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Finnish bank reference calculator in ruby
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# Array#sum is needed for nice code outside rails projects | |
require 'active_support' | |
require 'active_support/core_ext' | |
# Module for creating valid Finnish bank references | |
module FinnishBankRefence | |
# Generates reference from a input or a random number | |
def self.generate( base = rand(10**3..(10**19-1)) ) | |
if base < 10**3 or base >= 10**19 | |
raise ArgumentError, "Valid reference has 3..19 digits, #{base} has #{base.to_s.length}" | |
end | |
"#{base}#{checksum(base)}" | |
end | |
# Calculates Finnish bank reference checksum. | |
# Checksum is calculated from a sum where all digits are weighted with coefficient | |
# The coefficient is from 7,3,1 sequence starting from the smallest digit | |
# Checksum is the reverse of modulo10 which can be done with x = -y % 10 | |
# For example: "617435 4" | |
# 6 1 7 4 3 5 4 | |
# 1 3 7 1 3 7 | |
# 6 3 49 4 9 35 = 106 → 4 | |
# | |
# Source http://tarkistusmerkit.teppovuori.fi/tarkmerk.htm#viitenumero | |
def self.checksum(base) | |
weighted_sum = base.to_s.reverse.each_char.with_index.map { |digit,index| digit.to_i * [7,3,1].at(index%3) }.sum | |
-weighted_sum % 10 | |
end | |
end | |
20.times { puts FinnishBankRefence::generate } |
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