vox-types 0.4.0

use std::{future::Future, pin::Pin, sync::Arc};

use crate::{
    ConnectionId, MaybeSend, MaybeSendFuture, MaybeSync, Metadata, MethodId, RequestCall,
    RequestId, RequestResponse, SchemaRecvTracker, SelfRef, VoxError,
};

/// A boxed future that is `Send` on native targets and `!Send` on wasm32.
pub type BoxFut<'a, T> = Pin<Box<dyn MaybeSendFuture<Output = T> + 'a>>;

/// Result type for one caller-visible RPC call: either a tracked response or an error.
///
/// The tracked value is the wire-level [`RequestResponse`] that resolved the
/// current request attempt for that call.
pub type CallResult = Result<crate::WithTracker<SelfRef<RequestResponse<'static>>>, VoxError>;

// As a recap, a service defined like so:
//
// #[vox::service]
// trait Hash {
//   async fn hash(&self, payload: &[u8]) -> Result<&[u8], E>;
// }
//
// Would expand to the following caller:
//
// impl HashClient {
//   async fn hash(&self, payload: &[u8]) -> Result<SelfRef<&[u8]>, VoxError<E>>;
// }
//
// Would expand to a service trait (what users implement):
//
// trait Hash {
//   async fn hash(&self, call: impl Call<&[u8], E>, payload: &[u8]);
// }
//
// And a HashDispatcher<S: Hash> that implements Handler<R: ReplySink>:
// it deserializes args, constructs an ErasedCall<T, E> from the ReplySink,
// and routes to the appropriate method by method ID.
//
// For owned success returns, generated methods return values directly and
// the dispatcher sends replies on their behalf.
//
// HashDispatcher<S> implements Handler<R>, and can be stored as
// Box<dyn Handler<R>> to erase both S and the service type.
//
// Why impl Call in HashServer? So that the server can reply with something
// _borrowed_ from its own stack frame.
//
// For example:
//
// impl Hash for MyHasher {
//   async fn hash(&self, call: impl Call<&[u8], E>, payload: &[u8]) {
//     let result: [u8; 16] = compute_hash(payload);
//     call.ok(&result).await;
//   }
// }
//
// Call's public API is:
//
// trait Call<T, E> {
//   async fn reply(self, result: Result<T, E>);
//   async fn ok(self, value: T) { self.reply(Ok(value)).await }
//   async fn err(self, error: E) { self.reply(Err(error)).await }
// }
//
// If a Call is dropped before reply/ok/err is called, the caller will
// receive a VoxError::Cancelled error. This is to ensure that the caller
// is always notified, even if the handler panics or otherwise fails to
// reply.

/// Represents an in-progress API-level call as seen by a server handler.
///
/// A `Call` is handed to a [`Handler`] implementation for one incoming
/// request attempt. It provides the mechanism for sending the terminal
/// response for that attempt back to the caller. The response can be sent
/// via [`Call::reply`], [`Call::ok`], or [`Call::err`].
///
/// In the retry model, one logical operation may span multiple request
/// attempts over time, but each `Call` value corresponds to exactly one
/// request attempt currently being handled.
///
/// # Cancellation
///
/// If a `Call` is dropped without a reply being sent, the caller will
/// automatically receive a [`VoxError::Cancelled`] error. This guarantees
/// that the caller is always notified, even if the handler panics or
/// otherwise fails to produce a reply.
///
/// # Type Parameters
///
/// - `T`: The success value type of the response.
/// - `E`: The error value type of the response.
pub trait Call<'wire, T, E>: MaybeSend
where
    T: facet::Facet<'wire> + MaybeSend,
    E: facet::Facet<'wire> + MaybeSend,
{
    /// Send the terminal response for this request attempt, consuming this `Call`.
    fn reply(self, result: Result<T, E>) -> impl Future<Output = ()> + MaybeSend;

    /// Send a successful response for this request attempt, consuming this `Call`.
    ///
    /// Equivalent to `self.reply(Ok(value)).await`.
    fn ok(self, value: T) -> impl Future<Output = ()> + MaybeSend
    where
        Self: Sized,
    {
        self.reply(Ok(value))
    }

    /// Send an error response for this request attempt, consuming this `Call`.
    ///
    /// Equivalent to `self.reply(Err(error)).await`.
    fn err(self, error: E) -> impl Future<Output = ()> + MaybeSend
    where
        Self: Sized,
    {
        self.reply(Err(error))
    }
}

