use std::fs;
use std::env;

fn main() {
    println!("Hello, AoC day 07!");

    let args: Vec<String> = env::args().collect();
    if args.len() != 2 {
        println!("wrong number of arguments!");
        std::process::exit(1);
    }

    let file_path = &args[1];

    let contents = fs::read_to_string(file_path).expect("Should have been able to read the file");

    let mut sum_a: i128 = 0;
    let mut sum_b: i128 = 0;
    for line in contents.lines() {
        let (target_string, many_string) = line.split_once(":").expect("found a bad line w/o :");
        let (target, many): (i128, Vec<i128>) = (
            target_string.parse().expect("bad int"), 
            many_string.trim().split(" ").map(|s| s.parse::<i128>().expect(&format!("bad int: {s}"))).collect()
            );

        for x in 0..(1 << many.len()) {
            if target == equation_result_a(&many, x) {
                sum_a += target;
                break;
            }
        }

        for x in 0..(1 << (many.len()*2)) {
            if target == equation_result_b(&many, x) {
                sum_b += target;
                break;
            }
        }
    }

    println!("sum of valid targets is {sum_a}, part b is {sum_b}");
}

fn equation_result_a(numbers: &[i128], bitmask: usize) -> i128 {
    let mut sum = numbers[0];
    for i in 1..numbers.len() {
        sum = match (bitmask >> (i-1)) & 1 {
            0 => sum + numbers[i],
            1 => sum * numbers[i],
            _ => panic!("how did this happen"),
        }
    }
    return sum;
}

fn equation_result_b(numbers: &[i128], bitmask: usize) -> i128 {
    let mut sum = numbers[0];
    for i in 1..numbers.len() {
        sum = match (bitmask >> ((i-1)*2)) & 0b11 {
            0 => sum + numbers[i],
            1 => sum * numbers[i],
            2 => concatenate(sum, numbers[i]),
            3 => { return -1; },
            _ => panic!("how did this happen"),
        }
    }
    return sum;
}

fn concatenate(a: i128, b: i128) -> i128 {
    return (a * (10_i128).pow(b.ilog10()+1)) + b;
}