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    use std::{collections::VecDeque, io};

    use actix::prelude::*;
    use actix_rt::net::TcpStream;
    use actix_service::boxed::{self, BoxService};
    use actix_tls::connect::{ConnectError, ConnectInfo, Connection, ConnectorService};
    use backoff::{backoff::Backoff, ExponentialBackoff};
    use log::{error, info, warn};
    use redis_async::{
        error::Error as RespError,
        resp::{RespCodec, RespValue},
    };
    use tokio::{
        io::{split, WriteHalf},
        sync::oneshot,
    };
    use tokio_util::codec::FramedRead;

    use crate::Error;

    /// Command for sending data to Redis.
    #[derive(Debug)]
    pub struct Command(pub RespValue);

    impl Message for Command {
        type Result = Result<RespValue, Error>;
    }

    /// Redis communication actor.
    pub struct RedisActor {
        addr: String,
        connector: BoxService<ConnectInfo<String>, Connection<String, TcpStream>, ConnectError>,
        backoff: ExponentialBackoff,
        cell: Option<actix::io::FramedWrite<RespValue, WriteHalf<TcpStream>, RespCodec>>,
        queue: VecDeque<oneshot::Sender<Result<RespValue, Error>>>,
    }

    impl RedisActor {
        /// Start new `Supervisor` with `RedisActor`.
        pub fn start<S: Into<String>>(addr: S) -> Addr<RedisActor> {
            let addr = addr.into();

            let backoff = ExponentialBackoff {
                max_elapsed_time: None,
                ..Default::default()
            };

            Supervisor::start(|_| RedisActor {
                addr,
                connector: boxed::service(ConnectorService::default()),
                cell: None,
                backoff,
                queue: VecDeque::new(),
            })
        }
    }

    impl Actor for RedisActor {
        type Context = Context<Self>;

        fn started(&mut self, ctx: &mut Context<Self>) {
            let req = ConnectInfo::new(self.addr.to_owned());
            self.connector
                .call(req)
                .into_actor(self)
                .map(|res, act, ctx| match res {
                    Ok(conn) => {
                        let stream = conn.into_parts().0;
                        info!("Connected to redis server: {}", act.addr);

                        let (r, w) = split(stream);

                        // configure write side of the connection
                        let framed = actix::io::FramedWrite::new(w, RespCodec, ctx);
                        act.cell = Some(framed);

                        // read side of the connection
                        ctx.add_stream(FramedRead::new(r, RespCodec));

                        act.backoff.reset();
                    }
                    Err(err) => {
                        error!("Can not connect to redis server: {}", err);
                        // re-connect with backoff time.
                        // we stop current context, supervisor will restart it.
                        if let Some(timeout) = act.backoff.next_backoff() {
                            ctx.run_later(timeout, |_, ctx| ctx.stop());
                        }
                    }
                })
                .wait(ctx);
        }
    }

    impl Supervised for RedisActor {
        fn restarting(&mut self, _: &mut Self::Context) {
            self.cell.take();
            for tx in self.queue.drain(..) {
                let _ = tx.send(Err(Error::Disconnected));
            }
        }
    }

    impl actix::io::WriteHandler<io::Error> for RedisActor {
        fn error(&mut self, err: io::Error, _: &mut Self::Context) -> Running {
            warn!("Redis connection dropped: {} error: {}", self.addr, err);
            Running::Stop
        }
    }

    impl StreamHandler<Result<RespValue, RespError>> for RedisActor {
        fn handle(&mut self, msg: Result<RespValue, RespError>, ctx: &mut Self::Context) {
            match msg {
                Err(e) => {
                    if let Some(tx) = self.queue.pop_front() {
                        let _ = tx.send(Err(e.into()));
                    }
                    ctx.stop();
                }
                Ok(val) => {
                    if let Some(tx) = self.queue.pop_front() {
                        let _ = tx.send(Ok(val));
                    }
                }
            }
        }
    }

    impl Handler<Command> for RedisActor {
        type Result = ResponseFuture<Result<RespValue, Error>>;

        fn handle(&mut self, msg: Command, _: &mut Self::Context) -> Self::Result {
            let (tx, rx) = oneshot::channel();
            if let Some(ref mut cell) = self.cell {
                self.queue.push_back(tx);
                cell.write(msg.0);
            } else {
                let _ = tx.send(Err(Error::NotConnected));
            }

            Box::pin(async move { rx.await.map_err(|_| Error::Disconnected)? })
        }
    }