// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
use crate::resources::Resource;
use deno::ErrBox;
use futures;
use futures::Future;
use futures::Poll;
use std::io;
use std::mem;
use std::net::SocketAddr;
use std::ops::FnOnce;
use tokio;
use tokio::net::TcpStream;
use tokio::runtime;

pub fn create_threadpool_runtime(
) -> Result<tokio::runtime::Runtime, tokio::io::Error> {
  runtime::Builder::new()
    .panic_handler(|err| std::panic::resume_unwind(err))
    .build()
}

pub fn run<F>(future: F)
where
  F: Future<Item = (), Error = ()> + Send + 'static,
{
  // tokio::runtime::current_thread::run(future)
  let rt = create_threadpool_runtime().expect("Unable to create Tokio runtime");
  rt.block_on_all(future).unwrap();
}

pub fn run_on_current_thread<F>(future: F)
where
  F: Future<Item = (), Error = ()> + Send + 'static,
{
  tokio::runtime::current_thread::run(future);
}

/// THIS IS A HACK AND SHOULD BE AVOIDED.
///
/// This spawns a new thread and creates a single-threaded tokio runtime on that thread,
/// to execute the given future.
///
/// This is useful when we want to block the main runtime to
/// resolve a future without worrying that we'll use up all the threads in the
/// main runtime.
pub fn block_on<F, R>(future: F) -> Result<R, ErrBox>
where
  F: Send + 'static + Future<Item = R, Error = ErrBox>,
  R: Send + 'static,
{
  use std::sync::mpsc::channel;
  use std::thread;
  let (sender, receiver) = channel();
  // Create a new runtime to evaluate the future asynchronously.
  thread::spawn(move || {
    let r = tokio::runtime::current_thread::block_on_all(future);
    sender
      .send(r)
      .expect("Unable to send blocking future result")
  });
  receiver
    .recv()
    .expect("Unable to receive blocking future result")
}

// Set the default executor so we can use tokio::spawn(). It's difficult to
// pass around mut references to the runtime, so using with_default is
// preferable. Ideally Tokio would provide this function.
#[cfg(test)]
pub fn init<F>(f: F)
where
  F: FnOnce(),
{
  let rt = create_threadpool_runtime().expect("Unable to create Tokio runtime");
  let mut executor = rt.executor();
  let mut enter = tokio_executor::enter().expect("Multiple executors at once");
  tokio_executor::with_default(&mut executor, &mut enter, move |_enter| f());
}

#[derive(Debug)]
enum AcceptState {
  Eager(Resource),
  Pending(Resource),
  Empty,
}

/// Simply accepts a connection.
pub fn accept(r: Resource) -> Accept {
  Accept {
    state: AcceptState::Eager(r),
  }
}

/// A future which can be used to easily read available number of bytes to fill
/// a buffer.
///
/// Created by the [`read`] function.
#[derive(Debug)]
pub struct Accept {
  state: AcceptState,
}
impl Future for Accept {
  type Item = (TcpStream, SocketAddr);
  type Error = io::Error;

  fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
    let (stream, addr) = match self.state {
      // Similar to try_ready!, but also track/untrack accept task
      // in TcpListener resource.
      // In this way, when the listener is closed, the task can be
      // notified to error out (instead of stuck forever).
      AcceptState::Eager(ref mut r) => match r.poll_accept() {
        Ok(futures::prelude::Async::Ready(t)) => t,
        Ok(futures::prelude::Async::NotReady) => {
          self.state = AcceptState::Pending(r.to_owned());
          return Ok(futures::prelude::Async::NotReady);
        }
        Err(e) => {
          return Err(e);
        }
      },
      AcceptState::Pending(ref mut r) => match r.poll_accept() {
        Ok(futures::prelude::Async::Ready(t)) => {
          r.untrack_task();
          t
        }
        Ok(futures::prelude::Async::NotReady) => {
          // Would error out if another accept task is being tracked.
          r.track_task()?;
          return Ok(futures::prelude::Async::NotReady);
        }
        Err(e) => {
          r.untrack_task();
          return Err(e);
        }
      },
      AcceptState::Empty => panic!("poll Accept after it's done"),
    };

    match mem::replace(&mut self.state, AcceptState::Empty) {
      AcceptState::Empty => panic!("invalid internal state"),
      _ => Ok((stream, addr).into()),
    }
  }
}

/// `futures::future::poll_fn` only support `F: FnMut()->Poll<T, E>`
/// However, we require that `F: FnOnce()->Poll<T, E>`.
/// Therefore, we created our version of `poll_fn`.
pub fn poll_fn<T, E, F>(f: F) -> PollFn<F>
where
  F: FnOnce() -> Poll<T, E>,
{
  PollFn { inner: Some(f) }
}

pub struct PollFn<F> {
  inner: Option<F>,
}

impl<T, E, F> Future for PollFn<F>
where
  F: FnOnce() -> Poll<T, E>,
{
  type Item = T;
  type Error = E;

  fn poll(&mut self) -> Poll<T, E> {
    let f = self.inner.take().expect("Inner fn has been taken.");
    f()
  }
}

pub fn panic_on_error<I, E, F>(f: F) -> impl Future<Item = I, Error = ()>
where
  F: Future<Item = I, Error = E>,
  E: std::fmt::Debug,
{
  f.map_err(|err| panic!("Future got unexpected error: {:?}", err))
}

#[cfg(test)]
pub fn run_in_task<F>(f: F)
where
  F: FnOnce() + Send + 'static,
{
  let fut = futures::future::lazy(move || {
    f();
    futures::future::ok(())
  });

  run(fut)
}