def splitNum(param)
    stringNum = param.to_s.split('')
    addToArray(stringNum)
end

def addToArray(param)
    array = []
    param.each do |x|
        array.push(x.to_i)
    end
    findLength(array)
end

def findLength(param)
    if param.length == 16
        puts "Visa, Mastercard, and Discover use 16 digit cards."
        everySecondDigit(param)
    elsif param.length < 16
        if param.length == 13
            puts "Visa uses 14 digit credit cards"
            everySecondDigit(param)
        elsif param.length == 15
            puts "American Express uses 15 digit credit cards"
            everySecondDigit(param)
        else
            puts "Invalid: Too many digits in Credit Card."
            return false
        end
    elsif param.length > 16
        puts "Invalid: Too many digits in Credit Card."
        return false
    end
end

def everySecondDigit(param)
    newArray = []
    param.reverse.each_with_index do |x,index|
        if index % 2 == 1
            x = x * 2
            if x >= 10
                x = x - 9
                newArray.push(x)
            else
                newArray.push(x)
            end
        else
            newArray.push(x)
        end
    end
    multiply(newArray)
end

def multiply(param)
    arraySum = param.reverse.sum
    p arraySum
    if arraySum % 10 == 0
        puts "Valid Number!"
        return true
    else
        puts "Invalid Number!"
        return false
    end
end

a = 4194560385008504

splitNum(a)