// Copyright 2015-2020 Parity Technologies (UK) Ltd.
// This file is part of OpenEthereum.

// OpenEthereum is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// OpenEthereum is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with OpenEthereum.  If not, see <http://www.gnu.org/licenses/>.

use deque;
use mio::{
    deprecated::{EventLoop, EventLoopBuilder, Handler, Sender},
    timer::Timeout,
    *,
};
use parking_lot::{Condvar, Mutex, RwLock};
use slab::Slab;
use std::{
    collections::HashMap,
    sync::{Arc, Weak},
    thread::{self, JoinHandle},
    time::Duration,
};
use worker::{Work, WorkType, Worker};
use IoError;
use IoHandler;

/// Timer ID
pub type TimerToken = usize;
/// Timer ID
pub type StreamToken = usize;
/// IO Handler ID
pub type HandlerId = usize;

/// Maximum number of tokens a handler can use
pub const TOKENS_PER_HANDLER: usize = 16384;
const MAX_HANDLERS: usize = 8;

/// Messages used to communicate with the event loop from other threads.
#[derive(Clone)]
pub enum IoMessage<Message>
where
    Message: Send + Sized,
{
    /// Shutdown the event loop
    Shutdown,
    /// Register a new protocol handler.
    AddHandler {
        handler: Arc<dyn IoHandler<Message> + Send>,
    },
    RemoveHandler {
        handler_id: HandlerId,
    },
    AddTimer {
        handler_id: HandlerId,
        token: TimerToken,
        delay: Duration,
        once: bool,
    },
    RemoveTimer {
        handler_id: HandlerId,
        token: TimerToken,
    },
    RegisterStream {
        handler_id: HandlerId,
        token: StreamToken,
    },
    DeregisterStream {
        handler_id: HandlerId,
        token: StreamToken,
    },
    UpdateStreamRegistration {
        handler_id: HandlerId,
        token: StreamToken,
    },
    /// Broadcast a message across all protocol handlers.
    UserMessage(Arc<Message>),
}

/// IO access point. This is passed to all IO handlers and provides an interface to the IO subsystem.
pub struct IoContext<Message>
where
    Message: Send + Sync + 'static,
{
    channel: IoChannel<Message>,
    handler: HandlerId,
}

impl<Message> IoContext<Message>
where
    Message: Send + Sync + 'static,
{
    /// Create a new IO access point. Takes references to all the data that can be updated within the IO handler.
    pub fn new(channel: IoChannel<Message>, handler: HandlerId) -> IoContext<Message> {
        IoContext {
            handler: handler,
            channel: channel,
        }
    }

    /// Register a new recurring IO timer. 'IoHandler::timeout' will be called with the token.
    pub fn register_timer(&self, token: TimerToken, delay: Duration) -> Result<(), IoError> {
        self.channel.send_io(IoMessage::AddTimer {
            token,
            delay,
            handler_id: self.handler,
            once: false,
        })?;
        Ok(())
    }

    /// Register a new IO timer once. 'IoHandler::timeout' will be called with the token.
    pub fn register_timer_once(&self, token: TimerToken, delay: Duration) -> Result<(), IoError> {
        self.channel.send_io(IoMessage::AddTimer {
            token,
            delay,
            handler_id: self.handler,
            once: true,
        })?;
        Ok(())
    }

    /// Delete a timer.
    pub fn clear_timer(&self, token: TimerToken) -> Result<(), IoError> {
        self.channel.send_io(IoMessage::RemoveTimer {
            token: token,
            handler_id: self.handler,
        })?;
        Ok(())
    }

    /// Register a new IO stream.
    pub fn register_stream(&self, token: StreamToken) -> Result<(), IoError> {
        self.channel.send_io(IoMessage::RegisterStream {
            token: token,
            handler_id: self.handler,
        })?;
        Ok(())
    }

    /// Deregister an IO stream.
    pub fn deregister_stream(&self, token: StreamToken) -> Result<(), IoError> {
        self.channel.send_io(IoMessage::DeregisterStream {
            token: token,
            handler_id: self.handler,
        })?;
        Ok(())
    }

    /// Reregister an IO stream.
    pub fn update_registration(&self, token: StreamToken) -> Result<(), IoError> {
        self.channel.send_io(IoMessage::UpdateStreamRegistration {
            token: token,
            handler_id: self.handler,
        })?;
        Ok(())
    }

    /// Broadcast a message to other IO clients
    pub fn message(&self, message: Message) -> Result<(), IoError> {
        self.channel.send(message)?;
        Ok(())
    }

