tootlab-mastodon/app/validators/existing_username_validator.rb

# frozen_string_literal: true

class ExistingUsernameValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    return if value.blank?

    usernames_and_domains = begin
      value.split(',').map do |str|
        username, domain = str.strip.gsub(/\A@/, '').split('@')
        domain = nil if TagManager.instance.local_domain?(domain)

        next if username.blank?

        [str, username, domain]
      end.compact
    end

    usernames_with_no_accounts = usernames_and_domains.filter_map do |(str, username, domain)|
      str unless Account.find_remote(username, domain)
    end

    if options[:multiple]
      record.errors.add(attribute, I18n.t('existing_username_validator.not_found_multiple', usernames: usernames_with_no_accounts.join(', '))) if usernames_with_no_accounts.any?
    else
      record.errors.add(attribute, I18n.t('existing_username_validator.not_found')) if usernames_with_no_accounts.any? || usernames_and_domains.size > 1
    end
  end
end