# Copyright 2014 Amazon.com, Inc. or its affiliates. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License"). You
# may not use this file except in compliance with the License. A copy of
# the License is located at
#
# http://aws.amazon.com/apache2.0/
#
# or in the "license" file accompanying this file. This file 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.
"""Resolves regions and endpoints.

This module implements endpoint resolution, including resolving endpoints for a
given service and region and resolving the available endpoints for a service
in a specific AWS partition.
"""
import logging
import re

from ooscore.exceptions import NoRegionError

LOG = logging.getLogger(__name__)
DEFAULT_URI_TEMPLATE = '{service}.{region}.{dnsSuffix}'
DEFAULT_SERVICE_DATA = {'endpoints': {}}


class BaseEndpointResolver(object):
    """Resolves regions and endpoints. Must be subclassed."""
    def construct_endpoint(self, service_name, region_name=None):
        """Resolves an endpoint for a service and region combination.

        :type service_name: string
        :param service_name: Name of the service to resolve an endpoint for
            (e.g., s3)

        :type region_name: string
        :param region_name: Region/endpoint name to resolve (e.g., us-east-1)
            if no region is provided, the first found partition-wide endpoint
            will be used if available.

        :rtype: dict
        :return: Returns a dict containing the following keys:
            - partition: (string, required) Resolved partition name
            - endpointName: (string, required) Resolved endpoint name
            - hostname: (string, required) Hostname to use for this endpoint
            - sslCommonName: (string) sslCommonName to use for this endpoint.
            - credentialScope: (dict) Signature version 4 credential scope
              - region: (string) region name override when signing.
              - service: (string) service name override when signing.
            - signatureVersions: (list<string>) A list of possible signature
              versions, including s3, v4, v2, and s3v4
            - protocols: (list<string>) A list of supported protocols
              (e.g., http, https)
            - ...: Other keys may be included as well based on the metadata
        """
        raise NotImplementedError

    def get_available_partitions(self):
        """Lists the partitions available to the endpoint resolver.

        :return: Returns a list of partition names (e.g., ["aws", "aws-cn"]).
        """
        raise NotImplementedError

    def get_available_endpoints(self, service_name, partition_name='aws',
                                allow_non_regional=False):
        """Lists the endpoint names of a particular partition.

        :type service_name: string
        :param service_name: Name of a service to list endpoint for (e.g., s3)

        :type partition_name: string
        :param partition_name: Name of the partition to limit endpoints to.
            (e.g., aws for the public AWS endpoints, aws-cn for AWS China
            endpoints, aws-us-gov for AWS GovCloud (US) Endpoints, etc.

        :type allow_non_regional: bool
        :param allow_non_regional: Set to True to include endpoints that are
             not regional endpoints (e.g., s3-external-1,
             fips-us-gov-west-1, etc).
        :return: Returns a list of endpoint names (e.g., ["us-east-1"]).
        """
        raise NotImplementedError


class EndpointResolver(BaseEndpointResolver):
    """Resolves endpoints based on partition endpoint metadata"""
    def __init__(self, endpoint_data):
        """
        :param endpoint_data: A dict of partition data.
        """
        if 'partitions' not in endpoint_data:
            raise ValueError('Missing "partitions" in endpoint data')
        self._endpoint_data = endpoint_data

    def get_available_partitions(self):
        result = []
        for partition in self._endpoint_data['partitions']:
            result.append(partition['partition'])
        return result

    def get_available_endpoints(self, service_name, partition_name='aws',
                                allow_non_regional=False):
        result = []
        for partition in self._endpoint_data['partitions']:
            if partition['partition'] != partition_name:
                continue
            services = partition['services']
            if service_name not in services:
                continue
            for endpoint_name in services[service_name]['endpoints']:
                if allow_non_regional or endpoint_name in partition['regions']:
                    result.append(endpoint_name)
        return result

    def construct_endpoint(self, service_name, region_name=None):
        # Iterate over each partition until a match is found.
        for partition in self._endpoint_data['partitions']:
            result = self._endpoint_for_partition(
                partition, service_name, region_name)
            if result:
                return result

    def _endpoint_for_partition(self, partition, service_name, region_name):
        # Get the service from the partition, or an empty template.
        service_data = partition['services'].get(
            service_name, DEFAULT_SERVICE_DATA)
        # Use the partition endpoint if no region is supplied.
        if region_name is None:
            if 'partitionEndpoint' in service_data:
                region_name = service_data['partitionEndpoint']
            else:
                raise NoRegionError()
        # Attempt to resolve the exact region for this partition.
        if region_name in service_data['endpoints']:
            return self._resolve(
                partition, service_name, service_data, region_name)
        # Check to see if the endpoint provided is valid for the partition.
        if self._region_match(partition, region_name):
            # Use the partition endpoint if set and not regionalized.
            partition_endpoint = service_data.get('partitionEndpoint')
            is_regionalized = service_data.get('isRegionalized', True)
            if partition_endpoint and not is_regionalized:
                LOG.debug('Using partition endpoint for %s, %s: %s',
                          service_name, region_name, partition_endpoint)
                return self._resolve(
                    partition, service_name, service_data, partition_endpoint)
            LOG.debug('Creating a regex based endpoint for %s, %s',
                      service_name, region_name)
            return self._resolve(
                partition, service_name, service_data, region_name)

    def _region_match(self, partition, region_name):
        if region_name in partition['regions']:
            return True
        if 'regionRegex' in partition:
            return re.compile(partition['regionRegex']).match(region_name)
        return False

    def _resolve(self, partition, service_name, service_data, endpoint_name):
        result = service_data['endpoints'].get(endpoint_name, {})
        result['partition'] = partition['partition']
        result['endpointName'] = endpoint_name
        # Merge in the service defaults then the partition defaults.
        self._merge_keys(service_data.get('defaults', {}), result)
        self._merge_keys(partition.get('defaults', {}), result)
        hostname = result.get('hostname', DEFAULT_URI_TEMPLATE)
        result['hostname'] = self._expand_template(
            partition, result['hostname'], service_name, endpoint_name)
        if 'sslCommonName' in result:
            result['sslCommonName'] = self._expand_template(
                partition, result['sslCommonName'], service_name,
                endpoint_name)
        result['dnsSuffix'] = partition['dnsSuffix']
        return result

    def _merge_keys(self, from_data, result):
        for key in from_data:
            if key not in result:
                result[key] = from_data[key]

    def _expand_template(self, partition, template, service_name,
                         endpoint_name):
        return template.format(
            service=service_name, region=endpoint_name,
            dnsSuffix=partition['dnsSuffix'])