/// Sink for sending the terminal response for one request attempt.
///
/// Implemented by the session driver. Provides backpressure: `send_reply`
/// awaits until the transport can accept the response before serializing it.
///
/// # Cancellation
///
/// If the `ReplySink` is dropped without `send_reply` being called, the caller
/// will automatically receive a [`crate::VoxError::Cancelled`] error.
pub trait ReplySink: MaybeSend + MaybeSync + 'static {
    /// Send the terminal response for this request attempt, consuming the sink.
    /// Any error that happens during `send_reply` must set a flag in the driver
    /// for it to resolve the attempt as failed.
    ///
    /// This cannot return a `Result` because we cannot trust callers to deal
    /// with it, and they cannot try sending a second response anyway.
    ///
    /// Do not spawn a task to send the error because it too, might fail.
    fn send_reply(self, response: RequestResponse<'_>) -> impl Future<Output = ()> + MaybeSend;

    /// Send an error response for this request attempt, consuming the sink.
    ///
    /// This is a convenience method used by generated dispatchers when
    /// deserialization fails or the method ID is unknown.
    fn send_error<E: for<'a> facet::Facet<'a> + MaybeSend>(
        self,
        error: VoxError<E>,
    ) -> impl Future<Output = ()> + MaybeSend
    where
        Self: Sized,
    {
        use crate::{Payload, RequestResponse};
        // Wire format is always Result<T, VoxError<E>>. We don't know T here,
        // but postcard encodes () as zero bytes, so Result<(), VoxError<E>>
        // produces the same Err variant encoding as any Result<T, VoxError<E>>.
        async move {
            let wire: Result<(), VoxError<E>> = Err(error);
            self.send_reply(RequestResponse {
                ret: Payload::outgoing(&wire),
                metadata: Default::default(),
                schemas: Default::default(),
            })
            .await;
        }
    }

    /// Send an error response using the full wire shape `Result<T, VoxError<E>>`.
    ///
    /// This preserves the method's real `Ok` type for schema extraction.
    fn send_typed_error<'wire, T, E>(
        self,
        error: VoxError<E>,
    ) -> impl Future<Output = ()> + MaybeSend
    where
        Self: Sized,
        T: facet::Facet<'wire> + MaybeSend,
        E: facet::Facet<'wire> + MaybeSend,
    {
        use crate::{Payload, RequestResponse};
        async move {
            let wire: Result<T, VoxError<E>> = Err(error);
            let ptr = facet::PtrConst::new((&wire as *const Result<T, VoxError<E>>).cast::<u8>());
            let shape = <Result<T, VoxError<E>> as facet::Facet<'wire>>::SHAPE;
            let ret = unsafe { Payload::outgoing_unchecked(ptr, shape) };
            self.send_reply(RequestResponse {
                ret,
                metadata: Default::default(),
                schemas: Default::default(),
            })
            .await;
        }
    }

    /// Return a channel binder for binding Tx/Rx handles in deserialized args.
    ///
    /// Returns `None` by default. The driver's `ReplySink` implementation
    /// overrides this to provide actual channel binding.
    fn channel_binder(&self) -> Option<&dyn crate::ChannelBinder> {
        None
    }

    /// Return the wire-level request identifier for this reply sink when available.
    fn request_id(&self) -> Option<RequestId> {
        None
    }

    /// Return the virtual connection identifier for this reply sink when available.
    fn connection_id(&self) -> Option<ConnectionId> {
        None
    }
}

/// Type-erased handler for incoming service calls.
///
/// Implemented (by the macro-generated dispatch code) for server-side types.
/// Takes a fully decoded [`RequestCall`](crate::RequestCall) — one wire-level
/// request attempt already parsed from the connection — and a [`ReplySink`]
/// through which the terminal response for that attempt is sent.
///
/// The dispatch impl decodes the args, routes by [`crate::MethodId`], and
/// invokes the appropriate typed [`Call`]-based method on the concrete server type.
///
/// Generated clients hold a `Caller` (from `vox-core`) as a public field
/// and use it to start API-level calls.
pub trait Handler<R: ReplySink>: MaybeSend + MaybeSync + 'static {
    /// Return the static retry policy for a method ID served by this handler.
    fn retry_policy(&self, _method_id: MethodId) -> crate::RetryPolicy {
        crate::RetryPolicy::VOLATILE
    }

    /// Return whether the method's argument shape contains any channels.
    fn args_have_channels(&self, _method_id: MethodId) -> bool {
        false
    }

