You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: signature_sheet.rb
    path of file: ./repos/consuldemocracy/app/models
    
    the code of the file until where you have to start completion: class SignatureSheet < ApplicationRecord
  belongs_to :signable, polymorphic: true
  belongs_to :author, class_name: "User"

  VALID_SIGNABLES = %w[Proposal Budget::Investment].freeze

  has_many :signatures

  validates :author, presence: true
  validates :signable_type, inclusion: { in: ->(*) { VALID_SIGNABLES }}
  validates :required_fields_to_verify, presence: true
  validates :signable, presence: true
  validate  :signable_found

  def name
    if title.present?
      "#{signable_name} #{signable_id}: #{title}"
    else
      "#{signable_name} #{signable_id}"

    
  def verify_signatures
    parsed_required_fields_to_verify_groups.each do |required_fields_to_verify|
      document_number = required_fields_to_verify[0]
      date_of_birth = parse_date_of_birth(required_fields_to_verify)
      postal_code = parse_postal_code(required_fields_to_verify)

      signature = signatures.where(document_number: document_number,
                                   date_of_birth: date_of_birth,
                                   postal_code: postal_code).first_or_create!
      signature.verify
    end
    update!(processed: true)
  end

  def parsed_required_fields_to_verify_groups
    required_fields_to_verify.split(/[;]/).map { |d| d.gsub(/\s+/, "") }.map { |group| group.split(/[,]/) }
  end

  def signable_found
    errors.add(:signable_id, :not_found) if errors.messages[:signable].present?
  end

  private

    def parse_date_of_birth(required_fields_to_verify)
      return required_fields_to_verify[1] if Setting.force_presence_date_of_birth?

      nil
    end

    def parse_postal_code(required_fields_to_verify)
      if Setting.force_presence_date_of_birth? && Setting.force_presence_postal_code?
        required_fields_to_verify[2]
      elsif Setting.force_presence_postal_code?
        required_fields_to_verify[1]
      else
        nil
      end
    end