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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, SameSite},
        dev::{forward_ready, ResponseHead, Service, ServiceRequest, ServiceResponse, Transform},
        http::header::{HeaderValue, SET_COOKIE},
        HttpResponse,
    };
    use anyhow::Context;
    use time::Duration;

    use crate::{
        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.
    ///
    /// ```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::{cookie::Key, web, App, HttpServer, HttpResponse, Error};
    /// use actix_session::{Session, SessionMiddleware, storage::RedisActorSessionStore, SessionLength};
    ///
    /// // 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_length(SessionLength::Predetermined {
    ///                     max_session_length: Some(time::Duration::days(5)),
    ///                 })
    ///                 .build(),
    ///             )
    ///             .default_service(web::to(|| HttpResponse::Ok())))
    ///         .bind(("127.0.0.1", 8080))?
    ///         .run()
    ///         .await
    /// }
    /// ```
    ///
    /// ## 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.
    #[derive(Clone)]
    pub struct SessionMiddleware<Store: SessionStore> {
        storage_backend: Rc<Store>,
        configuration: Rc<Configuration>,
    }

    #[derive(Clone)]
    struct Configuration {
        cookie: CookieConfiguration,
        session: SessionConfiguration,
    }

    #[derive(Clone)]
    struct SessionConfiguration {
        state_ttl: Duration,
    }

    #[derive(Clone)]
    struct CookieConfiguration {
        secure: bool,
        http_only: bool,
        name: String,
        same_site: SameSite,
        path: String,
        domain: Option<String>,
        max_age: Option<Duration>,
        content_security: CookieContentSecurity,
        key: Key,
    }

    /// Describes how long a session should last.
    ///
    /// Used by [`SessionMiddlewareBuilder::session_length`].
    #[derive(Clone, Debug)]
    pub enum SessionLength {
        /// The session cookie will expire when the current browser session ends.
        ///
        /// When does a browser session end? It depends on the browser! Chrome, for example, will often
        /// continue running in the background when the browser is closed—session cookies are not
        /// deleted and they will still be available when the browser is opened again. Check the
        /// documentation of the browsers you are targeting for up-to-date information.
        BrowserSession {
            /// We must provide a time-to-live (TTL) when storing the session state in the storage
            /// backend—we do not want to store session states indefinitely, otherwise we will
            /// inevitably run out of storage by holding on to the state of countless abandoned or
            /// expired sessions!
            ///
            /// We are dealing with the lifecycle of two uncorrelated object here: the session cookie
            /// and the session state. It is not a big issue if the session state outlives the cookie—
            /// we are wasting some space in the backend storage, but it will be cleaned up eventually.
            /// What happens, instead, if the cookie outlives the session state? A new session starts—
            /// e.g. if sessions are being used for authentication, the user is de-facto logged out.
            ///
            /// It is not possible to predict with certainty how long a browser session is going to
            /// last—you need to provide a reasonable upper bound. You do so via `state_ttl`—it dictates
            /// what TTL should be used for session state when the lifecycle of the session cookie is
            /// tied to the browser session length. [`SessionMiddleware`] will default to 1 day if
            /// `state_ttl` is left unspecified.
            state_ttl: Option<Duration>,
        },

        /// The session cookie will be a [persistent cookie].
        ///
        /// Persistent cookies have a pre-determined lifetime, specified via the `Max-Age` or `Expires`
        /// attribute. They do not disappear when the current browser session ends.
        ///
        /// [persistent cookie]: https://www.whitehatsec.com/glossary/content/persistent-session-cookie
        Predetermined {
            /// Set `max_session_length` to specify how long the session cookie should live.
            /// [`SessionMiddleware`] will default to 1 day if `max_session_length` is set to `None`.
            ///
            /// `max_session_length` is also used as the TTL for the session state in the
            /// storage backend.
            max_session_length: Option<Duration>,
        },
    }

    /// Used by [`SessionMiddlewareBuilder::cookie_content_security`] to determine how to secure
    /// the content of the session cookie.
    #[derive(Debug, Clone, Copy)]
    pub enum CookieContentSecurity {
        /// The cookie content is encrypted when using `CookieContentSecurity::Private`.
        ///
        /// Encryption guarantees confidentiality and integrity: the client cannot tamper with the
        /// cookie content nor decode it, as long as the encryption key remains confidential.
        Private,

        /// The cookie content is signed when using `CookieContentSecurity::Signed`.
        ///
        /// Signing guarantees integrity, but it doesn't ensure confidentiality: the client cannot
        /// tamper with the cookie content, but they can read it.
        Signed,
    }

    fn default_configuration(key: Key) -> Configuration {
        Configuration {
            cookie: CookieConfiguration {
                secure: true,
                http_only: true,
                name: "id".into(),
                same_site: SameSite::Lax,
                path: "/".into(),
                domain: None,
                max_age: None,
                content_security: CookieContentSecurity::Private,
                key,
            },
            session: SessionConfiguration {
                state_ttl: default_ttl(),
            },
        }
    }

    fn default_ttl() -> Duration {
        Duration::days(1)
    }

    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 {
                storage_backend: Rc::new(store),
                configuration: Rc::new(default_configuration(key)),
            }
        }

