use std::future::IntoFuture;
use std::os::fd::{FromRawFd, OwnedFd};
use std::path::PathBuf;
use std::sync::Arc;

use anyhow::{bail, Context, Result};
use blahd::config::{Config, ListenConfig};
use blahd::{AppState, Database};
use tokio::net::TcpListener;
use tokio::signal::unix::{signal, SignalKind};

/// Blah Chat Server
#[derive(Debug, clap::Parser)]
#[clap(about, version = env!("CFG_RELEASE"))]
enum Cli {
    /// Run the server with given configuration.
    Serve {
        /// The path to the configuration file.
        #[arg(long, short)]
        config: PathBuf,
    },

    /// Validate the configuration file and exit.
    Validate {
        /// The path to the configuration file.
        #[arg(long, short)]
        config: PathBuf,
    },
}

fn main() -> Result<()> {
    tracing_subscriber::fmt::init();
    let cli = <Cli as clap::Parser>::parse();

    fn parse_config(path: &std::path::Path) -> Result<Config> {
        let src = std::fs::read_to_string(path)?;
        let config = toml::from_str::<Config>(&src)?;
        Ok(config)
    }

    match cli {
        Cli::Serve { config } => {
            let config = parse_config(&config)?;
            let db = Database::open(&config.database).context("failed to open database")?;
            tokio::runtime::Builder::new_multi_thread()
                .enable_all()
                .build()
                .context("failed to initialize tokio runtime")?
                .block_on(main_serve(db, config))
        }
        Cli::Validate { config } => {
            parse_config(&config)?;
            Ok(())
        }
    }
}

async fn main_serve(db: Database, config: Config) -> Result<()> {
    let st = AppState::new(db, config.server);

    let mut listen_fds = sd_notify::listen_fds()
        .context("failed to get fds from sd_listen_fds(3)")?
        // SAFETY: `fd` is valid by sd_listen_fds(3) protocol.
        .map(|fd| unsafe { Some(OwnedFd::from_raw_fd(fd)) })
        .collect::<Vec<_>>();

    let mut get_listener = move |name: &'static str, fd_idx: usize, listen: ListenConfig| {
        let fd = listen_fds.get_mut(0).and_then(|opt| opt.take());
        async move {
            match listen {
                ListenConfig::Address(addr) => {
                    tracing::info!("serve {name} on address {addr:?}");
                    TcpListener::bind(addr)
                        .await
                        .context("failed to listen on socket")
                }
                ListenConfig::Systemd(_) => {
                    use rustix::net::{getsockname, SocketAddrAny};

                    let fd = fd.with_context(|| format!("missing LISTEN_FDS[{fd_idx}]"))?;
                    let addr = getsockname(&fd).context("failed to getsockname")?;
                    match addr {
                        SocketAddrAny::V4(_) | SocketAddrAny::V6(_) => {
                            let listener = std::net::TcpListener::from(fd);
                            listener
                                .set_nonblocking(true)
                                .context("failed to set socket non-blocking")?;
                            let listener = TcpListener::from_std(listener)
                                .context("failed to register async socket")?;
                            tracing::info!(
                                "serve {name} on tcp socket {addr:?} from LISTEN_FDS[{fd_idx}"
                            );
                            Ok(listener)
                        }
                        // Unix socket support for axum is currently overly complex.
                        // WAIT: https://github.com/tokio-rs/axum/pull/2479
                        _ => bail!("unsupported socket type from LISTEN_FDS[{fd_idx}]: {addr:?}"),
                    }
                }
            }
        }
    };

    let router = blahd::router(Arc::new(st));

    #[cfg(not(feature = "prometheus"))]
    anyhow::ensure!(
        config.metric.is_none(),
        "metric support is disabled at compile time",
    );

    #[cfg(feature = "prometheus")]
    let router = if let Some(metric_config) = &config.metric {
        let blahd::config::MetricConfig::Prometheus(prom_config) = metric_config;
        let metric_listener = get_listener("metrics", 1, prom_config.listen.clone()).await?;
        let (metric_router, recorder, upkeeper) = blahd::metrics_router(metric_config);
        metrics::set_global_recorder(recorder).expect("only set once");
        tokio::spawn(upkeeper);
        tokio::spawn(axum::serve(metric_listener, metric_router).into_future());
        router.layer(axum_metrics::MetricLayer::default())
    } else {
        router
    };

    let mut sigterm = signal(SignalKind::terminate()).context("failed to listen on SIGTERM")?;
    let listener = get_listener("main", 0, config.listen.clone()).await?;
    let service = axum::serve(listener, router)
        .with_graceful_shutdown(async move {
            sigterm.recv().await;
            tracing::info!("received SIGTERM, shutting down gracefully");
        })
        .into_future();

    let _ = sd_notify::notify(true, &[sd_notify::NotifyState::Ready]);
    service.await.context("failed to serve")?;
    Ok(())
}