# Copyright 2016 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""OAuth 2.0 client.

This is a client for interacting with an OAuth 2.0 authorization server's
token endpoint.

For more information about the token endpoint, see
`Section 3.1 of rfc6749`_

.. _Section 3.1 of rfc6749: https://tools.ietf.org/html/rfc6749#section-3.2
"""

import datetime
import http.client as http_client
import json
import logging
import urllib

from google.auth import _exponential_backoff
from google.auth import _helpers
from google.auth import credentials
from google.auth import exceptions
from google.auth import jwt
from google.auth import metrics
from google.auth import transport

_LOGGER = logging.getLogger(__name__)

_URLENCODED_CONTENT_TYPE = "application/x-www-form-urlencoded"
_JSON_CONTENT_TYPE = "application/json"
_JWT_GRANT_TYPE = "urn:ietf:params:oauth:grant-type:jwt-bearer"
_REFRESH_GRANT_TYPE = "refresh_token"
_BLOCKING_REGIONAL_ACCESS_BOUNDARY_LOOKUP_TIMEOUT = 3


def _handle_error_response(response_data, retryable_error):
    """Translates an error response into an exception.

    Args:
        response_data (Mapping | str): The decoded response data.
        retryable_error Optional[bool]: A boolean indicating if an error is retryable.
            Defaults to False.

    Raises:
        google.auth.exceptions.RefreshError: The errors contained in response_data.
    """

    retryable_error = retryable_error if retryable_error else False

    if isinstance(response_data, str):
        raise exceptions.RefreshError(response_data, retryable=retryable_error)
    try:
        error_details = "{}: {}".format(
            response_data["error"], response_data.get("error_description")
        )
    # If no details could be extracted, use the response data.
    except (KeyError, ValueError):
        error_details = json.dumps(response_data)

    raise exceptions.RefreshError(
        error_details, response_data, retryable=retryable_error
    )


def _can_retry(status_code, response_data):
    """Checks if a request can be retried by inspecting the status code
    and response body of the request.

    Args:
        status_code (int): The response status code.
        response_data (Mapping | str): The decoded response data.

    Returns:
      bool: True if the response is retryable. False otherwise.
    """
    if status_code in transport.DEFAULT_RETRYABLE_STATUS_CODES:
        return True

    try:
        # For a failed response, response_body could be a string
        error_desc = response_data.get("error_description") or ""
        error_code = response_data.get("error") or ""

        if not isinstance(error_code, str) or not isinstance(error_desc, str):
            return False

        # Per Oauth 2.0 RFC https://www.rfc-editor.org/rfc/rfc6749.html#section-4.1.2.1
        # This is needed because a redirect will not return a 500 status code.
        retryable_error_descriptions = {
            "internal_failure",
            "server_error",
            "temporarily_unavailable",
        }

        if any(e in retryable_error_descriptions for e in (error_code, error_desc)):
            return True

    except AttributeError:
        pass

    return False


def _parse_expiry(response_data):
    """Parses the expiry field from a response into a datetime.

    Args:
        response_data (Mapping): The JSON-parsed response data.

    Returns:
        Optional[datetime]: The expiration or ``None`` if no expiration was
            specified.
    """
    expires_in = response_data.get("expires_in", None)

    if expires_in is not None:
        # Some services do not respect the OAUTH2.0 RFC and send expires_in as a
        # JSON String.
        if isinstance(expires_in, str):
            expires_in = int(expires_in)

        return _helpers.utcnow() + datetime.timedelta(seconds=expires_in)
    else:
        return None


def _token_endpoint_request_no_throw(
    request,
    token_uri,
    body,
    access_token=None,
    use_json=False,
    can_retry=True,
    headers=None,
    **kwargs
):
    """Makes a request to the OAuth 2.0 authorization server's token endpoint.
    This function doesn't throw on response errors.

