Simple command line random password generator (Ruby)

random_password_generator.rb

#!/usr/bin/env ruby

require 'optparse'
require 'ostruct'

class RandomPasswordGenerator
  VERSION = %w(0.1.0)

  CORE_CHARACTER_SET = [('a'..'z').to_a,
                        ('A'..'Z').to_a,
                        (0..9).map(&:to_s)].flatten.freeze

  BASIC_SYMBOL_SET = ['$', '_', '-', '+', '='].freeze
  BASIC_SYMBOL_SET_KEY = 'basic'
  EMPTY_SYMBOL_SET = [].freeze
  EMPTY_SYMBOL_SET_KEY = 'empty'
  FULL_SYMBOL_SET = # Higher chance of experiencing compatibility issues
    ['`', '~', '!', '@', '#', '$', '%', '^',
     '&', '*', '(', ')', '_', '-', '=', '+',
     '[', ']', '{', '}', '\\', '|', ':', ';',
     '\'', '"', ',', '.', '<', '>', '/', '?'].freeze
  FULL_SYMBOL_SET_KEY = 'full'

  SYMBOL_SETS = [BASIC_SYMBOL_SET_KEY, EMPTY_SYMBOL_SET_KEY, FULL_SYMBOL_SET_KEY].freeze
  SYMBOL_SET_ALIASES = SYMBOL_SETS.map { |s| [s[0], s] }.to_h.freeze
  SYMBOL_SET_MAX_KEY_LENGTH = SYMBOL_SETS.map(&:length).max
  DEFAULT_SYMBOL_SET_KEY = BASIC_SYMBOL_SET_KEY
  DEFAULT_MINIMUM_LENGTH = 12
  DEFAULT_MAXIMUM_LENGTH = 25

  def initialize
    # Note that the standard library OptionParser library invoked in the following method has access
    # to ARGV and removes any options that it found and parsed in ARGV (argument vector).
    @options = parse_command_line_arguments
    puts generate_random_password
  end

  private
  def parse_command_line_arguments
    options = OpenStruct.new
    options.symbol_set = DEFAULT_SYMBOL_SET_KEY
    options.minimum_length = DEFAULT_MINIMUM_LENGTH
    options.maximum_length = DEFAULT_MAXIMUM_LENGTH

    OptionParser.new do |opts|
      opts.banner = 'Usage: random_password_generator [options]'
      opts.separator ''
      opts.separator 'Specific options:'

      opts.on('-sSYMBOL_SET', '--symbol-set=SYMBOL_SET', SYMBOL_SETS, SYMBOL_SET_ALIASES,
              <<MESSAGE) do |symbol_set|
Select which symbol-set to use from the following (default=#{DEFAULT_SYMBOL_SET_KEY}):

  #{BASIC_SYMBOL_SET_KEY.ljust(SYMBOL_SET_MAX_KEY_LENGTH)}\t\t#{BASIC_SYMBOL_SET.join(' ')}
  #{EMPTY_SYMBOL_SET_KEY}
  #{FULL_SYMBOL_SET_KEY.ljust(SYMBOL_SET_MAX_KEY_LENGTH)}\t\t#{FULL_SYMBOL_SET.join(' ')}
MESSAGE
        options.symbol_set = symbol_set
      end

      opts.on('--minimum-length=MIN',
              "Set minimum length of generated random password (default=#{DEFAULT_MINIMUM_LENGTH})") do |minimum_length|
        options.minimum_length = Integer(minimum_length)
      end

      opts.on('--maximum-length=MAX',
              "Set maximum length of generated random password (default=#{DEFAULT_MAXIMUM_LENGTH})") do |maximum_length|
        options.maximum_length = Integer(maximum_length)
      end

      opts.separator ''
      opts.separator 'Common options:'

      opts.on_tail('-h', '--help', 'Show this message') do
        puts opts
        exit
      end

      opts.on_tail('-v', '--version', 'Show version') do
        puts "Version: #{VERSION.join('.')}"
        exit
      end
    end.parse!

    check_option_invariants(options)
    options
  end

  def check_option_invariants(options)
    fail "Program invariant violated (maximum_length cannot be less than minimum length)" if options.maximum_length < options.minimum_length
  end

  def symbol_set
    case @options.symbol_set
    when BASIC_SYMBOL_SET_KEY
      BASIC_SYMBOL_SET
    when EMPTY_SYMBOL_SET_KEY
      EMPTY_SYMBOL_SET
    when FULL_SYMBOL_SET_KEY
      FULL_SYMBOL_SET
    else
      fail "Program invariant violated (unknown symbol set: ). GUID: e9ab3fd0-c17e-41da-a72a-a68855a253a0"
    end
  end

  def acceptable_characters
    @acceptable_characters ||= [
      CORE_CHARACTER_SET,
      symbol_set
    ].flatten.freeze
  end

  def generate_random_password
    password_length = ((@options.minimum_length)..(@options.maximum_length)).to_a.sample
    Array.new(password_length, nil).to_a.map { |_| acceptable_characters.sample }.join('')
  end
end

RandomPasswordGenerator.new