//! Windows-specific types for signal handling.
//!
//! This module is only defined on Windows and contains the primary `Event` type
//! for receiving notifications of events. These events are listened for via the
//! `SetConsoleCtrlHandler` function which receives events of the type
//! `CTRL_C_EVENT` and `CTRL_BREAK_EVENT`

#![cfg(windows)]

use crate::signal::registry::{globals, EventId, EventInfo, Init, Storage};
use crate::sync::mpsc::{channel, Receiver};

use std::convert::TryFrom;
use std::io;
use std::sync::Once;
use std::task::{Context, Poll};
use winapi::shared::minwindef::{BOOL, DWORD, FALSE, TRUE};
use winapi::um::consoleapi::SetConsoleCtrlHandler;
use winapi::um::wincon::{CTRL_BREAK_EVENT, CTRL_C_EVENT};

#[derive(Debug)]
pub(crate) struct OsStorage {
    ctrl_c: EventInfo,
    ctrl_break: EventInfo,
}

impl Init for OsStorage {
    fn init() -> Self {
        Self {
            ctrl_c: EventInfo::default(),
            ctrl_break: EventInfo::default(),
        }
    }
}

impl Storage for OsStorage {
    fn event_info(&self, id: EventId) -> Option<&EventInfo> {
        match DWORD::try_from(id) {
            Ok(CTRL_C_EVENT) => Some(&self.ctrl_c),
            Ok(CTRL_BREAK_EVENT) => Some(&self.ctrl_break),
            _ => None,
        }
    }

    fn for_each<'a, F>(&'a self, mut f: F)
    where
        F: FnMut(&'a EventInfo),
    {
        f(&self.ctrl_c);
        f(&self.ctrl_break);
    }
}

#[derive(Debug)]
pub(crate) struct OsExtraData {}

impl Init for OsExtraData {
    fn init() -> Self {
        Self {}
    }
}

/// Stream of events discovered via `SetConsoleCtrlHandler`.
///
/// This structure can be used to listen for events of the type `CTRL_C_EVENT`
/// and `CTRL_BREAK_EVENT`. The `Stream` trait is implemented for this struct
/// and will resolve for each notification received by the process. Note that
/// there are few limitations with this as well:
///
/// * A notification to this process notifies *all* `Event` streams for that
///   event type.
/// * Notifications to an `Event` stream **are coalesced** if they aren't
///   processed quickly enough. This means that if two notifications are
///   received back-to-back, then the stream may only receive one item about the
///   two notifications.
#[must_use = "streams do nothing unless polled"]
#[derive(Debug)]
pub(crate) struct Event {
    rx: Receiver<()>,
}

pub(crate) fn ctrl_c() -> io::Result<Event> {
    Event::new(CTRL_C_EVENT)
}

impl Event {
    fn new(signum: DWORD) -> io::Result<Self> {
        global_init()?;

        let (tx, rx) = channel(1);
        globals().register_listener(signum as EventId, tx);

        Ok(Event { rx })
    }

    pub(crate) async fn recv(&mut self) -> Option<()> {
        use crate::future::poll_fn;
        poll_fn(|cx| self.rx.poll_recv(cx)).await
    }
}

fn global_init() -> io::Result<()> {
    static INIT: Once = Once::new();

    let mut init = None;

    INIT.call_once(|| unsafe {
        let rc = SetConsoleCtrlHandler(Some(handler), TRUE);
        let ret = if rc == 0 {
            Err(io::Error::last_os_error())
        } else {
            Ok(())
        };

        init = Some(ret);
    });

    init.unwrap_or_else(|| Ok(()))
}

unsafe extern "system" fn handler(ty: DWORD) -> BOOL {
    let globals = globals();
    globals.record_event(ty as EventId);

    // According to https://docs.microsoft.com/en-us/windows/console/handlerroutine
    // the handler routine is always invoked in a new thread, thus we don't
    // have the same restrictions as in Unix signal handlers, meaning we can
    // go ahead and perform the broadcast here.
    if globals.broadcast() {
        TRUE
    } else {
        // No one is listening for this notification any more
        // let the OS fire the next (possibly the default) handler.
        FALSE
    }
}

