import datetime

import requests


API_URL = 'https://api.exchangeratesapi.io/latest'


class ExchangeRatesError(Exception):
    pass


class ExchangeRates(object):
    def __init__(self):
        self.cache = {}

    def query(self):
        today = datetime.datetime.utcnow().date().isoformat()
        try:
            base, rates = self.cache[today]
        except KeyError:
            try:
                data = requests.get(API_URL).json()
                base, rates = data['base'], data['rates']
                self.cache[today] = base, rates
            except Exception as e:
                raise ExchangeRatesError(str(e))
        return base, rates