# Copyright 2011 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.

require 'aws/naming'

module AWS

  # @private
  module Cacheable

    # @private
    class NoData < StandardError; end

    def self.included base
      base.extend Naming unless base.respond_to?(:service_ruby_name)
    end

    # @private
    protected
    def local_cache_key
      raise NotImplementedError
    end

    # @private
    protected
    def cache_key
      @cache_key ||= begin
        endpoint_method = self.class.service_ruby_name + "_endpoint"
        config.signer.access_key_id + ":" +
          config.send(endpoint_method) + ":" +
          self.class.name + ":" +
          local_cache_key
      end
    end

    # @private
    public
    def retrieve_attribute attr, &block

      if cache = AWS.response_cache

        if cache.resource_cache.cached?(cache_key, attr.name)
          return cache.resource_cache.get(cache_key, attr.name)
        end

        cache.select(*attr.request_types).each do |response|
          if attributes = attributes_from_response(response)
            cache.resource_cache.store(cache_key, attributes)
            return attributes[attr.name] if attributes.key?(attr.name)
          end
        end

      end

      response = yield

      if attributes = attributes_from_response(response)
        if cache = AWS.response_cache
          cache.resource_cache.store(cache_key, attributes)
        end
        attributes[attr.name] if attributes.key?(attr.name)
      else
        raise NoData.new("no data in #{response.request_type} response")
      end
    end

  end

end