#!/usr/bin/env python
# Copyright 2020 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.

"""Identity Pool Credentials.

This module provides credentials to access Google Cloud resources from on-prem
or non-Google Cloud platforms which support external credentials (e.g. OIDC ID
tokens) retrieved from local file locations or local servers. This includes
Microsoft Azure and OIDC identity providers (e.g. K8s workloads registered with
Hub with Hub workload identity enabled).

These credentials are recommended over the use of service account credentials
in on-prem/non-Google Cloud platforms as they do not involve the management of
long-live service account private keys.

Identity Pool Credentials are initialized using external_account
arguments which are typically loaded from an external credentials file or
an external credentials URL. Unlike other Credentials that can be initialized
with a list of explicit arguments, secrets or credentials, external account
clients use the environment and hints/guidelines provided by the
external_account JSON file to retrieve credentials and exchange them for Google
access tokens.
"""

try:
    from collections.abc import Mapping
# Python 2.7 compatibility
except ImportError:  # pragma: NO COVER
    from collections import Mapping
import io
import json
import os

from google.auth import _helpers
from google.auth import exceptions
from google.auth import external_account


class Credentials(external_account.Credentials):
    """External account credentials sourced from files and URLs."""

    def __init__(
        self,
        audience,
        subject_token_type,
        token_url,
        credential_source,
        *args,
        **kwargs
    ):
        """Instantiates an external account credentials object from a file/URL.

        Args:
            audience (str): The STS audience field.
            subject_token_type (str): The subject token type.
            token_url (str): The STS endpoint URL.
            credential_source (Mapping): The credential source dictionary used to
                provide instructions on how to retrieve external credential to be
                exchanged for Google access tokens.

                Example credential_source for url-sourced credential::

                    {
                        "url": "http://www.example.com",
                        "format": {
                            "type": "json",
                            "subject_token_field_name": "access_token",
                        },
                        "headers": {"foo": "bar"},
                    }

                Example credential_source for file-sourced credential::

                    {
                        "file": "/path/to/token/file.txt"
                    }
            args (List): Optional positional arguments passed into the underlying :meth:`~external_account.Credentials.__init__` method.
            kwargs (Mapping): Optional keyword arguments passed into the underlying :meth:`~external_account.Credentials.__init__` method.

        Raises:
            google.auth.exceptions.RefreshError: If an error is encountered during
                access token retrieval logic.
            ValueError: For invalid parameters.

        .. note:: Typically one of the helper constructors
            :meth:`from_file` or
            :meth:`from_info` are used instead of calling the constructor directly.
        """

        super(Credentials, self).__init__(
            audience=audience,
            subject_token_type=subject_token_type,
            token_url=token_url,
            credential_source=credential_source,
            *args,
            **kwargs
        )
        if not isinstance(credential_source, Mapping):
            self._credential_source_file = None
            self._credential_source_url = None
        else:
            self._credential_source_file = credential_source.get("file")
            self._credential_source_url = credential_source.get("url")
            self._credential_source_headers = credential_source.get("headers")
            credential_source_format = credential_source.get("format", {})
            # Get credential_source format type. When not provided, this
            # defaults to text.
            self._credential_source_format_type = (
                credential_source_format.get("type") or "text"
            )
            # environment_id is only supported in AWS or dedicated future external
            # account credentials.
            if "environment_id" in credential_source:
                raise exceptions.MalformedError(
                    "Invalid Identity Pool credential_source field 'environment_id'"
                )
            if self._credential_source_format_type not in ["text", "json"]:
                raise exceptions.MalformedError(
                    "Invalid credential_source format '{}'".format(
                        self._credential_source_format_type
                    )
                )
            # For JSON types, get the required subject_token field name.
            if self._credential_source_format_type == "json":
                self._credential_source_field_name = credential_source_format.get(
                    "subject_token_field_name"
                )
                if self._credential_source_field_name is None:
                    raise exceptions.MalformedError(
                        "Missing subject_token_field_name for JSON credential_source format"
                    )
            else:
                self._credential_source_field_name = None

        if self._credential_source_file and self._credential_source_url:
            raise exceptions.MalformedError(
                "Ambiguous credential_source. 'file' is mutually exclusive with 'url'."
            )
        if not self._credential_source_file and not self._credential_source_url:
            raise exceptions.MalformedError(
                "Missing credential_source. A 'file' or 'url' must be provided."
            )

    @_helpers.copy_docstring(external_account.Credentials)
    def retrieve_subject_token(self, request):
        return self._parse_token_data(
            self._get_token_data(request),
            self._credential_source_format_type,
            self._credential_source_field_name,
        )

    def _get_token_data(self, request):
        if self._credential_source_file:
            return self._get_file_data(self._credential_source_file)
        else:
            return self._get_url_data(
                request, self._credential_source_url, self._credential_source_headers
            )

    def _get_file_data(self, filename):
        if not os.path.exists(filename):
            raise exceptions.RefreshError("File '{}' was not found.".format(filename))

        with io.open(filename, "r", encoding="utf-8") as file_obj:
            return file_obj.read(), filename

    def _get_url_data(self, request, url, headers):
        response = request(url=url, method="GET", headers=headers)

        # support both string and bytes type response.data
        response_body = (
            response.data.decode("utf-8")
            if hasattr(response.data, "decode")
            else response.data
        )

        if response.status != 200:
            raise exceptions.RefreshError(
                "Unable to retrieve Identity Pool subject token", response_body
            )

        return response_body, url

    def _parse_token_data(
        self, token_content, format_type="text", subject_token_field_name=None
    ):
        content, filename = token_content
        if format_type == "text":
            token = content
        else:
            try:
                # Parse file content as JSON.
                response_data = json.loads(content)
                # Get the subject_token.
                token = response_data[subject_token_field_name]
            except (KeyError, ValueError):
                raise exceptions.RefreshError(
                    "Unable to parse subject_token from JSON file '{}' using key '{}'".format(
                        filename, subject_token_field_name
                    )
                )
        if not token:
            raise exceptions.RefreshError(
                "Missing subject_token in the credential_source file"
            )
        return token

    @classmethod
    def from_info(cls, info, **kwargs):
        """Creates an Identity Pool Credentials instance from parsed external account info.

        Args:
            info (Mapping[str, str]): The Identity Pool external account info in Google
                format.
            kwargs: Additional arguments to pass to the constructor.

        Returns:
            google.auth.identity_pool.Credentials: The constructed
                credentials.

        Raises:
            ValueError: For invalid parameters.
        """
        return super(Credentials, cls).from_info(info, **kwargs)

    @classmethod
    def from_file(cls, filename, **kwargs):
        """Creates an IdentityPool Credentials instance from an external account json file.

        Args:
            filename (str): The path to the IdentityPool external account json file.
            kwargs: Additional arguments to pass to the constructor.

        Returns:
            google.auth.identity_pool.Credentials: The constructed
                credentials.
        """
        return super(Credentials, cls).from_file(filename, **kwargs)
