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    use actix::Addr;
    use actix_redis::{resp_array, Command, RedisActor, RespValue};
    use actix_web::cookie::time::Duration;
    use anyhow::Error;

    use super::SessionKey;
    use crate::storage::{
        interface::{LoadError, SaveError, SessionState, UpdateError},
        utils::generate_session_key,
        SessionStore,
    };

    /// Use Redis as session storage backend.
    ///
    /// ```no_run
    /// use actix_web::{web, App, HttpServer, HttpResponse, Error};
    /// use actix_session::{SessionMiddleware, storage::RedisActorSessionStore};
    /// use actix_web::cookie::Key;
    ///
    /// // The secret key would usually be read from a configuration file/environment variables.
    /// fn get_secret_key() -> Key {
    ///     # todo!()
    ///     // [...]
    /// }
    ///
    /// #[actix_web::main]
    /// async fn main() -> std::io::Result<()> {
    ///     let secret_key = get_secret_key();
    ///     let redis_connection_string = "127.0.0.1:6379";
    ///     HttpServer::new(move ||
    ///             App::new()
    ///             .wrap(
    ///                 SessionMiddleware::new(
    ///                     RedisActorSessionStore::new(redis_connection_string),
    ///                     secret_key.clone()
    ///                 )
    ///             )
    ///             .default_service(web::to(|| HttpResponse::Ok())))
    ///         .bind(("127.0.0.1", 8080))?
    ///         .run()
    ///         .await
    /// }
    /// ```
    ///
    /// # Implementation notes
    ///
    /// `RedisActorSessionStore` leverages `actix-redis`'s `RedisActor` implementation - each thread
    /// worker gets its own connection to Redis.
    ///
    /// ## Limitations
    ///
    /// `RedisActorSessionStore` does not currently support establishing authenticated connections to
    /// Redis. Use [`RedisSessionStore`] if you need TLS support.
    ///
    /// [`RedisSessionStore`]: crate::storage::RedisSessionStore
    pub struct RedisActorSessionStore {
        configuration: CacheConfiguration,
        addr: Addr<RedisActor>,
    }

    impl RedisActorSessionStore {
        /// A fluent API to configure [`RedisActorSessionStore`].
        ///
        /// It takes as input the only required input to create a new instance of
        /// [`RedisActorSessionStore`]—a connection string for Redis.
        pub fn builder<S: Into<String>>(connection_string: S) -> RedisActorSessionStoreBuilder {
            RedisActorSessionStoreBuilder {
                configuration: CacheConfiguration::default(),
                connection_string: connection_string.into(),
            }
        }

        /// Create a new instance of [`RedisActorSessionStore`] using the default configuration.
        /// It takes as input the only required input to create a new instance of [`RedisActorSessionStore`] - a
        /// connection string for Redis.
        pub fn new<S: Into<String>>(connection_string: S) -> RedisActorSessionStore {
            Self::builder(connection_string).build()
        }
    }

    struct CacheConfiguration {
        cache_keygen: Box<dyn Fn(&str) -> String>,
    }

    impl Default for CacheConfiguration {
        fn default() -> Self {
            Self {
                cache_keygen: Box::new(str::to_owned),
            }
        }
    }

    /// A fluent builder to construct a [`RedisActorSessionStore`] instance with custom configuration
    /// parameters.
    #[must_use]
    pub struct RedisActorSessionStoreBuilder {
        connection_string: String,
        configuration: CacheConfiguration,
    }

    impl RedisActorSessionStoreBuilder {
        /// Set a custom cache key generation strategy, expecting a session key as input.
        pub fn cache_keygen<F>(mut self, keygen: F) -> Self
        where
            F: Fn(&str) -> String + 'static,
        {
            self.configuration.cache_keygen = Box::new(keygen);
            self
        }

        /// Finalise the builder and return a [`RedisActorSessionStore`] instance.
        #[must_use]
        pub fn build(self) -> RedisActorSessionStore {
            RedisActorSessionStore {
                configuration: self.configuration,
                addr: RedisActor::start(self.connection_string),
            }
        }
    }

    impl SessionStore for RedisActorSessionStore {
        async fn load(&self, session_key: &SessionKey) -> Result<Option<SessionState>, LoadError> {
            let cache_key = (self.configuration.cache_keygen)(session_key.as_ref());
            let val = self
                .addr
                .send(Command(resp_array!["GET", cache_key]))
                .await
                .map_err(Into::into)
                .map_err(LoadError::Other)?
                .map_err(Into::into)
                .map_err(LoadError::Other)?;

            match val {
                RespValue::Error(err) => Err(LoadError::Other(anyhow::anyhow!(err))),

                RespValue::SimpleString(s) => Ok(serde_json::from_str(&s)
                    .map_err(Into::into)
                    .map_err(LoadError::Deserialization)?),

                RespValue::BulkString(s) => Ok(serde_json::from_slice(&s)
                    .map_err(Into::into)
                    .map_err(LoadError::Deserialization)?),

