Blocks that know where their towel is.

floodwall.rb

# Rails.configuration.permit_automated_emails = true

class Floodwall
  def initialize(context, bypass = false, **data, &action)
    @context = context
    @data = OpenStruct.new(data || {})
    @permit = Rails.configuration.permit_automated_emails || bypass || false

    Rails.logger.warn { 'Floodwall has been bypassed and will allow emails through' } if bypass

    process(action)
  end

  private

  def permitted?
    @permit
  end

  attr_reader :context
  attr_reader :permit, :data

  def gate
    return if permitted?

    raise FloodwallBreachedError
  end

  def process(action)
    gate

    Rails.logger.debug { 'Floodwall is permitting emails' }

    mod = Module.new
    mod.send(:define_method, :try_send, action)

    extend(mod)
  end
end

floodwall_breached_error.rb

class FloodwallBreachedError < StandardError
  def initialize(msg: 'Floodwall was breached')
    super(msg)
  end
end

usage_example_01.rb

=begin

  Floodwall.new(self) do

    MyAppMailer.
      delay.
      emailering('foo', 123)

  end.try_send

=end

usage_example_02.rb

=begin

  Floodwall.new(self) do

    MyAppMailer.
      delay.
      processering_emailinator

  end.try_send

=end

usage_example_03.rb

=begin

  # This mailer was being invoked from a nested module that references the
  # parent class. That's kind of an awkward situation to metaprogram for
  # without going down a rabbithole. Just added note to expose the instance
  # variable via an attr. In the meantime reference the class variable manually.
  Floodwall.new(self) do

    thing = context.instance_variable_get(:@thing)

    MyAppMailer.
      delay.
      processering(thing)

  end.try_send

=end

usage_example_04.rb

=begin

  Floodwall.new(self) do

    ::SomeUpstreamConst.
      delay(queue: 'optimus_prime').
      public_send(template, *context.mailer[:params])

  end.try_send if success? # Don't try to send unless necessary

=end