For a final bit of code to roast, here is the bot that posted the daily threads:

::: spoiler Bot code

use std::process::exit;
use chrono::{Datelike, Timelike};
use lemmy_client::lemmy_api_common::community::GetCommunity;
use lemmy_client::lemmy_api_common::person::Login;
use lemmy_client::lemmy_api_common::post::CreatePost;
use lemmy_client::{ClientOptions, LemmyClient};
use rand::seq::IndexedRandom;
use regex::Regex;

static TARGET_COMMUNITY: &str = "[email protected]";

async fn get_advent_emoji() -> String {
    let choices = ['🎄','🎁','🧦','🕯','🌟','✨','🧸','⛄','☃','❄','🏔','🎅','🤶','🧑','🦌','👼','👪','🍽','🥛','🍷','🍗','🥧','🍬','🍫','🎶','🎶','🔔','🎊','🎉','💃'];
    choices.choose(&mut rand::rng()).unwrap().to_string()
}

async fn get_advent_title(year: i32, day: u32) -> String {
    let url = format!("https://adventofcode.com/%7B%7D/day/%7B%7D", year, day);

    let resp = reqwest::get(url).await.unwrap();
    let body = String::from_utf8(resp.bytes().await.unwrap().to_vec()).unwrap();

    let re = Regex::new(r"---(.*)---").unwrap();

    for (_, [line]) in re.captures_iter(&body).map(|c| c.extract()) {
        return line.trim().to_string();
    }

    panic!("could not find advent title - {body}");
}

#[tokio::main]
async fn main() {
    let time = chrono::Utc::now();
    let year = time.year();
    let day = time.day();

    if time.hour() != 5 {
        println!("Wrong time: {time}");
        exit(0);
    }

    let title = get_advent_title(year, day).await;
    println!("Title: {:#?}", title);

    post_to_lemmy(year, day, title).await;
}

async fn post_to_lemmy(year: i32, day:u32, challenge_title: String) {
    let emoji = get_advent_emoji().await;
    let post_title = format!("{emoji} - {year} DAY {day} SOLUTIONS - {emoji}");
    let post_body = format!("# {challenge_title}

## Megathread guidelines
- Keep top level comments as only solutions, if you want to say something other than a solution put it in a new post. (replies to comments can be whatever)
- You can send code in code blocks by using three backticks, the code, and then three backticks or use something such as https://topaz.github.io/paste/ if you prefer sending it through a URL

## FAQ
- What is this?: Here is a post with a large amount of details: https://programming.dev/post/6637268
- Where do I participate?: https://adventofcode.com/
- Is there a leaderboard for the community?: We have a programming.dev leaderboard with the info on how to join in this post: https://programming.dev/post/6631465");

    let mut client = LemmyClient::new(ClientOptions {
        domain: "programming.dev".to_string(),
        secure: true,
    });

    let auth = client.login(Login {
        username_or_email: "HARDCODED".to_string().into(),
        password: "HARDCODED".to_string().into(),
        totp_2fa_token: None,
    }).await.unwrap();

    client.headers_mut().insert("Authorization".to_string(),
                                format!("Bearer {}", auth.jwt.unwrap().to_string()));

    let community = client.get_community(GetCommunity {
        id: None,
        name: Some(TARGET_COMMUNITY.to_string()),
    }).await.unwrap();
    let community_id = community.community_view.community.id;

    client.create_post(CreatePost {
        name: post_title,
        community_id,
        url: None,
        body: Some(post_body),
        alt_text: None,
        honeypot: None,
        nsfw: None,
        language_id: None,
        custom_thumbnail: None,
    }).await.unwrap();

}

:::

I still have day 12 to do. Got stuck on day 10, refused to use third party solver and persevered. Day 11 was quite basic compared with 10.

Even though it wasn't remotely in my control, I love my nice even score this year.