Ruby on Rails code explainers

class WeeklySignupsReport
  DEFAULT_WEEKS = 12
 
  def initialize(weeks: DEFAULT_WEEKS, source: User.all)

class ApplicationController < ActionController::Base
  EXPERIMENTS = {
    checkout_button_color: %w[control blue green],
    onboarding_flow: %w[control streamlined]

class Coupon < ApplicationRecord
  has_many :redemptions, dependent: :destroy
 
  validates :code, presence: true, uniqueness: { case_sensitive: false }

class AdminConstraint
  def self.matches?(request)
    new(request).matches?
  end

class ReverseGeocodeSignupJob < ApplicationJob
  queue_as :default
 
  retry_on Geocoder::OverQueryLimitError, wait: 5.minutes, attempts: 3

class SyncInventoryJob < ApplicationJob
  queue_as :integrations
 
  retry_on Faraday::TimeoutError,

module MarkdownHelper
  ALLOWED_TAGS = %w[
    p br strong em del a ul ol li blockquote code pre
    h1 h2 h3 h4 h5 h6 hr img table thead tbody tr th td

class ActivityFeed
  include Enumerable
 
  Entry = Struct.new(:record, :type, :occurred_at, keyword_init: true) do

class Current < ActiveSupport::CurrentAttributes
  attribute :user, :request_id, :user_agent, :ip_address
 
  resets { Time.zone = nil }

class Category < ApplicationRecord
  belongs_to :parent, class_name: "Category", optional: true
  has_many :children,
           -> { order(:position) },

class ReportingQuery
  def initialize(scope = ApplicationRecord)
    @scope = scope
  end

class WeatherLookup
  Result = Struct.new(:temperature, :conditions, keyword_init: true)
 
  class TimeoutError < StandardError; end

class Post < ApplicationRecord
  belongs_to :author, counter_cache: false
  has_many :comments, dependent: :destroy
end

namespace :active_storage do
  desc "Purge blobs that have been unattached for more than 48 hours"
  task purge_stale: :environment do
    cutoff = 48.hours.ago

class Article < ApplicationRecord
  belongs_to :author
  has_many :taggings, dependent: :destroy
  has_many :tags, through: :taggings

class ApplicationController < ActionController::Base
  INACTIVITY_TIMEOUT = 30.minutes
 
  before_action :expire_stale_session

class ChatChannel < ApplicationCable::Channel
  periodically :sweep_stale_typists, every: 3.seconds
 
  def subscribed

class Author < ApplicationRecord
  has_many :posts
 
  scope :with_post_stats, -> {