//! Module exposing the relay circuit reactor subsystem.

//!

//! See [`reactor`](crate::circuit::reactor) for a description of the overall architecture.

//!

//! #### `ForwardReactor`

//!

//! It handles

//!

//!  * unrecognized RELAY cells, by moving them in the forward direction (towards the exit)

//!  * recognized RELAY cells, by splitting each cell into messages, and handling

//!    each message individually as described in the table below

//!    (Note: since prop340 is not yet implemented, in practice there is only 1 message per cell).

//!  * RELAY_EARLY cells (**not yet implemented**)

//!  * DESTROY cells (**not yet implemented**)

//!  * PADDING_NEGOTIATE cells (**not yet implemented**)

//!

//! ```text

//!

//! Legend: `F` = "forward reactor", `B` = "backward reactor", `S` = "stream reactor"

//!

//! | RELAY cmd         | Received in | Handled in | Description                            |

//! |-------------------|-------------|------------|----------------------------------------|

//! | DROP              | F           | F          | Passed to PaddingController for        |

//! |                   |             |            | validation                             |

//! |-------------------|-------------|------------|----------------------------------------|

//! | EXTEND2           | F           |            | Handled by instructing the channel     |

//! |                   |             |            | provider to launch a new channel, and  |

//! |                   |             |            | waiting for the new channel on its     |

//! |                   |             |            | outgoing_chan_rx receiver              |

//! |                   |             |            | (**not yet implemented**)              |

//! |-------------------|-------------|------------|----------------------------------------|

//! | TRUNCATE          | F           | F          | (**not yet implemented**)              |

//! |                   |             |            |                                        |

//! |-------------------|-------------|------------|----------------------------------------|

//! | TODO              |             |            |                                        |

//! |                   |             |            |                                        |

//! ```

pub(crate) mod backward;

pub(crate) mod forward;

use std::sync::Arc;

use futures::channel::mpsc;

use tor_cell::chancell::CircId;

use tor_linkspec::OwnedChanTarget;

use tor_rtcompat::Runtime;

use crate::channel::Channel;

use crate::circuit::circhop::HopSettings;

use crate::circuit::reactor::Reactor as BaseReactor;

use crate::circuit::reactor::hop_mgr::HopMgr;

use crate::circuit::{CircuitRxReceiver, UniqId};

use crate::crypto::cell::{InboundRelayLayer, OutboundRelayLayer};

use crate::memquota::CircuitAccount;

use crate::relay::RelayCirc;

use crate::relay::channel_provider::ChannelProvider;

use crate::relay::reactor::backward::Backward;

use crate::relay::reactor::forward::Forward;

use crate::util::timeout::TimeoutEstimator;

// TODO(circpad): once padding is stabilized, the padding module will be moved out of client.

use crate::client::circuit::padding::{PaddingController, PaddingEventStream};

/// Type-alias for the relay base reactor type.

type RelayBaseReactor<R> = BaseReactor<R, Forward, Backward>;

/// The entry point of the circuit reactor subsystem.

#[allow(unused)] // TODO(relay)

#[must_use = "If you don't call run() on a reactor, the circuit won't work."]

pub(crate) struct Reactor<R: Runtime>(RelayBaseReactor<R>);

#[allow(unused)] // TODO(relay)

impl<R: Runtime> Reactor<R> {

    /// Create a new circuit reactor.

    ///

    /// The reactor will send outbound messages on `channel`, receive incoming

    /// messages on `input`, and identify this circuit by the channel-local

    /// [`CircId`] provided.

    ///

    /// The internal unique identifier for this circuit will be `unique_id`.

    #[allow(clippy::too_many_arguments)] // TODO

        // NOTE: not registering this channel with the memquota subsystem is okay,

        // because it has no buffering (if ever decide to make the size of this buffer

        // non-zero for whatever reason, we must remember to register it with memquota

        // so that it counts towards the total memory usage for the circuit.

        #[allow(clippy::disallowed_methods)]

        );

        // On the relay side, we always have one "hop" (ourselves).

        //

        // Clients will need to call this function in response to CtrlMsg::Create

        // (TODO: for clients, we probably will need to store a bunch more state here)

        // TODO(relay): currently we don't need buffering on this channel,

        // but we might need it if we start using it for more than just EXTENDED2 events

        #[allow(clippy::disallowed_methods)]

    /// Launch the reactor, and run until the circuit closes or we

    /// encounter an error.

    ///

    /// Once this method returns, the circuit is dead and cannot be

    /// used again.

}