import time

from twilio.jwt import Jwt


class AccessTokenGrant(object):
    """A Grant giving access to a Twilio Resource"""
    @property
    def key(self):
        """:rtype str Grant's twilio specific key"""
        raise NotImplementedError('Grant must have a key property.')

    def to_payload(self):
        """:return: dict something"""
        raise NotImplementedError('Grant must implement to_payload.')

    def __str__(self):
        '<{} {}>'.format(self.__class__.__name__, self.to_payload())


class AccessToken(Jwt):
    """Access Token containing one or more AccessTokenGrants used to access Twilio Resources"""
    def __init__(self, account_sid, signing_key_sid, secret, grants=None,
                 identity=None, nbf=Jwt.GENERATE, ttl=3600, valid_until=None):
        grants = grants or []
        if any(not isinstance(g, AccessTokenGrant) for g in grants):
            raise ValueError('Grants must be instances of AccessTokenGrant.')

        self.account_sid = account_sid
        self.signing_key_sid = signing_key_sid
        self.identity = identity
        self.grants = grants
        super(AccessToken, self).__init__(
            secret_key=secret,
            algorithm='HS256',
            issuer=signing_key_sid,
            subject=self.account_sid,
            nbf=nbf,
            ttl=ttl,
            valid_until=valid_until,
        )

    def add_grant(self, grant):
        """Add a grant to this AccessToken"""
        if not isinstance(grant, AccessTokenGrant):
            raise ValueError('Grant must be an instance of AccessTokenGrant.')
        self.grants.append(grant)

    def _generate_headers(self):
        return {
            'cty': 'twilio-fpa;v=1'
        }

    def _generate_payload(self):
        now = int(time.time())
        payload = {
            'jti': '{}-{}'.format(self.signing_key_sid, now),
            'grants': {grant.key: grant.to_payload() for grant in self.grants}
        }
        if self.identity:
            payload['grants']['identity'] = self.identity
        return payload

    def __str__(self):
        return '<AccessToken {}>'.format(self.to_jwt())