    /// Get message channel
    pub fn channel(&self) -> IoChannel<Message> {
        self.channel.clone()
    }

    /// Unregister current IO handler.
    pub fn unregister_handler(&self) {
        // `send_io` returns an error only if the channel is closed, which means that the
        // background thread is no longer running. Therefore the handler is no longer active and
        // can be considered as unregistered.
        let _ = self.channel.send_io(IoMessage::RemoveHandler {
            handler_id: self.handler,
        });
    }
}

#[derive(Clone)]
struct UserTimer {
    delay: Duration,
    timeout: Timeout,
    once: bool,
}

/// Root IO handler. Manages user handlers, messages and IO timers.
pub struct IoManager<Message>
where
    Message: Send + Sync,
{
    timers: Arc<RwLock<HashMap<HandlerId, UserTimer>>>,
    handlers: Arc<RwLock<Slab<Arc<dyn IoHandler<Message>>>>>,
    workers: Vec<Worker>,
    worker_channel: deque::Worker<Work<Message>>,
    work_ready: Arc<Condvar>,
}

impl<Message> IoManager<Message>
where
    Message: Send + Sync + 'static,
{
    /// Creates a new instance and registers it with the event loop.
    pub fn start(
        symbolic_name: &str,
        event_loop: &mut EventLoop<IoManager<Message>>,
        handlers: Arc<RwLock<Slab<Arc<dyn IoHandler<Message>>>>>,
    ) -> Result<(), IoError> {
        let (worker, stealer) = deque::fifo();
        let num_workers = 4;
        let work_ready_mutex = Arc::new(Mutex::new(()));
        let work_ready = Arc::new(Condvar::new());
        let workers = (0..num_workers)
            .map(|i| {
                Worker::new(
                    &format!("{}{}", symbolic_name, i),
                    stealer.clone(),
                    IoChannel::new(event_loop.channel(), Arc::downgrade(&handlers)),
                    work_ready.clone(),
                    work_ready_mutex.clone(),
                )
            })
            .collect();

        let mut io = IoManager {
            timers: Arc::new(RwLock::new(HashMap::new())),
            handlers: handlers,
            worker_channel: worker,
            workers: workers,
            work_ready: work_ready,
        };
        event_loop.run(&mut io)?;
        Ok(())
    }
}

impl<Message> Handler for IoManager<Message>
where
    Message: Send + Sync + 'static,
{
    type Timeout = Token;
    type Message = IoMessage<Message>;

    fn ready(&mut self, _event_loop: &mut EventLoop<Self>, token: Token, events: Ready) {
        let handler_index = token.0 / TOKENS_PER_HANDLER;
        let token_id = token.0 % TOKENS_PER_HANDLER;
        if let Some(handler) = self.handlers.read().get(handler_index) {
            if events.is_hup() {
                self.worker_channel.push(Work {
                    work_type: WorkType::Hup,
                    token: token_id,
                    handler: handler.clone(),
                    handler_id: handler_index,
                });
            } else {
                if events.is_readable() {
                    self.worker_channel.push(Work {
                        work_type: WorkType::Readable,
                        token: token_id,
                        handler: handler.clone(),
                        handler_id: handler_index,
                    });
                }
                if events.is_writable() {
                    self.worker_channel.push(Work {
                        work_type: WorkType::Writable,
                        token: token_id,
                        handler: handler.clone(),
                        handler_id: handler_index,
                    });
                }
            }
            self.work_ready.notify_all();
        }
    }

    fn timeout(&mut self, event_loop: &mut EventLoop<Self>, token: Token) {
        let handler_index = token.0 / TOKENS_PER_HANDLER;
        let token_id = token.0 % TOKENS_PER_HANDLER;
        if let Some(handler) = self.handlers.read().get(handler_index) {
            let maybe_timer = self.timers.read().get(&token.0).cloned();
            if let Some(timer) = maybe_timer {
                if timer.once {
                    self.timers.write().remove(&token_id);
                    event_loop.clear_timeout(&timer.timeout);
                } else {
                    event_loop
                        .timeout(token, timer.delay)
                        .expect("Error re-registering user timer");
                }
                self.worker_channel.push(Work {
                    work_type: WorkType::Timeout,
                    token: token_id,
                    handler: handler.clone(),
                    handler_id: handler_index,
                });
                self.work_ready.notify_all();
            }
        }
    }

