// Copyright (C) 2018 Sebastian Dröge <sebastian@centricular.com>
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Library General Public
// License as published by the Free Software Foundation; either
// version 2 of the License, or (at your option) any later version.
//
// This library 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
// Library General Public License for more details.
//
// You should have received a copy of the GNU Library General Public
// License along with this library; if not, write to the
// Free Software Foundation, Inc., 51 Franklin Street, Suite 500,
// Boston, MA 02110-1335, USA.

use std::collections::HashMap;
use std::io;
use std::mem;
use std::sync::{atomic, mpsc};
use std::sync::{Arc, Mutex, Weak};
use std::thread;

use futures::future;
use futures::stream::futures_unordered::FuturesUnordered;
use futures::sync::oneshot;
use futures::{Future, Stream};
use tokio::reactor;
use tokio_current_thread;
use tokio_timer::timer;

use glib;
use gst;

lazy_static! {
    static ref CONTEXTS: Mutex<HashMap<String, Weak<IOContextInner>>> = Mutex::new(HashMap::new());
    static ref CONTEXT_CAT: gst::DebugCategory = gst::DebugCategory::new(
        "ts-context",
        gst::DebugColorFlags::empty(),
        Some("Thread-sharing Context"),
    );
}

// Our own simplified implementation of reactor::Background to allow hooking into its internals
const RUNNING: usize = 0;
const SHUTDOWN_NOW: usize = 1;

struct IOContextRunner {
    name: String,
    shutdown: Arc<atomic::AtomicUsize>,
}

impl IOContextRunner {
    fn start(
        name: &str,
        wait: u32,
        reactor: reactor::Reactor,
    ) -> (tokio_current_thread::Handle, IOContextShutdown) {
        let handle = reactor.handle().clone();
        let shutdown = Arc::new(atomic::AtomicUsize::new(RUNNING));
        let shutdown_clone = shutdown.clone();
        let name_clone = name.into();

        let mut runner = IOContextRunner {
            shutdown: shutdown_clone,
            name: name_clone,
        };

        let (sender, receiver) = mpsc::channel();

        let join = thread::spawn(move || {
            runner.run(wait, reactor, sender);
        });

        let shutdown = IOContextShutdown {
            name: name.into(),
            shutdown,
            handle,
            join: Some(join),
        };

        let runtime_handle = receiver.recv().unwrap();

        (runtime_handle, shutdown)
    }

    fn run(
        &mut self,
        wait: u32,
        reactor: reactor::Reactor,
        sender: mpsc::Sender<tokio_current_thread::Handle>,
    ) {
        use std::time;
        let wait = time::Duration::from_millis(wait as u64);

        gst_debug!(CONTEXT_CAT, "Started reactor thread '{}'", self.name);

        let handle = reactor.handle();
        let mut enter = ::tokio_executor::enter().unwrap();
        let timer = timer::Timer::new(reactor);
        let timer_handle = timer.handle();
        let mut current_thread = tokio_current_thread::CurrentThread::new_with_park(timer);

        let _ = sender.send(current_thread.handle());

        let mut now = time::Instant::now();

        ::tokio_timer::with_default(&timer_handle, &mut enter, |mut enter| {
            ::tokio_reactor::with_default(&handle, &mut enter, |enter| loop {
                if self.shutdown.load(atomic::Ordering::SeqCst) > RUNNING {
                    break;
                }

                gst_trace!(CONTEXT_CAT, "Turning current thread '{}'", self.name);
                while current_thread
                    .enter(enter)
                    .turn(Some(time::Duration::from_millis(0)))
                    .unwrap()
                    .has_polled()
                {}
                gst_trace!(CONTEXT_CAT, "Turned current thread '{}'", self.name);

                let elapsed = now.elapsed();
                if elapsed < wait {
                    gst_trace!(
                        CONTEXT_CAT,
                        "Waiting for {:?} before polling again",
                        wait - elapsed
                    );
                    thread::sleep(wait - elapsed);
                }
                now += wait;
            })
        });
    }
}

impl Drop for IOContextRunner {
    fn drop(&mut self) {
        gst_debug!(CONTEXT_CAT, "Shut down reactor thread '{}'", self.name);
    }
}

struct IOContextShutdown {
    name: String,
    shutdown: Arc<atomic::AtomicUsize>,
    handle: reactor::Handle,
    join: Option<thread::JoinHandle<()>>,
}

impl Drop for IOContextShutdown {
    fn drop(&mut self) {
        use tokio_executor::park::Unpark;

        gst_debug!(CONTEXT_CAT, "Shutting down reactor thread '{}'", self.name);
        self.shutdown.store(SHUTDOWN_NOW, atomic::Ordering::SeqCst);
        gst_trace!(CONTEXT_CAT, "Waiting for reactor '{}' shutdown", self.name);
        // After being unparked, the next turn() is guaranteed to finish immediately,
        // as such there is no race condition between checking for shutdown and setting
        // shutdown.
        self.handle.unpark();
        let _ = self.join.take().unwrap().join();
    }
}

