# Copyright (c) 2009 the authors listed at the following URL, and/or
# the authors of referenced articles or incorporated external code:
# http://en.literateprograms.org/Quadruple_Turing_Machine_(Ruby)?action=history&offset=20081007052617
# 
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
# 
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
# IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
# CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
# TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
# SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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# Retrieved from: http://en.literateprograms.org/Quadruple_Turing_Machine_(Ruby)?oldid=14850

class State
  attr_reader :tape
  attr_reader :head
  attr_reader :control_state

  def initialize(initial_state, input_string)
    @tape = input_string.dup
    @head = 0
    @control_state = initial_state
  end

  def update(action, next_state, map)
    raise "Crash!" if next_state == :invalid
    @control_state = next_state
    case action
    when :L
      if (@head <= 0)
        @tape.unshift(:b)
        @head = 0
      else
        @head -= 1
      end
    when :R
      @head += 1
    else
      @tape[@head] = action
    end
  end

  def trace(map)
    if @head < 60
      puts " " * (@head + 17) + "v"
    else
      puts
    end
    tape = (0..60).collect{ |i| map[tape_at(i)] }.join
    puts "%15s: %s" % [ @control_state, tape ]
  end

  def tape_at(pos)
    @tape[pos] || :blank
  end

  def current_symbol
    tape_at(@head)
  end

end