// This file is part of Substrate.

// Copyright (C) 2020 Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0

// 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.

//! Features to meter unbounded channels

#[cfg(not(feature = "metered"))]
mod inner {
	// just aliased, non performance implications
	use futures::channel::mpsc::{self, UnboundedReceiver, UnboundedSender};
	pub type TracingUnboundedSender<T> = UnboundedSender<T>;
	pub type TracingUnboundedReceiver<T> = UnboundedReceiver<T>;

	/// Alias `mpsc::unbounded`
	pub fn tracing_unbounded<T>(_key: &'static str) ->(TracingUnboundedSender<T>, TracingUnboundedReceiver<T>) {
		mpsc::unbounded()
	}
}


#[cfg(feature = "metered")]
mod inner {
	//tracing implementation
	use futures::channel::mpsc::{self,
		UnboundedReceiver, UnboundedSender,
		TryRecvError, TrySendError, SendError
	};
	use futures::{sink::Sink, task::{Poll, Context}, stream::{Stream, FusedStream}};
	use std::pin::Pin;
	use crate::metrics::UNBOUNDED_CHANNELS_COUNTER;

	/// Wrapper Type around `UnboundedSender` that increases the global
	/// measure when a message is added
	#[derive(Debug)]
	pub struct TracingUnboundedSender<T>(&'static str, UnboundedSender<T>);

	// Strangely, deriving `Clone` requires that `T` is also `Clone`.
	impl<T> Clone for TracingUnboundedSender<T> {
		fn clone(&self) -> Self {
			Self(self.0, self.1.clone())
		}
	}

	/// Wrapper Type around `UnboundedReceiver` that decreases the global
	/// measure when a message is polled
	#[derive(Debug)]
	pub struct TracingUnboundedReceiver<T>(&'static str, UnboundedReceiver<T>);

	/// Wrapper around `mpsc::unbounded` that tracks the in- and outflow via
	/// `UNBOUNDED_CHANNELS_COUNTER`
	pub fn tracing_unbounded<T>(key: &'static str) ->(TracingUnboundedSender<T>, TracingUnboundedReceiver<T>) {
		let (s, r) = mpsc::unbounded();
		(TracingUnboundedSender(key, s), TracingUnboundedReceiver(key,r))
	}

	impl<T> TracingUnboundedSender<T> {
		/// Proxy function to mpsc::UnboundedSender
		pub fn poll_ready(&self, ctx: &mut Context) -> Poll<Result<(), SendError>> {
			self.1.poll_ready(ctx)
		}

		/// Proxy function to mpsc::UnboundedSender
		pub fn is_closed(&self) -> bool {
			self.1.is_closed()
		}

		/// Proxy function to mpsc::UnboundedSender
		pub fn close_channel(&self) {
			self.1.close_channel()
		}

		/// Proxy function to mpsc::UnboundedSender
		pub fn disconnect(&mut self) {
			self.1.disconnect()
		}

		/// Proxy function to mpsc::UnboundedSender
		pub fn start_send(&mut self, msg: T) -> Result<(), SendError> {
			self.1.start_send(msg)
		}

		/// Proxy function to mpsc::UnboundedSender
		pub fn unbounded_send(&self, msg: T) -> Result<(), TrySendError<T>> {
			self.1.unbounded_send(msg).map(|s|{
				UNBOUNDED_CHANNELS_COUNTER.with_label_values(&[self.0, &"send"]).inc();
				s
			})
		}

		/// Proxy function to mpsc::UnboundedSender
		pub fn same_receiver(&self, other: &UnboundedSender<T>) -> bool {
			self.1.same_receiver(other)
		}
	}

	impl<T> TracingUnboundedReceiver<T> {

		fn consume(&mut self) {
			// consume all items, make sure to reflect the updated count
			let mut count = 0;
			loop {
				if self.1.is_terminated() {
					break;
				}

				match self.try_next() {
					Ok(Some(..)) => count += 1,
					_ => break
				}
			}
			// and discount the messages
			if count > 0 {
				UNBOUNDED_CHANNELS_COUNTER.with_label_values(&[self.0, &"dropped"]).inc_by(count);
			}

