#![allow(clippy::module_name_repetitions)]

use std::pin::Pin;

use futures::Stream;

/// inner module, used to group feature-specific imports
#[cfg(async_channel_impl = "tokio")]
mod inner {
    pub use tokio::sync::mpsc::error::{
        SendError as UnboundedSendError, TryRecvError as UnboundedTryRecvError,
    };
    use tokio::sync::mpsc::{UnboundedReceiver as InnerReceiver, UnboundedSender as InnerSender};

    /// A receiver error returned from [`UnboundedReceiver`]'s `recv`
    #[derive(Debug, PartialEq, Eq, Clone)]
    pub struct UnboundedRecvError;

    impl std::fmt::Display for UnboundedRecvError {
        fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
            write!(fmt, stringify!(UnboundedRecvError))
        }
    }

    impl std::error::Error for UnboundedRecvError {}

    use tokio::sync::Mutex;

    /// An unbounded sender, created with [`unbounded`]
    pub struct UnboundedSender<T>(pub(super) InnerSender<T>);
    /// An unbounded receiver, created with [`unbounded`]
    pub struct UnboundedReceiver<T>(pub(super) Mutex<InnerReceiver<T>>);

    /// An unbounded stream, created with a channel
    pub struct UnboundedStream<T>(pub(super) tokio_stream::wrappers::UnboundedReceiverStream<T>);

    /// Turn a `TryRecvError` into a `RecvError` if it's not `Empty`
    pub(super) fn try_recv_error_to_recv_error(
        e: UnboundedTryRecvError,
    ) -> Option<UnboundedRecvError> {
        match e {
            UnboundedTryRecvError::Empty => None,
            UnboundedTryRecvError::Disconnected => Some(UnboundedRecvError),
        }
    }

    /// Create an unbounded channel. This will dynamically allocate whenever the internal buffer is full and a new message is added.
    ///
    /// The names of the [`UnboundedSender`] and [`UnboundedReceiver`] are specifically chosen to be less ergonomic than the [`bounded`] channels. Please consider using a bounded channel instead for performance reasons.
    #[must_use]
    pub fn unbounded<T>() -> (UnboundedSender<T>, UnboundedReceiver<T>) {
        let (sender, receiver) = tokio::sync::mpsc::unbounded_channel();
        let receiver = Mutex::new(receiver);
        (UnboundedSender(sender), UnboundedReceiver(receiver))
    }
}

/// inner module, used to group feature-specific imports
#[cfg(async_channel_impl = "flume")]
mod inner {
    use flume::{r#async::RecvStream, Receiver, Sender};
    pub use flume::{
        RecvError as UnboundedRecvError, SendError as UnboundedSendError,
        TryRecvError as UnboundedTryRecvError,
    };

    /// An unbounded sender, created with [`unbounded`]
    pub struct UnboundedSender<T>(pub(super) Sender<T>);
    /// An unbounded receiver, created with [`unbounded`]
    pub struct UnboundedReceiver<T>(pub(super) Receiver<T>);
    /// A bounded stream, created with a channel
    pub struct UnboundedStream<T: 'static>(pub(super) RecvStream<'static, T>);

    /// Turn a `TryRecvError` into a `RecvError` if it's not `Empty`
    pub(super) fn try_recv_error_to_recv_error(
        e: UnboundedTryRecvError,
    ) -> Option<UnboundedRecvError> {
        match e {
            UnboundedTryRecvError::Empty => None,
            UnboundedTryRecvError::Disconnected => Some(UnboundedRecvError::Disconnected),
        }
    }

    /// Create an unbounded channel. This will dynamically allocate whenever the internal buffer is full and a new message is added.
    ///
    /// The names of the [`UnboundedSender`] and [`UnboundedReceiver`] are specifically chosen to be less ergonomic than the [`bounded`] channels. Please consider using a bounded channel instead for performance reasons.
    #[must_use]
    pub fn unbounded<T>() -> (UnboundedSender<T>, UnboundedReceiver<T>) {
        let (sender, receiver) = flume::unbounded();
        (UnboundedSender(sender), UnboundedReceiver(receiver))
    }
}

/// inner module, used to group feature-specific imports
#[cfg(not(any(async_channel_impl = "flume", async_channel_impl = "tokio")))]
mod inner {
    use async_std::channel::{Receiver, Sender};
    pub use async_std::channel::{
        RecvError as UnboundedRecvError, SendError as UnboundedSendError,
        TryRecvError as UnboundedTryRecvError,
    };

    /// An unbounded sender, created with [`unbounded`]
    pub struct UnboundedSender<T>(pub(super) Sender<T>);
    /// An unbounded receiver, created with [`unbounded`]
    pub struct UnboundedReceiver<T>(pub(super) Receiver<T>);
    /// An unbounded stream, created with a channel
    pub struct UnboundedStream<T>(pub(super) Receiver<T>);

    /// Turn a `TryRecvError` into a `RecvError` if it's not `Empty`
    pub(super) fn try_recv_error_to_recv_error(
        e: UnboundedTryRecvError,
    ) -> Option<UnboundedRecvError> {
        match e {
            UnboundedTryRecvError::Empty => None,
            UnboundedTryRecvError::Closed => Some(UnboundedRecvError),
        }
    }