    fn notify(&mut self, event_loop: &mut EventLoop<Self>, msg: Self::Message) {
        match msg {
            IoMessage::Shutdown => {
                self.workers.clear();
                event_loop.shutdown();
            }
            IoMessage::AddHandler { handler } => {
                let handler_id = self.handlers.write().insert(handler.clone());
                assert!(handler_id <= MAX_HANDLERS, "Too many handlers registered");
                handler.initialize(&IoContext::new(
                    IoChannel::new(event_loop.channel(), Arc::downgrade(&self.handlers)),
                    handler_id,
                ));
            }
            IoMessage::RemoveHandler { handler_id } => {
                // TODO: flush event loop
                self.handlers.write().remove(handler_id);
                // unregister timers
                let mut timers = self.timers.write();
                let to_remove: Vec<_> = timers
                    .keys()
                    .cloned()
                    .filter(|timer_id| timer_id / TOKENS_PER_HANDLER == handler_id)
                    .collect();
                for timer_id in to_remove {
                    let timer = timers
                        .remove(&timer_id)
                        .expect("to_remove only contains keys from timers; qed");
                    event_loop.clear_timeout(&timer.timeout);
                }
            }
            IoMessage::AddTimer {
                handler_id,
                token,
                delay,
                once,
            } => {
                let timer_id = token + handler_id * TOKENS_PER_HANDLER;
                let timeout = event_loop
                    .timeout(Token(timer_id), delay)
                    .expect("Error registering user timer");
                self.timers.write().insert(
                    timer_id,
                    UserTimer {
                        delay: delay,
                        timeout: timeout,
                        once: once,
                    },
                );
            }
            IoMessage::RemoveTimer { handler_id, token } => {
                let timer_id = token + handler_id * TOKENS_PER_HANDLER;
                if let Some(timer) = self.timers.write().remove(&timer_id) {
                    event_loop.clear_timeout(&timer.timeout);
                }
            }
            IoMessage::RegisterStream { handler_id, token } => {
                if let Some(handler) = self.handlers.read().get(handler_id) {
                    handler.register_stream(
                        token,
                        Token(token + handler_id * TOKENS_PER_HANDLER),
                        event_loop,
                    );
                }
            }
            IoMessage::DeregisterStream { handler_id, token } => {
                if let Some(handler) = self.handlers.read().get(handler_id) {
                    handler.deregister_stream(token, event_loop);
                    // unregister a timer associated with the token (if any)
                    let timer_id = token + handler_id * TOKENS_PER_HANDLER;
                    if let Some(timer) = self.timers.write().remove(&timer_id) {
                        event_loop.clear_timeout(&timer.timeout);
                    }
                }
            }
            IoMessage::UpdateStreamRegistration { handler_id, token } => {
                if let Some(handler) = self.handlers.read().get(handler_id) {
                    handler.update_stream(
                        token,
                        Token(token + handler_id * TOKENS_PER_HANDLER),
                        event_loop,
                    );
                }
            }
            IoMessage::UserMessage(data) => {
                //TODO: better way to iterate the slab
                for id in 0..MAX_HANDLERS {
                    if let Some(h) = self.handlers.read().get(id) {
                        let handler = h.clone();
                        self.worker_channel.push(Work {
                            work_type: WorkType::Message(data.clone()),
                            token: 0,
                            handler: handler,
                            handler_id: id,
                        });
                    }
                }
                self.work_ready.notify_all();
            }
        }
    }
}

enum Handlers<Message>
where
    Message: Send,
{
    SharedCollection(Weak<RwLock<Slab<Arc<dyn IoHandler<Message>>>>>),
    Single(Weak<dyn IoHandler<Message>>),
}

impl<Message: Send> Clone for Handlers<Message> {
    fn clone(&self) -> Self {
        use self::Handlers::*;

        match *self {
            SharedCollection(ref w) => SharedCollection(w.clone()),
            Single(ref w) => Single(w.clone()),
        }
    }
}

/// Allows sending messages into the event loop. All the IO handlers will get the message
/// in the `message` callback.
pub struct IoChannel<Message>
where
    Message: Send,
{
    channel: Option<Sender<IoMessage<Message>>>,
    handlers: Handlers<Message>,
}

impl<Message> Clone for IoChannel<Message>
where
    Message: Send + Sync + 'static,
{
    fn clone(&self) -> IoChannel<Message> {
        IoChannel {
            channel: self.channel.clone(),
            handlers: self.handlers.clone(),
        }
    }
}

impl<Message> IoChannel<Message>
where
    Message: Send + Sync + 'static,
{
    /// Send a message through the channel
    pub fn send(&self, message: Message) -> Result<(), IoError> {
        match self.channel {
            Some(ref channel) => channel.send(IoMessage::UserMessage(Arc::new(message)))?,
            None => self.send_sync(message)?,
        }
        Ok(())
    }

