module DataMapper
  module Aggregates
    module DataObjectsAdapter
      extend Chainable

      def aggregate(query)
        fields = query.fields
        types  = fields.map { |p| p.respond_to?(:operator) ? String : p.dump_class }

        field_size = fields.size

        records = []

        with_connection do |connection|
          statement, bind_values = select_statement(query)

          command = connection.create_command(statement)
          command.set_types(types)

          reader = command.execute_reader(*bind_values)

          begin
            while reader.next!
              row = fields.zip(reader.values).map do |field, value|
                if field.respond_to?(:operator)
                  send(field.operator, field.target, value)
                else
                  field.load(value)
                end
              end

              records << ((field_size > 1) ? row : row[0])
            end
          ensure
            reader.close
          end
        end

        records
      end

      private def count(_property, value)
        value.to_i
      end

      private def min(property, value)
        property.load(value)
      end

      private def max(property, value)
        property.load(value)
      end

      private def avg(property, value)
        property.dump_class.equal?(::Integer) ? value.to_f : property.load(value)
      end

      private def sum(property, value)
        property.load(value)
      end

      chainable do
        def property_to_column_name(property, qualify)
          case property
          when DataMapper::Query::Operator
            aggregate_field_statement(property.operator, property.target, qualify)

          when Property, DataMapper::Query::Path
            super

          else
            raise ArgumentError, '+property+ must be a DataMapper::Query::Operator, a DataMapper::Property or a Query::Path, but was a ' \
                                 "#{property.class} (#{property.inspect})"
          end
        end
      end

      private def aggregate_field_statement(aggregate_function, property, qualify)
        column_name = if aggregate_function == :count && property == :all
                        '*'
                      else
                        property_to_column_name(property, qualify)
                      end

        function_name = case aggregate_function
                        when :count then 'COUNT'
                        when :min   then 'MIN'
                        when :max   then 'MAX'
                        when :avg   then 'AVG'
                        when :sum   then 'SUM'
                        else raise "Invalid aggregate function: #{aggregate_function.inspect}"
                        end

        "#{function_name}(#{column_name})"
      end
    end
  end
end