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    use std::{
        cell::{Ref, RefCell},
        collections::HashMap,
        error::Error as StdError,
        mem,
        rc::Rc,
    };

    use actix_utils::future::{ready, Ready};
    use actix_web::{
        body::BoxBody,
        dev::{Extensions, Payload, ServiceRequest, ServiceResponse},
        error::Error,
        FromRequest, HttpMessage, HttpRequest, HttpResponse, ResponseError,
    };
    use anyhow::Context;
    use derive_more::{Display, From};
    use serde::{de::DeserializeOwned, Serialize};

    /// The primary interface to access and modify session state.
    ///
    /// [`Session`] is an [extractor](#impl-FromRequest)—you can specify it as an input type for your
    /// request handlers and it will be automatically extracted from the incoming request.
    ///
    /// ```
    /// use actix_session::Session;
    ///
    /// async fn index(session: Session) -> actix_web::Result<&'static str> {
    ///     // access session data
    ///     if let Some(count) = session.get::<i32>("counter")? {
    ///         session.insert("counter", count + 1)?;
    ///     } else {
    ///         session.insert("counter", 1)?;
    ///     }
    ///
    ///     Ok("Welcome!")
    /// }
    /// # actix_web::web::to(index);
    /// ```
    ///
    /// You can also retrieve a [`Session`] object from an `HttpRequest` or a `ServiceRequest` using
    /// [`SessionExt`].
    ///
    /// [`SessionExt`]: crate::SessionExt
    #[derive(Clone)]
    pub struct Session(Rc<RefCell<SessionInner>>);

    /// Status of a [`Session`].
    #[derive(Debug, Clone, Default, PartialEq, Eq)]
    pub enum SessionStatus {
        /// Session state has been updated - the changes will have to be persisted to the backend.
        Changed,

        /// The session has been flagged for deletion - the session cookie will be removed from
        /// the client and the session state will be deleted from the session store.
        ///
        /// Most operations on the session after it has been marked for deletion will have no effect.
        Purged,

        /// The session has been flagged for renewal.
        ///
        /// The session key will be regenerated and the time-to-live of the session state will be
        /// extended.
        Renewed,

        /// The session state has not been modified since its creation/retrieval.
        #[default]
        Unchanged,
    }

    #[derive(Default)]
    struct SessionInner {
        state: HashMap<String, String>,
        status: SessionStatus,
    }

    impl Session {
        /// Get a `value` from the session.
        ///
        /// It returns an error if it fails to deserialize as `T` the JSON value associated with `key`.
        pub fn get<T: DeserializeOwned>(&self, key: &str) -> Result<Option<T>, SessionGetError> {
            if let Some(val_str) = self.0.borrow().state.get(key) {
                Ok(Some(
                    serde_json::from_str(val_str)
                        .with_context(|| {
                            format!(
                                "Failed to deserialize the JSON-encoded session data attached to key \
                                `{}` as a `{}` type",
                                key,
                                std::any::type_name::<T>()
                            )
                        })
                        .map_err(SessionGetError)?,
                ))
            } else {
                Ok(None)
            }
        }

        /// Get all raw key-value data from the session.
        ///
        /// Note that values are JSON encoded.
        pub fn entries(&self) -> Ref<'_, HashMap<String, String>> {
            Ref::map(self.0.borrow(), |inner| &inner.state)
        }

        /// Returns session status.
        pub fn status(&self) -> SessionStatus {
            Ref::map(self.0.borrow(), |inner| &inner.status).clone()
        }

        /// Inserts a key-value pair into the session.
        ///
        /// Any serializable value can be used and will be encoded as JSON in session data, hence why
        /// only a reference to the value is taken.
        ///
        /// It returns an error if it fails to serialize `value` to JSON.
        pub fn insert<T: Serialize>(
            &self,
            key: impl Into<String>,
            value: T,
        ) -> Result<(), SessionInsertError> {
            let mut inner = self.0.borrow_mut();

            if inner.status != SessionStatus::Purged {
                if inner.status != SessionStatus::Renewed {
                    inner.status = SessionStatus::Changed;
                }

                let key = key.into();
                let val = serde_json::to_string(&value)
                    .with_context(|| {
                        format!(
                            "Failed to serialize the provided `{}` type instance as JSON in order to \
                            attach as session data to the `{}` key",
                            std::any::type_name::<T>(),
                            &key
                        )
                    })
                    .map_err(SessionInsertError)?;

                inner.state.insert(key, val);
            }

            Ok(())
        }

        /// Remove value from the session.
        ///
        /// If present, the JSON encoded value is returned.
        pub fn remove(&self, key: &str) -> Option<String> {
            let mut inner = self.0.borrow_mut();

            if inner.status != SessionStatus::Purged {
                if inner.status != SessionStatus::Renewed {
                    inner.status = SessionStatus::Changed;
                }
                return inner.state.remove(key);
            }

