Ruby code explainers

require "csv"
 
class SalesReport
  def initialize(path)

module DurationFormatter
  UNITS = [
    ['week', 604_800],
    ['day', 86_400],

class Comment < ApplicationRecord
  belongs_to :post
  belongs_to :author, class_name: "User"
 

require 'json'
require 'set'
 
class SensitiveScrubber

class ReportBatcher
  BATCH_SIZE = 500
 
  def initialize(account)

class Comment < ApplicationRecord
  belongs_to :commentable, polymorphic: true, counter_cache: true
  belongs_to :author, class_name: "User"
 

class SessionsController < ApplicationController
  MAX_ATTEMPTS = 5
  THROTTLE_WINDOW = 15.minutes
 

class ProductsController < ApplicationController
  def index
    @products = Product
      .includes(:category, :brand)

module LogParser
  class AccessLogStreamer
    SEVERITY_PATTERN = /\b(ERROR|WARN|FATAL)\b/
 

class HostnameValidator < ActiveModel::EachValidator
  MAX_LENGTH = 253
  LABEL = /\A(?!-)[a-z0-9-]{1,63}(?<!-)\z/i
 

class PaymentsController < ApplicationController
  before_action :require_idempotency_key
 
  def create

class Survey < ApplicationRecord
  has_many :questions, dependent: :destroy
  has_many :respondents, dependent: :nullify
 

class OrderConfirmationJob < ApplicationJob
  queue_as :mailers
 
  retry_on Net::OpenTimeout, wait: :polynomially_longer, attempts: 5

module SoftDeletable
  extend ActiveSupport::Concern
 
  included do

class Post < ApplicationRecord
  before_validation :generate_slug, on: :create
 
  validates :slug, presence: true, uniqueness: true

module TextAnalysis
  module_function
 
  WORD_PATTERN = /[\p{Alpha}']+/

module Fibonacci
  CACHE = Hash.new do |cache, n|
    cache[n] = cache[n - 1] + cache[n - 2]
  end

class EventEmitter
  def initialize
    @listeners = Hash.new { |hash, key| hash[key] = [] }
  end