		}

		/// Proxy function to mpsc::UnboundedReceiver
		/// that consumes all messages first and updates the counter
		pub fn close(&mut self) {
			self.consume();
			self.1.close()
		}

		/// Proxy function to mpsc::UnboundedReceiver
		/// that discounts the messages taken out
		pub fn try_next(&mut self) -> Result<Option<T>, TryRecvError> {
			self.1.try_next().map(|s| {
				if s.is_some() {
					UNBOUNDED_CHANNELS_COUNTER.with_label_values(&[self.0, &"received"]).inc();
				}
				s
			})
		}
	}

	impl<T> Drop for TracingUnboundedReceiver<T> {
		fn drop(&mut self) {
			self.consume();
		}
	}

	impl<T> Unpin for TracingUnboundedReceiver<T> {}

	impl<T> Stream for TracingUnboundedReceiver<T> {
		type Item = T;

		fn poll_next(
			self: Pin<&mut Self>,
			cx: &mut Context<'_>,
		) -> Poll<Option<T>> {
			let s = self.get_mut();
			match Pin::new(&mut s.1).poll_next(cx) {
				Poll::Ready(msg) => {
					if msg.is_some() {
						UNBOUNDED_CHANNELS_COUNTER.with_label_values(&[s.0, "received"]).inc();
				   	}
					Poll::Ready(msg)
				}
				Poll::Pending => {
					Poll::Pending
				}
			}
		}
	}

	impl<T> FusedStream for TracingUnboundedReceiver<T> {
		fn is_terminated(&self) -> bool {
			self.1.is_terminated()
		}
	}

	impl<T> Sink<T> for TracingUnboundedSender<T> {
		type Error = SendError;

		fn poll_ready(
			self: Pin<&mut Self>,
			cx: &mut Context<'_>,
		) -> Poll<Result<(), Self::Error>> {
			TracingUnboundedSender::poll_ready(&*self, cx)
		}

		fn start_send(
			mut self: Pin<&mut Self>,
			msg: T,
		) -> Result<(), Self::Error> {
			TracingUnboundedSender::start_send(&mut *self, msg)
		}

		fn poll_flush(
			self: Pin<&mut Self>,
			_: &mut Context<'_>,
		) -> Poll<Result<(), Self::Error>> {
			Poll::Ready(Ok(()))
		}

		fn poll_close(
			mut self: Pin<&mut Self>,
			_: &mut Context<'_>,
		) -> Poll<Result<(), Self::Error>> {
			self.disconnect();
			Poll::Ready(Ok(()))
		}
	}

	impl<T> Sink<T> for &TracingUnboundedSender<T> {
		type Error = SendError;

		fn poll_ready(
			self: Pin<&mut Self>,
			cx: &mut Context<'_>,
		) -> Poll<Result<(), Self::Error>> {
			TracingUnboundedSender::poll_ready(*self, cx)
		}

		fn start_send(self: Pin<&mut Self>, msg: T) -> Result<(), Self::Error> {
			self.unbounded_send(msg)
				.map_err(TrySendError::into_send_error)
		}

		fn poll_flush(
			self: Pin<&mut Self>,
			_: &mut Context<'_>,
		) -> Poll<Result<(), Self::Error>> {
			Poll::Ready(Ok(()))
		}

		fn poll_close(
			self: Pin<&mut Self>,
			_: &mut Context<'_>,
		) -> Poll<Result<(), Self::Error>> {
			self.close_channel();
			Poll::Ready(Ok(()))
		}
	}
}

pub use inner::{tracing_unbounded, TracingUnboundedSender, TracingUnboundedReceiver};
