use crate::{
    provider::ProviderError,
    transports::common::{JsonRpcError, Notification, Request, Response},
    JsonRpcClient, PubsubClient,
};
use ethers_core::types::U256;

use async_trait::async_trait;
use futures_channel::mpsc;
use futures_util::stream::{Fuse, StreamExt};
use oneshot::error::RecvError;
use serde::{de::DeserializeOwned, Serialize};
use std::sync::atomic::Ordering;
use std::{
    collections::HashMap,
    path::Path,
    sync::{atomic::AtomicU64, Arc},
};
use thiserror::Error;
use tokio::{
    io::{AsyncRead, AsyncWrite, AsyncWriteExt, ReadHalf, WriteHalf},
    net::UnixStream,
    sync::oneshot,
};
use tokio_util::io::ReaderStream;
use tracing::{error, warn};

/// Unix Domain Sockets (IPC) transport.
#[derive(Debug, Clone)]
pub struct Ipc {
    id: Arc<AtomicU64>,
    messages_tx: mpsc::UnboundedSender<TransportMessage>,
}

type Pending = oneshot::Sender<serde_json::Value>;
type Subscription = mpsc::UnboundedSender<serde_json::Value>;

#[derive(Debug)]
enum TransportMessage {
    Request {
        id: u64,
        request: String,
        sender: Pending,
    },
    Subscribe {
        id: U256,
        sink: Subscription,
    },
    Unsubscribe {
        id: U256,
    },
}

impl Ipc {
    /// Creates a new IPC transport from a Async Reader / Writer
    fn new<S: AsyncRead + AsyncWrite + Send + 'static>(stream: S) -> Self {
        let id = Arc::new(AtomicU64::new(1));
        let (messages_tx, messages_rx) = mpsc::unbounded();

        IpcServer::new(stream, messages_rx).spawn();
        Self { id, messages_tx }
    }

    /// Creates a new IPC transport from a given path using Unix sockets
    #[cfg(unix)]
    pub async fn connect<P: AsRef<Path>>(path: P) -> Result<Self, IpcError> {
        let ipc = UnixStream::connect(path).await?;
        Ok(Self::new(ipc))
    }

    fn send(&self, msg: TransportMessage) -> Result<(), IpcError> {
        self.messages_tx
            .unbounded_send(msg)
            .map_err(|_| IpcError::ChannelError("IPC server receiver dropped".to_string()))?;

        Ok(())
    }
}

#[async_trait]
impl JsonRpcClient for Ipc {
    type Error = IpcError;

    async fn request<T: Serialize + Send + Sync, R: DeserializeOwned>(
        &self,
        method: &str,
        params: T,
    ) -> Result<R, IpcError> {
        let next_id = self.id.fetch_add(1, Ordering::SeqCst);

        // Create the request and initialize the response channel
        let (sender, receiver) = oneshot::channel();
        let payload = TransportMessage::Request {
            id: next_id,
            request: serde_json::to_string(&Request::new(next_id, method, params))?,
            sender,
        };

        // Send the request to the IPC server to be handled.
        self.send(payload)?;

        // Wait for the response from the IPC server.
        let res = receiver.await?;

        // Parse JSON response.
        Ok(serde_json::from_value(res)?)
    }
}

impl PubsubClient for Ipc {
    type NotificationStream = mpsc::UnboundedReceiver<serde_json::Value>;

    fn subscribe<T: Into<U256>>(&self, id: T) -> Result<Self::NotificationStream, IpcError> {
        let (sink, stream) = mpsc::unbounded();
        self.send(TransportMessage::Subscribe {
            id: id.into(),
            sink,
        })?;
        Ok(stream)
    }

    fn unsubscribe<T: Into<U256>>(&self, id: T) -> Result<(), IpcError> {
        self.send(TransportMessage::Unsubscribe { id: id.into() })
    }
}

struct IpcServer<T> {
    socket_reader: Fuse<ReaderStream<ReadHalf<T>>>,
    socket_writer: WriteHalf<T>,
    requests: Fuse<mpsc::UnboundedReceiver<TransportMessage>>,
    pending: HashMap<u64, Pending>,
    subscriptions: HashMap<U256, Subscription>,
}

