Implement a ruby method to find the next largest number with the same digits of the input number. Ex: 38276 would return 38627.

next_greater_permutation.rb

class NextGreaterPermutation
  attr_reader :digits

  def initialize(number)
    @digits = number.to_s.chars
  end

  def display
    return 'Not Possible' if smaller_digit_idx.nil? 
    digits[smaller_digit_idx], digits[larger_digit_idx] = digits[larger_digit_idx], digits[smaller_digit_idx]      
    [digits[0..smaller_digit_idx], digits[smaller_digit_idx+1..-1].reverse].join.to_i
  end

  private

  def smaller_digit_idx
    @smaller_digit_idx ||= digits.each_cons(2).to_a.rindex { |a, b| a < b }
  end

  def larger_digit_idx
    @larger_digit_idx ||= digits.rindex { |n| digits[smaller_digit_idx] < n }    
  end
end

p '----------------------------------------------------------'
p "Input: 38276"
next_greater_permutation = NextGreaterPermutation.new(38276)
p "Output: #{next_greater_permutation.display}"

p '----------------------------------------------------------'
p "Input: 218765"
next_greater_permutation = NextGreaterPermutation.new(218765)
p "Output: #{next_greater_permutation.display}"

p '----------------------------------------------------------'
p "Input: 4321"
next_greater_permutation = NextGreaterPermutation.new(4321)
p "Output: #{next_greater_permutation.display}"
p '----------------------------------------------------------'