/*
 * Brainfuck interpreter.
 */

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(int argc, char **argv) {
  char program[10000];
  int fd = open(argv[1], O_RDONLY);
  if (fd < 0) {
    perror(argv[1]);
    return 1;
  }

  int progsize = read(fd, program, sizeof(program));
  close(fd);

  unsigned char memory[30001];
  int pc = 0, mp = 0;
  while (pc < progsize) {
    /* printf("[%d]", pc); */
    /* fflush(stdout); */
    switch (program[pc]) {
    case '>': mp++; pc++; break;
    case '<': mp--; pc++; break;
    case '+': memory[mp]++; pc++; break;
    case '-': memory[mp]--; pc++; break;
    case ',': read(0, &memory[mp], 1); pc++; break;
    case '.': write(1, &memory[mp], 1); pc++; break;
    case '[':
      if (memory[mp]) {
        pc++;
        break;
      }
      int bc = 0;
      do {
        if (program[pc] == '[') bc++;
        if (program[pc] == ']') bc--;
        pc++;
        if (pc >= progsize) {
          fprintf(stderr, "unmatched [\n");
          return 1;
        }
      } while (bc);
      break;
    case ']':
      if (!memory[mp]) {
        pc++;
        break;
      }
      int bbc = 0;
      do {
        if (program[pc] == ']') bbc++;
        if (program[pc] == '[') bbc--;
        pc--;
        if (pc < 0) {
          fprintf(stderr, "unmatched ]\n");
          return 1;
        }
      } while (bbc);
      pc++;
      pc++;
      break;
    default:                    /* comment! */
      pc++;
      break;
    }
  }
  return 0;
}