#![warn(clippy::pedantic, clippy::nursery)]

use axum::extract::ConnectInfo;
use axum::handler::get;
use axum::http::{HeaderMap, HeaderValue};
use axum::{Router, Server};
use std::net::{Ipv4Addr, Ipv6Addr, SocketAddr};

#[tokio::main]
async fn main() {
    let app = Router::new().route("/", get(root));

    let addr = SocketAddr::from(([127, 0, 0, 1], 3000));
    Server::bind(&addr)
        .serve(app.into_make_service_with_connect_info::<SocketAddr, _>())
        .await
        .unwrap();
}

#[allow(clippy::unused_async)]
async fn root(header: HeaderMap, ConnectInfo(socket_info): ConnectInfo<SocketAddr>) -> String {
    if let Some(Ok(value)) = header.get("Forwarded").map(HeaderValue::to_str) {
        let match_str = "or="; // the `for` key is case-insensitive
        let maybe_index = value.find(match_str);
        if let Some(index) = maybe_index {
            let ip_start = value.split_at(index + match_str.len()).1;

            let mut chars = ip_start.chars().peekable();

            if let Some('"') = chars.peek() {
                // We're dealing with an ipv6 address

                // skip first character, since we know it's an `"`
                chars.next();
                let res: String = chars.take_while(|c| *c != '"').collect();
                if res.parse::<Ipv6Addr>().is_ok() {
                    return res;
                }
            } else {
                let res: String = chars.take_while(|c| *c != 'c').collect();
                if res.parse::<Ipv4Addr>().is_ok() {
                    return res;
                }
            }
        }
    }

    if let Some(Ok(value)) = header.get("X-Forwarded-For").map(HeaderValue::to_str) {
        return match value.split_once(',').map(|v| v.0) {
            Some(v) => v,
            None => value,
        }
        .to_string();
    }

    socket_info.ip().to_string()
}