next_version.rb

require 'minitest/autorun'
require 'minitest/emoji'

class Version
  def self.next_version version
    next_version_3 version
  end

  def self.next_version_1 version
    number_as_string = version.split(".").join('')

    string_length = number_as_string.length

    next_version_string = (number_as_string.to_i+1).to_s

    if next_version_string.length==string_length
      next_version_string.split('').join(".")
    else
      next_version_string[0..1] + "." + next_version_string[2..-1].split('').join(".")
    end
  end

  def self.next_version_2 version
    number_as_string = version.split(".").join('')

    starts_with_zero = number_as_string[0].to_i == 0

    string_length = number_as_string.length

    next_version_string = (number_as_string.to_i+1).to_s

    if next_version_string.length > string_length
      next_version_string[0..1] + "." + next_version_string[2..-1].split('').join(".")
    else
      next_version_string = "0" + next_version_string if starts_with_zero && next_version_string.length < string_length
      next_version_string.split('').join(".")
    end
  end

  def self.next_version_3 version
    version_array = version.split(".").reverse.map(&:to_i)

    version_array[0] = version_array.first + 1

    version_array = version_array.each_with_index.map do |n,index|
      if index == version_array.size - 1
        n
      else
        if n > 9
          version_array[index+1]=version_array[index+1]+1
          0
        else
          n
        end
      end
    end

    version_array.reverse.join(".")
  end
end

# tests
class VersionTest < Minitest::Test

  def test_1_2_3
    assert_equal "1.2.4", Version.next_version("1.2.3")
  end

  def test_0_9_9
    assert_equal "1.0.0", Version.next_version("0.9.9")
  end

  def test_1
    assert_equal "2", Version.next_version("1")
  end

  def test_1_2_3_4_5_6_7_8
    assert_equal "1.2.3.4.5.6.7.9", Version.next_version("1.2.3.4.5.6.7.8")
  end

  def test_9_9
    assert_equal "10.0", Version.next_version("9.9")
  end

  def test_0_8_7_9
    assert_equal "0.8.8.0", Version.next_version("0.8.7.9")
  end

  def test_13_9_9_9_9_9
    assert_equal "14.0.0.0.0.0", Version.next_version("13.9.9.9.9.9")
  end
end