# Copyright (C) 2014-2015 MongoDB, 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.

module Mongo
  module Operation
    module Read
      class ListCollections

        # Defines custom behaviour of results when using the
        # listCollections command.
        #
        # @since 2.0.0
        class Result < Operation::Result

          # The field name for the cursor document in a listCollections result.
          #
          # @since 2.0.0
          CURSOR = 'cursor'.freeze

          # The cursor id field in the cursor document.
          #
          # @since 2.0.0
          CURSOR_ID = 'id'.freeze

          # The namespace field in the cursor document.
          #
          # @since 2.0.0
          NAMESPACE = 'ns'.freeze

          # The field name for the first batch of a cursor.
          #
          # @since 2.0.0
          FIRST_BATCH = 'firstBatch'.freeze

          # Get the cursor id for the result.
          #
          # @example Get the cursor id.
          #   result.cursor_id
          #
          # @note Even though the wire protocol has a cursor_id field for all
          #   messages of type reply, it is always zero when using the
          #   listCollections command and must be retrieved from the cursor
          #   document itself.
          #
          # @return [ Integer ] The cursor id.
          #
          # @since 2.0.0
          def cursor_id
            cursor_document ? cursor_document[CURSOR_ID] : super
          end

          # Get the namespace for the cursor.
          #
          # @example Get the namespace.
          #   result.namespace
          #
          # @return [ String ] The namespace.
          #
          # @since 2.0.0
          def namespace
            cursor_document ? cursor_document[NAMESPACE] : super
          end

          # Get the documents for the listCollections result. It is the 'firstBatch'
          #   field in the 'cursor' field of the first document returned.
          #
          # @example Get the documents.
          #   result.documents
          #
          # @return [ Array<BSON::Document> ] The documents.
          #
          # @since 2.0.0
          def documents
            cursor_document[FIRST_BATCH]
          end

          # Validate the result. In the case where an unauthorized client tries
          # to run the command we need to generate the proper error.
          #
          # @example Validate the result.
          #   result.validate!
          #
          # @return [ Result ] Self if successful.
          #
          # @since 2.0.0
          def validate!
            !successful? ? raise(Error::OperationFailure.new(parser.message)) : self
          end

          private

          def cursor_document
            @cursor_document ||= first_document[CURSOR]
          end

          def first_document
            @first_document ||= reply.documents[0]
          end
        end
      end
    end
  end
end