module main;
import std::io;

fn int main(String[] args) {

    if (args.len < 2) {
      io::printn("Usage: HelloWorld <filename>");
      return -1;
    }
    String filename = args[1];

    int? answer = getSum(filename);
    if (catch error = answer) {
        io::printfn("error opening file: %s", error);
        return -1;
    }
    io::printfn("%d", answer);


    return 0;
}

fn int? getSum(String filename) {
    File? file = file::open(filename, "r")!;

    defer (void)file.close();

    int sum = 0;

    while (try line = io::treadline(&file)) {
        char first = getFirst(line);
        char last = getLast(line);
        String digits = {first, last};
        int? number = digits.to_int();
        if (catch error = number) {
            io::printfn("Error converting to number: %s", error);
            continue;
        }
        sum += number;
    }
    return sum;
}

fn char getLast(String line) {
    char last;
    int length = line.len - 1;
    for (int i=length; i>=0; i--) {
        if (ascii::is_digit(line[i])) {
            last = line[i];
            break;
        }
    }
    return last;
}

fn char getFirst(String line) {
    char first;
    foreach (ch : line) {
        if (ascii::is_digit(ch)) {
            first = ch;
            break;
        }
    }
    return first;
}