1,679,616 unique 4-character ID possibilities. Each generated in < 2ms

gistfile1.rb

module Arbiter
  class Identity
    
    @@data = Arbiter.db.collection('data')
    @@coll = Arbiter.db.collection('page_ids')
    
    def initialize
      @length = identity_matrix['length']
      @last   = identity_matrix['last']
      @idx    = identity_matrix['idx']
            
      @c = '0123456789abcdefghijklmnopqrstuvwxyz'.split(//)
      @mtrx = @last.split(//).map {|x| @c.index(x) }
      
      @id = generate
    end
    
    def to_s
      @id
    end
    
    def generate
      new_mtrx = @mtrx.dup
    
      # assign current const column to next character in array
      new_mtrx[@idx] = (@mtrx[@idx] + 1) % @c.size
    
      new_id = new_mtrx.map {|x| @c[x] }.join
      
      if @@coll.find_one('_id' => new_id)
        
        # switch to next column in matrix
        @idx = update 'idx', (@idx + 1) % @length
        
        # Go again
        generate
      else
        @@coll.insert('_id' => new_id)
        
        # Update last
        @last = update 'last', new_id
        
        new_id
      end
    end
    
    private
    
    def update(field, val)
      (mtrx = identity_matrix)[field] = val
      @@data.update({'_id' => 'identity_matrix'}, mtrx)
      val
    end
    
    def identity_matrix
      document = @@data.find_one('_id' => 'identity_matrix')
      if !document
        document = {
          '_id' => 'identity_matrix',
          'length' => 4,
          'last'   => '8a5j',
          'idx'    => 0
        }
        @@data.insert(document)
      end
      document
    end
    
  end
end