
import json

from calendar import timegm
from collections import Mapping
from datetime import datetime
from datetime import timedelta
from six import string_types

from jose import jws

from .exceptions import JWSError
from .exceptions import JWTClaimsError
from .exceptions import JWTError
from .exceptions import ExpiredSignatureError
from .constants import ALGORITHMS
from .utils import timedelta_total_seconds, calculate_at_hash


def encode(claims, key, algorithm=ALGORITHMS.HS256, headers=None, access_token=None):
    """Encodes a claims set and returns a JWT string.

    JWTs are JWS signed objects with a few reserved claims.

    Args:
        claims (dict): A claims set to sign
        key (str or dict): The key to use for signing the claim set. Can be
            individual JWK or JWK set.
        algorithm (str, optional): The algorithm to use for signing the
            the claims.  Defaults to HS256.
        headers (dict, optional): A set of headers that will be added to
            the default headers.  Any headers that are added as additional
            headers will override the default headers.
        access_token (str, optional): If present, the 'at_hash' claim will
            be calculated and added to the claims present in the 'claims'
            parameter.

    Returns:
        str: The string representation of the header, claims, and signature.

    Raises:
        JWTError: If there is an error encoding the claims.

    Examples:

        >>> jwt.encode({'a': 'b'}, 'secret', algorithm='HS256')
        'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJhIjoiYiJ9.jiMyrsmD8AoHWeQgmxZ5yq8z0lXS67_QGs52AzC8Ru8'

    """

    for time_claim in ['exp', 'iat', 'nbf']:

        # Convert datetime to a intDate value in known time-format claims
        if isinstance(claims.get(time_claim), datetime):
            claims[time_claim] = timegm(claims[time_claim].utctimetuple())

    if access_token:
        claims['at_hash'] = calculate_at_hash(access_token,
                                              ALGORITHMS.HASHES[algorithm])

    return jws.sign(claims, key, headers=headers, algorithm=algorithm)


def decode(token, key, algorithms=None, options=None, audience=None,
           issuer=None, subject=None, access_token=None):
    """Verifies a JWT string's signature and validates reserved claims.

    Args:
        token (str): A signed JWS to be verified.
        key (str or dict): A key to attempt to verify the payload with. Can be
            individual JWK or JWK set.
        algorithms (str or list): Valid algorithms that should be used to verify the JWS.
        audience (str): The intended audience of the token.  If the "aud" claim is
            included in the claim set, then the audience must be included and must equal
            the provided claim.
        issuer (str or iterable): Acceptable value(s) for the issuer of the token.
            If the "iss" claim is included in the claim set, then the issuer must be
            given and the claim in the token must be among the acceptable values.
        subject (str): The subject of the token.  If the "sub" claim is
            included in the claim set, then the subject must be included and must equal
            the provided claim.
        access_token (str): An access token string. If the "at_hash" claim is included in the
            claim set, then the access_token must be included, and it must match
            the "at_hash" claim.
        options (dict): A dictionary of options for skipping validation steps.

            defaults = {
                'verify_signature': True,
                'verify_aud': True,
                'verify_iat': True,
                'verify_exp': True,
                'verify_nbf': True,
                'verify_iss': True,
                'verify_sub': True,
                'verify_jti': True,
                'verify_at_hash': True,
                'leeway': 0,
            }

    Returns:
        dict: The dict representation of the claims set, assuming the signature is valid
            and all requested data validation passes.

    Raises:
        JWTError: If the signature is invalid in any way.
        ExpiredSignatureError: If the signature has expired.
        JWTClaimsError: If any claim is invalid in any way.

    Examples:

        >>> payload = 'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJhIjoiYiJ9.jiMyrsmD8AoHWeQgmxZ5yq8z0lXS67_QGs52AzC8Ru8'
        >>> jwt.decode(payload, 'secret', algorithms='HS256')

    """

    defaults = {
        'verify_signature': True,
        'verify_aud': True,
        'verify_iat': True,
        'verify_exp': True,
        'verify_nbf': True,
        'verify_iss': True,
        'verify_sub': True,
        'verify_jti': True,
        'verify_at_hash': True,
        'leeway': 0,
    }

    if options:
        defaults.update(options)

    verify_signature = defaults.get('verify_signature', True)

    try:
        payload = jws.verify(token, key, algorithms, verify=verify_signature)
    except JWSError as e:
        raise JWTError(e)

    # Needed for at_hash verification
    algorithm = jws.get_unverified_header(token)['alg']

    try:
        claims = json.loads(payload.decode('utf-8'))
    except ValueError as e:
        raise JWTError('Invalid payload string: %s' % e)

    if not isinstance(claims, Mapping):
        raise JWTError('Invalid payload string: must be a json object')

    _validate_claims(claims, audience=audience, issuer=issuer,
                     subject=subject, algorithm=algorithm,
                     access_token=access_token,
                     options=defaults)

    return claims


def get_unverified_header(token):
    """Returns the decoded headers without verification of any kind.

