#!/usr/bin/env python
#Author: Shriphani Palakodety
#Mail: spalakod@purdue.edu
#Alternate Mail: shriphani@shriphani.com
#Blog: http://shriphani.com/blog

class Cell:
    '''Class describing the cell of a tape'''

    def __init__(self, mark=0):
	'''Each cell is unmarked by default'''
	self.mark = mark

    def setMark(self):
	self.mark = 1

    def remMark(self):
	self.mark = 0 
	
class Tape:
    '''Class describing the infinite reel in the machine'''

    def __init__(self):
	'''Each tape has an infinite number of cells both ways'''
	self.reel = []
	for i in xrange(5): #we display only the required elements at a time
	    cell = Cell()
	    self.reel.append(cell)

    def __str__(self):
	printstr = "....."
	for cell in self.reel:
	    printstr += str(cell.mark)+","
	printstr += "....."
	return printstr

class Head:
    '''Class describing the head'''

    def __init__(self, tape, position=0):
	self.position = position
	self.tape = tape

    def moveLeft(self):
	if self.position != 0:
	    self.position -= 1

	else:
	    extension = []
	    extension.append(Cell())
	    self.tape = extension + tape.reel

    def etchMark(self):
	self.tape.reel[self.position].setMark()

    def remMark(self):
	self.tape.reel[self.position].remMark()
	    

    def moveRight(self):
	if self.position == len(self.tape.reel) - 1:
	    self.tape.reel.append(Cell())
	self.position += 1

    def getPosition(self):
	return self.position

class Machine:
    '''Class describing the Post Machine'''

    def __init__(self, tape):
	self.tape = tape
	self.head = Head(tape)
	self.commands = {}
	
    def parseInstruction(self, number, action, jump):
	'''Instruction is of form "[number, action, jump]"'''
	self.commands[number] = [action, jump]


    def beginExecution(self):
	instruction = 0
	action = self.commands[instruction][0]
	
	while action != "exit":
	    if action == "<":
		self.head.moveLeft()
	    elif action == ">":
	        self.head.moveRight()
	    elif action == "mark":
		self.head.etchMark()
	    elif action == "unmark":
		self.head.remMark()

	    print self
	    instruction = self.commands[instruction][1]
	    action = self.commands[instruction][0]
	
	return

    def __str__(self):
	'''This returns tape with the head displayed'''
	a = str(self.tape)
	posn = self.head.getPosition()
	temp = "....."
	for i in xrange(len(self.tape.reel)):
	    if i == posn:
		temp += "["+str(self.tape.reel[i].mark)+"], "
	    else:
		temp += str(self.tape.reel[i].mark) + ", "
	temp += "....."
	return temp
    
    
tape = Tape()
a = Machine(tape)
print "Initial Stage"
print a

def run(input_file):
    infile = open(input_file, 'r')
    b = infile.readlines()
    for instruction in b:
	try:
	    splits = instruction.split(",")
	    number = int(splits[0].strip())
	    action = splits[1].strip()
	    if action == "exit":
		a.parseInstruction(number, action, 0)
	    else:
		jump = int(splits[2].strip())
		a.parseInstruction(number, action, jump)
	except KeyError:
	    return
    infile.close()
    a.beginExecution()


filename = raw_input("File: ")
run(filename)