#!/usr/bin/env python
# Copyright 2022 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.

"""Pluggable Credentials.
Pluggable Credentials are initialized using external_account arguments which
are typically loaded from third-party executables. 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.

Example credential_source for pluggable credential:
{
    "executable": {
        "command": "/path/to/get/credentials.sh --arg1=value1 --arg2=value2",
        "timeout_millis": 5000,
        "output_file": "/path/to/generated/cached/credentials"
    }
}
"""

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

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

# The max supported executable spec version.
EXECUTABLE_SUPPORTED_MAX_VERSION = 1

EXECUTABLE_TIMEOUT_MILLIS_DEFAULT = 30 * 1000  # 30 seconds
EXECUTABLE_TIMEOUT_MILLIS_LOWER_BOUND = 5 * 1000  # 5 seconds
EXECUTABLE_TIMEOUT_MILLIS_UPPER_BOUND = 120 * 1000  # 2 minutes

EXECUTABLE_INTERACTIVE_TIMEOUT_MILLIS_LOWER_BOUND = 30 * 1000  # 30 seconds
EXECUTABLE_INTERACTIVE_TIMEOUT_MILLIS_UPPER_BOUND = 30 * 60 * 1000  # 30 minutes


class Credentials(external_account.Credentials):
    """External account credentials sourced from executables."""

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

        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 pluggable credential:

                    {
                        "executable": {
                            "command": "/path/to/get/credentials.sh --arg1=value1 --arg2=value2",
                            "timeout_millis": 5000,
                            "output_file": "/path/to/generated/cached/credentials"
                        }
                    }
            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.
            google.auth.exceptions.InvalidValue: For invalid parameters.
            google.auth.exceptions.MalformedError: 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.
        """

        self.interactive = kwargs.pop("interactive", False)
        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_executable = None
            raise exceptions.MalformedError(
                "Missing credential_source. The credential_source is not a dict."
            )
        self._credential_source_executable = credential_source.get("executable")
        if not self._credential_source_executable:
            raise exceptions.MalformedError(
                "Missing credential_source. An 'executable' must be provided."
            )
        self._credential_source_executable_command = self._credential_source_executable.get(
            "command"
        )
        self._credential_source_executable_timeout_millis = self._credential_source_executable.get(
            "timeout_millis"
        )
        self._credential_source_executable_interactive_timeout_millis = self._credential_source_executable.get(
            "interactive_timeout_millis"
        )
        self._credential_source_executable_output_file = self._credential_source_executable.get(
            "output_file"
        )

        # Dummy value. This variable is only used via injection, not exposed to ctor
        self._tokeninfo_username = ""

        if not self._credential_source_executable_command:
            raise exceptions.MalformedError(
                "Missing command field. Executable command must be provided."
            )
        if not self._credential_source_executable_timeout_millis:
            self._credential_source_executable_timeout_millis = (
                EXECUTABLE_TIMEOUT_MILLIS_DEFAULT
            )
        elif (
            self._credential_source_executable_timeout_millis
            < EXECUTABLE_TIMEOUT_MILLIS_LOWER_BOUND
            or self._credential_source_executable_timeout_millis
            > EXECUTABLE_TIMEOUT_MILLIS_UPPER_BOUND
        ):
            raise exceptions.InvalidValue("Timeout must be between 5 and 120 seconds.")

        if self._credential_source_executable_interactive_timeout_millis:
            if (
                self._credential_source_executable_interactive_timeout_millis
                < EXECUTABLE_INTERACTIVE_TIMEOUT_MILLIS_LOWER_BOUND
                or self._credential_source_executable_interactive_timeout_millis
                > EXECUTABLE_INTERACTIVE_TIMEOUT_MILLIS_UPPER_BOUND
            ):
                raise exceptions.InvalidValue(
                    "Interactive timeout must be between 30 seconds and 30 minutes."
                )

    @_helpers.copy_docstring(external_account.Credentials)
    def retrieve_subject_token(self, request):
        self._validate_running_mode()

