intercession.rb

class Intercession

  # Duh.
  VERSION = "3.0.0"

  def initialize app, behavior
    @app      = app
    @behavior = behavior
    @after    = @behavior.instance_methods.map(&:to_s).include? "after"
  end

  def call env
    if session = env["rack.session"]
      session.extend @behavior
    end

    result = @app.call env
    session.after if @after

    result
  end
end