#! /usr/bin/python2.7

import sys
import fileinput
import subprocess


class RejectError(Exception):

    code = 255
    msg = ""

    def reject(self):
        if self.msg:
            sys.stdout.write(self.msg)
        sys.exit(self.code)


class ProtectMasterBranchError(RejectError):

    code = 1
    msg = "branch master is protected, no one can delete or force push"


class Git(object):

    @staticmethod
    def is_null_commit(commit_id):
        return True if commit_id == '0' * len(commit_id) else False

    @staticmethod
    def is_force_push(old_commit_id, new_commit_id):
        merge_base = subprocess.check_output(
            "git merge-base %s %s" % (old_commit_id, new_commit_id),
            shell=True,
        )
        return old_commit_id != merge_base


def protect_master_branch(ref, old_commit_id, new_commit_id):
    if ref != 'refs/heads/master':
        return
    if Git.is_null_commit(old_commit_id):
        return
    if Git.is_null_commit(new_commit_id):
        raise ProtectMasterBranchError()
    if Git.is_force_push(old_commit_id, new_commit_id):
        raise ProtectMasterBranchError()


def main():
    try:
        for line in fileinput.input():
            old_commit_id, new_commit_id, ref = line.split()
            protect_master_branch(ref, old_commit_id, new_commit_id)
    except RejectError as error:
        error.reject()

main()