//! Support for reporting the status of an onion service.

use crate::internal_prelude::*;

/// The current reported status of an onion service.
#[derive(Debug, Clone, Eq, PartialEq)]
pub struct OnionServiceStatus {
    /// The current high-level state for the IPT manager.
    ipt_mgr: ComponentStatus,

    /// The current high-level state for the descriptor publisher.
    publisher: ComponentStatus,
    // TODO (#1194): Add key expiration
    //
    // NOTE: Do _not_ add general metrics (like failure/success rates , number
    // of intro points, etc) here.
}

/// The current reported status of an onion service subsystem.
#[derive(Debug, Clone)]
struct ComponentStatus {
    /// The current high-level state.
    state: State,

    /// The last error we have seen.
    latest_error: Option<Problem>,
}

impl ComponentStatus {
    /// Create a new ComponentStatus for a component that has not been bootstrapped.
    fn new_shutdown() -> Self {
        Self {
            state: State::Shutdown,
            latest_error: None,
        }
    }
}

impl PartialEq for ComponentStatus {
    fn eq(&self, other: &Self) -> bool {
        let Self {
            state,
            latest_error,
        } = self;
        let Self {
            state: state_other,
            latest_error: lastest_error_other,
        } = other;

        // NOTE: Errors are never equal. We _could_ add half-baked PartialEq implementations for
        // all of our error types, but it doesn't seem worth it. If there is a state change, or if
        // we've encountered an error (even if it's the same as the previous one), we'll notify the
        // watchers.
        state == state_other && latest_error.is_none() && lastest_error_other.is_none()
    }
}

impl Eq for ComponentStatus {}

/// The high-level state of an onion service.
///
/// This type summarizes the most basic information about an onion service's
/// status.
#[derive(Copy, Clone, Debug, Eq, PartialEq)]
#[non_exhaustive]
pub enum State {
    /// The service is not launched.
    ///
    /// Either [`OnionService::launch`](crate::OnionService::launch) has not
    /// been called, or the service has been shut down.
    ///
    /// ## Reachability
    ///
    /// The service is not reachable.
    Shutdown,
    /// The service is bootstrapping.
    ///
    /// Specifically, we have been offline, or we just initialized:
    /// We are trying to build introduction points and publish a descriptor,
    /// and haven't hit any significant problems yet.
    ///
    /// ## Reachability
    ///
    /// The service is not fully reachable, but may be reachable by some clients.
    Bootstrapping,
    /// The service is running in a degraded state.
    ///
    /// Specifically, we are not satisfied with our introduction points, but
    /// we do have a number of working introduction points,
    /// and our descriptor is up-to-date.
    ///
    /// ## Reachability
    ///
    /// The service is reachable.
    ///
    // TODO: this variant is only used by the IptManager.
    // We should split this enum into IptManagerState and PublisherState.
    Degraded,
    /// The service is running.
    ///
    /// Specifically, we are satisfied with our introduction points, and our
    /// descriptor is up-to-date.
    ///
    /// ## Reachability
    ///
    /// The service is believed to be fully reachable.
    Running,
    /// The service is trying to recover from a minor interruption.
    ///
    /// Specifically:
    ///   * We have encountered a problem (like a dead intro point or an
    ///     intermittent failure to upload a descriptor)
    ///   * We are trying to recover from the problem.
    ///   * We have not yet failed.
    ///
    /// ## Reachability
    ///
    /// The service is unlikely to be reachable.
    ///
    //
    // NOTE: this status is currently only set by `IptManager` whenever:
    //   * there are no good IPTs (so the service will be unreachable); or
    //   * there aren't enough good IPTs to publish (AFAICT in this case the service
    //   may be reachable, if the IPTs we _do_ have are have previously been published).
    //
    // TODO (#1270): split this state into 2 different states (one for the "service is
    // still reachable" case, and another for the "unreachable" one).
    Recovering,
    /// The service is not working.
    ///
    /// Specifically, there is a problem with this onion service, and either it
    /// is one we cannot recover from, or we have tried for a while to recover
    /// and have failed.
    ///
    /// ## Reachability
    ///
    /// The service is not fully reachable. It may temporarily be reachable by some clients.
    Broken,
}

/// A problem encountered by an onion service.
#[derive(Clone, Debug, derive_more::From)]
#[non_exhaustive]
pub enum Problem {
    /// A fatal error occurred.
    Runtime(FatalError),

    /// We failed to upload a descriptor.
    DescriptorUpload(RetryError<DescUploadError>),

    /// We failed to establish one or more introduction points.
    Ipt(Vec<IptError>),
    // TODO: add variants for other transient errors?
}

impl OnionServiceStatus {
    /// Create a new OnionServiceStatus for a service that has not been bootstrapped.
    pub(crate) fn new_shutdown() -> Self {
        Self {
            ipt_mgr: ComponentStatus::new_shutdown(),
            publisher: ComponentStatus::new_shutdown(),
        }
    }

    /// Return the current high-level state of this onion service.
    ///
    /// The overall state is derived from the `State`s of its underlying components
    /// (i.e. the IPT manager and descriptor publisher).
    pub fn state(&self) -> State {
        use State::*;

        match (self.ipt_mgr.state, self.publisher.state) {
            (Shutdown, _) | (_, Shutdown) => Shutdown,
            (Bootstrapping, _) | (_, Bootstrapping) => Bootstrapping,
            (Running, Running) => Running,
            (Recovering, _) | (_, Recovering) => Recovering,
            (Broken, _) | (_, Broken) => Broken,
            (Degraded, Running) | (Running, Degraded) | (Degraded, Degraded) => Degraded,
        }
    }

