/*

 * Copyright 2020, gRPC Authors All rights reserved.

 *

 * Licensed under the Apache License, Version 2.0 (the "License");

 * you may not use this file except in compliance with the License.

 * You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

import NIOCore

/// A base class for server interceptors.

///

/// Interceptors allow request and response and response parts to be observed, mutated or dropped

/// as necessary. The default behaviour for this base class is to forward any events to the next

/// interceptor.

///

/// Interceptors may observe two different types of event:

/// - receiving request parts with ``receive(_:context:)``,

/// - sending response parts with ``send(_:promise:context:)``.

///

/// These events flow through a pipeline of interceptors for each RPC. Request parts will enter

/// the head of the interceptor pipeline once the request router has determined that there is a

/// service provider which is able to handle the request stream. Response parts from the service

/// provider enter the tail of the interceptor pipeline and will be sent to the client after

/// traversing the pipeline through to the head.

///

/// Each of the interceptor functions is provided with a `context` which exposes analogous functions

/// (``receive(_:context:)`` and ``send(_:promise:context:)``) which may be called to forward events to the next

/// interceptor.

///

/// ### Thread Safety

///

/// Functions on `context` are not thread safe and **must** be called on the `EventLoop` found on

/// the `context`. Since each interceptor is invoked on the same `EventLoop` this does not usually

/// require any extra attention. However, if work is done on a `DispatchQueue` or _other_

/// `EventLoop` then implementers should ensure that they use `context` from the correct

/// `EventLoop`.

open class ServerInterceptor<Request, Response>: @unchecked Sendable {

  public init() {}

  /// Called when the interceptor has received a request part to handle.

  /// - Parameters:

  ///   - part: The request part which has been received from the client.

  ///   - context: An interceptor context which may be used to forward the response part.

  open func receive(

    _ part: GRPCServerRequestPart<Request>,

    context: ServerInterceptorContext<Request, Response>

  ) {

    context.receive(part)

  }

  /// Called when the interceptor has received a response part to handle.

  /// - Parameters:

  ///   - part: The request part which should be sent to the client.

  ///   - promise: A promise which should be completed when the response part has been written.

  ///   - context: An interceptor context which may be used to forward the request part.

  open func send(

    _ part: GRPCServerResponsePart<Response>,

    promise: EventLoopPromise<Void>?,

    context: ServerInterceptorContext<Request, Response>

  ) {

    context.send(part, promise: promise)

  }

}