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

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

#define MEM_SIZE 30000
#define GOTO_NEXT goto *labels[op_char]

void engine_run(FILE* file) {
    void** labels[127]; /* We will address each char */
    unsigned char op_char = 0;
    fpos_t* loop_start_position = calloc(3000,sizeof(fpos_t));
    
    for (int i = 0; i <= 127; i++) labels[i] = &&unknown_char;
    
    labels['>'] = &&ptr_increment;
    labels['<'] = &&ptr_decrement;
    
    labels['+'] = &&value_increment;
    labels['-'] = &&value_decrement;
    
    labels['.'] = &&value_output;
    labels[','] = &&value_input;
    
    labels['['] = &&loop_start;
    labels[']'] = &&loop_end;
    
    op_char = getc(file);
    if (op_char > 127) return;
    GOTO_NEXT;
    
ptr_increment: {
    if (data_ptr + 1 > data_start + MEM_SIZE) data_ptr = data_start;
    ++data_ptr;
    op_char = getc(file);
    if (op_char > 127) return;
    GOTO_NEXT;
}

ptr_decrement: {
    if (data_ptr - 1 < data_start) data_ptr = data_start + MEM_SIZE;
    --data_ptr;
    op_char = getc(file);
    if (op_char > 127) return;
    GOTO_NEXT;
}

value_increment: {
    ++*data_ptr;
    op_char = getc(file);
    if (op_char > 127) return;
    GOTO_NEXT;
}

value_decrement: {
    --*data_ptr;
    op_char = getc(file);
    if (op_char > 127) return;
    GOTO_NEXT;
}

value_output: {
    putchar(*data_ptr);
    op_char = getc(file);
    if (op_char > 127) return;
    GOTO_NEXT;
}

value_input: {
    *data_ptr = getchar();
    op_char = getc(file);
    if (op_char > 127) return;
    GOTO_NEXT;
}

loop_start: {
    fgetpos(file, loop_start_position);
    loop_start_position++;
    
    op_char = getc(file);
    if (op_char > 127) return;
    GOTO_NEXT;
}

loop_end: {
    if (*data_ptr != 0) {
        fsetpos(file, loop_start_position-1);
    } else {
        loop_start_position--;
    }
    
    op_char = getc(file);
    if (op_char > 127) return;
    GOTO_NEXT;
}

unknown_char: {
    op_char = getc(file);
    if (op_char > 127) return;
    GOTO_NEXT;
}
}

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

    if (argc <= 1) {
        fprintf(stderr, "Usage: %s source_file\n", argv[0]);
        return 1;
    }
    
    FILE *file = fopen(argv[1], "r");

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

    engine_run(file);
    
    fclose(file);
    return 0;
}