Ruby script for calculating the checksum of a 2..20 range integer following the 7-3-1 method. Estonian Bank Union / Eesti Pangaliit - Reference number / Viitenumber

reference_number_viitenumber_estonian_bank_union_eesti_pangaliit.rb

#!/usr/bin/env ruby
#
########################################################
#
# What is this?
#
# script can calculate the checksum of a 2..20 range integer following the 7-3-1 method. 
#
# Details
# 1. run on cli, script asks for number entry
# 2. calculates checksum
# 3. spits out original value and checksum
#
# Gossip
# This is the produce of a beginner ruby scripter, so any best-practice/bug-slashing/constructive 
# comments are more than # appreciated. I hope this will help implement the reference number 
# calculation more quickly for other starters than it took me.
#
# Credits
# def calc_ref_number is a translation of a php method from here:
# Estonian Bank Union / Eesti Pangaliit - Reference number / Viitenumber
# http://www.pangaliit.ee/en/settlements-and-standards/check-digit-calculator-of-domestic-account-number
#
############################################################

#### Methods

# for use on cli, not sure if the instance method is good practice, but it works
def get_value
	print '> '
	@value = gets.chomp
end

# Rescueing rather than regexing the check for an integer
# problems: 09, 08 trigger because they are interpreted as octal ( did not matter for use case)
def integer?(str)
	!!Integer(str) rescue false
end

# check if this a valid entry (length, integer)
# i dare you, make this shorter
def check_value(str)
	if integer?(str)
		puts 'Value is integer'

		#not sure if this is needed?
		@value = str

		case 
			when @value.length < 2
				puts "Value needs to be longer than 1"
				get_value
				check_value(@value)
			when @value.length > 19
				puts "Value needs to be shortern than 19"
				get_value
				check_value(@value)
			else
				puts "Alright, here's your Reference number"
				calc_ref_number(@value)
		end

	else 
		puts "Please enter a number"
		get_value
		check_value(@value)
	end
end

#do the actual calculation
def calc_ref_number(int)
	# split string of numbers and push it into array
	
	weight = [1,3,7]
	# associating sl and st with the integer value of the amount of digits
  sl = st = int.length
  total = 0

  # while lenght is higher than 0 and the last position on the string is higher than 0
  while sl > 0 && int[sl - 1]  >= '0'
  	# calculate the last digit's product with the associated member of the array
    total += subtotal = (int[st-1-sl].to_i * weight[ sl%3 ])
    sl = sl-1
  end
    kontrollnr = (total.to_f / 10).ceil * 10 - total
    puts int.to_s + kontrollnr.to_s
  	
end

#### Program
puts 'Calculate reference number'
puts
puts 'Enter value between 2 and 20'

get_value
check_value(@value)

maybe you could use regexp to validate the input:

def check_value(str)
    if /^[1-9]{1}[0-9]{1,18}$/.match(str) == nil
        puts "incorrect format."
    else 
        puts "do stuff"
    end
end

https://github.com/internetee/registry/blob/214b7e435defa623116b8f47a25232ab5f4db726/app/models/billing/reference_no/base.rb

Tested class for reference number generation.