Thoughts on improvements to the Vanity developer interface

[bensheldon]

I wanted to document the helper that I've been using in my projects with Vanity. The intentions behind it:

• Allow Vanity to be easily used outside of controllers (e.g. in jobs and scripts)
• Be easier to differentiate between whether or not someone is a participant experiment, and then what treatment group they're in. This is frequently used for multipage experiments in which we don't want to add someone to an experiment if they've already passed one of the earlier pages in a flow.

class VanityDispatcher
  attr_reader :id

  def initialize(id = nil)
    @id = id
  end

  def track!(metric_name)
    within_context { Vanity.track!(metric_name) }
  end

  def ab_test(experiment_id)
    within_context { Vanity.ab_test(experiment_id) }
  end

  def within_context
    old_context = Vanity.context
    context = OpenStruct.new(vanity_identity: id)

    Vanity.context = context
    result = yield
    Vanity.context = old_context

    result
  end

  def experiment_participant?(experiment_id)
    Vanity.playground.participant_info(id).any? { |info| info[0].id == experiment_id }
  end

  def self.in_experiment_treatment_group?(experiment_id:, user:)
    return unless VanityDispatcher.new(user.vanity_id).experiment_participant?(experiment_id)

    VanityDispatcher.new(user.vanity_id).ab_test(experiment_id)
  end
end

This allows more simple usage, e.g.:

VanityDispatcher.new(user.vanity_id).ab_test  #or 
VanityDispatcher.new(user.vanity_id).track 

It's not the best interface as-is, but the main intention was to avoid having to wrap things manually with Vanity.context as well as be able to use a vanity id directly, rather than pass an object.