    Args:
        request (google.auth.transport.Request): A callable used to make
            HTTP requests.
        token_uri (str): The OAuth 2.0 authorizations server's token endpoint
            URI.
        body (Mapping[str, str]): The parameters to send in the request body.
        access_token (Optional(str)): The access token needed to make the request.
        use_json (Optional(bool)): Use urlencoded format or json format for the
            content type. The default value is False.
        can_retry (bool): Enable or disable request retry behavior.
        headers (Optional[Mapping[str, str]]): The headers for the request.
        kwargs: Additional arguments passed on to the request method. The
            kwargs will be passed to `requests.request` method, see:
            https://docs.python-requests.org/en/latest/api/#requests.request.
            For example, you can use `cert=("cert_pem_path", "key_pem_path")`
            to set up client side SSL certificate, and use
            `verify="ca_bundle_path"` to set up the CA certificates for sever
            side SSL certificate verification.

    Returns:
        Tuple(bool, Mapping[str, str], Optional[bool]): A boolean indicating
          if the request is successful, a mapping for the JSON-decoded response
          data and in the case of an error a boolean indicating if the error
          is retryable.
    """
    if use_json:
        headers_to_use = {"Content-Type": _JSON_CONTENT_TYPE}
        body = json.dumps(body).encode("utf-8")
    else:
        headers_to_use = {"Content-Type": _URLENCODED_CONTENT_TYPE}
        body = urllib.parse.urlencode(body).encode("utf-8")

    if access_token:
        headers_to_use["Authorization"] = "Bearer {}".format(access_token)

    if headers:
        headers_to_use.update(headers)

    response_data = {}
    retryable_error = False

    retries = _exponential_backoff.ExponentialBackoff()
    for _ in retries:
        response = request(
            method="POST", url=token_uri, headers=headers_to_use, body=body, **kwargs
        )
        response_body = (
            response.data.decode("utf-8")
            if hasattr(response.data, "decode")
            else response.data
        )

        try:
            # response_body should be a JSON
            response_data = json.loads(response_body)
        except ValueError:
            response_data = response_body

        if response.status == http_client.OK:
            return True, response_data, None

        retryable_error = _can_retry(
            status_code=response.status, response_data=response_data
        )

        if not can_retry or not retryable_error:
            return False, response_data, retryable_error

    return False, response_data, retryable_error


def _token_endpoint_request(
    request,
    token_uri,
    body,
    access_token=None,
    use_json=False,
    can_retry=True,
    headers=None,
    **kwargs
):
    """Makes a request to the OAuth 2.0 authorization server's token endpoint.

    Args:
        request (google.auth.transport.Request): A callable used to make
            HTTP requests.
        token_uri (str): The OAuth 2.0 authorizations server's token endpoint
            URI.
        body (Mapping[str, str]): The parameters to send in the request body.
        access_token (Optional(str)): The access token needed to make the request.
        use_json (Optional(bool)): Use urlencoded format or json format for the
            content type. The default value is False.
        can_retry (bool): Enable or disable request retry behavior.
        headers (Optional[Mapping[str, str]]): The headers for the request.
        kwargs: Additional arguments passed on to the request method. The
            kwargs will be passed to `requests.request` method, see:
            https://docs.python-requests.org/en/latest/api/#requests.request.
            For example, you can use `cert=("cert_pem_path", "key_pem_path")`
            to set up client side SSL certificate, and use
            `verify="ca_bundle_path"` to set up the CA certificates for sever
            side SSL certificate verification.

    Returns:
        Mapping[str, str]: The JSON-decoded response data.

    Raises:
        google.auth.exceptions.RefreshError: If the token endpoint returned
            an error.
    """

    (
        response_status_ok,
        response_data,
        retryable_error,
    ) = _token_endpoint_request_no_throw(
        request,
        token_uri,
        body,
        access_token=access_token,
        use_json=use_json,
        can_retry=can_retry,
        headers=headers,
        **kwargs
    )
    if not response_status_ok:
        _handle_error_response(response_data, retryable_error)
    return response_data


def jwt_grant(request, token_uri, assertion, can_retry=True):
    """Implements the JWT Profile for OAuth 2.0 Authorization Grants.