/// Represents a stream which receives "ctrl-break" notifications sent to the process
/// via `SetConsoleCtrlHandler`.
///
/// A notification to this process notifies *all* streams listening for
/// this event. Moreover, the notifications **are coalesced** if they aren't processed
/// quickly enough. This means that if two notifications are received back-to-back,
/// then the stream may only receive one item about the two notifications.
#[must_use = "streams do nothing unless polled"]
#[derive(Debug)]
pub struct CtrlBreak {
    inner: Event,
}

impl CtrlBreak {
    /// Receives the next signal notification event.
    ///
    /// `None` is returned if no more events can be received by this stream.
    ///
    /// # Examples
    ///
    /// ```rust,no_run
    /// use tokio::signal::windows::ctrl_break;
    ///
    /// #[tokio::main]
    /// async fn main() -> Result<(), Box<dyn std::error::Error>> {
    ///     // An infinite stream of CTRL-BREAK events.
    ///     let mut stream = ctrl_break()?;
    ///
    ///     // Print whenever a CTRL-BREAK event is received
    ///     loop {
    ///         stream.recv().await;
    ///         println!("got signal CTRL-BREAK");
    ///     }
    /// }
    /// ```
    pub async fn recv(&mut self) -> Option<()> {
        use crate::future::poll_fn;
        poll_fn(|cx| self.poll_recv(cx)).await
    }

    /// Polls to receive the next signal notification event, outside of an
    /// `async` context.
    ///
    /// `None` is returned if no more events can be received by this stream.
    ///
    /// # Examples
    ///
    /// Polling from a manually implemented future
    ///
    /// ```rust,no_run
    /// use std::pin::Pin;
    /// use std::future::Future;
    /// use std::task::{Context, Poll};
    /// use tokio::signal::windows::CtrlBreak;
    ///
    /// struct MyFuture {
    ///     ctrl_break: CtrlBreak,
    /// }
    ///
    /// impl Future for MyFuture {
    ///     type Output = Option<()>;
    ///
    ///     fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
    ///         println!("polling MyFuture");
    ///         self.ctrl_break.poll_recv(cx)
    ///     }
    /// }
    /// ```
    pub fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<()>> {
        self.inner.rx.poll_recv(cx)
    }
}

cfg_stream! {
    impl crate::stream::Stream for CtrlBreak {
        type Item = ();

        fn poll_next(mut self: std::pin::Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<()>> {
            self.poll_recv(cx)
        }
    }
}

/// Creates a new stream which receives "ctrl-break" notifications sent to the
/// process.
///
/// # Examples
///
/// ```rust,no_run
/// use tokio::signal::windows::ctrl_break;
///
/// #[tokio::main]
/// async fn main() -> Result<(), Box<dyn std::error::Error>> {
///     // An infinite stream of CTRL-BREAK events.
///     let mut stream = ctrl_break()?;
///
///     // Print whenever a CTRL-BREAK event is received
///     loop {
///         stream.recv().await;
///         println!("got signal CTRL-BREAK");
///     }
/// }
/// ```
pub fn ctrl_break() -> io::Result<CtrlBreak> {
    Event::new(CTRL_BREAK_EVENT).map(|inner| CtrlBreak { inner })
}

#[cfg(all(test, not(loom)))]
mod tests {
    use super::*;
    use crate::runtime::Runtime;
    use crate::stream::StreamExt;

    use tokio_test::{assert_ok, assert_pending, assert_ready_ok, task};

    #[test]
    fn ctrl_c() {
        let rt = rt();
        let _enter = rt.enter();

        let mut ctrl_c = task::spawn(crate::signal::ctrl_c());

        assert_pending!(ctrl_c.poll());

        // Windows doesn't have a good programmatic way of sending events
        // like sending signals on Unix, so we'll stub out the actual OS
        // integration and test that our handling works.
        unsafe {
            super::handler(CTRL_C_EVENT);
        }

        assert_ready_ok!(ctrl_c.poll());
    }

    #[test]
    fn ctrl_break() {
        let rt = rt();

        rt.block_on(async {
            let mut ctrl_break = assert_ok!(super::ctrl_break());

            // Windows doesn't have a good programmatic way of sending events
            // like sending signals on Unix, so we'll stub out the actual OS
            // integration and test that our handling works.
            unsafe {
                super::handler(CTRL_BREAK_EVENT);
            }

            ctrl_break.next().await.unwrap();
        });
    }

    fn rt() -> Runtime {
        crate::runtime::Builder::new_current_thread()
            .build()
            .unwrap()
    }
}