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use std::io;
use std::net::SocketAddr;

use futures::{self, Future, IntoFuture};
use futures::stream::Stream;
use tokio_core::io::IoFuture;
use tokio_core::net::{TcpListener, TcpStream, UdpSocket};
use tokio_core::reactor::{Handle, Remote};

use super::resolver::{CpuPoolResolver, Resolver};
use super::{Endpoint, ToEndpoint};

lazy_static! {
    static ref POOL: CpuPoolResolver = CpuPoolResolver::new(5);
}

/// Connect to the endpoint using the default resolver.
pub fn tcp_connect<'a, T>(ep: T, handle: Remote) -> IoFuture<TcpStream>
    where T: ToEndpoint<'a>
{
    tcp_connect_with(ep, handle, POOL.clone())
}

/// Connect to the endpoint using a custom resolver.
pub fn tcp_connect_with<'a, T, R>(ep: T, remote: Remote, resolver: R) -> IoFuture<TcpStream>
    where T: ToEndpoint<'a>, R: Resolver
{
    resolve_endpoint(ep, resolver).and_then(move |addrs| {
        try_until_ok(addrs, move |addr| {
            with_handle(&remote, move |handle| TcpStream::connect(&addr, handle))
        })
    }).boxed()
}

/// Bind to the endpoint using the default resolver.
pub fn tcp_bind<'a, T>(ep: T, remote: Remote) -> IoFuture<TcpListener>
    where T: ToEndpoint<'a>
{
    tcp_bind_with(ep, remote, POOL.clone())
}

/// Bind to the endpoint using a custom resolver.
pub fn tcp_bind_with<'a, T, R>(ep: T, remote: Remote, resolver: R) -> IoFuture<TcpListener>
    where T: ToEndpoint<'a>, R: Resolver
{
    resolve_endpoint(ep, resolver).and_then(move |addrs| {
        try_until_ok(addrs, move |addr| {
            with_handle(&remote, move |handle| TcpListener::bind(&addr, handle))
        })
    }).boxed()
}

/// Bind to the endpoint using the default resolver.
pub fn udp_bind<'a, T>(ep: T, remote: Remote) -> IoFuture<UdpSocket>
    where T: ToEndpoint<'a>
{
    udp_bind_with(ep, remote, POOL.clone())
}

/// Bind to the endpoint using a custom resolver.
pub fn udp_bind_with<'a, T, R>(ep: T, remote: Remote, resolver: R) -> IoFuture<UdpSocket>
    where T: ToEndpoint<'a>, R: Resolver
{
    resolve_endpoint(ep, resolver).and_then(move |addrs| {
        try_until_ok(addrs, move |addr| {
            with_handle(&remote, move |handle| UdpSocket::bind(&addr, handle))
        })
    }).boxed()
}

/// Resolves endpoint into a vector of socket addresses.
fn resolve_endpoint<'a, T, R>(ep: T, resolver: R) -> IoFuture<Vec<SocketAddr>>
    where R: Resolver,
          T: ToEndpoint<'a>
{
    let ep = match ep.to_endpoint() {
        Ok(ep) => ep,
        Err(e) => return futures::failed(e).boxed()
    };
    match ep {
        Endpoint::Host(host, port) => {
            resolver.resolve(host).map(move |addrs| {
                addrs.into_iter().map(|addr| SocketAddr::new(addr, port)).collect()
            }).boxed()
        }
        Endpoint::SocketAddr(addr) => {
            futures::finished(vec![addr]).boxed()
        }
    }
}

fn try_until_ok<F, R, I>(addrs: Vec<SocketAddr>, f: F) -> IoFuture<I>
    where F: Fn(SocketAddr) -> R + Send + 'static,
          R: IntoFuture<Item=I, Error=io::Error> + Send + 'static,
          R::Future: Send + 'static,
          <R::Future as Future>::Error: From<io::Error>,
          I: Send + 'static
{
    let result = Err(io::Error::new(io::ErrorKind::Other, "could not resolve to any address"));
    futures::stream::iter(addrs.into_iter().map(Ok)).fold(result, move |prev, addr| {
        match prev {
            Ok(i) => {
                // Keep first successful result.
                futures::finished(Ok(i)).boxed()
            }
            Err(..) => {
                // Ignore previous error and try next address.
                let future = f(addr).into_future();
                // Lift future error into item to avoid short-circuit exit from fold.
                future.then(Ok).boxed()
            }
        }
    }).and_then(|r| r).boxed()
}

/// Invokes functor with event loop handle obtained from a remote.
fn with_handle<F, R, I>(remote: &Remote, f: F) -> IoFuture<I>
    where F: FnOnce(&Handle) -> R + Send + 'static,
          R: IntoFuture<Item=I, Error=io::Error> + Send + 'static,
          R::Future: Send + 'static
{
    let (tx, rx) = futures::oneshot();
    remote.spawn(move |handle| {
        tx.complete(f(handle));
        Ok(())
    });
    rx.then(|r| r.expect("canceled")).boxed()
}