application_service.rb

class ApplicationService
  class ServiceValidation
    def initialize(opts = {})
      @method = opts[:method]
      @message = opts[:message]
      @exception = opts.fetch(:exception, Errors::ServiceError)
    end

    def validate
      unless yield @method
        raise_exception
      end
    end

    private

    def raise_exception
      raise @exception, @message
    end
  end

  class ModelValidation < ServiceValidation
    def initialize(opts = {})
      super(
        method: opts[:method],
        exception: Errors::ModelValidationError
      )
    end

    def validate
      super do |method|
        object = yield method
        valid = object.valid?
        @message = object.errors.full_messages.first

        valid
      end
    end
  end

  class << self
    def validations
      @validations ||= Array.new
    end

    def validates(method, message, exception = Errors::ServiceError)
      validations << ServiceValidation.new(
        method: method,
        message: message,
        exception: exception
      )
    end

    def validate_model(attribute)
      validations << ModelValidation.new(method: attribute)
    end
  end

  def validate
    self.class.validations.each do |validation|
      validation.validate do |method|
        send(method)
      end
    end
  end

  def perform
    validate
    yield if block_given?
  end
end