use anyhow::anyhow;
use clap::Parser;
use tokio::io::{AsyncReadExt, AsyncWriteExt};
use tokio_listener::{self, SystemOptions, UserOptions};
use tracing::{debug, error, info, instrument, Level};

use nix_compat::wire::{
    bytes, primitive,
    worker_protocol::{self, ClientSettings},
};

#[derive(Parser, Debug)]
struct Cli {
    /// Listening unix socket path
    #[arg(short, long)]
    socket: Option<String>,
    /// Log verbosity level. Can be "error", "warn", "info", "debug", "trace", or a number 1-5
    #[arg(short, long, env)]
    verbosity: Option<Level>,
}

/// Structure used to hold the client socket connection and some
/// metadata about the connection.
#[derive(Debug)]
struct ClientConnection<R: AsyncReadExt + AsyncWriteExt + Unpin> {
    conn: R,
    version_minor: u64,
    client_settings: Option<ClientSettings>,
}

#[tokio::main]
#[instrument()]
async fn main() {
    let args = Cli::parse();
    tracing_subscriber::fmt()
        .compact()
        .with_max_level(
            args.verbosity
                .unwrap_or_else(|| panic!("Can't parse log verbosity")),
        )
        .try_init()
        .unwrap();
    info!("Started Tvix daemon");
    let addr = args
        .socket
        .unwrap_or_else(|| "sd_listen_unix".to_string())
        .parse()
        .expect("Invalid listening socket address");
    let system_options: SystemOptions = Default::default();
    let mut user_options: UserOptions = Default::default();
    user_options.recv_buffer_size = Some(1024);
    user_options.send_buffer_size = Some(1024);
    info!(user_options.send_buffer_size);
    info!(user_options.recv_buffer_size);
    let mut listener = tokio_listener::Listener::bind(&addr, &system_options, &user_options)
        .await
        .unwrap();
    info!(listener_address = ?listener, "Listening for incoming connections");
    while let Ok((conn, addr)) = listener.accept().await {
        info!(addr = %addr, "Incoming connection");
        tokio::spawn(async move { worker(conn).await });
    }
}

/// Worker in charge to respond a Nix client using the Nix wire
/// protocol.
#[instrument()]
async fn worker<R>(mut conn: R)
where
    R: AsyncReadExt + AsyncWriteExt + Unpin + std::fmt::Debug,
{
    match perform_init_handshake(&mut conn).await {
        Ok(mut client_connection) => {
            debug!("Client hanshake succeeded");
            // TODO: implement logging. For now, we'll just send
            // STDERR_LAST, which is good enough to get Nix respond to
            // us.
            primitive::write_u64(&mut client_connection.conn, worker_protocol::STDERR_LAST)
                .await
                .unwrap();
            loop {
                let op = worker_protocol::read_op(&mut client_connection.conn)
                    .await
                    .unwrap();
                match op {
                    worker_protocol::Operation::SetOptions => {
                        let settings = op_set_options(&mut client_connection).await.unwrap();
                        client_connection.client_settings = Some(settings);
                        debug!(settings = ?client_connection.client_settings, "Received client settings");
                    }
                    _ => {
                        error!(op = ?op, "Unimplemented operation");
                        break;
                    }
                }
            }
        }
        Err(e) => error!("Client handshake failed: {}", e),
    }
}

async fn op_set_options<R>(conn: &mut ClientConnection<R>) -> std::io::Result<ClientSettings>
where
    R: AsyncReadExt + AsyncWriteExt + Unpin + std::fmt::Debug,
{
    let settings =
        worker_protocol::read_client_settings(&mut conn.conn, conn.version_minor).await?;
    // The client expects us to send some logs when we're processing
    // the settings. Sending STDERR_LAST signal we're done processing.
    primitive::write_u64(&mut conn.conn, worker_protocol::STDERR_LAST).await?;
    Ok(settings)
}

