// Copyright 2015-2019 Parity Technologies (UK) Ltd.
// This file is part of Parity Ethereum.

// Parity Ethereum 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.

// Parity Ethereum 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 Parity Ethereum.  If not, see <http://www.gnu.org/licenses/>.

//! Tokio Runtime wrapper.

pub extern crate futures;
pub extern crate tokio;

use futures::{future, Future, IntoFuture};
use std::{
    fmt,
    sync::mpsc,
    thread,
    time::{Duration, Instant},
};
pub use tokio::{
    runtime::{Builder as TokioRuntimeBuilder, Runtime as TokioRuntime, TaskExecutor},
    timer::Delay,
};

/// Runtime for futures.
///
/// Runs in a separate thread.
pub struct Runtime {
    executor: Executor,
    handle: RuntimeHandle,
}

impl Runtime {
    fn new(runtime_bldr: &mut TokioRuntimeBuilder) -> Self {
        let mut runtime = runtime_bldr.build().expect(
            "Building a Tokio runtime will only fail when mio components \
				cannot be initialized (catastrophic)",
        );
        let (stop, stopped) = futures::oneshot();
        let (tx, rx) = mpsc::channel();
        let handle = thread::spawn(move || {
            tx.send(runtime.executor())
                .expect("Rx is blocking upper thread.");
            runtime
                .block_on(futures::empty().select(stopped).map(|_| ()).map_err(|_| ()))
                .expect("Tokio runtime should not have unhandled errors.");
        });
        let executor = rx
            .recv()
            .expect("tx is transfered to a newly spawned thread.");

        Runtime {
            executor: Executor {
                inner: Mode::Tokio(executor),
            },
            handle: RuntimeHandle {
                close: Some(stop),
                handle: Some(handle),
            },
        }
    }

    /// Spawns a new tokio runtime with a default thread count on a background
    /// thread and returns a `Runtime` which can be used to spawn tasks via
    /// its executor.
    pub fn with_default_thread_count() -> Self {
        let mut runtime_bldr = TokioRuntimeBuilder::new();
        Self::new(&mut runtime_bldr)
    }

    /// Spawns a new tokio runtime with a the specified thread count on a
    /// background thread and returns a `Runtime` which can be used to spawn
    /// tasks via its executor.
    pub fn with_thread_count(thread_count: usize) -> Self {
        let mut runtime_bldr = TokioRuntimeBuilder::new();
        runtime_bldr.core_threads(thread_count);

        Self::new(&mut runtime_bldr)
    }

    /// Returns this runtime raw executor.
    ///
    /// Deprecated: Exists only to connect with current JSONRPC implementation.
    pub fn raw_executor(&self) -> TaskExecutor {
        if let Mode::Tokio(ref executor) = self.executor.inner {
            executor.clone()
        } else {
            panic!("Runtime is not initialized in Tokio mode.")
        }
    }

    /// Returns runtime executor.
    pub fn executor(&self) -> Executor {
        self.executor.clone()
    }
}

#[derive(Clone)]
enum Mode {
    Tokio(TaskExecutor),
    Sync,
    ThreadPerFuture,
}

impl fmt::Debug for Mode {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        use self::Mode::*;

        match *self {
            Tokio(_) => write!(fmt, "tokio"),
            Sync => write!(fmt, "synchronous"),
            ThreadPerFuture => write!(fmt, "thread per future"),
        }
    }
}

/// Returns a future which runs `f` until `duration` has elapsed, at which
/// time `on_timeout` is run and the future resolves.
fn timeout<F, R, T>(
    f: F,
    duration: Duration,
    on_timeout: T,
) -> impl Future<Item = (), Error = ()> + Send + 'static
where
    T: FnOnce() -> () + Send + 'static,
    F: FnOnce() -> R + Send + 'static,
    R: IntoFuture<Item = (), Error = ()> + Send + 'static,
    R::Future: Send + 'static,
{
    let future = future::lazy(f);
    let timeout = Delay::new(Instant::now() + duration).then(move |_| {
        on_timeout();
        Ok(())
    });
    future.select(timeout).then(|_| Ok(()))
}

