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

int main(int argc, char *argv[]) {
	int fd;
	struct stat sb;
	char *code;
	unsigned int pc = 0;
	unsigned int idx = 0, size = 1;
	int *data = calloc(size, sizeof(int));

	if (argc != 2) {
		fprintf(stderr, "Usage: %s <file>\n", argv[0]);
		exit(EXIT_FAILURE);
	}
	if ((fd = open(argv[1], O_RDONLY)) == -1 || fstat(fd, &sb) == -1) {
		perror("Error opening file");
		exit(EXIT_FAILURE);
	}
	if (!S_ISREG(sb.st_mode)) {
		fprintf(stderr, "%s is not a file\n", argv[1]);
		exit(EXIT_FAILURE);
	}
	if ((code = mmap(0, sb.st_size, PROT_READ, MAP_SHARED, fd, 0)) == MAP_FAILED) {
		perror("Error mapping file into memory");
		exit(EXIT_FAILURE);
	}
	close(fd);

	for (pc = 0; pc < sb.st_size; pc++) {
		switch (code[pc]) {
			case '>':
				idx++;
				if (idx == size) {
					unsigned int old = size;
					int *ptr = data;
					size += old;
					if ((data = realloc(ptr, size * sizeof(int))) == NULL) {
						perror("Out of memory");
						exit(EXIT_FAILURE);
					}
					else
						memset(data + old, 0, (size - old) * sizeof(int));
				}
				break;
			case '<':
				idx--;
				break;
			case '+':
				data[idx]++;
				break;
			case '-':
				data[idx]--;
				break;
			case '.':
				putchar(data[idx]);
				break;
			case ',':
				data[idx] = getchar();
				break;
			case '[':
				if (data[idx] == 0) {
					int b = 0;
					for (unsigned int i = pc + 1; i < sb.st_size; i++) {
						if (code[i] == ']') {
							if (b == 0) {
								pc = i;
								break;
							}
							b--;
						}
						else if (code[i] == '[')
							b++;
					}
				}
				break;
			case ']':
				if (data[idx] != 0) {
					int b = 0;
					for (unsigned int i = pc - 1; i > 0; i--) {
						if (code[i] == '[') {
							if (b == 0) {
								pc = i;
								break;
							}
							b--;
						}
						else if (code[i] == ']')
							b++;
					}
				}
				break;
			default:
				break;
		}
	}

	free(data);
	munmap(code, sb.st_size);
	return EXIT_SUCCESS;
}