#include "my_atoi.h"

int my_atoi(const char *str)
{
    int res = 0;

    // str error check
    if (str == NULL || *str == '0')
    {
        return 0;
    }

    // trim whitespaces
    for (; *str && *str == ' '; str++)
    {
        continue;
    }

    // move to end of str
    size_t l;
    for (l = 0; str[l]; l++)
    {
        continue;
    }
    l--;

    // prepare for calculations
    int factor = 1;

    // actual conversion of up to the second element of str (potential sign)
    for (; l > 0; l--)
    {
        char val = str[l];
        if (val < '0' || val > '9')
        {
            return 0;
        }
        val -= '0';
        res += val * factor;

        factor *= 10;
    }

    // l should be 0 by now
    if (str[l] == '-')
    {
        return -res;
    }
    else if (str[l] != '+')
    {
        int val = str[l];
        if (val < '0' || val > '9')
        {
            return 0;
        }
        val -= '0';
        return res + val * factor;
    }

    return res;
}