import time
import json
import binascii
import contextlib

import tornado.stack_context
from Crypto.PublicKey import RSA
from Crypto.Hash import SHA512
from Crypto.Signature import PKCS1_v1_5

current_iden = None

class Auth:
    def __init__(self):
        global current_iden

        self._cache_hashmap = {}
        current_iden = None

    @staticmethod
    def get_current_iden():
        global current_iden

        return current_iden

    @staticmethod
    def change_current_iden(iden):
        @contextlib.contextmanager
        def context():
            global current_iden

            old_iden = current_iden
            current_iden = iden
            
            try:
                yield

            finally:
                current_iden = old_iden

        return tornado.stack_context.StackContext(context)

    def set_signkey(self,key):
        self._signer = PKCS1_v1_5.new(RSA.importKey(key))

    def set_verifykey(self,key):
        self._verifier = PKCS1_v1_5.new(RSA.importKey(key))

    def sign_iden(self,iden):
        data = json.dumps(iden)
        sign = binascii.hexlify(self._sign(bytes(data,'utf-8'))).decode('utf-8')

        return json.dumps([data,sign])

    def get_iden(self,idendesc):
        pair = json.loads(idendesc)
        data = pair[0]
        sign = pair[1]

        if self._verify(bytes(data,'utf-8'),binascii.unhexlify(sign)):
            return json.loads(data)

        else:
            return None

    def _sign(self,data):
        return self._signer.sign(SHA512.new(data))

    def _verify(self,data,sig):
        h = SHA512.new(data)
        if h in self._cache_hashmap:
            return True

        if self._verifier.verify(h,sig) == True:
            self._cache_hashmap[h] = True

            return True
        else:
            return False