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    use std::sync::Arc;

    use actix_web::cookie::time::Duration;
    use anyhow::Error;
    use redis::{aio::ConnectionManager, AsyncCommands, Cmd, FromRedisValue, RedisResult, Value};

    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::RedisSessionStore};
    /// 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 = "redis://127.0.0.1:6379";
    ///     let store = RedisSessionStore::new(redis_connection_string).await.unwrap();
    ///
    ///     HttpServer::new(move ||
    ///             App::new()
    ///             .wrap(SessionMiddleware::new(
    ///                 store.clone(),
    ///                 secret_key.clone()
    ///             ))
    ///             .default_service(web::to(|| HttpResponse::Ok())))
    ///         .bind(("127.0.0.1", 8080))?
    ///         .run()
    ///         .await
    /// }
    /// ```
    ///
    /// # TLS support
    /// Add the `redis-rs-tls-session` feature flag to enable TLS support. You can then establish a TLS
    /// connection to Redis using the `rediss://` URL scheme:
    ///
    /// ```no_run
    /// use actix_session::{storage::RedisSessionStore};
    ///
    /// # actix_web::rt::System::new().block_on(async {
    /// let redis_connection_string = "rediss://127.0.0.1:6379";
    /// let store = RedisSessionStore::new(redis_connection_string).await.unwrap();
    /// # })
    /// ```
    ///
    /// # Implementation notes
    /// `RedisSessionStore` leverages [`redis-rs`] as Redis client.
    ///
    /// [`redis-rs`]: https://github.com/mitsuhiko/redis-rs
    #[derive(Clone)]
    pub struct RedisSessionStore {
        configuration: CacheConfiguration,
        client: ConnectionManager,
    }

    #[derive(Clone)]
    struct CacheConfiguration {
        cache_keygen: Arc<dyn Fn(&str) -> String + Send + Sync>,
    }

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

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

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

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

    impl RedisSessionStoreBuilder {
        /// 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 + Send + Sync,
        {
            self.configuration.cache_keygen = Arc::new(keygen);
            self
        }

        /// Finalise the builder and return a [`RedisActorSessionStore`] instance.
        ///
        /// [`RedisActorSessionStore`]: crate::storage::RedisActorSessionStore
        pub async fn build(self) -> Result<RedisSessionStore, anyhow::Error> {
            let client = ConnectionManager::new(redis::Client::open(self.connection_string)?).await?;
            Ok(RedisSessionStore {
                configuration: self.configuration,
                client,
            })
        }
    }

    impl SessionStore for RedisSessionStore {
        async fn load(&self, session_key: &SessionKey) -> Result<Option<SessionState>, LoadError> {
            let cache_key = (self.configuration.cache_keygen)(session_key.as_ref());

            let value: Option<String> = self
                .execute_command(redis::cmd("GET").arg(&[&cache_key]))
                .await
                .map_err(Into::into)
                .map_err(LoadError::Other)?;

            match value {
                None => Ok(None),
                Some(value) => Ok(serde_json::from_str(&value)
                    .map_err(Into::into)
                    .map_err(LoadError::Deserialization)?),
            }
        }

        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());

            self.execute_command(redis::cmd("SET").arg(&[
                &cache_key,
                &body,
                "NX", // NX: only set the key if it does not already exist
                "EX", // EX: set expiry
                &format!("{}", ttl.whole_seconds()),
            ]))
            .await
            .map_err(Into::into)
            .map_err(SaveError::Other)?;

            Ok(session_key)
        }

        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 v: redis::Value = self
                .execute_command(redis::cmd("SET").arg(&[
                    &cache_key,
                    &body,
                    "XX", // XX: Only set the key if it already exist.
                    "EX", // EX: set expiry
                    &format!("{}", ttl.whole_seconds()),
                ]))
                .await
                .map_err(Into::into)
                .map_err(UpdateError::Other)?;

            match v {
                Value::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),
                        })
                }
                Value::Int(_) | Value::Okay | Value::Status(_) => 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());

            self.client
                .clone()
                .expire(&cache_key, ttl.whole_seconds())
                .await?;
            Ok(())
        }

        async fn delete(&self, session_key: &SessionKey) -> Result<(), anyhow::Error> {
            let cache_key = (self.configuration.cache_keygen)(session_key.as_ref());
            self.execute_command(redis::cmd("DEL").arg(&[&cache_key]))
                .await
                .map_err(Into::into)
                .map_err(UpdateError::Other)?;

            Ok(())
        }
    }

    impl RedisSessionStore {
        /// Execute Redis command and retry once in certain cases.
        ///
        /// `ConnectionManager` automatically reconnects when it encounters an error talking to Redis.
        /// The request that bumped into the error, though, fails.
        ///
        /// This is generally OK, but there is an unpleasant edge case: Redis client timeouts. The
        /// server is configured to drop connections who have been active longer than a pre-determined
        /// threshold. `redis-rs` does not proactively detect that the connection has been dropped - you
        /// only find out when you try to use it.
        ///
        /// This helper method catches this case (`.is_connection_dropped`) to execute a retry. The
        /// retry will be executed on a fresh connection, therefore it is likely to succeed (or fail for
        /// a different more meaningful reason).
        #[allow(clippy::needless_pass_by_ref_mut)]
        async fn execute_command<T: FromRedisValue>(&self, cmd: &mut Cmd) -> RedisResult<T> {
            let mut can_retry = true;

            loop {
                match cmd.query_async(&mut self.client.clone()).await {
                    Ok(value) => return Ok(value),
                    Err(err) => {
                        if can_retry && err.is_connection_dropped() {
                            tracing::debug!(
                                "Connection dropped while trying to talk to Redis. Retrying."
                            );

                            // Retry at most once
                            can_retry = false;

                            continue;
                        } else {
                            return Err(err);
                        }
                    }
                }
            }
        }
    }

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

        use actix_web::cookie::time;
        use redis::AsyncCommands;

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

        async fn redis_store() -> RedisSessionStore {
            RedisSessionStore::new("redis://127.0.0.1:6379")
                .await
                .unwrap()
        }

        #[actix_web::test]
        async fn test_session_workflow() {
            let redis_store = redis_store().await;
            acceptance_test_suite(move || redis_store.clone(), true).await;
        }

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

        #[actix_web::test]
        async fn loading_an_invalid_session_state_returns_deserialization_error() {
            let store = redis_store().await;
            let session_key = generate_session_key();
            store
                .client
                .clone()
                .set::<_, _, ()>(session_key.as_ref(), "random-thing-which-is-not-json")
                .await
                .unwrap();
            assert!(matches!(
                store.load(&session_key).await.unwrap_err(),
                LoadError::Deserialization(_),
            ));
        }

        #[actix_web::test]
        async fn updating_of_an_expired_state_is_handled_gracefully() {
            let store = redis_store().await;
            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(), &time::Duration::seconds(1))
                .await
                .unwrap();
            assert_ne!(initial_session_key, updated_session_key.as_ref());
        }
    }