import json
from enum import Enum
from functools import wraps

VALID_HTTP_METHODS = ['GET', 'POST']

def register_url(url, http_method):
    def actual_decorator(f):
        @wraps(f)
        def _impl(self, *f_args, **f_kwargs):
            RestAPI._register_url(self, f, url, http_method)
            return f(self, *f_args, **f_kwargs)
    return actual_decorator

class RestAPI:
    def __init__(self, database=None):
        self._rest_methods = {}
        self._database = database if database else {}

    def get(self, url, payload=None):
        methods = self._rest_methods['GET']
        if url in methods.keys():
            return methods[url](payload)
        else:
            raise Exception('Error 404')

    def post(self, url, payload=None):
        methods = self._rest_methods['POST']
        if url in methods.keys():
            return methods[url](payload)
        else:
            raise Exception('Error 404')

    def _register_url(self, f, url, http_method):

        if http_method not in VALID_HTTP_METHODS:
            raise Exception('Invalid Http method')

        self._rest_methods[http_method][url] = f

    @register_url('/users', 'GET')
    def users(self, payload=None):
        pass

    @register_url('/add', 'POST')
    def add(self, payload=None):
        pass

    @register_url('/iou', 'POST')
    def iou(self, payload=None):
        pass