        /// 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 {
                storage_backend: Rc::new(store),
                configuration: default_configuration(key),
            }
        }
    }

    /// A fluent builder to construct a [`SessionMiddleware`] instance with custom configuration
    /// parameters.
    #[must_use]
    pub struct SessionMiddlewareBuilder<Store: SessionStore> {
        storage_backend: Rc<Store>,
        configuration: Configuration,
    }

    impl<Store: SessionStore> SessionMiddlewareBuilder<Store> {
        /// Set the name of the cookie used to store the session ID.
        ///
        /// Defaults to `id`.
        pub fn cookie_name(mut self, name: String) -> Self {
            self.configuration.cookie.name = name;
            self
        }

        /// Set the `Secure` attribute for the cookie used to store the session ID.
        ///
        /// If the cookie is set as secure, it will only be transmitted when the connection is secure
        /// (using `https`).
        ///
        /// Default is `true`.
        pub fn cookie_secure(mut self, secure: bool) -> Self {
            self.configuration.cookie.secure = secure;
            self
        }

        /// Determine how long a session should last - check out [`SessionLength`]'s documentation for
        /// more details on the available options.
        ///
        /// Default is [`SessionLength::BrowserSession`].
        pub fn session_length(mut self, session_length: SessionLength) -> Self {
            match session_length {
                SessionLength::BrowserSession { state_ttl } => {
                    self.configuration.cookie.max_age = None;
                    self.configuration.session.state_ttl = state_ttl.unwrap_or_else(default_ttl);
                }
                SessionLength::Predetermined { max_session_length } => {
                    let ttl = max_session_length.unwrap_or_else(default_ttl);
                    self.configuration.cookie.max_age = Some(ttl);
                    self.configuration.session.state_ttl = ttl;
                }
            }

            self
        }

        /// Set the `SameSite` attribute for the cookie used to store the session ID.
        ///
        /// By default, the attribute is set to `Lax`.
        pub fn cookie_same_site(mut self, same_site: SameSite) -> Self {
            self.configuration.cookie.same_site = same_site;
            self
        }

        /// Set the `Path` attribute for the cookie used to store the session ID.
        ///
        /// By default, the attribute is set to `/`.
        pub fn cookie_path(mut self, path: String) -> Self {
            self.configuration.cookie.path = path;
            self
        }

        /// Set the `Domain` attribute for the cookie used to store the session ID.
        ///
        /// Use `None` to leave the attribute unspecified. If unspecified, the attribute defaults
        /// to the same host that set the cookie, excluding subdomains.
        ///
        /// By default, the attribute is left unspecified.
        pub fn cookie_domain(mut self, domain: Option<String>) -> Self {
            self.configuration.cookie.domain = domain;
            self
        }

        /// Choose how the session cookie content should be secured.
        ///
        /// - [`CookieContentSecurity::Private`] selects encrypted cookie content.
        /// - [`CookieContentSecurity::Signed`] selects signed cookie content.
        ///
        /// # Default
        /// By default, the cookie content is encrypted. Encrypted was chosen instead of signed as
        /// default because it reduces the chances of sensitive information being exposed in the session
        /// key by accident, regardless of [`SessionStore`] implementation you chose to use.
        ///
        /// For example, if you are using cookie-based storage, you definitely want the cookie content
        /// to be encrypted—the whole session state is embedded in the cookie! If you are using
        /// Redis-based storage, signed is more than enough - the cookie content is just a unique
        /// tamper-proof session key.
        pub fn cookie_content_security(mut self, content_security: CookieContentSecurity) -> Self {
            self.configuration.cookie.content_security = content_security;
            self
        }

        /// Set the `HttpOnly` attribute for the cookie used to store the session ID.
        ///
        /// If the cookie is set as `HttpOnly`, it will not be visible to any JavaScript snippets
        /// running in the browser.
        ///
        /// Default is `true`.
        pub fn cookie_http_only(mut self, http_only: bool) -> Self {
            self.configuration.cookie.http_only = http_only;
            self
        }

        /// Finalise the builder and return a [`SessionMiddleware`] instance.
        #[must_use]
        pub fn build(self) -> SessionMiddleware<Store> {
            SessionMiddleware {
                storage_backend: self.storage_backend,
                configuration: Rc::new(self.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 => {
                                // Nothing to do; we avoid the unnecessary call to the storage.
                            }
                        }
                    }
                };
                Ok(res)
            })
        }
    }

    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())
            .http_only(config.http_only);

        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(())
    }