module Devise::Models::Confirmable::ClassMethods

def confirm_by_token(confirmation_token)

Options must have the confirmation_token
If the user is already confirmed, create an error for the user
If no user is found, returns a new user with an error.
Find a user by its confirmation token and try to confirm it. 
def confirm_by_token(confirmation_token)
  confirmable = find_or_initialize_with_error_by(:confirmation_token, confirmation_token)
  confirmable.confirm! if confirmable.persisted?
  confirmable
end

def confirmation_token

Generate a token checking if one does not already exist in the database. 
def confirmation_token
  generate_token(:confirmation_token)
end

def find_by_unconfirmed_email_with_errors(attributes = {})

Find a record for confirmation by unconfirmed email field 
def find_by_unconfirmed_email_with_errors(attributes = {})
  unconfirmed_required_attributes = confirmation_keys.map { |k| k == :email ? :unconfirmed_email : k }
  unconfirmed_attributes = attributes.symbolize_keys
  unconfirmed_attributes[:unconfirmed_email] = unconfirmed_attributes.delete(:email)
  find_or_initialize_with_errors(unconfirmed_required_attributes, unconfirmed_attributes, :not_found)
end

def send_confirmation_instructions(attributes={})

Options must contain the user email
field. If no user is found, returns a new user with an email not found error.
confirmation instructions to it. If not, try searching for a user by unconfirmed_email
Attempt to find a user by its email. If a record is found, send new 
def send_confirmation_instructions(attributes={})
  confirmable = find_by_unconfirmed_email_with_errors(attributes) if reconfirmable
  unless confirmable.try(:persisted?)
    confirmable = find_or_initialize_with_errors(confirmation_keys, attributes, :not_found)
  end
  confirmable.resend_confirmation_token if confirmable.persisted?
  confirmable
end