use axum::{
  routing::get,
  Router,
  response::{
      IntoResponse,
      Response,
  },
  http::StatusCode,
};

use std::net::SocketAddr;
use std::str::FromStr;

#[tokio::main]
async fn main() {
  let mut listen = String::from("[::]:9152");
  let mut args = std::env::args();
  args.next();
  loop {
    let arg = if let Some(arg) = args.next() {
      arg
    } else {
      break
    };

    match arg.as_str() {
      "--help" | "-h" => {
          println!("Prometheus exporter for NixOS systems");
          println!("Use --listen <addr:port> bind the web service.");
          println!("Output will be on /metrics endpoint. HTTP 500 if something broke while scraping.");
          std::process::exit(0);
      },
      "--listen" => {
        listen = args.next().unwrap();
      },
      unknown => {
        println!("unknown option: {}", unknown);
        std::process::exit(1)
      }
    }
  }

  let app = Router::new().route("/metrics", get(metrics));

  let addr = SocketAddr::from_str(&listen).unwrap();
  println!("listening on http://{}", addr);
  axum::Server::bind(&addr)
    .serve(app.into_make_service())
    .await
    .unwrap();
}

fn get_current_system() -> Result<(String, String), String> {
  let symlink = match std::fs::read_link("/run/current-system") {
    Ok(symlink) => symlink,
    Err(err) => return Err(err.to_string())
  };

  let (hash, name) = symlink.file_name()
    .ok_or_else(String::default)?
    .to_str()
    .ok_or_else(String::default)?
    .split_once("-")
    .ok_or_else(String::default)?;

  Ok((String::from(hash), String::from(name)))
}

async fn metrics() -> Response {
  let current_system = get_current_system();
  let (hash, name) = match current_system {
    Ok((hash, name)) => (hash, name),
    Err(err) => {
      println!("failed: {}", err);
      return (StatusCode::INTERNAL_SERVER_ERROR, "").into_response()
    }
  };

  (
    StatusCode::OK,
    format!("nixos_nixos_current_system_hash{{hash=\"{}\"}}\nnixos_current_system_name{{name=\"{}\"}}", hash, name)
  ).into_response()
}