    /// Return the most severe current problem
    pub fn current_problem(&self) -> Option<&Problem> {
        match (&self.ipt_mgr.latest_error, &self.publisher.latest_error) {
            (None, None) => None,
            (Some(e), Some(_)) => {
                // For now, assume IPT manager errors are always more severe
                // TODO: decide which error is the more severe (or return both)
                Some(e)
            }
            (_, Some(e)) | (Some(e), _) => Some(e),
        }
    }

    /// Return a time before which the user must re-provision this onion service
    /// with new keys.
    ///
    /// Returns `None` if the onion service is able to generate and sign new
    /// keys as needed.
    pub fn provisioned_key_expiration(&self) -> Option<SystemTime> {
        None // TODO (#1194): Implement
    }
}

/// A stream of OnionServiceStatus events, returned by an onion service.
///
/// Note that multiple status change events may be coalesced into one if the
/// receiver does not read them as fast as they are generated.  Note also
/// that it's possible for an item to arise in this stream without an underlying
/// change having occurred.
///
//
// We define this so that we aren't exposing postage in our public API.
#[derive(Clone)]
pub struct OnionServiceStatusStream(postage::watch::Receiver<OnionServiceStatus>);

impl futures::Stream for OnionServiceStatusStream {
    type Item = OnionServiceStatus;

    fn poll_next(
        mut self: std::pin::Pin<&mut Self>,
        cx: &mut std::task::Context<'_>,
    ) -> std::task::Poll<Option<Self::Item>> {
        self.0.poll_next_unpin(cx)
    }
}

/// A shared handle to a postage::watch::Sender that we can use to update an OnionServiceStatus.
//
// TODO: Possibly, we don't need this to be Clone: as we implement the code
// that adjusts the status, we might find that only a single location needs to
// hold the Sender.  If that turns out to be the case, we should remove the
// `Arc<Mutex<.>>` here.  If not, we should remove this comment.
#[derive(Clone)]
pub(crate) struct StatusSender(Arc<Mutex<postage::watch::Sender<OnionServiceStatus>>>);

/// A handle that can be used by the [`IptManager`]
/// to update the [`OnionServiceStatus`].
#[derive(Clone, derive_more::From)]
pub(crate) struct IptMgrStatusSender(StatusSender);

/// A handle that can be used by the [`Publisher`]
/// to update the [`OnionServiceStatus`].
#[derive(Clone, derive_more::From)]
pub(crate) struct PublisherStatusSender(StatusSender);

/// A helper for implementing [`PublisherStatusSender`] and [`IptMgrStatusSender`].
///
/// TODO: this macro is a bit repetitive, it would be nice if we could reduce duplication even
/// further (and auto-generate a `note_<state>` function for every `State` variant).
macro_rules! impl_status_sender {
    ($sender:ident, $field:ident) => {
        impl $sender {
            /// Update `latest_error` and set the underlying state to `Broken`.
            ///
            /// If the new state is different, this updates the current status
            /// and notifies all listeners.
            #[allow(dead_code)]
            pub(crate) fn send_broken(&self, err: impl Into<Problem>) {
                self.send(State::Broken, Some(err.into()));
            }

            /// Update `latest_error` and set the underlying state to `Recovering`.
            ///
            /// If the new state is different, this updates the current status
            /// and notifies all listeners.
            #[allow(dead_code)]
            pub(crate) fn send_recovering(&self, err: impl Into<Problem>) {
                self.send(State::Recovering, Some(err.into()));
            }

            /// Set `latest_error` to `None` and the underlying state to `Shutdown`.
            ///
            /// If the new state is different, this updates the current status
            /// and notifies all listeners.
            #[allow(dead_code)]
            pub(crate) fn send_shutdown(&self) {
                self.send(State::Shutdown, None);
            }

            /// Update the underlying state and latest_error.
            ///
            /// If the new state is different, this updates the current status
            /// and notifies all listeners.
            #[allow(dead_code)]
            pub(crate) fn send(&self, state: State, err: Option<Problem>) {
                let sender = &self.0;
                let mut tx = sender.0.lock().expect("Poisoned lock");
                let mut svc_status = tx.borrow().clone();
                svc_status.$field.state = state;
                svc_status.$field.latest_error = err;
                tx.maybe_send(|_| svc_status);
            }
        }
    };
}

impl_status_sender!(IptMgrStatusSender, ipt_mgr);
impl_status_sender!(PublisherStatusSender, publisher);

impl StatusSender {
    /// Create a new StatusSender with a given initial status.
    pub(crate) fn new(initial_status: OnionServiceStatus) -> Self {
        let (tx, _) = postage::watch::channel_with(initial_status);
        StatusSender(Arc::new(Mutex::new(tx)))
    }

    /// Return a copy of the current status.
    pub(crate) fn get(&self) -> OnionServiceStatus {
        self.0.lock().expect("Poisoned lock").borrow().clone()
    }

    /// Return a new OnionServiceStatusStream to return events from this StatusSender.
    pub(crate) fn subscribe(&self) -> OnionServiceStatusStream {
        OnionServiceStatusStream(self.0.lock().expect("Poisoned lock").subscribe())
    }
}
