card_issuer.rb

require 'luhn'
require 'json'
require 'uri'
require 'net/http'

notes = ["Note: spaces and dashes aren't allowed. If you are going to write\n",
         "4444 4444 4444 4448 or 4444-4444-4444-4448, write:\n",
         "4444444444444448.\n",
         "Note 2:If your Diners Club card begins with 5 and is 16 digits,\n",
         'it will be treated as a Mastercard.'
        ]

inod = ['Visa (invalid number of digits)',
        'Mastercard (invalid number of digits)',
        'American Express (invalid number of digits)',
        'Diners Club (invalid number of digits)',
        'Discover (invalid number of digits)',
        'JCB (invalid number of digits)'
       ]

puts notes.join
puts 'Credit card number:'
num = gets.chomp.to_s

case num
when /^4\d{12}(?:\d{3})?$/ then puts 'Visa'
when /^5[1-5]\d{14}$/ then puts 'Mastercard'
when /^3[47]\d{13}$/ then puts 'American Express'
when /^3(?:0[0-5]|[68]\d)\d{11}$/ then puts 'Diners Club'
when /^6(?:011|5\d{2})\d{12}$/ then puts 'Discover'
when /^(?:2131|1800|35\d{3})\d{11}$/ then puts 'JCB'

when /^4(\d{0,11}|\d{11}(?=\d{1,2})|\d{13,14}|\d{16,})$/ then puts inod[0]
when /^5[1-5](\d{0,13}|\d{15,})$/ then puts inod[1]
when /^3[47](\d{0,12}|\d{14,})$/ then puts inod[2]
when /^3(?:0[0-5]|[68])(\d{0,10}|\d{12,})$/ then puts inod[3]
when /^(6(?:011|5\d{2})(\d{0,11}|\d{13,})|65\d{0,2})$/ then puts inod[4]
when /^((?:2131|1800|35\d{3})(\d{0,10}|\d{12,})|35\d{0,2})$/ then puts inod[5]

else
  puts 'Unknown'
end

puts 'Invalid credit card!' unless num.valid_luhn?

uri = URI.parse("http://www.binlist.net/json/#{num.split('').first(6).join}")
http = Net::HTTP.new(uri.host, uri.port)
request = Net::HTTP::Get.new(uri.request_uri)
response = http.request(request)
info = JSON.parse(response.body)

puts 'Bank is:' + info['bank']