class ObjectIdEncoder
  attr_accessor :id
  
  def initialize(id)
    @id = id.to_a
    raise "invalid ID!" unless @id.size == 12
  end
  
  def encode
    result = []

    4.times do |i|
      base = i * 3
      tmp = @id[base + 2]
      tmp |= @id[base + 1] << 8
      tmp |= @id[base] << 16

      result << TABLE[tmp >> 18]
      result << TABLE[(tmp >> 12) & 0x3f]
      result << TABLE[(tmp >> 6) & 0x3f]
      result << TABLE[tmp & 0x3f]
    end

    result.join
  end
end

class ObjectIdDecoder
  attr_accessor :str_id
  
  def initialize(str_id)
    raise "invalid ID!" unless str_id.size == 16
    @str_id = str_id
  end
  
  def decode
    result = []

    4.times do |i|
      base = i * 4
      tmp = TABLE.index(@str_id[base + 3])
      tmp |= TABLE.index(@str_id[base + 2]) << 6
      tmp |= TABLE.index(@str_id[base + 1]) << 12
      tmp |= TABLE.index(@str_id[base]) << 18

      result << (tmp >> 16)
      result << ((tmp >> 8) & 0xFF)
      result << (tmp & 0xFF)
    end

    str_id = result.map { |x| "%.2x" % x }.join
    BSON::ObjectId(str_id)
  end
end