    /// Return the canonical wire response shape for a method, if known.
    ///
    /// This is the full wire type `Result<T, VoxError<E>>`, not the
    /// user-facing return type `T` or `Result<T, E>`.
    fn response_wire_shape(&self, _method_id: MethodId) -> Option<&'static facet::Shape> {
        None
    }

    /// Dispatch an incoming call to the appropriate method implementation.
    fn handle(
        &self,
        call: SelfRef<RequestCall<'static>>,
        reply: R,
        schemas: Arc<SchemaRecvTracker>,
    ) -> impl Future<Output = ()> + MaybeSend + '_;
}

impl<R: ReplySink> Handler<R> for () {
    async fn handle(
        &self,
        _call: SelfRef<RequestCall<'static>>,
        _reply: R,
        _schemas: Arc<SchemaRecvTracker>,
    ) {
    }
}

/// A decoded response value paired with response metadata.
///
/// This helper is available for lower-level callers that need both the
/// decoded value and metadata together. Generated Rust client methods do
/// not expose response metadata in their return types.
pub struct ResponseParts<'a, T> {
    /// The decoded return value.
    pub ret: T,
    /// Metadata attached to the response by the server.
    pub metadata: Metadata<'a>,
}

impl<'a, T> std::ops::Deref for ResponseParts<'a, T> {
    type Target = T;
    fn deref(&self) -> &T {
        &self.ret
    }
}

/// Concrete [`Call`] implementation backed by a [`ReplySink`].
///
/// Constructed by the dispatcher and handed to the server method.
/// When the server calls [`Call::reply`], the result is serialized and
/// sent through the sink.
pub struct SinkCall<R: ReplySink> {
    reply: R,
}

impl<R: ReplySink> SinkCall<R> {
    pub fn new(reply: R) -> Self {
        Self { reply }
    }
}

impl<'wire, T, E, R> Call<'wire, T, E> for SinkCall<R>
where
    T: facet::Facet<'wire> + MaybeSend,
    E: facet::Facet<'wire> + MaybeSend,
    R: ReplySink,
{
    async fn reply(self, result: Result<T, E>) {
        use crate::{Payload, RequestResponse};
        let wire: Result<T, VoxError<E>> = result.map_err(VoxError::User);
        let ptr = facet::PtrConst::new((&wire as *const Result<T, VoxError<E>>).cast::<u8>());
        let shape = <Result<T, VoxError<E>> as facet::Facet<'wire>>::SHAPE;
        // SAFETY: `wire` lives until `send_reply(...).await` completes in this function,
        // and `shape` matches the pointed value exactly.
        let ret = unsafe { Payload::outgoing_unchecked(ptr, shape) };

        self.reply
            .send_reply(RequestResponse {
                ret,
                metadata: Default::default(),
                schemas: Default::default(),
            })
            .await;
    }
}

#[cfg(test)]
mod tests {
    use std::sync::{Arc, Mutex};

    use crate::{MaybeSend, Metadata, Payload, RequestCall, RequestResponse};

    use super::{Call, Handler, ReplySink, ResponseParts};

    struct RecordingCall<T, E> {
        observed: Arc<Mutex<Option<Result<T, E>>>>,
    }

    impl<'wire, T, E> Call<'wire, T, E> for RecordingCall<T, E>
    where
        T: facet::Facet<'wire> + MaybeSend + Send + 'static,
        E: facet::Facet<'wire> + MaybeSend + Send + 'static,
    {
        async fn reply(self, result: Result<T, E>) {
            let mut guard = self.observed.lock().expect("recording mutex poisoned");
            *guard = Some(result);
        }
    }

    struct RecordingReplySink {
        saw_send_reply: Arc<Mutex<bool>>,
        saw_outgoing_payload: Arc<Mutex<bool>>,
    }

    impl ReplySink for RecordingReplySink {
        async fn send_reply(self, response: RequestResponse<'_>) {
            let mut saw_send_reply = self
                .saw_send_reply
                .lock()
                .expect("send-reply mutex poisoned");
            *saw_send_reply = true;

            let mut saw_outgoing = self
                .saw_outgoing_payload
                .lock()
                .expect("payload-kind mutex poisoned");
            *saw_outgoing = matches!(response.ret, Payload::Value { .. });
        }
    }

