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// Copyright 2019-2021 Parity Technologies (UK) Ltd.
//
// Permission is hereby granted, free of charge, to any
// person obtaining a copy of this software and associated
// documentation files (the "Software"), to deal in the
// Software without restriction, including without
// limitation the rights to use, copy, modify, merge,
// publish, distribute, sublicense, and/or sell copies of
// the Software, and to permit persons to whom the Software
// is furnished to do so, subject to the following
// conditions:
//
// The above copyright notice and this permission notice
// shall be included in all copies or substantial portions
// of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
// ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
// TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
// PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
// SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
// CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
// IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.

//! Utilities for handling async code.

use jsonrpsee_core::Error;
use std::sync::Arc;
use tokio::sync::{watch, OwnedSemaphorePermit, Semaphore, TryAcquireError};

/// Represent a stop handle which is a wrapper over a `multi-consumer receiver`
/// and cloning [`StopHandle`] will get a separate instance of the underlying receiver.
#[derive(Debug, Clone)]
pub(crate) struct StopHandle(watch::Receiver<()>);

impl StopHandle {
	pub(crate) fn new(rx: watch::Receiver<()>) -> Self {
		Self(rx)
	}

	/// A future that resolves when server has been stopped
	/// it consumes the stop handle.
	pub(crate) async fn shutdown(mut self) {
		let _ = self.0.changed().await;
	}
}

/// Server handle.
///
/// When all [`StopHandle`]'s have been `dropped` or `stop` has been called
/// the server will be stopped.
#[derive(Debug, Clone)]
pub struct ServerHandle(Arc<watch::Sender<()>>);

impl ServerHandle {
	/// Create a new server handle.
	pub fn new(tx: watch::Sender<()>) -> Self {
		Self(Arc::new(tx))
	}

	/// Tell the server to stop without waiting for the server to stop.
	pub fn stop(&self) -> Result<(), Error> {
		self.0.send(()).map_err(|_| Error::AlreadyStopped)
	}

	/// Wait for the server to stop.
	pub async fn stopped(self) {
		self.0.closed().await
	}

	/// Check if the server has been stopped.
	pub fn is_stopped(&self) -> bool {
		self.0.is_closed()
	}
}

/// Limits the number of connections.
#[derive(Debug)]
pub(crate) struct ConnectionGuard(Arc<Semaphore>);

impl ConnectionGuard {
	pub(crate) fn new(limit: usize) -> Self {
		Self(Arc::new(Semaphore::new(limit)))
	}

	pub(crate) fn try_acquire(&self) -> Option<OwnedSemaphorePermit> {
		match self.0.clone().try_acquire_owned() {
			Ok(guard) => Some(guard),
			Err(TryAcquireError::Closed) => unreachable!("Semaphore::Close is never called and can't be closed; qed"),
			Err(TryAcquireError::NoPermits) => None,
		}
	}

	pub(crate) fn available_connections(&self) -> usize {
		self.0.available_permits()
	}
}