            None
        }

        /// Remove value from the session and deserialize.
        ///
        /// Returns `None` if key was not present in session. Returns `T` if deserialization succeeds,
        /// otherwise returns un-deserialized JSON string.
        pub fn remove_as<T: DeserializeOwned>(&self, key: &str) -> Option<Result<T, String>> {
            self.remove(key)
                .map(|val_str| match serde_json::from_str(&val_str) {
                    Ok(val) => Ok(val),
                    Err(_err) => {
                        tracing::debug!(
                            "Removed value (key: {}) could not be deserialized as {}",
                            key,
                            std::any::type_name::<T>()
                        );

                        Err(val_str)
                    }
                })
        }

        /// Clear the session.
        pub fn clear(&self) {
            let mut inner = self.0.borrow_mut();

            if inner.status != SessionStatus::Purged {
                if inner.status != SessionStatus::Renewed {
                    inner.status = SessionStatus::Changed;
                }
                inner.state.clear()
            }
        }

        /// Removes session both client and server side.
        pub fn purge(&self) {
            let mut inner = self.0.borrow_mut();
            inner.status = SessionStatus::Purged;
            inner.state.clear();
        }

        /// Renews the session key, assigning existing session state to new key.
        pub fn renew(&self) {
            let mut inner = self.0.borrow_mut();

            if inner.status != SessionStatus::Purged {
                inner.status = SessionStatus::Renewed;
            }
        }

        /// Adds the given key-value pairs to the session on the request.
        ///
        /// Values that match keys already existing on the session will be overwritten. Values should
        /// already be JSON serialized.
        #[allow(clippy::needless_pass_by_ref_mut)]
        pub(crate) fn set_session(
            req: &mut ServiceRequest,
            data: impl IntoIterator<Item = (String, String)>,
        ) {
            let session = Session::get_session(&mut req.extensions_mut());
            let mut inner = session.0.borrow_mut();
            inner.state.extend(data);
        }

        /// Returns session status and iterator of key-value pairs of changes.
        ///
        /// This is a destructive operation - the session state is removed from the request extensions
        /// typemap, leaving behind a new empty map. It should only be used when the session is being
        /// finalised (i.e. in `SessionMiddleware`).
        #[allow(clippy::needless_pass_by_ref_mut)]
        pub(crate) fn get_changes<B>(
            res: &mut ServiceResponse<B>,
        ) -> (SessionStatus, HashMap<String, String>) {
            if let Some(s_impl) = res
                .request()
                .extensions()
                .get::<Rc<RefCell<SessionInner>>>()
            {
                let state = mem::take(&mut s_impl.borrow_mut().state);
                (s_impl.borrow().status.clone(), state)
            } else {
                (SessionStatus::Unchanged, HashMap::new())
            }
        }

        pub(crate) fn get_session(extensions: &mut Extensions) -> Session {
            if let Some(s_impl) = extensions.get::<Rc<RefCell<SessionInner>>>() {
                return Session(Rc::clone(s_impl));
            }

            let inner = Rc::new(RefCell::new(SessionInner::default()));
            extensions.insert(inner.clone());

            Session(inner)
        }
    }

    /// Extractor implementation for [`Session`]s.
    ///
    /// # Examples
    /// ```
    /// # use actix_web::*;
    /// use actix_session::Session;
    ///
    /// #[get("/")]
    /// async fn index(session: Session) -> Result<impl Responder> {
    ///     // access session data
    ///     if let Some(count) = session.get::<i32>("counter")? {
    ///         session.insert("counter", count + 1)?;
    ///     } else {
    ///         session.insert("counter", 1)?;
    ///     }
    ///
    ///     let count = session.get::<i32>("counter")?.unwrap();
    ///     Ok(format!("Counter: {}", count))
    /// }
    /// ```
    impl FromRequest for Session {
        type Error = Error;
        type Future = Ready<Result<Session, Error>>;

        #[inline]
        fn from_request(req: &HttpRequest, _: &mut Payload) -> Self::Future {
            ready(Ok(Session::get_session(&mut req.extensions_mut())))
        }
    }

    /// Error returned by [`Session::get`].
    #[derive(Debug, Display, From)]
    #[display(fmt = "{_0}")]
    pub struct SessionGetError(anyhow::Error);

    impl StdError for SessionGetError {
        fn source(&self) -> Option<&(dyn StdError + 'static)> {
            Some(self.0.as_ref())
        }
    }

    impl ResponseError for SessionGetError {
        fn error_response(&self) -> HttpResponse<BoxBody> {
            HttpResponse::new(self.status_code())
        }
    }

    /// Error returned by [`Session::insert`].
    #[derive(Debug, Display, From)]
    #[display(fmt = "{_0}")]
    pub struct SessionInsertError(anyhow::Error);

    impl StdError for SessionInsertError {
        fn source(&self) -> Option<&(dyn StdError + 'static)> {
            Some(self.0.as_ref())
        }
    }

    impl ResponseError for SessionInsertError {
        fn error_response(&self) -> HttpResponse<BoxBody> {
            HttpResponse::new(self.status_code())
        }
    }