#include <stdio.h>
#include <error.h>
#include <stdlib.h>

static unsigned char *data_start;
static unsigned char *data_ptr;

void process_command(char command, FILE *file) {
    
    switch(command) {
    case '>':
        /* increment the data pointer (to point to the next cell to the right). */
        ++data_ptr;
        /* TODO : Check if over allocated memory */
        break;
    case '<':
        /* decrement the data pointer (to point to the next cell to the left). */
        --data_ptr;
        /* TODO : Check if under allocated memory */
        break;
    case '+':
        /* increment (increase by one) the byte at the data pointer. */
        ++*data_ptr;
        break;
    case '-':
        /* decrement (decrease by one) the byte at the data pointer. */
        --*data_ptr;
        break;
    case '.':
        /* output a character, the ASCII value of which being the byte at the
         * data pointer. */
        putchar(*data_ptr);
        break;
    case ',':
        /* accept one byte of input, storing its value in the byte at the data
         * pointer. */
        *data_ptr = getchar();
        break;
    case '[':
        /* [ : if the byte at the data pointer is zero, then instead of moving the
         * instruction pointer forward to the next command, jump it forward to
         * the command after the matching ] command. 
         * ] : if the byte at the data pointer is nonzero, then instead of moving
         * the instruction pointer forward to the next command, jump it back to
         * the command after the matching [ command. */
        {
            fpos_t position;
            fgetpos(file, &position);
            while(*data_ptr != 0) {
                fsetpos(file, &position);
                char c = getc(file);
                while( c!= ']' && c != EOF) {
                    process_command(c, file);
                    c = getc(file);
                }
            }
        }
        break;
    case ']':
        /* if we encounter one here, it means there are not balanced */
        fprintf(stderr, "Error in the source file, unbalanced ']'\n");
        exit(2);
        break;
    default:
        /* Brainfuck ignores all characters except the eight commands +-<>[],. */
        break;
    }

}

int main(int argc, char **argv)
{
    data_start = calloc(30000, sizeof(char));
    data_ptr = data_start;

    if (argc > 1) {
        char command;
        FILE *file = fopen(argv[1], "r");

        if (!file) {
            fprintf(stderr, "Error: No such file %s\n", argv[1]);
            return 2;
        }

        while((command = getc(file)) != EOF) {
            process_command(command, file);
        }
        
        fclose(file);
        return 0;
    } else {
        fprintf(stderr, "Usage: %s source_file\n", argv[0]);
        return 1;
    }
    return 0;
}