    Args:
        token (str): A signed JWT to decode the headers from.

    Returns:
        dict: The dict representation of the token headers.

    Raises:
        JWTError: If there is an exception decoding the token.
    """
    try:
        headers = jws.get_unverified_headers(token)
    except Exception:
        raise JWTError('Error decoding token headers.')

    return headers


def get_unverified_headers(token):
    """Returns the decoded headers without verification of any kind.

    This is simply a wrapper of get_unverified_header() for backwards
    compatibility.

    Args:
        token (str): A signed JWT to decode the headers from.

    Returns:
        dict: The dict representation of the token headers.

    Raises:
        JWTError: If there is an exception decoding the token.
    """
    return get_unverified_header(token)


def get_unverified_claims(token):
    """Returns the decoded claims without verification of any kind.

    Args:
        token (str): A signed JWT to decode the headers from.

    Returns:
        dict: The dict representation of the token claims.

    Raises:
        JWTError: If there is an exception decoding the token.
    """
    try:
        claims = jws.get_unverified_claims(token)
    except Exception:
        raise JWTError('Error decoding token claims.')

    try:
        claims = json.loads(claims.decode('utf-8'))
    except ValueError as e:
        raise JWTError('Invalid claims string: %s' % e)

    if not isinstance(claims, Mapping):
        raise JWTError('Invalid claims string: must be a json object')

    return claims


def _validate_iat(claims):
    """Validates that the 'iat' claim is valid.

    The "iat" (issued at) claim identifies the time at which the JWT was
    issued.  This claim can be used to determine the age of the JWT.  Its
    value MUST be a number containing a NumericDate value.  Use of this
    claim is OPTIONAL.

    Args:
        claims (dict): The claims dictionary to validate.
    """

    if 'iat' not in claims:
        return

    try:
        int(claims['iat'])
    except ValueError:
        raise JWTClaimsError('Issued At claim (iat) must be an integer.')


def _validate_nbf(claims, leeway=0):
    """Validates that the 'nbf' claim is valid.

    The "nbf" (not before) claim identifies the time before which the JWT
    MUST NOT be accepted for processing.  The processing of the "nbf"
    claim requires that the current date/time MUST be after or equal to
    the not-before date/time listed in the "nbf" claim.  Implementers MAY
    provide for some small leeway, usually no more than a few minutes, to
    account for clock skew.  Its value MUST be a number containing a
    NumericDate value.  Use of this claim is OPTIONAL.

    Args:
        claims (dict): The claims dictionary to validate.
        leeway (int): The number of seconds of skew that is allowed.
    """

    if 'nbf' not in claims:
        return

    try:
        nbf = int(claims['nbf'])
    except ValueError:
        raise JWTClaimsError('Not Before claim (nbf) must be an integer.')

    now = timegm(datetime.utcnow().utctimetuple())

    if nbf > (now + leeway):
        raise JWTClaimsError('The token is not yet valid (nbf)')


def _validate_exp(claims, leeway=0):
    """Validates that the 'exp' claim is valid.

    The "exp" (expiration time) claim identifies the expiration time on
    or after which the JWT MUST NOT be accepted for processing.  The
    processing of the "exp" claim requires that the current date/time
    MUST be before the expiration date/time listed in the "exp" claim.
    Implementers MAY provide for some small leeway, usually no more than
    a few minutes, to account for clock skew.  Its value MUST be a number
    containing a NumericDate value.  Use of this claim is OPTIONAL.

    Args:
        claims (dict): The claims dictionary to validate.
        leeway (int): The number of seconds of skew that is allowed.
    """

    if 'exp' not in claims:
        return

    try:
        exp = int(claims['exp'])
    except ValueError:
        raise JWTClaimsError('Expiration Time claim (exp) must be an integer.')

    now = timegm(datetime.utcnow().utctimetuple())

    if exp < (now - leeway):
        raise ExpiredSignatureError('Signature has expired.')


def _validate_aud(claims, audience=None):
    """Validates that the 'aud' claim is valid.

    The "aud" (audience) claim identifies the recipients that the JWT is
    intended for.  Each principal intended to process the JWT MUST
    identify itself with a value in the audience claim.  If the principal
    processing the claim does not identify itself with a value in the
    "aud" claim when this claim is present, then the JWT MUST be
    rejected.  In the general case, the "aud" value is an array of case-
    sensitive strings, each containing a StringOrURI value.  In the
    special case when the JWT has one audience, the "aud" value MAY be a
    single case-sensitive string containing a StringOrURI value.  The
    interpretation of audience values is generally application specific.
    Use of this claim is OPTIONAL.

