// Copyright 2019 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
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// DEALINGS IN THE SOFTWARE.

use crate::protocols_handler::{ProtocolsHandler, ProtocolsHandlerEvent, ProtocolsHandlerUpgrErr};
use crate::upgrade::{InboundUpgrade, OutboundUpgrade};
use futures::prelude::*;
use smallvec::SmallVec;
use std::{error, marker::PhantomData};
use tokio_io::{AsyncRead, AsyncWrite};

/// Implementation of `ProtocolsHandler` that opens a new substream for each individual message.
///
/// This struct is meant to be a helper for other implementations to use.
// TODO: Debug
pub struct OneShotHandler<TSubstream, TInProto, TOutProto, TOutEvent>
where TOutProto: OutboundUpgrade<TSubstream>
{
    /// The upgrade for inbound substreams.
    listen_protocol: TInProto,
    /// If true, we should return as soon as possible.
    shutting_down: bool,
    /// If `Some`, something bad happened and we should shut down the handler with an error.
    pending_error: Option<ProtocolsHandlerUpgrErr<<TOutProto as OutboundUpgrade<TSubstream>>::Error>>,
    /// Queue of events to produce in `poll()`.
    events_out: SmallVec<[TOutEvent; 4]>,
    /// Queue of outbound substreams to open.
    dial_queue: SmallVec<[TOutProto; 4]>,
    /// Current number of concurrent outbound substreams being opened.
    dial_negotiated: u32,
    /// Maximum number of concurrent outbound substreams being opened. Value is never modified.
    max_dial_negotiated: u32,
    /// Pin the `TSubstream` generic.
    marker: PhantomData<TSubstream>,
}

impl<TSubstream, TInProto, TOutProto, TOutEvent>
    OneShotHandler<TSubstream, TInProto, TOutProto, TOutEvent>
where TOutProto: OutboundUpgrade<TSubstream>
{
    /// Creates a `OneShotHandler`.
    #[inline]
    pub fn new(listen_protocol: TInProto) -> Self {
        OneShotHandler {
            listen_protocol,
            shutting_down: false,
            pending_error: None,
            events_out: SmallVec::new(),
            dial_queue: SmallVec::new(),
            dial_negotiated: 0,
            max_dial_negotiated: 8,
            marker: PhantomData,
        }
    }

    /// Returns the number of pending requests.
    #[inline]
    pub fn pending_requests(&self) -> u32 {
        self.dial_negotiated + self.dial_queue.len() as u32
    }

    /// Returns a reference to the listen protocol configuration.
    ///
    /// > **Note**: If you modify the protocol, modifications will only applies to future inbound
    /// >           substreams, not the ones already being negotiated.
    #[inline]
    pub fn listen_protocol_ref(&self) -> &TInProto {
        &self.listen_protocol
    }

    /// Returns a mutable reference to the listen protocol configuration.
    ///
    /// > **Note**: If you modify the protocol, modifications will only applies to future inbound
    /// >           substreams, not the ones already being negotiated.
    #[inline]
    pub fn listen_protocol_mut(&mut self) -> &mut TInProto {
        &mut self.listen_protocol
    }

    /// Opens an outbound substream with `upgrade`.
    #[inline]
    pub fn send_request(&mut self, upgrade: TOutProto) {
        self.dial_queue.push(upgrade);
    }
}

impl<TSubstream, TInProto, TOutProto, TOutEvent> Default for
    OneShotHandler<TSubstream, TInProto, TOutProto, TOutEvent>
where TOutProto: OutboundUpgrade<TSubstream>,
      TInProto: Default
{
    #[inline]
    fn default() -> Self {
        OneShotHandler::new(Default::default())
    }
}

impl<TSubstream, TInProto, TOutProto, TOutEvent> ProtocolsHandler for
    OneShotHandler<TSubstream, TInProto, TOutProto, TOutEvent>
where
    TSubstream: AsyncRead + AsyncWrite,
    TInProto: InboundUpgrade<TSubstream> + Clone,
    TOutProto: OutboundUpgrade<TSubstream>,
    TInProto::Output: Into<TOutEvent>,
    TOutProto::Output: Into<TOutEvent>,
    TOutProto::Error: error::Error + 'static,
{
    type InEvent = TOutProto;
    type OutEvent = TOutEvent;
    type Error = ProtocolsHandlerUpgrErr<<Self::OutboundProtocol as OutboundUpgrade<Self::Substream>>::Error>;
    type Substream = TSubstream;
    type InboundProtocol = TInProto;
    type OutboundProtocol = TOutProto;
    type OutboundOpenInfo = ();

    #[inline]
    fn listen_protocol(&self) -> Self::InboundProtocol {
        self.listen_protocol.clone()
    }

    #[inline]
    fn inject_fully_negotiated_inbound(
        &mut self,
        out: <Self::InboundProtocol as InboundUpgrade<Self::Substream>>::Output
    ) {
        if self.shutting_down {
            return;
        }

        self.events_out.push(out.into());
    }

    #[inline]
    fn inject_fully_negotiated_outbound(
        &mut self,
        out: <Self::OutboundProtocol as OutboundUpgrade<Self::Substream>>::Output,
        _: Self::OutboundOpenInfo
    ) {
        self.dial_negotiated -= 1;

        if self.shutting_down {
            return;
        }

        self.events_out.push(out.into());
    }

    #[inline]
    fn inject_event(&mut self, event: Self::InEvent) {
        self.send_request(event);
    }

    #[inline]
    fn inject_dial_upgrade_error(&mut self, _: Self::OutboundOpenInfo, error: ProtocolsHandlerUpgrErr<<Self::OutboundProtocol as OutboundUpgrade<Self::Substream>>::Error>) {
        if self.pending_error.is_none() {
            self.pending_error = Some(error);
        }
    }

    #[inline]
    fn inject_inbound_closed(&mut self) {}

    #[inline]
    fn connection_keep_alive(&self) -> bool {
        self.dial_negotiated != 0 || !self.dial_queue.is_empty()
    }

    #[inline]
    fn shutdown(&mut self) {
        self.shutting_down = true;
    }

    fn poll(&mut self) -> Poll<ProtocolsHandlerEvent<Self::OutboundProtocol, Self::OutboundOpenInfo, Self::OutEvent>, Self::Error> {
        if let Some(err) = self.pending_error.take() {
            return Err(err);
        }

        if !self.events_out.is_empty() {
            return Ok(Async::Ready(ProtocolsHandlerEvent::Custom(self.events_out.remove(0))));
        } else {
            self.events_out.shrink_to_fit();
        }

        if self.shutting_down && self.dial_negotiated == 0 {
            return Ok(Async::Ready(ProtocolsHandlerEvent::Shutdown));
        }

        if !self.dial_queue.is_empty() {
            if !self.shutting_down && self.dial_negotiated < self.max_dial_negotiated {
                self.dial_negotiated += 1;
                return Ok(Async::Ready(ProtocolsHandlerEvent::OutboundSubstreamRequest {
                    upgrade: self.dial_queue.remove(0),
                    info: (),
                }));
            }
        } else {
            self.dial_queue.shrink_to_fit();
        }

        Ok(Async::NotReady)
    }
}