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    use std::{collections::HashMap, convert::TryInto, fmt, future::Future, pin::Pin, rc::Rc};

    use actix_utils::future::{ready, Ready};
    use actix_web::{
        body::MessageBody,
        cookie::{Cookie, CookieJar, Key},
        dev::{forward_ready, ResponseHead, Service, ServiceRequest, ServiceResponse, Transform},
        http::header::{HeaderValue, SET_COOKIE},
        HttpResponse,
    };
    use anyhow::Context;

    use crate::{
        config::{
            self, Configuration, CookieConfiguration, CookieContentSecurity, SessionMiddlewareBuilder,
            TtlExtensionPolicy,
        },
        storage::{LoadError, SessionKey, SessionStore},
        Session, SessionStatus,
    };

    /// A middleware for session management in Actix Web applications.
    ///
    /// [`SessionMiddleware`] takes care of a few jobs:
    ///
    /// - Instructs the session storage backend to create/update/delete/retrieve the state attached to
    ///   a session according to its status and the operations that have been performed against it;
    /// - Set/remove a cookie, on the client side, to enable a user to be consistently associated with
    ///   the same session across multiple HTTP requests.
    ///
    /// Use [`SessionMiddleware::new`] to initialize the session framework using the default parameters.
    /// To create a new instance of [`SessionMiddleware`] you need to provide:
    ///
    /// - an instance of the session storage backend you wish to use (i.e. an implementation of
    ///   [`SessionStore`]);
    /// - a secret key, to sign or encrypt the content of client-side session cookie.
    ///
    /// # How did we choose defaults?
    /// You should not regret adding `actix-session` to your dependencies and going to production using
    /// the default configuration. That is why, when in doubt, we opt to use the most secure option for
    /// each configuration parameter.
    ///
    /// We expose knobs to change the default to suit your needs—i.e., if you know what you are doing,
    /// we will not stop you. But being a subject-matter expert should not be a requirement to deploy
    /// reasonably secure implementation of sessions.
    ///
    /// # Examples
    /// ```no_run
    /// use actix_web::{web, App, HttpServer, HttpResponse, Error};
    /// use actix_session::{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()
    ///             // Add session management to your application using Redis for session state storage
    ///             .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
    /// }
    /// ```
    ///
    /// If you want to customise use [`builder`](Self::builder) instead of [`new`](Self::new):
    ///
    /// ```no_run
    /// use actix_web::{App, cookie::{Key, time}, Error, HttpResponse, HttpServer, web};
    /// use actix_session::{Session, SessionMiddleware, storage::RedisActorSessionStore};
    /// use actix_session::config::PersistentSession;
    ///
    /// // 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()
    ///             // Customise session length!
    ///             .wrap(
    ///                 SessionMiddleware::builder(
    ///                     RedisActorSessionStore::new(redis_connection_string),
    ///                     secret_key.clone()
    ///                 )
    ///                 .session_lifecycle(
    ///                     PersistentSession::default()
    ///                         .session_ttl(time::Duration::days(5))
    ///                 )
    ///                 .build(),
    ///             )
    ///             .default_service(web::to(|| HttpResponse::Ok())))
    ///         .bind(("127.0.0.1", 8080))?
    ///         .run()
    ///         .await
    /// }
    /// ```
    #[derive(Clone)]
    pub struct SessionMiddleware<Store: SessionStore> {
        storage_backend: Rc<Store>,
        configuration: Rc<Configuration>,
    }

    impl<Store: SessionStore> SessionMiddleware<Store> {
        /// Use [`SessionMiddleware::new`] to initialize the session framework using the default
        /// parameters.
        ///
        /// To create a new instance of [`SessionMiddleware`] you need to provide:
        /// - an instance of the session storage backend you wish to use (i.e. an implementation of
        ///   [`SessionStore`]);
        /// - a secret key, to sign or encrypt the content of client-side session cookie.
        pub fn new(store: Store, key: Key) -> Self {
            Self::builder(store, key).build()
        }

        /// A fluent API to configure [`SessionMiddleware`].
        ///
        /// It takes as input the two required inputs to create a new instance of [`SessionMiddleware`]:
        /// - an instance of the session storage backend you wish to use (i.e. an implementation of
        ///   [`SessionStore`]);
        /// - a secret key, to sign or encrypt the content of client-side session cookie.
        pub fn builder(store: Store, key: Key) -> SessionMiddlewareBuilder<Store> {
            SessionMiddlewareBuilder::new(store, config::default_configuration(key))
        }

        pub(crate) fn from_parts(store: Store, configuration: Configuration) -> Self {
            Self {
                storage_backend: Rc::new(store),
                configuration: Rc::new(configuration),
            }
        }
    }

