module Turing
  class Machine
    attr_accessor :rules, :pos, :state
    def initialize
      @rules = {}
      @pos, @state = 0, 0
      @tape = []
    end
    def tape
      @tape.join
    end
    def tape=( str )
      @tape.clear
      @tape.push *str.split('').map { |x| x.to_i }
    end
    def run
      before = tape
      puts "  pos  state   chr  mv"
      loop do
        chr = @tape[@pos] || 0
        newstate, newchr, mv = @rules[@state][chr]
        puts " #{@pos.to_s.rjust(4)}   #{@state}->#{newstate}  #{chr}->#{newchr}   #{mv}"
        # update this position on tape
        @tape[@pos] = newchr
        # update state
        @state = newstate
        # move read head
        case mv
        when :r
          @pos += 1
        when :l
          @pos -= 1
        when :x
          @pos += 1
          break
        end
      end
      [ before, tape ]
    end
  end
end

UNARY_INC = [
  [
    [0, 0, :r],
    [1, 1, :r],
  ],
  [
    [0, 1, :x],
    [1, 1, :r],
  ]
]


UNARY_DBL = [
  [
    [0, 0, :r],
    [1, 0, :r]
  ],
  [
    [2, 1, :l],
    [1, 1, :r]
  ],
  [
    [3, 0, :r],
    [4, 0, :r]
  ],
  [
    [0, 1, :x],
    [3, 1, :r]
  ],
  [
    [5, 1, :l],
    [4, 1, :r]
  ],
  [
    [2, 1, :l],
    [5, 1, :l]
  ]
]

if $0 == __FILE__
  t = Turing::Machine.new
  if ARGV.length == 2
    t.rules = Object.const_get(ARGV.shift)
    t.tape = ARGV.shift
  else
    t.rules = UNARY_INC
    t.tape = "00000111"
  end
  o = t.run
  puts " in: #{o.first}"
  puts "out: #{o.last}"
end