impl<T> IpcServer<T>
where
    T: AsyncRead + AsyncWrite,
{
    /// Instantiates the Websocket Server
    pub fn new(ipc: T, requests: mpsc::UnboundedReceiver<TransportMessage>) -> Self {
        let (socket_reader, socket_writer) = tokio::io::split(ipc);
        let socket_reader = ReaderStream::new(socket_reader).fuse();
        Self {
            socket_reader,
            socket_writer,
            requests: requests.fuse(),
            pending: HashMap::default(),
            subscriptions: HashMap::default(),
        }
    }

    /// Spawns the event loop
    fn spawn(mut self)
    where
        T: 'static + Send,
    {
        let f = async move {
            let mut read_buffer = Vec::new();
            loop {
                let closed = self
                    .process(&mut read_buffer)
                    .await
                    .expect("WS Server panic");
                if closed && self.pending.is_empty() {
                    break;
                }
            }
        };

        tokio::spawn(f);
    }

    /// Processes 1 item selected from the incoming `requests` or `socket`
    #[allow(clippy::single_match)]
    async fn process(&mut self, read_buffer: &mut Vec<u8>) -> Result<bool, IpcError> {
        futures_util::select! {
            // Handle requests
            msg = self.requests.next() => match msg {
                Some(msg) => self.handle_request(msg).await?,
                None => return Ok(true),
            },
            // Handle socket messages
            msg = self.socket_reader.next() => match msg {
                Some(Ok(msg)) => self.handle_socket(read_buffer, msg).await?,
                Some(Err(err)) => {
                    error!("IPC read error: {:?}", err);
                    return Err(err.into());
                },
                None => {},
            },
            // finished
            complete => {},
        };

        Ok(false)
    }

    async fn handle_request(&mut self, msg: TransportMessage) -> Result<(), IpcError> {
        match msg {
            TransportMessage::Request {
                id,
                request,
                sender,
            } => {
                if self.pending.insert(id, sender).is_some() {
                    warn!("Replacing a pending request with id {:?}", id);
                }

                if let Err(err) = self.socket_writer.write(request.as_bytes()).await {
                    error!("WS connection error: {:?}", err);
                    self.pending.remove(&id);
                }
            }
            TransportMessage::Subscribe { id, sink } => {
                if self.subscriptions.insert(id, sink).is_some() {
                    warn!("Replacing already-registered subscription with id {:?}", id);
                }
            }
            TransportMessage::Unsubscribe { id } => {
                if self.subscriptions.remove(&id).is_none() {
                    warn!(
                        "Unsubscribing from non-existent subscription with id {:?}",
                        id
                    );
                }
            }
        };

        Ok(())
    }

    async fn handle_socket(
        &mut self,
        read_buffer: &mut Vec<u8>,
        bytes: bytes::Bytes,
    ) -> Result<(), IpcError> {
        // Extend buffer of previously unread with the new read bytes
        read_buffer.extend_from_slice(&bytes);

        let read_len = {
            // Deserialize as many full elements from the stream as exists
            let mut de: serde_json::StreamDeserializer<_, serde_json::Value> =
                serde_json::Deserializer::from_slice(read_buffer).into_iter();

            // Iterate through these elements, and handle responses/notifications
            while let Some(Ok(value)) = de.next() {
                if let Ok(notification) =
                    serde_json::from_value::<Notification<serde_json::Value>>(value.clone())
                {
                    // Send notify response if okay.
                    if let Err(e) = self.notify(notification) {
                        error!("Failed to send IPC notification: {}", e)
                    }
                } else if let Ok(response) =
                    serde_json::from_value::<Response<serde_json::Value>>(value)
                {
                    if let Err(e) = self.respond(response) {
                        error!("Failed to send IPC response: {}", e)
                    }
                } else {
                    warn!("JSON from IPC stream is not a response or notification");
                }
            }

            // Get the offset of bytes to handle partial buffer reads
            de.byte_offset()
        };

