use std::os::fd::{FromRawFd, IntoRawFd, OwnedFd};

use futures_util::stream::StreamExt;

use netlink_packet_audit::AuditMessage;

use netlink_proto::sys::TokioSocket;

use tokio::sync::mpsc;

/// `AUDIT_USER_START` is emitted when a PAM session is opened

const AUDIT_USER_START: u16 = 1105;

/// `AUDIT_USER_END` is emitted when a PAM session is closed

const AUDIT_USER_END: u16 = 1106;

/// Listens for audit messages on the systemd-provided netlink socket and sends a

/// notification on the provided channel whenever a user session is opened or closed,

/// indicating that there rwhod status may have changed.

    // SAFETY: `socket_fd` is a systemd-provided netlink socket, already

    // bound and subscribed to the audit multicast group.

    let socket = unsafe { TokioSocket::from_raw_fd(socket_fd.into_raw_fd()) };

    let (connection, _handle, mut messages) = netlink_proto::from_socket_with_codec::<

        AuditMessage,

        TokioSocket,

        netlink_packet_audit::NetlinkAuditCodec,

    >(socket);

    tokio::spawn(connection);

    tracing::info!("Listening for realtime session updates via the Linux audit log");

    loop {

        match messages.next().await {

            Some((msg, _addr))

                if matches!(msg.header.message_type, AUDIT_USER_START | AUDIT_USER_END) =>

            {

                tracing::debug!("Received session-related audit message: {:?}", msg);

                if sender.send(()).await.is_err() {

                    tracing::debug!("Realtime update receiver dropped, stopping audit watcher");

                    return;

                }

            }

            Some((msg, _addr)) => {

                tracing::trace!(

                    "Ignoring audit message unrelated to sessions (type {})",

                    msg.header.message_type

                );

            }

            None => {

                tracing::warn!(

                    "Audit netlink connection closed unexpectedly; realtime updates disabled \

                     for the rest of this run"

                );

                return;

            }

        }

    }

}