#include <ctype.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>

/*
 * Each line of the input file contains a string with a mix of letters and digits
 * Each line's "calibration value" is a single two digit number, made up of the first and last
 * digit found in the string
 * Print out the sum of all the calibration values. 
 */

char buffer[2048];

void read_line(char* linebuf, FILE* file) 
{
    char* str = fgets(linebuf, 2048, file);
    if (feof(file))
    {
        return;
    }
    if (str == NULL)
    {
        fprintf(stderr, "Fgets error");
        linebuf[0] = '\0';
    }
}

void extract_digits(char* str, char *first, char *last)
{
    char *p,*q,*r;
    p = str;
    while (*p != '\0' && !isdigit(*p))
        p++; // find first digit
    *first = *last = *p;
    q = p;
    while (*q != '\0') // find digits until end of string
    {
        q++;
        if (isdigit(*q))
        {
            *last = *q;
        }
    }
}

long convert_chars(char first, char last)
{
    char num[3] = { first, last, '\0' };
    return strtoul(num, NULL, 10);
}

int main(int argc, char *argv[])
{
    FILE* input = fopen("input", "r"); 
    if (input == NULL)
    {
        fprintf(stderr, "error opening file");
        return EXIT_FAILURE;
    }
    long sum = 0;
    char first, last;
    
    while(true)
    {
        read_line(buffer, input);
        if (feof(input))
            break;
        extract_digits(buffer, &first, &last);
        long value = convert_chars(first, last);
        printf("%ld\t%s", value, buffer);
        sum += value;
    }

    printf("%ld", sum);
    return EXIT_SUCCESS;
}