Add ability to block words in usernames (#35407)

app/models/username_block.rb

@@ -0,0 +1,62 @@
+# frozen_string_literal: true
+
+# == Schema Information
+#
+# Table name: username_blocks
+#
+#  id                  :bigint(8)        not null, primary key
+#  allow_with_approval :boolean          default(FALSE), not null
+#  exact               :boolean          default(FALSE), not null
+#  normalized_username :string           not null
+#  username            :string           not null
+#  created_at          :datetime         not null
+#  updated_at          :datetime         not null
+#
+
+class UsernameBlock < ApplicationRecord
+  HOMOGLYPHS = {
+    '1' => 'i',
+    '2' => 'z',
+    '3' => 'e',
+    '4' => 'a',
+    '5' => 's',
+    '7' => 't',
+    '8' => 'b',
+    '9' => 'g',
+    '0' => 'o',
+  }.freeze
+
+  validates :username, presence: true, uniqueness: true
+
+  scope :matches_exactly, ->(str) { where(exact: true).where(normalized_username: str) }
+  scope :matches_partially, ->(str) { where(exact: false).where(Arel::Nodes.build_quoted(str).matches(Arel::Nodes.build_quoted('%').concat(arel_table[:normalized_username]).concat(Arel::Nodes.build_quoted('%')))) }
+
+  before_save :set_normalized_username
+
+  def comparison
+    exact? ? 'equals' : 'contains'
+  end
+
+  def comparison=(val)
+    self.exact = val == 'equals'
+  end
+
+  def self.matches?(str, allow_with_approval: false)
+    normalized_str = str.downcase.gsub(Regexp.union(HOMOGLYPHS.keys), HOMOGLYPHS)
+    where(allow_with_approval: allow_with_approval).matches_exactly(normalized_str).or(matches_partially(normalized_str)).any?
+  end
+
+  def to_log_human_identifier
+    username
+  end
+
+  private
+
+  def set_normalized_username
+    self.normalized_username = normalize(username)
+  end
+
+  def normalize(str)
+    str.downcase.gsub(Regexp.union(HOMOGLYPHS.keys), HOMOGLYPHS)
+  end
+end