action="store_true",
                        help="Continue after fixing merging errors.")
    args = parser.parse_args()

    tmp_branch = "automatic_merge_from_{}_to_{}_branch".format(
        args.from_branch, args.to_branch)

    if not vars(args)["continue"]:
        if not args.yes and raw_input("This will destroy all local changes. " +
                                      "Continue? [y/n]: ") != "y":
            return 1
        check_call("git reset --hard", shell=True)
        check_call("git clean -df", shell=True)
        check_call("git fetch", shell=True)

        check_call("git checkout {}".format(args.from_branch), shell=True)
        check_call("git pull", shell=True)

        check_call("git checkout {}".format(args.to_branch), shell=True)
        check_call("git pull", shell=True)
        call("git branch -D {} > /dev/null".format(tmp_branch), shell=True)
        check_call("git checkout -b {}".format(tmp_branch), shell=True)
        if call("git merge {}".format(args.from_branch), shell=True) != 0:
            print("Looks like you have merge errors.")
            print("Fix them, commit, then run: {} --continue"
                  .format(" ".join(sys.argv)))
            return 1

    if len(check_output("git status -s", shell=True).strip()) > 0:
        print("Looks like you have uncommitted changes")
        return 1

    if len(check_output("git log HEAD...{}".format(args.to_branch),
                        shell=True).strip()) == 0:
        print("No commit to push")
        return 1

    print("Ready to push branch.")
    remote = raw_input("To which remote should I push? (your fork): ")
    call("git push {} :{} > /dev/null".format(remote, tmp_branch),
         shell=True)
    check_call("git push --set-upstream {} {}"
               .format(remote, tmp_branch), shell=True)
    print("Done. Go to Github and open the PR")

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