    /// Create an unbounded channel. This will dynamically allocate whenever the internal buffer is full and a new message is added.
    ///
    /// The names of the [`UnboundedSender`] and [`UnboundedReceiver`] are specifically chosen to be less ergonomic than the [`bounded`] channels. Please consider using a bounded channel instead for performance reasons.
    #[must_use]
    pub fn unbounded<T>() -> (UnboundedSender<T>, UnboundedReceiver<T>) {
        let (sender, receiver) = async_std::channel::unbounded();
        (UnboundedSender(sender), UnboundedReceiver(receiver))
    }
}

pub use inner::*;

impl<T> UnboundedSender<T> {
    /// Send a value to the sender half of this channel.
    ///
    /// # Errors
    ///
    /// This may fail if the receiver is dropped.
    #[allow(clippy::unused_async)] // under tokio this function is actually sync
    pub async fn send(&self, msg: T) -> Result<(), UnboundedSendError<T>> {
        #[cfg(async_channel_impl = "flume")]
        let result = self.0.send_async(msg).await;
        #[cfg(async_channel_impl = "tokio")]
        let result = self.0.send(msg);
        #[cfg(not(any(async_channel_impl = "flume", async_channel_impl = "tokio")))]
        let result = self.0.send(msg).await;
        result
    }
}

impl<T> UnboundedReceiver<T> {
    /// Receive a value from the receiver half of this channel.
    ///
    /// Will block until a value is received
    ///
    /// # Errors
    ///
    /// Will produce an error if all senders are dropped
    pub async fn recv(&self) -> Result<T, UnboundedRecvError> {
        #[cfg(async_channel_impl = "flume")]
        let result = self.0.recv_async().await;
        #[cfg(async_channel_impl = "tokio")]
        let result = self.0.lock().await.recv().await.ok_or(UnboundedRecvError);
        #[cfg(not(any(async_channel_impl = "flume", async_channel_impl = "tokio")))]
        let result = self.0.recv().await;
        result
    }
    /// Turn this receiver into a stream.
    pub fn into_stream(self) -> UnboundedStream<T> {
        #[cfg(not(any(async_channel_impl = "flume", async_channel_impl = "tokio")))]
        let result = self.0;
        #[cfg(async_channel_impl = "tokio")]
        let result = tokio_stream::wrappers::UnboundedReceiverStream::new(self.0.into_inner());
        #[cfg(async_channel_impl = "flume")]
        let result = self.0.into_stream();

        UnboundedStream(result)
    }
    /// Try to receive a value from the receiver.
    ///
    /// # Errors
    ///
    /// Will return an error if no value is currently queued. This function will not block.
    pub fn try_recv(&self) -> Result<T, UnboundedTryRecvError> {
        #[cfg(async_channel_impl = "tokio")]
        let result = self
            .0
            .try_lock()
            .map_err(|_| UnboundedTryRecvError::Empty)?
            .try_recv();

        #[cfg(not(async_channel_impl = "tokio"))]
        let result = self.0.try_recv();

        result
    }
    /// Asynchronously wait for at least 1 value to show up, then will greedily try to receive values until this receiver would block. The resulting values are returned.
    ///
    /// It is guaranteed that the returning vec contains at least 1 value
    ///
    /// # Errors
    ///
    /// Will return an error if there was an error retrieving the first value.
    pub async fn drain_at_least_one(&self) -> Result<Vec<T>, UnboundedRecvError> {
        // Wait for the first message to come up
        let first = self.recv().await?;
        let mut ret = vec![first];
        loop {
            match self.try_recv() {
                Ok(x) => ret.push(x),
                Err(e) => {
                    if let Some(e) = try_recv_error_to_recv_error(e) {
                        tracing::error!(
                            "Tried to empty {:?} queue but it disconnected while we were emptying it ({} items are being dropped)",
                            std::any::type_name::<Self>(),
                            ret.len()
                        );
                        return Err(e);
                    }
                    break;
                }
            }
        }
        Ok(ret)
    }
    /// Drains the receiver from all messages in the queue, but will not poll for more messages
    ///
    /// # Errors
    ///
    /// Will return an error if all the senders get dropped before this ends.
    pub fn drain(&self) -> Result<Vec<T>, UnboundedRecvError> {
        let mut result = Vec::new();
        loop {
            match self.try_recv() {
                Ok(t) => result.push(t),
                Err(e) => {
                    if let Some(e) = try_recv_error_to_recv_error(e) {
                        return Err(e);
                    }
                    break;
                }
            }
        }
        Ok(result)
    }
    /// Attempt to load the length of the messages in queue.
    ///
    /// On some implementations this value does not exist, and this will return `None`.
    #[allow(clippy::len_without_is_empty, clippy::unused_self)]
    #[must_use]
    pub fn len(&self) -> Option<usize> {
        #[cfg(async_channel_impl = "tokio")]
        let result = None;
        #[cfg(not(all(async_channel_impl = "tokio")))]
        let result = Some(self.0.len());
        result
    }
}

impl<T> Stream for UnboundedStream<T> {
    type Item = T;

    fn poll_next(
        mut self: std::pin::Pin<&mut Self>,
        cx: &mut std::task::Context<'_>,
    ) -> std::task::Poll<Option<Self::Item>> {
        #[cfg(async_channel_impl = "flume")]
        return <flume::r#async::RecvStream<T>>::poll_next(Pin::new(&mut self.0), cx);
        #[cfg(async_channel_impl = "tokio")]
        return <tokio_stream::wrappers::UnboundedReceiverStream<T> as Stream>::poll_next(
            Pin::new(&mut self.0),
            cx,
        );
        #[cfg(not(any(async_channel_impl = "flume", async_channel_impl = "tokio")))]
        return <async_std::channel::Receiver<T> as Stream>::poll_next(Pin::new(&mut self.0), cx);
    }
}

// Clone impl
impl<T> Clone for UnboundedSender<T> {
    fn clone(&self) -> Self {
        Self(self.0.clone())
    }
}

// Debug impl
impl<T> std::fmt::Debug for UnboundedSender<T> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("UnboundedSender").finish()
    }
}
impl<T> std::fmt::Debug for UnboundedReceiver<T> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("UnboundedReceiver").finish()
    }
}