Generate Random Password with SecureRandom

password_gen.rb

require 'securerandom'

class PasswordGen
  ALPHANUMERIC = ((48..57).to_a + (65..90).to_a + (97..122).to_a).pack('c*').freeze
  SYMBOL = ((33..47).to_a + (58..64).to_a + (91..96).to_a + (123..126).to_a).pack('c*').freeze

  attr_reader :length, :alphanumeric, :symbol

  def initialize(length: 20, alphanumeric: true, symbol: true)
    @length = length.to_i
    @alphanumeric = alphanumeric
    @symbol = symbol
  end

  def generate
    Array.new(length) do
      index = SecureRandom.random_number(char_table.length)
      char_table[index]
    end.join
  end

  private

  def char_table
    @char_table ||= "#{ALPHANUMERIC if alphanumeric}#{SYMBOL if symbol}".chars.shuffle.join
  end
end

print PasswordGen.new.generate