Obfuscated ids

gistfile1.rb

module Base62
  BASE_CHARS = '0SKVnQFHhGs9qo7p8cRW54duMYNXTCErx2tDmwO3kabfUB1elLvjiIgyJAZ6Pz'.split('')
  BASE = BASE_CHARS.length
  BASE_ENCODED_MIN_LENGTH = 1
  
  def self.decode(number)
    # assure string
    number = number.to_s.reverse.split('')
    
    decoded = 0
    digits = number.length
    
    # decode
    digits.times do |i|
      decoded+= BASE_CHARS.index(number[i]) * BASE**i
    end
    
    decoded
  end

  def self.encode(number)
    if number.nil?
      return nil
    end
    
    # assure numerical
    number = number.to_i(10) unless number.is_a? Integer
    
    encoded = ''
    digits = (number > 0) ? 1 + (Math.log(number)/Math.log(BASE)).to_i : 0
    
    # fill with leading zeros
    (BASE_ENCODED_MIN_LENGTH - digits).times do
      encoded << BASE_CHARS[0]
    end
    
    # convert the number
    digits.times do |i|
      divider = BASE**(digits - 1 - i)
      encoded << BASE_CHARS[(number / divider).to_i]
      number = number % divider
    end
    
    encoded
  end
  
end

# extend Integer and String
class Integer
  def to_base62
    Base62.encode self
  end
  def from_base62
    Base62.decode self
  end
end

class String
  def to_base62
    Base62.encode self
  end
  def from_base62
    Base62.decode self
  end
end

If anyone's looking for a terser version without the typechecks you can try this sucker:

module HandleMapper
  BASE_CHARS = '0SKVnQFHhGs9qo7p8cWR54duMYNXTCErx2tDmwO3kabfUB1elLvjiIgyJAZ6Pz'.split('')
  BASE = BASE_CHARS.length

  def self.decode(string)
    chars = string.split('')

    chars.each_with_index.inject(0) do |sum, (char, index)|
      sum + (BASE_CHARS.index(char) * BASE**index)
    end
  end

  def self.encode(number)
    digits = 1 + (Math.log(number)/Math.log(BASE)).to_i # floor'd log in the base of the string to get the length

    # loop over each digit removing the divisor at that digit position, capturing the number of times the divisor went into the number
    (0...digits).to_a.reverse!.inject([]) do |encoded, digit|
      divisor = BASE ** (digit)
      encoded << BASE_CHARS[(number / divisor).to_i]
      number = number % divisor
      encoded
    end.reverse!.join('')
  end
end