    impl<S, B, Store> Transform<S, ServiceRequest> for SessionMiddleware<Store>
    where
        S: Service<ServiceRequest, Response = ServiceResponse<B>, Error = actix_web::Error> + 'static,
        S::Future: 'static,
        B: MessageBody + 'static,
        Store: SessionStore + 'static,
    {
        type Response = ServiceResponse<B>;
        type Error = actix_web::Error;
        type Transform = InnerSessionMiddleware<S, Store>;
        type InitError = ();
        type Future = Ready<Result<Self::Transform, Self::InitError>>;

        fn new_transform(&self, service: S) -> Self::Future {
            ready(Ok(InnerSessionMiddleware {
                service: Rc::new(service),
                configuration: Rc::clone(&self.configuration),
                storage_backend: Rc::clone(&self.storage_backend),
            }))
        }
    }

    /// Short-hand to create an `actix_web::Error` instance that will result in an `Internal Server
    /// Error` response while preserving the error root cause (e.g. in logs).
    fn e500<E: fmt::Debug + fmt::Display + 'static>(err: E) -> actix_web::Error {
        // We do not use `actix_web::error::ErrorInternalServerError` because we do not want to
        // leak internal implementation details to the caller.
        //
        // `actix_web::error::ErrorInternalServerError` includes the error Display representation
        // as body of the error responses, leading to messages like "There was an issue persisting
        // the session state" reaching API clients. We don't want that, we want opaque 500s.
        actix_web::error::InternalError::from_response(
            err,
            HttpResponse::InternalServerError().finish(),
        )
        .into()
    }

    #[doc(hidden)]
    #[non_exhaustive]
    pub struct InnerSessionMiddleware<S, Store: SessionStore + 'static> {
        service: Rc<S>,
        configuration: Rc<Configuration>,
        storage_backend: Rc<Store>,
    }

    impl<S, B, Store> Service<ServiceRequest> for InnerSessionMiddleware<S, Store>
    where
        S: Service<ServiceRequest, Response = ServiceResponse<B>, Error = actix_web::Error> + 'static,
        S::Future: 'static,
        Store: SessionStore + 'static,
    {
        type Response = ServiceResponse<B>;
        type Error = actix_web::Error;
        #[allow(clippy::type_complexity)]
        type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>>>>;

        forward_ready!(service);

        fn call(&self, mut req: ServiceRequest) -> Self::Future {
            let service = Rc::clone(&self.service);
            let storage_backend = Rc::clone(&self.storage_backend);
            let configuration = Rc::clone(&self.configuration);

            Box::pin(async move {
                let session_key = extract_session_key(&req, &configuration.cookie);
                let (session_key, session_state) =
                    load_session_state(session_key, storage_backend.as_ref()).await?;

                Session::set_session(&mut req, session_state);

                let mut res = service.call(req).await?;
                let (status, session_state) = Session::get_changes(&mut res);

                match session_key {
                    None => {
                        // we do not create an entry in the session store if there is no state attached
                        // to a fresh session
                        if !session_state.is_empty() {
                            let session_key = storage_backend
                                .save(session_state, &configuration.session.state_ttl)
                                .await
                                .map_err(e500)?;

                            set_session_cookie(
                                res.response_mut().head_mut(),
                                session_key,
                                &configuration.cookie,
                            )
                            .map_err(e500)?;
                        }
                    }

                    Some(session_key) => {
                        match status {
                            SessionStatus::Changed => {
                                let session_key = storage_backend
                                    .update(
                                        session_key,
                                        session_state,
                                        &configuration.session.state_ttl,
                                    )
                                    .await
                                    .map_err(e500)?;

                                set_session_cookie(
                                    res.response_mut().head_mut(),
                                    session_key,
                                    &configuration.cookie,
                                )
                                .map_err(e500)?;
                            }

                            SessionStatus::Purged => {
                                storage_backend.delete(&session_key).await.map_err(e500)?;

                                delete_session_cookie(
                                    res.response_mut().head_mut(),
                                    &configuration.cookie,
                                )
                                .map_err(e500)?;
                            }

                            SessionStatus::Renewed => {
                                storage_backend.delete(&session_key).await.map_err(e500)?;

                                let session_key = storage_backend
                                    .save(session_state, &configuration.session.state_ttl)
                                    .await
                                    .map_err(e500)?;

                                set_session_cookie(
                                    res.response_mut().head_mut(),
                                    session_key,
                                    &configuration.cookie,
                                )
                                .map_err(e500)?;
                            }

                            SessionStatus::Unchanged => {
                                if matches!(
                                    configuration.ttl_extension_policy,
                                    TtlExtensionPolicy::OnEveryRequest
                                ) {
                                    storage_backend
                                        .update_ttl(&session_key, &configuration.session.state_ttl)
                                        .await
                                        .map_err(e500)?;