    Args:
        claims (dict): The claims dictionary to validate.
        audience (str): The audience that is verifying the token.
    """

    if 'aud' not in claims:
        # if audience:
        #     raise JWTError('Audience claim expected, but not in claims')
        return

    audience_claims = claims['aud']
    if isinstance(audience_claims, string_types):
        audience_claims = [audience_claims]
    if not isinstance(audience_claims, list):
        raise JWTClaimsError('Invalid claim format in token')
    if any(not isinstance(c, string_types) for c in audience_claims):
        raise JWTClaimsError('Invalid claim format in token')
    if audience not in audience_claims:
        raise JWTClaimsError('Invalid audience')


def _validate_iss(claims, issuer=None):
    """Validates that the 'iss' claim is valid.

    The "iss" (issuer) claim identifies the principal that issued the
    JWT.  The processing of this claim is generally application specific.
    The "iss" value is a case-sensitive string containing a StringOrURI
    value.  Use of this claim is OPTIONAL.

    Args:
        claims (dict): The claims dictionary to validate.
        issuer (str or iterable): Acceptable value(s) for the issuer that
                                  signed the token.
    """

    if issuer is not None:
        if isinstance(issuer, string_types):
            issuer = (issuer,)
        if claims.get('iss') not in issuer:
            raise JWTClaimsError('Invalid issuer')


def _validate_sub(claims, subject=None):
    """Validates that the 'sub' claim is valid.

    The "sub" (subject) claim identifies the principal that is the
    subject of the JWT.  The claims in a JWT are normally statements
    about the subject.  The subject value MUST either be scoped to be
    locally unique in the context of the issuer or be globally unique.
    The processing of this claim is generally application specific.  The
    "sub" value is a case-sensitive string containing a StringOrURI
    value.  Use of this claim is OPTIONAL.

    Args:
        claims (dict): The claims dictionary to validate.
        subject (str): The subject of the token.
    """

    if 'sub' not in claims:
        return

    if not isinstance(claims['sub'], string_types):
        raise JWTClaimsError('Subject must be a string.')

    if subject is not None:
        if claims.get('sub') != subject:
            raise JWTClaimsError('Invalid subject')


def _validate_jti(claims):
    """Validates that the 'jti' claim is valid.

    The "jti" (JWT ID) claim provides a unique identifier for the JWT.
    The identifier value MUST be assigned in a manner that ensures that
    there is a negligible probability that the same value will be
    accidentally assigned to a different data object; if the application
    uses multiple issuers, collisions MUST be prevented among values
    produced by different issuers as well.  The "jti" claim can be used
    to prevent the JWT from being replayed.  The "jti" value is a case-
    sensitive string.  Use of this claim is OPTIONAL.

    Args:
        claims (dict): The claims dictionary to validate.
    """
    if 'jti' not in claims:
        return

    if not isinstance(claims['jti'], string_types):
        raise JWTClaimsError('JWT ID must be a string.')


def _validate_at_hash(claims, access_token, algorithm):
    """
    Validates that the 'at_hash' parameter included in the claims matches
    with the access_token returned alongside the id token as part of
    the authorization_code flow.

    Args:
        claims (dict): The claims dictionary to validate.
        access_token (str): The access token returned by the OpenID Provider.
        algorithm (str): The algorithm used to sign the JWT, as specified by
            the token headers.
    """
    if 'at_hash' not in claims and not access_token:
        return
    elif 'at_hash' in claims and not access_token:
        msg = 'No access_token provided to compare against at_hash claim.'
        raise JWTClaimsError(msg)
    elif access_token and 'at_hash' not in claims:
        msg = 'at_hash claim missing from token.'
        raise JWTClaimsError(msg)

    try:
        expected_hash = calculate_at_hash(access_token,
                                          ALGORITHMS.HASHES[algorithm])
    except (TypeError, ValueError):
        msg = 'Unable to calculate at_hash to verify against token claims.'
        raise JWTClaimsError(msg)

    if claims['at_hash'] != expected_hash:
        raise JWTClaimsError('at_hash claim does not match access_token.')


def _validate_claims(claims, audience=None, issuer=None, subject=None,
                     algorithm=None, access_token=None, options=None):

    leeway = options.get('leeway', 0)

    if isinstance(leeway, timedelta):
        leeway = timedelta_total_seconds(leeway)

    if not isinstance(audience, (string_types, type(None))):
        raise JWTError('audience must be a string or None')

    if options.get('verify_iat'):
        _validate_iat(claims)

    if options.get('verify_nbf'):
        _validate_nbf(claims, leeway=leeway)

    if options.get('verify_exp'):
        _validate_exp(claims, leeway=leeway)

    if options.get('verify_aud'):
        _validate_aud(claims, audience=audience)

    if options.get('verify_iss'):
        _validate_iss(claims, issuer=issuer)

    if options.get('verify_sub'):
        _validate_sub(claims, subject=subject)

    if options.get('verify_jti'):
        _validate_jti(claims)

    if options.get('verify_at_hash'):
        _validate_at_hash(claims, access_token, algorithm)
