discourse/app/models/screened_email.rb

# frozen_string_literal: true

# A ScreenedEmail record represents an email address that is being watched,
# typically when creating a new User account. If the email of the signup form
# (or some other form) matches a ScreenedEmail record, an action can be
# performed based on the action_type.
class ScreenedEmail < ActiveRecord::Base
  include ScreeningModel

  default_action :block

  validates :email, presence: true, uniqueness: true

  before_save :downcase_email

  def downcase_email
    self.email = email.downcase
  end

  def self.canonical(email)
    name, domain = email.split("@", 2)
    name = name.gsub(/\+.*/, "")
    name = name.gsub(".", "") if %w[gmail.com googlemail.com].include?(domain.downcase)
    "#{name}@#{domain}".downcase
  end

  def self.block(email, opts = {})
    email = canonical(email)
    find_by_email(email) || create!(opts.slice(:action_type, :ip_address).merge(email: email))
  end

  def self.should_block?(email)
    email = canonical(email)

    screened_emails = ScreenedEmail.order(created_at: :desc).limit(100)

    distances = {}
    screened_emails.each do |se|
      distances[se.email] = levenshtein(se.email.downcase, email.downcase)
    end

    max_distance = SiteSetting.levenshtein_distance_spammer_emails
    screened_email =
      screened_emails
        .select { |se| distances[se.email] <= max_distance }
        .sort { |se| distances[se.email] }
        .first

    screened_email.record_match! if screened_email

    screened_email.try(:action_type) == actions[:block]
  end

  def self.levenshtein(first, second)
    matrix = [(0..first.length).to_a]
    (1..second.length).each { |j| matrix << [j] + [0] * (first.length) }

    (1..second.length).each do |i|
      (1..first.length).each do |j|
        if first[j - 1] == second[i - 1]
          matrix[i][j] = matrix[i - 1][j - 1]
        else
          matrix[i][j] = [matrix[i - 1][j], matrix[i][j - 1], matrix[i - 1][j - 1]].min + 1
        end
      end
    end
    matrix.last.last
  end
end

# == Schema Information
#
# Table name: screened_emails
#
#  id            :integer          not null, primary key
#  email         :string           not null
#  action_type   :integer          not null
#  match_count   :integer          default(0), not null
#  last_match_at :datetime
#  created_at    :datetime         not null
#  updated_at    :datetime         not null
#  ip_address    :inet
#
# Indexes
#
#  index_screened_emails_on_email          (email) UNIQUE
#  index_screened_emails_on_last_match_at  (last_match_at)
#