#!/usr/bin/env python3

import sys

TAPE_LEN = 30*1000

def build_jumps(prog):

    '''

    build a pair of dicts from

    a program.

    returns (forward, backward)

    forward maps forward->back

    backward maps backward->forward

    '''

    forward = {}

    backward = {}

    stack = []

    i = 0

    while i < len(prog):

        if prog[i] == '[':

            stack.append(i)

        elif prog[i] == ']':

            match = stack.pop()

            backward[i] = match

            forward[match] = i

        i += 1

        pass

    return (forward, backward)

def bf(prog):

    tape = [0]*TAPE_LEN

    (forward, backward) = build_jumps(prog)

    ptr = 0

    pc = 0

    end = len(prog)

    while pc < end:

        c = prog[pc]

        if c == '+':

            tape[ptr] = (tape[ptr]+1) % 255

        elif c == '-':

            tape[ptr] = (tape[ptr]-1) % 255

        elif c == '>':

            ptr += 1

        elif c == '<':

            ptr -= 1

        elif c =='[':

            if tape[ptr] == 0:

                pc = forward[pc]

        elif c == ']':

            if tape[ptr] != 0:

                pc = backward[pc]

        elif c == '.':

            print(chr(tape[ptr]), end='')

        elif c == ',':

            print(", unimplemented")

            sys.exit(1)

        else:

            print("unhandled instn: {}".format(c))

            sys.exit(1)

        pc += 1

def clean(lines):

    data = ""

    for line in lines:

        if line.startswith(';'):

            continue

        else:

            data += line

    data = data.replace('\n', '')

    data = data.replace(' ', '')

    return data

if __name__ == "__main__":

    with open(sys.argv[1]) as f:

        lines = f.readlines()

        bf(clean(lines))