                                    if configuration.cookie.max_age.is_some() {
                                        set_session_cookie(
                                            res.response_mut().head_mut(),
                                            session_key,
                                            &configuration.cookie,
                                        )
                                        .map_err(e500)?;
                                    }
                                }
                            }
                        };
                    }
                }

                Ok(res)
            })
        }
    }

    /// Examines the session cookie attached to the incoming request, if there is one, and tries
    /// to extract the session key.
    ///
    /// It returns `None` if there is no session cookie or if the session cookie is considered invalid
    /// (e.g., when failing a signature check).
    fn extract_session_key(req: &ServiceRequest, config: &CookieConfiguration) -> Option<SessionKey> {
        let cookies = req.cookies().ok()?;
        let session_cookie = cookies
            .iter()
            .find(|&cookie| cookie.name() == config.name)?;

        let mut jar = CookieJar::new();
        jar.add_original(session_cookie.clone());

        let verification_result = match config.content_security {
            CookieContentSecurity::Signed => jar.signed(&config.key).get(&config.name),
            CookieContentSecurity::Private => jar.private(&config.key).get(&config.name),
        };

        if verification_result.is_none() {
            tracing::warn!(
                "The session cookie attached to the incoming request failed to pass cryptographic \
                checks (signature verification/decryption)."
            );
        }

        match verification_result?.value().to_owned().try_into() {
            Ok(session_key) => Some(session_key),
            Err(err) => {
                tracing::warn!(
                    error.message = %err,
                    error.cause_chain = ?err,
                    "Invalid session key, ignoring."
                );

                None
            }
        }
    }

    async fn load_session_state<Store: SessionStore>(
        session_key: Option<SessionKey>,
        storage_backend: &Store,
    ) -> Result<(Option<SessionKey>, HashMap<String, String>), actix_web::Error> {
        if let Some(session_key) = session_key {
            match storage_backend.load(&session_key).await {
                Ok(state) => {
                    if let Some(state) = state {
                        Ok((Some(session_key), state))
                    } else {
                        // We discard the existing session key given that the state attached to it can
                        // no longer be found (e.g. it expired or we suffered some data loss in the
                        // storage). Regenerating the session key will trigger the `save` workflow
                        // instead of the `update` workflow if the session state is modified during the
                        // lifecycle of the current request.

                        tracing::info!(
                            "No session state has been found for a valid session key, creating a new \
                            empty session."
                        );

                        Ok((None, HashMap::new()))
                    }
                }

                Err(err) => match err {
                    LoadError::Deserialization(err) => {
                        tracing::warn!(
                            error.message = %err,
                            error.cause_chain = ?err,
                            "Invalid session state, creating a new empty session."
                        );

                        Ok((Some(session_key), HashMap::new()))
                    }

                    LoadError::Other(err) => Err(e500(err)),
                },
            }
        } else {
            Ok((None, HashMap::new()))
        }
    }

    fn set_session_cookie(
        response: &mut ResponseHead,
        session_key: SessionKey,
        config: &CookieConfiguration,
    ) -> Result<(), anyhow::Error> {
        let value: String = session_key.into();
        let mut cookie = Cookie::new(config.name.clone(), value);

        cookie.set_secure(config.secure);
        cookie.set_http_only(config.http_only);
        cookie.set_same_site(config.same_site);
        cookie.set_path(config.path.clone());

        if let Some(max_age) = config.max_age {
            cookie.set_max_age(max_age);
        }

        if let Some(ref domain) = config.domain {
            cookie.set_domain(domain.clone());
        }

        let mut jar = CookieJar::new();
        match config.content_security {
            CookieContentSecurity::Signed => jar.signed_mut(&config.key).add(cookie),
            CookieContentSecurity::Private => jar.private_mut(&config.key).add(cookie),
        }

        // set cookie
        let cookie = jar.delta().next().unwrap();
        let val = HeaderValue::from_str(&cookie.encoded().to_string())
            .context("Failed to attach a session cookie to the outgoing response")?;

        response.headers_mut().append(SET_COOKIE, val);

        Ok(())
    }

    fn delete_session_cookie(
        response: &mut ResponseHead,
        config: &CookieConfiguration,
    ) -> Result<(), anyhow::Error> {
        let removal_cookie = Cookie::build(config.name.clone(), "")
            .path(config.path.clone())
            .secure(config.secure)
            .http_only(config.http_only)
            .same_site(config.same_site);

        let mut removal_cookie = if let Some(ref domain) = config.domain {
            removal_cookie.domain(domain)
        } else {
            removal_cookie
        }
        .finish();

        removal_cookie.make_removal();

        let val = HeaderValue::from_str(&removal_cookie.to_string())
            .context("Failed to attach a session removal cookie to the outgoing response")?;
        response.headers_mut().append(SET_COOKIE, val);

        Ok(())
    }