    For more details, see `rfc7523 section 4`_.

    Args:
        request (google.auth.transport.Request): A callable used to make
            HTTP requests.
        token_uri (str): The OAuth 2.0 authorizations server's token endpoint
            URI.
        assertion (str): The OAuth 2.0 assertion.
        can_retry (bool): Enable or disable request retry behavior.

    Returns:
        Tuple[str, Optional[datetime], Mapping[str, str]]: The access token,
            expiration, and additional data returned by the token endpoint.

    Raises:
        google.auth.exceptions.RefreshError: If the token endpoint returned
            an error.

    .. _rfc7523 section 4: https://tools.ietf.org/html/rfc7523#section-4
    """
    body = {"assertion": assertion, "grant_type": _JWT_GRANT_TYPE}

    response_data = _token_endpoint_request(
        request,
        token_uri,
        body,
        can_retry=can_retry,
        headers={
            metrics.API_CLIENT_HEADER: metrics.token_request_access_token_sa_assertion()
        },
    )

    try:
        access_token = response_data["access_token"]
    except KeyError as caught_exc:
        new_exc = exceptions.RefreshError(
            "No access token in response.", response_data, retryable=False
        )
        raise new_exc from caught_exc

    expiry = _parse_expiry(response_data)

    return access_token, expiry, response_data


def call_iam_generate_id_token_endpoint(
    request,
    iam_id_token_endpoint,
    signer_email,
    audience,
    access_token,
    universe_domain=credentials.DEFAULT_UNIVERSE_DOMAIN,
):
    """Call iam.generateIdToken endpoint to get ID token.

    Args:
        request (google.auth.transport.Request): A callable used to make
            HTTP requests.
        iam_id_token_endpoint (str): The IAM ID token endpoint to use.
        signer_email (str): The signer email used to form the IAM
            generateIdToken endpoint.
        audience (str): The audience for the ID token.
        access_token (str): The access token used to call the IAM endpoint.
        universe_domain (str): The universe domain for the request. The
            default is ``googleapis.com``.

    Returns:
        Tuple[str, datetime]: The ID token and expiration.
    """
    body = {"audience": audience, "includeEmail": "true", "useEmailAzp": "true"}

    response_data = _token_endpoint_request(
        request,
        iam_id_token_endpoint.replace(
            credentials.DEFAULT_UNIVERSE_DOMAIN, universe_domain
        ).format(signer_email),
        body,
        access_token=access_token,
        use_json=True,
    )

    try:
        id_token = response_data["token"]
    except KeyError as caught_exc:
        new_exc = exceptions.RefreshError(
            "No ID token in response.", response_data, retryable=False
        )
        raise new_exc from caught_exc

    payload = jwt.decode(id_token, verify=False)
    expiry = _helpers.utcfromtimestamp(payload["exp"])

    return id_token, expiry


def id_token_jwt_grant(request, token_uri, assertion, can_retry=True):
    """Implements the JWT Profile for OAuth 2.0 Authorization Grants, but
    requests an OpenID Connect ID Token instead of an access token.

    This is a variant on the standard JWT Profile that is currently unique
    to Google. This was added for the benefit of authenticating to services
    that require ID Tokens instead of access tokens or JWT bearer tokens.

    Args:
        request (google.auth.transport.Request): A callable used to make
            HTTP requests.
        token_uri (str): The OAuth 2.0 authorization server's token endpoint
            URI.
        assertion (str): JWT token signed by a service account. The token's
            payload must include a ``target_audience`` claim.
        can_retry (bool): Enable or disable request retry behavior.

    Returns:
        Tuple[str, Optional[datetime], Mapping[str, str]]:
            The (encoded) Open ID Connect ID Token, expiration, and additional
            data returned by the endpoint.

