struct snake* add_snake(struct snake* old_head, int x, int y) {
    struct snake* new_head = (struct snake*) malloc(sizeof(struct snake));
    new_head->x = x;
    new_head->y = y;
    new_head->next = old_head;
    return new_head;
}

int is_snake(struct snake* snake, int x, int y) {
    while (snake != NULL) {
        if (snake->x == x && snake->y == y) {
            return 1;
        }
        snake = snake->next;
    }
    return 0;
}

void free_snake(struct snake* snake) {
    while (snake != NULL) {
        struct snake* next = snake->next;
        free(snake);
        snake = next;
    }
}

int step_state(struct state* state) {
    int new_x = state->snake->x + state->sx;
    int new_y = state->snake->y + state->sy;

    if (new_x < 0 || new_x >= state->width || new_y < 0 || new_y >= state->height) {
        return END_WALL;
    }

    if (is_snake(state->snake->next, new_x, new_y)) {
        return END_SNAKE;
    }

    for (int i = 0; i < FOOD_COUNT; i++) {
        if (state->foodx[i] == new_x && state->foody[i] == new_y) {
            state->foodx[i] = -1;
            state->foody[i] = -1;
            state->snake = add_snake(state->snake, new_x, new_y);
            return END_FOOD;
        }
    }

    state->snake = add_snake(state->snake, new_x, new_y);
    struct snake* tail = state->snake;
    while (tail->next->next != NULL) {
        tail = tail->next;
    }
    free(tail->next);
    tail->next = NULL;

    return END_CONTINUE;
}