skill-assessment-app/app/validators/email_format_validator.rb

class EmailFormatValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    # EMAIL regex test
    # (comma seperated) [any word combo] AT [any word combo] DOT [2 or more]
    # me@no.yes.x == invalid
    # some.thing+two@sub.domain.name == valid

    results = value.to_s.split(',').map do |v|
      (v.strip =~ /^([\w\.%\+\-]+)@([\w\-]+\.)+([\w]{2,})$/i) || v.strip.blank?
    end

    if results.include?(false)
      record.errors[attribute] << (options[:message] || "is not formatted properly")
    end
  end
end