    /// Send a message through the channel and handle it synchronously
    pub fn send_sync(&self, message: Message) -> Result<(), IoError> {
        match self.handlers {
            Handlers::SharedCollection(ref handlers) => {
                if let Some(handlers) = handlers.upgrade() {
                    for id in 0..MAX_HANDLERS {
                        if let Some(h) = handlers.read().get(id) {
                            let handler = h.clone();
                            handler.message(&IoContext::new(self.clone(), id), &message);
                        }
                    }
                }
            }
            Handlers::Single(ref handler) => {
                if let Some(handler) = handler.upgrade() {
                    handler.message(&IoContext::new(self.clone(), 0), &message);
                }
            }
        }
        Ok(())
    }

    /// Send low level io message
    pub fn send_io(&self, message: IoMessage<Message>) -> Result<(), IoError> {
        if let Some(ref channel) = self.channel {
            channel.send(message)?
        }
        Ok(())
    }
    /// Create a new channel disconnected from an event loop.
    pub fn disconnected() -> IoChannel<Message> {
        IoChannel {
            channel: None,
            handlers: Handlers::SharedCollection(Weak::default()),
        }
    }

    /// Create a new synchronous channel to a given handler.
    pub fn to_handler(handler: Weak<dyn IoHandler<Message>>) -> IoChannel<Message> {
        IoChannel {
            channel: None,
            handlers: Handlers::Single(handler),
        }
    }
    fn new(
        channel: Sender<IoMessage<Message>>,
        handlers: Weak<RwLock<Slab<Arc<dyn IoHandler<Message>>>>>,
    ) -> IoChannel<Message> {
        IoChannel {
            channel: Some(channel),
            handlers: Handlers::SharedCollection(handlers),
        }
    }
}

/// General IO Service. Starts an event loop and dispatches IO requests.
/// 'Message' is a notification message type
pub struct IoService<Message>
where
    Message: Send + Sync + 'static,
{
    thread: Option<JoinHandle<()>>,
    host_channel: Mutex<Sender<IoMessage<Message>>>,
    handlers: Arc<RwLock<Slab<Arc<dyn IoHandler<Message>>>>>,
}

impl<Message> IoService<Message>
where
    Message: Send + Sync + 'static,
{
    /// Starts IO event loop
    pub fn start(symbolic_name: &'static str) -> Result<IoService<Message>, IoError> {
        let mut config = EventLoopBuilder::new();
        config.messages_per_tick(1024);
        let mut event_loop = config.build().expect("Error creating event loop");
        let channel = event_loop.channel();
        let handlers = Arc::new(RwLock::new(Slab::with_capacity(MAX_HANDLERS)));
        let h = handlers.clone();
        let thread = thread::spawn(move || {
            IoManager::<Message>::start(symbolic_name, &mut event_loop, h)
                .expect("Error starting IO service");
        });
        Ok(IoService {
            thread: Some(thread),
            host_channel: Mutex::new(channel),
            handlers: handlers,
        })
    }

    pub fn stop(&mut self) {
        trace!(target: "shutdown", "[IoService] Closing...");
        // Clear handlers so that shared pointers are not stuck on stack
        // in Channel::send_sync
        self.handlers.write().clear();
        self.host_channel
            .lock()
            .send(IoMessage::Shutdown)
            .unwrap_or_else(|e| warn!("Error on IO service shutdown: {:?}", e));
        if let Some(thread) = self.thread.take() {
            thread.join().unwrap_or_else(|e| {
                debug!(target: "shutdown", "Error joining IO service event loop thread: {:?}", e);
            });
        }
        trace!(target: "shutdown", "[IoService] Closed.");
    }

    /// Regiter an IO handler with the event loop.
    pub fn register_handler(
        &self,
        handler: Arc<dyn IoHandler<Message> + Send>,
    ) -> Result<(), IoError> {
        self.host_channel
            .lock()
            .send(IoMessage::AddHandler { handler: handler })?;
        Ok(())
    }

    /// Send a message over the network. Normaly `HostIo::send` should be used. This can be used from non-io threads.
    pub fn send_message(&self, message: Message) -> Result<(), IoError> {
        self.host_channel
            .lock()
            .send(IoMessage::UserMessage(Arc::new(message)))?;
        Ok(())
    }

    /// Create a new message channel
    pub fn channel(&self) -> IoChannel<Message> {
        IoChannel::new(
            self.host_channel.lock().clone(),
            Arc::downgrade(&self.handlers),
        )
    }
}

impl<Message> Drop for IoService<Message>
where
    Message: Send + Sync,
{
    fn drop(&mut self) {
        self.stop()
    }
}