Random strings in Ruby

randomizer.rb

module Randomizer
  PATTERNS = {
    lowercase: Array("a".."z"),
    uppercase: Array("A".."Z"),
    numbers:   Array(0..9),
    special:   %w(- _ .)
  }

  module_function
  def configure(options)
    @patterns = options[:patterns] if options[:patterns]
    @extra    = options[:extra]    if options[:extra]
  end

  def patterns
    @patterns ||= PATTERNS.keys
  end

  def extra
    @extra
  end

  def next(size=10)
    source = patterns.map{ |p| PATTERNS.fetch(p) }.flatten
    source.concat(extra) if extra

    # Multiply size of source when needed
    iterations = (size / source.size.to_f).ceil

    chars = iterations.times.map{ source }.to_a.flatten
    chars.sample(size).join
  end
end

puts Randomizer.next(20) #=> bLVFpcDGm6_iClaTZSd0

Randomizer.configure(patterns: [:special], extra: ("a".."f").to_a)
puts Randomizer.next(20) #=> -ede.fffd._acbea-ba.

Randomizer.configure(patterns: [:uppercase, :lowercase])
puts Randomizer.next(20) #=> VfGhorYglBmKAcUnCbTO