#[derive(Debug, Clone)]
pub struct Executor {
    inner: Mode,
}

impl Executor {
    /// Executor for existing runtime.
    ///
    /// Deprecated: Exists only to connect with current JSONRPC implementation.
    pub fn new(executor: TaskExecutor) -> Self {
        Executor {
            inner: Mode::Tokio(executor),
        }
    }

    /// Synchronous executor, used mostly for tests.
    pub fn new_sync() -> Self {
        Executor { inner: Mode::Sync }
    }

    /// Spawns a new thread for each future (use only for tests).
    pub fn new_thread_per_future() -> Self {
        Executor {
            inner: Mode::ThreadPerFuture,
        }
    }

    /// Spawn a future to this runtime
    pub fn spawn<R>(&self, r: R)
    where
        R: IntoFuture<Item = (), Error = ()> + Send + 'static,
        R::Future: Send + 'static,
    {
        match self.inner {
            Mode::Tokio(ref executor) => executor.spawn(r.into_future()),
            Mode::Sync => {
                let _ = r.into_future().wait();
            }
            Mode::ThreadPerFuture => {
                thread::spawn(move || {
                    let _ = r.into_future().wait();
                });
            }
        }
    }

    /// Spawn a new future returned by given closure.
    pub fn spawn_fn<F, R>(&self, f: F)
    where
        F: FnOnce() -> R + Send + 'static,
        R: IntoFuture<Item = (), Error = ()> + Send + 'static,
        R::Future: Send + 'static,
    {
        match self.inner {
            Mode::Tokio(ref executor) => executor.spawn(future::lazy(f)),
            Mode::Sync => {
                let _ = future::lazy(f).wait();
            }
            Mode::ThreadPerFuture => {
                thread::spawn(move || {
                    let _ = f().into_future().wait();
                });
            }
        }
    }

    /// Spawn a new future and wait for it or for a timeout to occur.
    pub fn spawn_with_timeout<F, R, T>(&self, f: F, duration: Duration, on_timeout: T)
    where
        T: FnOnce() -> () + Send + 'static,
        F: FnOnce() -> R + Send + 'static,
        R: IntoFuture<Item = (), Error = ()> + Send + 'static,
        R::Future: Send + 'static,
    {
        match self.inner {
            Mode::Tokio(ref executor) => executor.spawn(timeout(f, duration, on_timeout)),
            Mode::Sync => {
                let _ = timeout(f, duration, on_timeout).wait();
            }
            Mode::ThreadPerFuture => {
                thread::spawn(move || {
                    let _ = timeout(f, duration, on_timeout).wait();
                });
            }
        }
    }
}

impl<F: Future<Item = (), Error = ()> + Send + 'static> future::Executor<F> for Executor {
    fn execute(&self, future: F) -> Result<(), future::ExecuteError<F>> {
        match self.inner {
            Mode::Tokio(ref executor) => executor.execute(future),
            Mode::Sync => {
                let _ = future.wait();
                Ok(())
            }
            Mode::ThreadPerFuture => {
                thread::spawn(move || {
                    let _ = future.wait();
                });
                Ok(())
            }
        }
    }
}

/// A handle to a runtime. Dropping the handle will cause runtime to shutdown.
pub struct RuntimeHandle {
    close: Option<futures::Complete<()>>,
    handle: Option<thread::JoinHandle<()>>,
}

impl From<Runtime> for RuntimeHandle {
    fn from(el: Runtime) -> Self {
        el.handle
    }
}

impl Drop for RuntimeHandle {
    fn drop(&mut self) {
        self.close.take().map(|v| v.send(()));
    }
}

impl RuntimeHandle {
    /// Blocks current thread and waits until the runtime is finished.
    pub fn wait(mut self) -> thread::Result<()> {
        self.handle
            .take()
            .expect("Handle is taken only in `wait`, `wait` is consuming; qed")
            .join()
    }

    /// Finishes this runtime.
    pub fn close(mut self) {
        let _ = self
            .close
            .take()
            .expect("Close is taken only in `close` and `drop`. `close` is consuming; qed")
            .send(());
    }
}