        // Reset buffer to just include the partial value bytes.
        read_buffer.copy_within(read_len.., 0);
        read_buffer.truncate(read_buffer.len() - read_len);

        Ok(())
    }

    /// Sends notification through the channel based on the ID of the subscription.
    /// This handles streaming responses.
    fn notify(&mut self, notification: Notification<serde_json::Value>) -> Result<(), IpcError> {
        let id = notification.params.subscription;
        if let Some(tx) = self.subscriptions.get(&id) {
            tx.unbounded_send(notification.params.result).map_err(|_| {
                IpcError::ChannelError(format!("Subscription receiver {} dropped", id))
            })?;
        }

        Ok(())
    }

    /// Sends JSON response through the channel based on the ID in that response.
    /// This handles RPC calls with only one response, and the channel entry is dropped after sending.
    fn respond(&mut self, output: Response<serde_json::Value>) -> Result<(), IpcError> {
        let id = output.id;

        // Converts output into result, to send data if valid response.
        let value = output.data.into_result()?;

        let response_tx = self.pending.remove(&id).ok_or_else(|| {
            IpcError::ChannelError("No response channel exists for the response ID".to_string())
        })?;

        response_tx.send(value).map_err(|_| {
            IpcError::ChannelError("Receiver channel for response has been dropped".to_string())
        })?;

        Ok(())
    }
}

#[derive(Error, Debug)]
/// Error thrown when sending or receiving an IPC message.
pub enum IpcError {
    /// Thrown if deserialization failed
    #[error(transparent)]
    JsonError(#[from] serde_json::Error),

    /// std IO error forwarding.
    #[error(transparent)]
    IoError(#[from] std::io::Error),

    #[error(transparent)]
    /// Thrown if the response could not be parsed
    JsonRpcError(#[from] JsonRpcError),

    #[error("{0}")]
    ChannelError(String),

    #[error(transparent)]
    Canceled(#[from] RecvError),
}

impl From<IpcError> for ProviderError {
    fn from(src: IpcError) -> Self {
        ProviderError::JsonRpcClientError(Box::new(src))
    }
}

#[cfg(all(test, unix))]
#[cfg(not(feature = "celo"))]
mod test {
    use super::*;
    use ethers_core::{utils::Geth, types::{Block, TxHash, U256}};
    use tempfile::NamedTempFile;

    #[tokio::test]
    async fn request() {
        let temp_file = NamedTempFile::new().unwrap();
        let path = temp_file.into_temp_path().to_path_buf();
        let _geth = Geth::new().block_time(1u64).ipc_path(&path).spawn();
        let ipc = Ipc::connect(path).await.unwrap();

        let block_num: U256 = ipc.request("eth_blockNumber", ()).await.unwrap();
        std::thread::sleep(std::time::Duration::new(3, 0));
        let block_num2: U256 = ipc.request("eth_blockNumber", ()).await.unwrap();
        assert!(block_num2 > block_num);
    }

    #[tokio::test]
    async fn subscription() {
        let temp_file = NamedTempFile::new().unwrap();
        let path = temp_file.into_temp_path().to_path_buf();
        let _geth = Geth::new().block_time(2u64).ipc_path(&path).spawn();
        let ipc = Ipc::connect(path).await.unwrap();

        let sub_id: U256 = ipc.request("eth_subscribe", ["newHeads"]).await.unwrap();
        let mut stream = ipc.subscribe(sub_id).unwrap();

        // Subscribing requires sending the sub request and then subscribing to
        // the returned sub_id
        let block_num: u64 = ipc
            .request::<_, U256>("eth_blockNumber", ())
            .await
            .unwrap()
            .as_u64();
        let mut blocks = Vec::new();
        for _ in 0..3 {
            let item = stream.next().await.unwrap();
            let block = serde_json::from_value::<Block<TxHash>>(item).unwrap();
            blocks.push(block.number.unwrap_or_default().as_u64());
        }
        let offset = blocks[0] - block_num;
        assert_eq!(
            blocks,
            &[
                block_num + offset,
                block_num + offset + 1,
                block_num + offset + 2
            ]
        )
    }
}