module MoreMath::NumberifyStringFunction

def compute_size(n, b)
  i = 0
  while n > 0
    i += 1
    n -= b ** i
  end
  i
end

def convert_alphabet(alphabet)
  if alphabet.respond_to?(:to_ary)
    alphabet.to_ary
  elsif alphabet.respond_to?(:to_str)
    alphabet.to_str.split(//)
  else
    alphabet.to_a
  end
end

def numberify_string(string, alphabet = 'a'..'z')
  alphabet = NumberifyStringFunction.convert_alphabet alphabet
  s, k = string.size, alphabet.size
  result = 0
  for i in 0...s
    c = string[i, 1]
    a = (alphabet.index(c) || raise(ArgumentError, "#{c.inspect} not in alphabet")) + 1
    j = s - i - 1
    result += a * k ** j
  end
  result
end

def stringify_number(number, alphabet = 'a'..'z')
  case
  when number < 0
    raise ArgumentError, "number is required to be >= 0"
  when number == 0
    return ''
  end
  alphabet = NumberifyStringFunction.convert_alphabet alphabet
  s = NumberifyStringFunction.compute_size(number, alphabet.size)
  k, m = alphabet.size, number
  result = ' ' * s
  q = m
  s.downto(1) do |i|
    r = q / k
    q = r * k < q ? r : r - 1
    result[i - 1] = alphabet[m - q * k - 1]
    m = q
  end
  result
end