                _ => Ok(None),
            }
        }

        async fn save(
            &self,
            session_state: SessionState,
            ttl: &Duration,
        ) -> Result<SessionKey, SaveError> {
            let body = serde_json::to_string(&session_state)
                .map_err(Into::into)
                .map_err(SaveError::Serialization)?;
            let session_key = generate_session_key();
            let cache_key = (self.configuration.cache_keygen)(session_key.as_ref());

            let cmd = Command(resp_array![
                "SET",
                cache_key,
                body,
                "NX", // NX: only set the key if it does not already exist
                "EX", // EX: set expiry
                format!("{}", ttl.whole_seconds())
            ]);

            let result = self
                .addr
                .send(cmd)
                .await
                .map_err(Into::into)
                .map_err(SaveError::Other)?
                .map_err(Into::into)
                .map_err(SaveError::Other)?;

            match result {
                RespValue::SimpleString(_) => Ok(session_key),
                RespValue::Nil => Err(SaveError::Other(anyhow::anyhow!(
                    "Failed to save session state. A record with the same key already existed in Redis"
                ))),
                err => Err(SaveError::Other(anyhow::anyhow!(
                    "Failed to save session state. {:?}",
                    err
                ))),
            }
        }

        async fn update(
            &self,
            session_key: SessionKey,
            session_state: SessionState,
            ttl: &Duration,
        ) -> Result<SessionKey, UpdateError> {
            let body = serde_json::to_string(&session_state)
                .map_err(Into::into)
                .map_err(UpdateError::Serialization)?;
            let cache_key = (self.configuration.cache_keygen)(session_key.as_ref());

            let cmd = Command(resp_array![
                "SET",
                cache_key,
                body,
                "XX", // XX: Only set the key if it already exist.
                "EX", // EX: set expiry
                format!("{}", ttl.whole_seconds())
            ]);

            let result = self
                .addr
                .send(cmd)
                .await
                .map_err(Into::into)
                .map_err(UpdateError::Other)?
                .map_err(Into::into)
                .map_err(UpdateError::Other)?;

            match result {
                RespValue::Nil => {
                    // The SET operation was not performed because the XX condition was not verified.
                    // This can happen if the session state expired between the load operation and the
                    // update operation. Unlucky, to say the least. We fall back to the `save` routine
                    // to ensure that the new key is unique.
                    self.save(session_state, ttl)
                        .await
                        .map_err(|err| match err {
                            SaveError::Serialization(err) => UpdateError::Serialization(err),
                            SaveError::Other(err) => UpdateError::Other(err),
                        })
                }
                RespValue::SimpleString(_) => Ok(session_key),
                val => Err(UpdateError::Other(anyhow::anyhow!(
                    "Failed to update session state. {:?}",
                    val
                ))),
            }
        }

        async fn update_ttl(&self, session_key: &SessionKey, ttl: &Duration) -> Result<(), Error> {
            let cache_key = (self.configuration.cache_keygen)(session_key.as_ref());

            let cmd = Command(resp_array![
                "EXPIRE",
                cache_key,
                ttl.whole_seconds().to_string()
            ]);

            match self.addr.send(cmd).await? {
                Ok(RespValue::Integer(_)) => Ok(()),
                val => Err(anyhow::anyhow!(
                    "Failed to update the session state TTL: {:?}",
                    val
                )),
            }
        }

        async fn delete(&self, session_key: &SessionKey) -> Result<(), anyhow::Error> {
            let cache_key = (self.configuration.cache_keygen)(session_key.as_ref());

            let res = self
                .addr
                .send(Command(resp_array!["DEL", cache_key]))
                .await?;

            match res {
                // Redis returns the number of deleted records
                Ok(RespValue::Integer(_)) => Ok(()),
                val => Err(anyhow::anyhow!(
                    "Failed to remove session from cache. {:?}",
                    val
                )),
            }
        }
    }

    #[cfg(test)]
    mod tests {
        use std::collections::HashMap;

        use actix_web::cookie::time::Duration;

        use super::*;
        use crate::test_helpers::acceptance_test_suite;

        fn redis_actor_store() -> RedisActorSessionStore {
            RedisActorSessionStore::new("127.0.0.1:6379")
        }

        #[actix_web::test]
        async fn test_session_workflow() {
            acceptance_test_suite(redis_actor_store, true).await;
        }

        #[actix_web::test]
        async fn loading_a_missing_session_returns_none() {
            let store = redis_actor_store();
            let session_key = generate_session_key();
            assert!(store.load(&session_key).await.unwrap().is_none());
        }

        #[actix_web::test]
        async fn updating_of_an_expired_state_is_handled_gracefully() {
            let store = redis_actor_store();
            let session_key = generate_session_key();
            let initial_session_key = session_key.as_ref().to_owned();
            let updated_session_key = store
                .update(session_key, HashMap::new(), &Duration::seconds(1))
                .await
                .unwrap();
            assert_ne!(initial_session_key, updated_session_key.as_ref());
        }
    }