module ComposableOperations
  class ComposedOperation < Operation

    class AutoConfiguringOperation < SimpleDelegator

      def initialize(operation_class, options = {})
        super(operation_class)
        @__options__ = options
      end

      def new(input = nil, options = {})
        options = Hash(__options__).merge(Hash(options))
        __getobj__.new(input, options)
      end

      protected

        attr_reader :__options__

    end

    class << self

      def operations
        [] + Array((super if defined? super)) + Array(@operations)
      end

      def use(operation, options = {})
        (@operations ||= []) << AutoConfiguringOperation.new(operation, options)
      end

      def compose(*operations, &block)
        raise ArgumentError, "Expects either an array of operations or a block with configuration instructions" unless !!block ^ !operations.empty?

        if block
          Class.new(self, &block)
        else
          Class.new(self) do
            operations.each do |operation|
              use operation
            end
          end
        end
      end

    end

    protected

      def execute
        self.class.operations.inject(input) do |data, operation_and_options|
          operation, options = *operation_and_options
          operation = operation.new(data, options)
          operation.perform

          if operation.failed?
            fail operation.message, operation.result, operation.backtrace
          elsif operation.halted?
            halt operation.message, operation.result
          end

          operation.result
        end
      end

  end
end