        # Check output file.
        if self._credential_source_executable_output_file is not None:
            try:
                with open(
                    self._credential_source_executable_output_file, encoding="utf-8"
                ) as output_file:
                    response = json.load(output_file)
            except Exception:
                pass
            else:
                try:
                    # If the cached response is expired, _parse_subject_token will raise an error which will be ignored and we will call the executable again.
                    subject_token = self._parse_subject_token(response)
                    if (
                        "expiration_time" not in response
                    ):  # Always treat missing expiration_time as expired and proceed to executable run.
                        raise exceptions.RefreshError
                except (exceptions.MalformedError, exceptions.InvalidValue):
                    raise
                except exceptions.RefreshError:
                    pass
                else:
                    return subject_token

        if not _helpers.is_python_3():
            raise exceptions.RefreshError(
                "Pluggable auth is only supported for python 3.7+"
            )

        # Inject env vars.
        env = os.environ.copy()
        self._inject_env_variables(env)
        env["GOOGLE_EXTERNAL_ACCOUNT_REVOKE"] = "0"

        # Run executable.
        exe_timeout = (
            self._credential_source_executable_interactive_timeout_millis / 1000
            if self.interactive
            else self._credential_source_executable_timeout_millis / 1000
        )
        exe_stdin = sys.stdin if self.interactive else None
        exe_stdout = sys.stdout if self.interactive else subprocess.PIPE
        exe_stderr = sys.stdout if self.interactive else subprocess.STDOUT

        result = subprocess.run(
            self._credential_source_executable_command.split(),
            timeout=exe_timeout,
            stdin=exe_stdin,
            stdout=exe_stdout,
            stderr=exe_stderr,
            env=env,
        )
        if result.returncode != 0:
            raise exceptions.RefreshError(
                "Executable exited with non-zero return code {}. Error: {}".format(
                    result.returncode, result.stdout
                )
            )

        # Handle executable output.
        response = json.loads(result.stdout.decode("utf-8")) if result.stdout else None
        if not response and self._credential_source_executable_output_file is not None:
            response = json.load(
                open(self._credential_source_executable_output_file, encoding="utf-8")
            )

        subject_token = self._parse_subject_token(response)
        return subject_token

    def revoke(self, request):
        """Revokes the subject token using the credential_source object.

        Args:
            request (google.auth.transport.Request): A callable used to make
                HTTP requests.
        Raises:
            google.auth.exceptions.RefreshError: If the executable revocation
                not properly executed.

        """
        if not self.interactive:
            raise exceptions.InvalidValue(
                "Revoke is only enabled under interactive mode."
            )
        self._validate_running_mode()

        if not _helpers.is_python_3():
            raise exceptions.RefreshError(
                "Pluggable auth is only supported for python 3.7+"
            )

        # Inject variables
        env = os.environ.copy()
        self._inject_env_variables(env)
        env["GOOGLE_EXTERNAL_ACCOUNT_REVOKE"] = "1"

        # Run executable
        result = subprocess.run(
            self._credential_source_executable_command.split(),
            timeout=self._credential_source_executable_interactive_timeout_millis
            / 1000,
            stdout=subprocess.PIPE,
            stderr=subprocess.STDOUT,
            env=env,
        )

        if result.returncode != 0:
            raise exceptions.RefreshError(
                "Auth revoke failed on executable. Exit with non-zero return code {}. Error: {}".format(
                    result.returncode, result.stdout
                )
            )

        response = json.loads(result.stdout.decode("utf-8"))
        self._validate_revoke_response(response)

    @property
    def external_account_id(self):
        """Returns the external account identifier.

        When service account impersonation is used the identifier is the service
        account email.

