# Copyright 2016 Google Inc.
#
# 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.

"""Provides helper methods for talking to the Compute Engine metadata server.

See https://cloud.google.com/compute/docs/metadata for more details.
"""

import datetime
import json
import logging
import os

import six
from six.moves import http_client
from six.moves.urllib import parse as urlparse

from google.auth import _helpers
from google.auth import environment_vars
from google.auth import exceptions

_LOGGER = logging.getLogger(__name__)

_METADATA_ROOT = 'http://{}/computeMetadata/v1/'.format(
    os.getenv(environment_vars.GCE_METADATA_ROOT, 'metadata.google.internal'))

# This is used to ping the metadata server, it avoids the cost of a DNS
# lookup.
_METADATA_IP_ROOT = 'http://{}'.format(
    os.getenv(environment_vars.GCE_METADATA_IP, '169.254.169.254'))
_METADATA_FLAVOR_HEADER = 'metadata-flavor'
_METADATA_FLAVOR_VALUE = 'Google'
_METADATA_HEADERS = {_METADATA_FLAVOR_HEADER: _METADATA_FLAVOR_VALUE}

# Timeout in seconds to wait for the GCE metadata server when detecting the
# GCE environment.
try:
    _METADATA_DEFAULT_TIMEOUT = int(os.getenv('GCE_METADATA_TIMEOUT', 3))
except ValueError:  # pragma: NO COVER
    _METADATA_DEFAULT_TIMEOUT = 3


def ping(request, timeout=_METADATA_DEFAULT_TIMEOUT, retry_count=3):
    """Checks to see if the metadata server is available.

    Args:
        request (google.auth.transport.Request): A callable used to make
            HTTP requests.
        timeout (int): How long to wait for the metadata server to respond.
        retry_count (int): How many times to attempt connecting to metadata
            server using above timeout.

    Returns:
        bool: True if the metadata server is reachable, False otherwise.
    """
    # NOTE: The explicit ``timeout`` is a workaround. The underlying
    #       issue is that resolving an unknown host on some networks will take
    #       20-30 seconds; making this timeout short fixes the issue, but
    #       could lead to false negatives in the event that we are on GCE, but
    #       the metadata resolution was particularly slow. The latter case is
    #       "unlikely".
    retries = 0
    while retries < retry_count:
        try:
            response = request(
                url=_METADATA_IP_ROOT, method='GET', headers=_METADATA_HEADERS,
                timeout=timeout)

            metadata_flavor = response.headers.get(_METADATA_FLAVOR_HEADER)
            return (response.status == http_client.OK and
                    metadata_flavor == _METADATA_FLAVOR_VALUE)

        except exceptions.TransportError:
            _LOGGER.info('Compute Engine Metadata server unavailable on'
                         'attempt %s of %s', retries+1, retry_count)
            retries += 1

    return False


def get(request, path, root=_METADATA_ROOT, recursive=False):
    """Fetch a resource from the metadata server.

    Args:
        request (google.auth.transport.Request): A callable used to make
            HTTP requests.
        path (str): The resource to retrieve. For example,
            ``'instance/service-accounts/default'``.
        root (str): The full path to the metadata server root.
        recursive (bool): Whether to do a recursive query of metadata. See
            https://cloud.google.com/compute/docs/metadata#aggcontents for more
            details.

    Returns:
        Union[Mapping, str]: If the metadata server returns JSON, a mapping of
            the decoded JSON is return. Otherwise, the response content is
            returned as a string.

    Raises:
        google.auth.exceptions.TransportError: if an error occurred while
            retrieving metadata.
    """
    base_url = urlparse.urljoin(root, path)
    query_params = {}

    if recursive:
        query_params['recursive'] = 'true'

    url = _helpers.update_query(base_url, query_params)

    response = request(url=url, method='GET', headers=_METADATA_HEADERS)

    if response.status == http_client.OK:
        content = _helpers.from_bytes(response.data)
        if response.headers['content-type'] == 'application/json':
            try:
                return json.loads(content)
            except ValueError as caught_exc:
                new_exc = exceptions.TransportError(
                    'Received invalid JSON from the Google Compute Engine'
                    'metadata service: {:.20}'.format(content))
                six.raise_from(new_exc, caught_exc)
        else:
            return content
    else:
        raise exceptions.TransportError(
            'Failed to retrieve {} from the Google Compute Engine'
            'metadata service. Status: {} Response:\n{}'.format(
                url, response.status, response.data), response)


def get_project_id(request):
    """Get the Google Cloud Project ID from the metadata server.

    Args:
        request (google.auth.transport.Request): A callable used to make
            HTTP requests.

    Returns:
        str: The project ID

    Raises:
        google.auth.exceptions.TransportError: if an error occurred while
            retrieving metadata.
    """
    return get(request, 'project/project-id')


def get_service_account_info(request, service_account='default'):
    """Get information about a service account from the metadata server.

    Args:
        request (google.auth.transport.Request): A callable used to make
            HTTP requests.
        service_account (str): The string 'default' or a service account email
            address. The determines which service account for which to acquire
            information.

    Returns:
        Mapping: The service account's information, for example::

            {
                'email': '...',
                'scopes': ['scope', ...],
                'aliases': ['default', '...']
            }

    Raises:
        google.auth.exceptions.TransportError: if an error occurred while
            retrieving metadata.
    """
    return get(
        request,
        'instance/service-accounts/{0}/'.format(service_account),
        recursive=True)


def get_service_account_token(request, service_account='default'):
    """Get the OAuth 2.0 access token for a service account.

    Args:
        request (google.auth.transport.Request): A callable used to make
            HTTP requests.
        service_account (str): The string 'default' or a service account email
            address. The determines which service account for which to acquire
            an access token.

    Returns:
        Union[str, datetime]: The access token and its expiration.

    Raises:
        google.auth.exceptions.TransportError: if an error occurred while
            retrieving metadata.
    """
    token_json = get(
        request,
        'instance/service-accounts/{0}/token'.format(service_account))
    token_expiry = _helpers.utcnow() + datetime.timedelta(
        seconds=token_json['expires_in'])
    return token_json['access_token'], token_expiry
