module PublicBodyDerivedFields

    extend ActiveSupport::Concern

    included do
        before_save :set_first_letter

        # When name or short name is changed, also change the url name
        def short_name=(short_name)
            super
            update_url_name
        end

        def name=(name)
            super
            update_url_name
        end

    end

    # Return the short name if present, or else long name
    def short_or_long_name
        if self.short_name.nil? || self.short_name.empty?
            self.name.nil? ? "" : self.name
        else
            self.short_name
        end
    end

    # Set the first letter, which is used for faster queries
    def set_first_letter
        unless name.blank?
            # we use a regex to ensure it works with utf-8/multi-byte
            first_letter = Unicode.upcase name.scan(/^./mu)[0]
            if first_letter != self.first_letter
                self.first_letter = first_letter
            end
        end
    end

    def update_url_name
        if changed.include?('name') || changed.include?('short_name')
            self.url_name = MySociety::Format.simplify_url_part(self.short_or_long_name, 'body')
        end
    end

end