#[derive(Clone)]
pub struct IOContext(Arc<IOContextInner>);

impl glib::subclass::boxed::BoxedType for IOContext {
    const NAME: &'static str = "TsIOContext";

    glib_boxed_type!();
}

glib_boxed_derive_traits!(IOContext);

struct IOContextInner {
    name: String,
    runtime_handle: Mutex<tokio_current_thread::Handle>,
    reactor_handle: reactor::Handle,
    // Only used for dropping
    _shutdown: IOContextShutdown,
    pending_futures: Mutex<(
        u64,
        HashMap<u64, FuturesUnordered<Box<Future<Item = (), Error = ()> + Send + 'static>>>,
    )>,
}

impl Drop for IOContextInner {
    fn drop(&mut self) {
        let mut contexts = CONTEXTS.lock().unwrap();
        gst_debug!(CONTEXT_CAT, "Finalizing context '{}'", self.name);
        contexts.remove(&self.name);
    }
}

impl IOContext {
    pub fn new(name: &str, wait: u32) -> Result<Self, io::Error> {
        let mut contexts = CONTEXTS.lock().unwrap();
        if let Some(context) = contexts.get(name) {
            if let Some(context) = context.upgrade() {
                gst_debug!(CONTEXT_CAT, "Reusing existing context '{}'", name);
                return Ok(IOContext(context));
            }
        }

        let reactor = reactor::Reactor::new()?;
        let reactor_handle = reactor.handle().clone();

        let (runtime_handle, shutdown) = IOContextRunner::start(name, wait, reactor);

        let context = Arc::new(IOContextInner {
            name: name.into(),
            runtime_handle: Mutex::new(runtime_handle),
            reactor_handle,
            _shutdown: shutdown,
            pending_futures: Mutex::new((0, HashMap::new())),
        });
        contexts.insert(name.into(), Arc::downgrade(&context));

        gst_debug!(CONTEXT_CAT, "Created new context '{}'", name);
        Ok(IOContext(context))
    }

    pub fn spawn<F>(&self, future: F)
    where
        F: Future<Item = (), Error = ()> + Send + 'static,
    {
        self.0.runtime_handle.lock().unwrap().spawn(future).unwrap();
    }

    pub fn reactor_handle(&self) -> &reactor::Handle {
        &self.0.reactor_handle
    }

    pub fn acquire_pending_future_id(&self) -> PendingFutureId {
        let mut pending_futures = self.0.pending_futures.lock().unwrap();
        let id = pending_futures.0;
        pending_futures.0 += 1;
        pending_futures.1.insert(id, FuturesUnordered::new());

        PendingFutureId(id)
    }

    pub fn release_pending_future_id(&self, id: PendingFutureId) {
        let mut pending_futures = self.0.pending_futures.lock().unwrap();
        if let Some(fs) = pending_futures.1.remove(&id.0) {
            self.spawn(fs.for_each(|_| Ok(())));
        }
    }

    pub fn add_pending_future<F>(&self, id: PendingFutureId, future: F)
    where
        F: Future<Item = (), Error = ()> + Send + 'static,
    {
        let mut pending_futures = self.0.pending_futures.lock().unwrap();
        let fs = pending_futures.1.get_mut(&id.0).unwrap();
        fs.push(Box::new(future))
    }

    pub fn drain_pending_futures<E: Send + 'static>(
        &self,
        id: PendingFutureId,
    ) -> (Option<oneshot::Sender<()>>, PendingFuturesFuture<E>) {
        let mut pending_futures = self.0.pending_futures.lock().unwrap();
        let fs = pending_futures.1.get_mut(&id.0).unwrap();

        let pending_futures = mem::replace(fs, FuturesUnordered::new());

        if !pending_futures.is_empty() {
            gst_log!(
                CONTEXT_CAT,
                "Scheduling {} pending futures for context '{}' with pending future id {:?}",
                pending_futures.len(),
                self.0.name,
                id,
            );

            let (sender, receiver) = oneshot::channel();

            let future = pending_futures
                .for_each(|_| Ok(()))
                .select(receiver.then(|_| Ok(())))
                .then(|_| Ok(()));

            (Some(sender), future::Either::A(Box::new(future)))
        } else {
            (None, future::Either::B(future::ok(())))
        }
    }
}

pub type PendingFuturesFuture<E> =
    future::Either<Box<Future<Item = (), Error = E> + Send + 'static>, future::FutureResult<(), E>>;

#[derive(Clone, Copy, Eq, PartialEq, Hash, Debug)]
pub struct PendingFutureId(u64);

impl glib::subclass::boxed::BoxedType for PendingFutureId {
    const NAME: &'static str = "TsPendingFutureId";

    glib_boxed_type!();
}

glib_boxed_derive_traits!(PendingFutureId);