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

int     is_operator(char c)
{
    return c == '*' || c == '+' || c == '-' || c == '/' || c == '%';
}

int     ft_is_digit(char c)
{
    return ('0' <= c && c <= '9');
}

int     valid_char(char c)
{
    return ft_is_digit(c) || c == ' ' || is_operator(c);
}

int     is_valid_rpn(char *str)
{
    int     optr_count = 0;
    int     oprd_count = 0;
    int     i = 0;

    while (str[i] == ' ')
        ++i;
    while (str[i])
    {
        if (!valid_char(str[i]))
            return (0);
        if (str[i] == ' ' && ft_is_digit(str[i - 1]))
            ++oprd_count;
        if ((str[i] == '+' || str[i] == '-') && ft_is_digit(str[i + 1]))
        {
            ++i;
            continue;
        }
        else if (is_operator(str[i]) && str[i - 1] != ' ')
            return (0);
        if (is_operator(str[i]) && (str[i + 1] == ' ' || str[i + 1] == '\0'))
            ++optr_count;
        if ((oprd_count < 2 && optr_count > 0) ||
            (oprd_count >= 2 && optr_count >= oprd_count))
            return (0);
        ++i;
    }
    if (optr_count != oprd_count - 1)
        return (0);
    return (1);
}

int     add(int a, int b)
{
    return a + b;
}

int     sub(int a, int b)
{
    return a - b;
}

int     mul(int a, int b)
{
    return a * b;
}

int     dvs(int a, int b)
{
    return a / b;
}

int     mod(int a, int b)
{
    return a % b;
}

int     find_a_index(char *str, int end_index)
{
    int     nbrs_to_pass = 1;

    while (end_index >= 0)
    {
        if (nbrs_to_pass == 0)
            return end_index;
        if (is_operator(str[end_index]))
        {
            ++nbrs_to_pass;
            end_index -= 2;
            continue;
        }
        else if (ft_is_digit(str[end_index]))
        {
            --nbrs_to_pass;
            while(end_index >= 1 && str[end_index] != ' ')
                --end_index;
            if (str[end_index] == ' ')
                --end_index;
        }
        else
            return (-20);
    }
    return (-42);
}

int     rec_rpn_read(char *str, int end_index)
{
    int     (*op)(int, int);
    int     a;
    int     b;

    switch (str[end_index])
    {
        case '+': op = &add; break;
        case '-': op = &sub; break;
        case '*': op = &mul; break;
        case '/': op = &dvs; break;
        case '%': op = &mod; break;
        default: printf("Unexpected op error\n"); break;
    }
    end_index -= 2;
    if (is_operator(str[end_index]))
    {
        b = rec_rpn_read(str, end_index);
        end_index = find_a_index(str, end_index);
        if (end_index < 0)
        {
            printf("Unexpected error %d\n", end_index);
            return (0);
        }
    }
    else
    {
        while (end_index >= 1 && str[end_index] != ' ')
            --end_index;
        if (str[end_index] == ' ')
            ++end_index;
        b = atoi(str + end_index);
        if (end_index >= 2)
            end_index -= 2;
    }
    if (is_operator(str[end_index]))
        a = rec_rpn_read(str, end_index);
    else
    {
        while (end_index >= 1 && str[end_index] != ' ')
            --end_index;
        if (str[end_index] == ' ')
            ++end_index;
        a = atoi(str + end_index);
    }
    return (op(a, b));
}

int     main(int argc, char **argv)
{
    int     result;
    int     len = 0;

    if (argc != 2 || !is_valid_rpn(argv[1]))
    {
        printf("Error\n");
        return (1);
    }
    while (argv[1][len])
        ++len;
    result = rec_rpn_read(argv[1], len - 1);
    printf("%d\n", result);
    return (0);
}
/*
echo "Test :"
./a.out
echo "Expected: Error\n"

echo "Test :"
./a.out "5 10 9 / 50 *"
echo "Expected: Error\n"

echo "Test :"
./a.out ""
echo "Expected: Error\n"

echo "Test :"
./a.out "5 10 9 / 50 *a"
echo "Expected: Error\n"

echo "Test :"
./a.out "2 3 * * 3"
echo "Expected: Error\n"

echo "Test :"
./a.out "2 3 * 4 5 * -"
echo "Expected: -14\n"

echo "Test :"
./a.out "3 4 +"
echo "Expected: 7\n"

echo "Test :"
./a.out "3 1 2 * * 4 -"
echo "Expected: 2\n"

echo "Test :"
./a.out "1 2 * 3 * 4 -"
echo "Expected: 2\n"

echo "Test :"
./a.out "1 2 * 3 * 4 +"
echo "Expected: 10\n"

echo "Test :"
./a.out "5 10 9 / - 50 *"
echo "Expected: 200\n"

echo "Test :"
./a.out "-200 6 +"
echo "Expected: -194\n"

echo "Test :"
./a.out "5 -10 +9 + * 50 *"
echo "Expected: -250\n"
*/