    #[tokio::test]
    async fn call_ok_and_err_route_through_reply() {
        let observed_ok: Arc<Mutex<Option<Result<u32, &'static str>>>> = Arc::new(Mutex::new(None));
        RecordingCall {
            observed: Arc::clone(&observed_ok),
        }
        .ok(7)
        .await;
        assert!(matches!(
            *observed_ok.lock().expect("ok mutex poisoned"),
            Some(Ok(7))
        ));

        let observed_err: Arc<Mutex<Option<Result<u32, &'static str>>>> =
            Arc::new(Mutex::new(None));
        RecordingCall {
            observed: Arc::clone(&observed_err),
        }
        .err("boom")
        .await;
        assert!(matches!(
            *observed_err.lock().expect("err mutex poisoned"),
            Some(Err("boom"))
        ));
    }

    #[tokio::test]
    async fn reply_sink_send_error_uses_outgoing_payload_and_reply_path() {
        let saw_send_reply = Arc::new(Mutex::new(false));
        let saw_outgoing_payload = Arc::new(Mutex::new(false));
        let sink = RecordingReplySink {
            saw_send_reply: Arc::clone(&saw_send_reply),
            saw_outgoing_payload: Arc::clone(&saw_outgoing_payload),
        };

        sink.send_error(crate::VoxError::<String>::Cancelled).await;

        assert!(*saw_send_reply.lock().expect("send-reply mutex poisoned"));
        assert!(
            *saw_outgoing_payload
                .lock()
                .expect("payload-kind mutex poisoned")
        );
    }

    #[tokio::test]
    async fn reply_sink_send_typed_error_preserves_ok_shape() {
        use crate::{
            SchemaKind, TypeRef, VariantPayload, VoxError, build_registry, extract_schemas,
        };

        struct ShapeReplySink {
            observed_root: Arc<Mutex<Option<TypeRef>>>,
        }

        impl ReplySink for ShapeReplySink {
            async fn send_reply(self, response: RequestResponse<'_>) {
                let Payload::Value { shape, .. } = response.ret else {
                    panic!("typed error should use outgoing payload");
                };
                let extracted = extract_schemas(shape).expect("response shape should extract");
                *self
                    .observed_root
                    .lock()
                    .expect("observed-root mutex poisoned") = Some(extracted.root.clone());
            }
        }

        let observed_root = Arc::new(Mutex::new(None));
        ShapeReplySink {
            observed_root: Arc::clone(&observed_root),
        }
        .send_typed_error::<(String, i32), String>(VoxError::Cancelled)
        .await;

        let root = observed_root
            .lock()
            .expect("observed-root mutex poisoned")
            .clone()
            .expect("typed error should record a root");
        let extracted =
            extract_schemas(<Result<(String, i32), VoxError<String>> as facet::Facet>::SHAPE)
                .expect("expected result shape should extract");
        let registry = build_registry(&extracted.schemas);
        let root_kind = root.resolve_kind(&registry).expect("root should resolve");
        let SchemaKind::Enum { variants, .. } = root_kind else {
            panic!("expected result enum root");
        };
        let ok_variant = variants
            .iter()
            .find(|variant| variant.name == "Ok")
            .expect("Result should have Ok variant");
        let VariantPayload::Newtype { type_ref } = &ok_variant.payload else {
            panic!("Ok variant should be newtype");
        };
        match type_ref
            .resolve_kind(&registry)
            .expect("Ok payload should resolve")
        {
            SchemaKind::Tuple { elements } => {
                assert_eq!(elements.len(), 2, "Ok tuple should have two elements");
            }
            other => panic!("expected Ok payload to be tuple, got {other:?}"),
        }
    }

    #[tokio::test]
    async fn unit_handler_is_noop() {
        let req = crate::SelfRef::owning(
            crate::Backing::Boxed(Box::<[u8]>::default()),
            RequestCall {
                method_id: crate::MethodId(1),
                metadata: Metadata::default(),
                args: Payload::PostcardBytes(&[]),
                schemas: Default::default(),
            },
        );
        ().handle(
            req,
            RecordingReplySink {
                saw_send_reply: Arc::new(Mutex::new(false)),
                saw_outgoing_payload: Arc::new(Mutex::new(false)),
            },
            Arc::new(crate::SchemaRecvTracker::new()),
        )
        .await;
    }

    #[test]
    fn response_parts_deref_exposes_ret() {
        let parts = ResponseParts {
            ret: 42_u32,
            metadata: Metadata::default(),
        };
        assert_eq!(*parts, 42);
    }

    #[test]
    fn default_channel_binder_accessor_for_reply_sink_returns_none() {
        let sink = RecordingReplySink {
            saw_send_reply: Arc::new(Mutex::new(false)),
            saw_outgoing_payload: Arc::new(Mutex::new(false)),
        };
        assert!(sink.channel_binder().is_none());
    }
}