// Copyright 2018 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
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// DEALINGS IN THE SOFTWARE.

use futures::{future::BoxFuture, prelude::*};
use libp2p_core::{InboundUpgrade, OutboundUpgrade, UpgradeInfo};
use log::debug;
use rand::{distributions, prelude::*};
use std::{io, iter, time::Duration};
use wasm_timer::Instant;

/// Represents a prototype for an upgrade to handle the ping protocol.
///
/// The protocol works the following way:
///
/// - Dialer sends 32 bytes of random data.
/// - Listener receives the data and sends it back.
/// - Dialer receives the data and verifies that it matches what it sent.
///
/// The dialer produces a `Duration`, which corresponds to the round-trip time
/// of the payload.
///
/// > **Note**: The round-trip time of a ping may be subject to delays induced
/// >           by the underlying transport, e.g. in the case of TCP there is
/// >           Nagle's algorithm, delayed acks and similar configuration options
/// >           which can affect latencies especially on otherwise low-volume
/// >           connections.
#[derive(Default, Debug, Copy, Clone)]
pub struct Ping;

const PING_SIZE: usize = 32;

impl UpgradeInfo for Ping {
    type Info = &'static [u8];
    type InfoIter = iter::Once<Self::Info>;

    fn protocol_info(&self) -> Self::InfoIter {
        iter::once(b"/ipfs/ping/1.0.0")
    }
}

impl<TSocket> InboundUpgrade<TSocket> for Ping
where
    TSocket: AsyncRead + AsyncWrite + Send + Unpin + 'static,
{
    type Output = ();
    type Error = io::Error;
    type Future = BoxFuture<'static, Result<(), io::Error>>;

    fn upgrade_inbound(self, mut socket: TSocket, _: Self::Info) -> Self::Future {
        async move {
            let mut payload = [0u8; PING_SIZE];
            while let Ok(_) = socket.read_exact(&mut payload).await {
                socket.write_all(&payload).await?;
            }
            Ok(())
        }.boxed()
    }
}

impl<TSocket> OutboundUpgrade<TSocket> for Ping
where
    TSocket: AsyncRead + AsyncWrite + Send + Unpin + 'static,
{
    type Output = Duration;
    type Error = io::Error;
    type Future = BoxFuture<'static, Result<Duration, io::Error>>;

    fn upgrade_outbound(self, mut socket: TSocket, _: Self::Info) -> Self::Future {
        let payload: [u8; PING_SIZE] = thread_rng().sample(distributions::Standard);
        debug!("Preparing ping payload {:?}", payload);
        async move {
            socket.write_all(&payload).await?;
            socket.close().await?;
            let started = Instant::now();

            let mut recv_payload = [0u8; 32];
            socket.read_exact(&mut recv_payload).await?;
            if recv_payload == payload {
                Ok(started.elapsed())
            } else {
                Err(io::Error::new(io::ErrorKind::InvalidData, "Ping payload mismatch"))
            }
        }.boxed()
    }
}

#[cfg(test)]
mod tests {
    use super::Ping;
    use futures::prelude::*;
    use libp2p_core::{
        upgrade,
        multiaddr::multiaddr,
        transport::{
            Transport,
            ListenerEvent,
            memory::MemoryTransport
        }
    };
    use rand::{thread_rng, Rng};
    use std::time::Duration;

    #[test]
    fn ping_pong() {
        let mem_addr = multiaddr![Memory(thread_rng().gen::<u64>())];
        let mut listener = MemoryTransport.listen_on(mem_addr).unwrap();

        let listener_addr =
            if let Some(Some(Ok(ListenerEvent::NewAddress(a)))) = listener.next().now_or_never() {
                a
            } else {
                panic!("MemoryTransport not listening on an address!");
            };
        
        async_std::task::spawn(async move {
            let listener_event = listener.next().await.unwrap();
            let (listener_upgrade, _) = listener_event.unwrap().into_upgrade().unwrap();
            let conn = listener_upgrade.await.unwrap();
            upgrade::apply_inbound(conn, Ping::default()).await.unwrap();
        });

        async_std::task::block_on(async move {
            let c = MemoryTransport.dial(listener_addr).unwrap().await.unwrap();
            let rtt = upgrade::apply_outbound(c, Ping::default(), upgrade::Version::V1).await.unwrap();
            assert!(rtt > Duration::from_secs(0));
        });
    }
}