        Without service account impersonation, this returns None, unless it is
        being used by the Google Cloud CLI which populates this field.
        """

        return self.service_account_email or self._tokeninfo_username

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

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

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

        Raises:
            google.auth.exceptions.InvalidValue: For invalid parameters.
            google.auth.exceptions.MalformedError: For invalid parameters.
        """
        return super(Credentials, cls).from_info(info, **kwargs)

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

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

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

    def _inject_env_variables(self, env):
        env["GOOGLE_EXTERNAL_ACCOUNT_AUDIENCE"] = self._audience
        env["GOOGLE_EXTERNAL_ACCOUNT_TOKEN_TYPE"] = self._subject_token_type
        env["GOOGLE_EXTERNAL_ACCOUNT_ID"] = self.external_account_id
        env["GOOGLE_EXTERNAL_ACCOUNT_INTERACTIVE"] = "1" if self.interactive else "0"

        if self._service_account_impersonation_url is not None:
            env[
                "GOOGLE_EXTERNAL_ACCOUNT_IMPERSONATED_EMAIL"
            ] = self.service_account_email
        if self._credential_source_executable_output_file is not None:
            env[
                "GOOGLE_EXTERNAL_ACCOUNT_OUTPUT_FILE"
            ] = self._credential_source_executable_output_file

    def _parse_subject_token(self, response):
        self._validate_response_schema(response)
        if not response["success"]:
            if "code" not in response or "message" not in response:
                raise exceptions.MalformedError(
                    "Error code and message fields are required in the response."
                )
            raise exceptions.RefreshError(
                "Executable returned unsuccessful response: code: {}, message: {}.".format(
                    response["code"], response["message"]
                )
            )
        if "expiration_time" in response and response["expiration_time"] < time.time():
            raise exceptions.RefreshError(
                "The token returned by the executable is expired."
            )
        if "token_type" not in response:
            raise exceptions.MalformedError(
                "The executable response is missing the token_type field."
            )
        if (
            response["token_type"] == "urn:ietf:params:oauth:token-type:jwt"
            or response["token_type"] == "urn:ietf:params:oauth:token-type:id_token"
        ):  # OIDC
            return response["id_token"]
        elif response["token_type"] == "urn:ietf:params:oauth:token-type:saml2":  # SAML
            return response["saml_response"]
        else:
            raise exceptions.RefreshError("Executable returned unsupported token type.")

    def _validate_revoke_response(self, response):
        self._validate_response_schema(response)
        if not response["success"]:
            raise exceptions.RefreshError("Revoke failed with unsuccessful response.")

    def _validate_response_schema(self, response):
        if "version" not in response:
            raise exceptions.MalformedError(
                "The executable response is missing the version field."
            )
        if response["version"] > EXECUTABLE_SUPPORTED_MAX_VERSION:
            raise exceptions.RefreshError(
                "Executable returned unsupported version {}.".format(
                    response["version"]
                )
            )

        if "success" not in response:
            raise exceptions.MalformedError(
                "The executable response is missing the success field."
            )

    def _validate_running_mode(self):
        env_allow_executables = os.environ.get(
            "GOOGLE_EXTERNAL_ACCOUNT_ALLOW_EXECUTABLES"
        )
        if env_allow_executables != "1":
            raise exceptions.MalformedError(
                "Executables need to be explicitly allowed (set GOOGLE_EXTERNAL_ACCOUNT_ALLOW_EXECUTABLES to '1') to run."
            )

        if self.interactive and not self._credential_source_executable_output_file:
            raise exceptions.MalformedError(
                "An output_file must be specified in the credential configuration for interactive mode."
            )

        if (
            self.interactive
            and not self._credential_source_executable_interactive_timeout_millis
        ):
            raise exceptions.InvalidOperation(
                "Interactive mode cannot run without an interactive timeout."
            )

        if self.interactive and not self.is_workforce_pool:
            raise exceptions.InvalidValue(
                "Interactive mode is only enabled for workforce pool."
            )

    def _create_default_metrics_options(self):
        metrics_options = super(Credentials, self)._create_default_metrics_options()
        metrics_options["source"] = "executable"
        return metrics_options