    Raises:
        google.auth.exceptions.RefreshError: If the token endpoint returned
            an error.
    """
    body = {"assertion": assertion, "grant_type": _JWT_GRANT_TYPE}

    response_data = _token_endpoint_request(
        request,
        token_uri,
        body,
        can_retry=can_retry,
        headers={
            metrics.API_CLIENT_HEADER: metrics.token_request_id_token_sa_assertion()
        },
    )

    try:
        id_token = response_data["id_token"]
    except KeyError as caught_exc:
        new_exc = exceptions.RefreshError(
            "No ID token in response.", response_data, retryable=False
        )
        raise new_exc from caught_exc

    payload = jwt.decode(id_token, verify=False)
    expiry = _helpers.utcfromtimestamp(payload["exp"])

    return id_token, expiry, response_data


def _handle_refresh_grant_response(response_data, refresh_token):
    """Extract tokens from refresh grant response.

    Args:
        response_data (Mapping[str, str]): Refresh grant response data.
        refresh_token (str): Current refresh token.

    Returns:
        Tuple[str, str, Optional[datetime], Mapping[str, str]]: The access token,
            refresh token, expiration, and additional data returned by the token
            endpoint. If response_data doesn't have refresh token, then the current
            refresh token will be returned.

    Raises:
        google.auth.exceptions.RefreshError: If the token endpoint returned
            an error.
    """
    try:
        access_token = response_data["access_token"]
    except KeyError as caught_exc:
        new_exc = exceptions.RefreshError(
            "No access token in response.", response_data, retryable=False
        )
        raise new_exc from caught_exc

    refresh_token = response_data.get("refresh_token", refresh_token)
    expiry = _parse_expiry(response_data)

    return access_token, refresh_token, expiry, response_data


def refresh_grant(
    request,
    token_uri,
    refresh_token,
    client_id,
    client_secret,
    scopes=None,
    rapt_token=None,
    can_retry=True,
):
    """Implements the OAuth 2.0 refresh token grant.

    For more details, see `rfc678 section 6`_.

    Args:
        request (google.auth.transport.Request): A callable used to make
            HTTP requests.
        token_uri (str): The OAuth 2.0 authorizations server's token endpoint
            URI.
        refresh_token (str): The refresh token to use to get a new access
            token.
        client_id (str): The OAuth 2.0 application's client ID.
        client_secret (str): The Oauth 2.0 appliaction's client secret.
        scopes (Optional(Sequence[str])): Scopes to request. If present, all
            scopes must be authorized for the refresh token. Useful if refresh
            token has a wild card scope (e.g.
            'https://www.googleapis.com/auth/any-api').
        rapt_token (Optional(str)): The reauth Proof Token.
        can_retry (bool): Enable or disable request retry behavior.

    Returns:
        Tuple[str, str, Optional[datetime], Mapping[str, str]]: The access
            token, new or current refresh token, expiration, and additional data
            returned by the token endpoint.

    Raises:
        google.auth.exceptions.RefreshError: If the token endpoint returned
            an error.

    .. _rfc6748 section 6: https://tools.ietf.org/html/rfc6749#section-6
    """
    body = {
        "grant_type": _REFRESH_GRANT_TYPE,
        "client_id": client_id,
        "client_secret": client_secret,
        "refresh_token": refresh_token,
    }
    if scopes:
        body["scope"] = " ".join(scopes)
    if rapt_token:
        body["rapt"] = rapt_token

    response_data = _token_endpoint_request(
        request, token_uri, body, can_retry=can_retry
    )
    return _handle_refresh_grant_response(response_data, refresh_token)


