codetest.rb

#Make it possile for euro symbol to display properly
#DANGEROUS, AS IT BREAKS RUBY STRING METHODS    
##
$KCODE = "u"
##

class Currency
    
    #format hash: containing the symbol, thousands (and higher) delimiter and decimal
    #usd_rate: some ratio when compaired to the dollar (ie the dollar is always 1) 
    attr_accessor :format, :usd_rate
    
    #define the format and the rate in terms of us dollars
    def initialize(format, usd_rate)
        @format, @usd_rate = format, usd_rate
    end
    
    #add the commas (or periods depending) to the integer part of the amount
    #add the period (or comma depending) to the decimal portion
    def format(amount)
        amtstr = '%.2f' % amount
        int, dec = amtstr.split(".")
        @format[:sym] + int.reverse.gsub(/(\d{3})(?=\d)/, '\&' + @format[:thou]).reverse + @format[:dec] + dec
    end

end

#converts amounts of currency to and from those currencies available in the currencies hash
#
#>> c = CurrencyConverter.new
#>> c.us_to_euro(10000)
#=> "€7.870,00"
class CurrencyConverter

    #the list of currencies available for use
    attr_accessor :currencies

    #define default currencies for use
    def initialize
        @currencies =   {   "us" => Currency.new({:sym => "$" , :thou => "," , :dec => "."}, 1), 
                            "euro" => Currency.new({:sym => "€" , :thou => "." , :dec => ","}, 0.787)}
    end

    #convert based on the currency name
    def convert(from, to, amount)
        value = amount * @currencies[to].usd_rate/@currencies[from].usd_rate
        @currencies[to].format(value)

    rescue NoMethodError
        puts "Oops! You did something funny, try again!"
    end
    
    #catch any currency_to_currency method calls
    def method_missing(method, *args)
        if method.to_s =~ /^([a-z]+)_to_([a-z]+)$/
           convert($1, $2, args.first)
        end
    end

end