module Scrivito
  module RequestHomepage
    HOMEPAGE_ENV_KEY = "SCRIVITO_HOMEPAGE"

    def self.call(env)
      env[HOMEPAGE_ENV_KEY] ||= fetch_homepage(env)
    end

    private_class_method def self.fetch_homepage(env)
      callback_result = Scrivito::Configuration.choose_homepage_callback.call(env)
      if callback_result.is_a?(Scrivito::BasicObj)
        callback_result
      else
        raise "choose_homepage callback did not return an Obj. "\
          "Instead saw #{callback_result.class}."
      end
    end
  end
end