def _lookup_regional_access_boundary(request, url, headers=None, fail_fast=False):
    """Implements the global lookup of a credential Regional Access Boundary.
    For the lookup, we send a request to the global lookup endpoint and then
    parse the response. Service account credentials, workload identity
    pools and workforce pools implementation may have Regional Access Boundaries configured.
    Args:
        request (google.auth.transport.Request): A callable used to make
            HTTP requests.
        url (str): The Regional Access Boundary lookup url.
        headers (Optional[Mapping[str, str]]): The headers for the request.
        fail_fast (bool): Whether the lookup should fail fast (uses a short timeout and no retries).
    Returns:
        Optional[Mapping[str,list|str]]: A dictionary containing
            "locations" as a list of allowed locations as strings and
            "encodedLocations" as a hex string.
            e.g:
            {
                "locations": [
                    "us-central1", "us-east1", "europe-west1", "asia-east1"
                ],
                "encodedLocations": "0xA30"
            }
    """

    response_data = _lookup_regional_access_boundary_request(
        request, url, headers=headers, fail_fast=fail_fast
    )
    if response_data is None:
        # Error was already logged by _lookup_regional_access_boundary_request
        return None

    if "encodedLocations" not in response_data:
        _LOGGER.error(
            "Regional Access Boundary response malformed: missing 'encodedLocations' key in %s",
            response_data,
        )
        return None
    return response_data


def _lookup_regional_access_boundary_request(
    request, url, can_retry=True, headers=None, fail_fast=False
):
    """Makes a request to the Regional Access Boundary lookup endpoint.

    Args:
        request (google.auth.transport.Request): A callable used to make
            HTTP requests.
        url (str): The Regional Access Boundary lookup url.
        can_retry (bool): Enable or disable request retry behavior. Defaults to true.
        headers (Optional[Mapping[str, str]]): The headers for the request.
        fail_fast (bool): Whether the lookup should fail fast (uses a short timeout and no retries).

    Returns:
        Optional[Mapping[str, str]]: The JSON-decoded response data on success, or None on failure.
    """
    (
        response_status_ok,
        response_data,
        retryable_error,
    ) = _lookup_regional_access_boundary_request_no_throw(
        request, url, can_retry=can_retry, headers=headers, fail_fast=fail_fast
    )
    if not response_status_ok:
        _LOGGER.warning(
            "Regional Access Boundary HTTP request failed after retries: response_data=%s, retryable_error=%s",
            response_data,
            retryable_error,
        )
        return None
    return response_data


def _lookup_regional_access_boundary_request_no_throw(
    request, url, can_retry=True, headers=None, fail_fast=False
):
    """Makes a request to the Regional Access Boundary lookup endpoint. This
        function doesn't throw on response errors.

    Args:
        request (google.auth.transport.Request): A callable used to make
            HTTP requests.
        url (str): The Regional Access Boundary lookup url.
        can_retry (bool): Enable or disable request retry behavior. Defaults to true.
        headers (Optional[Mapping[str, str]]): The headers for the request.
        fail_fast (bool): Whether the lookup should fail fast (uses a short timeout and no retries).

    Returns:
        Tuple(bool, Mapping[str, str], Optional[bool]): A boolean indicating
          if the request is successful, a mapping for the JSON-decoded response
          data and in the case of an error a boolean indicating if the error
          is retryable.
    """

    response_data = {}
    retryable_error = False

    timeout = _BLOCKING_REGIONAL_ACCESS_BOUNDARY_LOOKUP_TIMEOUT if fail_fast else None
    total_attempts = 1 if fail_fast else 6
    retries = _exponential_backoff.ExponentialBackoff(total_attempts=total_attempts)

    for _ in retries:
        response = request(method="GET", url=url, headers=headers, timeout=timeout)
        response_body = (
            response.data.decode("utf-8")
            if hasattr(response.data, "decode")
            else response.data
        )

        try:
            # response_body should be a JSON
            response_data = json.loads(response_body)
        except ValueError:
            response_data = response_body

        if response.status == http_client.OK:
            return True, response_data, None

        retryable_error = _can_retry(
            status_code=response.status, response_data=response_data
        )
        # Add 502 (Bad Gateway) as a retryable error for RAB lookups.
        if response.status == http_client.BAD_GATEWAY:
            retryable_error = True

        if not can_retry or not retryable_error:
            return False, response_data, retryable_error

    return False, response_data, retryable_error
