# 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.

require 'mongo/operation/commands/aggregate/result'

module Mongo
  module Operation

    # A MongoDB aggregate operation.
    #
    # @note An aggregate operation can behave like a read and return a 
    #   result set, or can behave like a write operation and
    #   output results to a user-specified collection.
    #
    # @example Create the aggregate operation.
    #   Aggregate.new({
    #     :selector => {
    #       :aggregate => 'test_coll', :pipeline => [{ '$out' => 'test-out' }]
    #     },
    #     :db_name => 'test_db'
    #   })
    #
    # Initialization:
    #   param [ Hash ] spec The specifications for the operation.
    #
    #   option spec :selector [ Hash ] The aggregate selector.
    #   option spec :db_name [ String ] The name of the database on which
    #     the operation should be executed.
    #   option spec :options [ Hash ] Options for the aggregate command.
    #
    # @since 2.0.0
    class Aggregate
      include Specifiable
      include Limited
      include Executable
      include ReadPreference

      private

      def query_coll
        Database::COMMAND
      end

      def filter_selector(context)
        return selector if context.features.write_command_enabled?
        selector.reject{ |option, value| option.to_s == 'cursor' }
      end

      def update_selector(context)
        if context.mongos? && read_pref = read.to_mongos
          sel = selector[:$query] ? filter_selector(context) : { :$query => filter_selector(context) }
          sel.merge(:$readPreference => read_pref)
        else
          filter_selector(context)
        end
      end
    end
  end
end