simple_middleware_pipeline.rb

pipeline = []

define_method :use, -> middleware do
  pipeline.unshift(middleware)
end

class One
  def initialize(app)
    @app = app
  end

  def call(env)
    env[:one] = '1'
    @app.call(env)
  end
end

class Two
  def initialize(app)
    @app = app
  end

  def call(env)
    env[:two] = '2'
    @app.call(env)
  end
end

class Three
  def initialize(_app)
  end

  def call(env)
    env[:three] = '3'
  end
end

use One
use Two
use Three

app = nil
pipeline.each do |middleware|
  app = middleware.new(app)
end
env = {start: :ok}
app.call(env)
p env