/// Performs the initial handshake. During the handshake, the client
/// will first send a magic u64, to which the daemon needs to respond
/// with another magic u64.
///
/// We then retrieve the client version, and discard a bunch of now
/// obsolete data.
#[instrument()]
async fn perform_init_handshake<'a, R: 'a>(
    mut conn: &'a mut R,
) -> anyhow::Result<ClientConnection<&'a mut R>>
where
    &'a mut R: AsyncReadExt + AsyncWriteExt + Unpin + std::fmt::Debug,
{
    let worker_magic_1 = primitive::read_u64(&mut conn).await?;
    debug!("Hello read");
    if worker_magic_1 != worker_protocol::WORKER_MAGIC_1 {
        Err(anyhow!(
            "Invalid client hello received: {:?}, expected {:?}",
            worker_magic_1,
            worker_protocol::WORKER_MAGIC_1
        ))
    } else {
        primitive::write_u64(&mut conn, worker_protocol::WORKER_MAGIC_2).await?;
        primitive::write_u64(&mut conn, worker_protocol::PROTOCOL_VERSION).await?;
        conn.flush().await?;
        debug!("Hello responded");
        let client_version = primitive::read_u64(&mut conn).await?;
        debug!("Version read");
        if client_version < 0x10a {
            return Err(anyhow!("The nix client version is too old"));
        }
        let protocol_minor = client_version & 0x00ff;
        let protocol_major = client_version & 0xff00;
        debug!(client.version = %client_version, client.minor = %protocol_minor, client.major = %protocol_major);
        if protocol_minor >= 14 {
            debug!("read cpu affinity");
            // Obsolete CPU affinity.
            let read_affinity = primitive::read_u64(&mut conn).await?;
            if read_affinity != 0 {
                skip_8_bytes(&mut conn).await?;
            };
        }
        if protocol_minor >= 11 {
            // Obsolete reserveSpace
            debug!("read reservespace");
            skip_8_bytes(&mut conn).await?;
        }
        if protocol_minor >= 33 {
            // Nix version. We're plain lying, we're not Nix, but eh…
            // Setting it to the 2.3 lineage. Not 100% sure this is a
            // good idea.
            debug!("write version");
            // Plain str padded to 64 bits.
            bytes::write_bytes(&mut conn, "2.3.17").await?;
            conn.flush().await?;
        }
        if protocol_minor >= 35 {
            worker_protocol::write_worker_trust_level(&mut conn, worker_protocol::Trust::Trusted)
                .await?;
            info!("Trust sent");
        }
        Ok(ClientConnection {
            conn,
            version_minor: protocol_minor,
            client_settings: None,
        })
    }
}

async fn skip_8_bytes<R>(conn: &mut R) -> anyhow::Result<()>
where
    R: AsyncReadExt + Unpin + std::fmt::Debug,
{
    let mut _discard_buffer = [0; 8];
    conn.read_exact(&mut _discard_buffer).await?;
    Ok(())
}

#[cfg(test)]
mod integration_tests {
    use nix_compat::wire::worker_protocol;
    #[tokio::test]
    async fn test_init_handshake() {
        let mut test_conn = tokio_test::io::Builder::new()
            .read(&worker_protocol::WORKER_MAGIC_1.to_le_bytes())
            .write(&worker_protocol::WORKER_MAGIC_2.to_le_bytes())
            .write(&worker_protocol::PROTOCOL_VERSION.to_le_bytes())
            // Let's say the client is in sync with the daemon
            // protocol-wise
            .read(&worker_protocol::PROTOCOL_VERSION.to_le_bytes())
            // cpu affinity
            .read(&vec![0; 8])
            // reservespace
            .read(&vec![0; 8])
            // version (size)
            .write(&vec![0x06, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00])
            // version (data == 2.2.17 + padding)
            .write(&vec![50, 46, 51, 46, 49, 55, 0, 0])
            // Trusted (1 == client trusted
            .write(&vec![1, 0, 0, 0, 0, 0, 0, 0])
            .build();
        crate::perform_init_handshake(&mut test_conn).await.unwrap();
    }
}