//! Code which enables sending messages between processes in the blocktree system.

pub use private::*;

mod private {
    use crate::{crypto::rand_array, BlockPath, Result, Writecap};
    use btserde::{read_from, write_to};
    use os_pipe::{PipeReader, PipeWriter};
    use serde::{Deserialize, Serialize};
    use std::io::{Read, Write};
    use zerocopy::FromBytes;

    #[derive(PartialEq, Eq, Serialize, Deserialize)]
    pub enum MsgError {}

    #[derive(Serialize, Deserialize)]
    pub enum MsgBody {
        Success,
        Fail(MsgError),
        Ping,
        Hello(Writecap),
        Read { offset: u64 },
        Write { offset: u64, data: Vec<u8> },
        Custom(Vec<u8>),
    }

    #[derive(Serialize, Deserialize)]
    pub struct Msg {
        from: BlockPath,
        to: BlockPath,
        id: u128,
        body: MsgBody,
    }

    impl Msg {
        pub fn from(&self) -> &BlockPath {
            &self.from
        }

        pub fn to(&self) -> &BlockPath {
            &self.to
        }

        pub fn id(&self) -> u128 {
            self.id
        }

        pub fn body(&self) -> &MsgBody {
            &self.body
        }
    }

    #[derive(Serialize, Deserialize)]
    pub enum VerMsg {
        V0(Msg),
    }

    pub trait Sender: Send {
        fn send(&mut self, msg: Msg) -> Result<()>;
        fn path(&self) -> &BlockPath;

        /// Generates and returns a new message ID.
        fn gen_id(&mut self) -> Result<u128> {
            const LEN: usize = std::mem::size_of::<u128>();
            let bytes = rand_array::<LEN>()?;
            let option = u128::read_from(bytes.as_slice());
            // Safety: because LEN == size_of::<u128>(), read_from should have returned Some.
            Ok(option.unwrap())
        }

        /// This is a convenience method which creates a new message, addresses it to the given
        /// path, sets it as from this sender's path, generates a new ID for it, puts the given
        /// body inside of it, and dispatches it with the `send` method.
        fn send_new(&mut self, to: BlockPath, body: MsgBody) -> Result<()> {
            let id = self.gen_id()?;
            let msg = Msg {
                to,
                from: self.path().to_owned(),
                id,
                body,
            };
            self.send(msg)
        }
    }

    pub trait Receiver {
        fn receive(&mut self) -> Result<Msg>;
        fn path(&self) -> &BlockPath;
    }

    pub trait Channel {
        type Sender: Sender;
        type Receiver: Receiver;

        fn new(path: BlockPath) -> Result<(Self::Sender, Self::Receiver)>;
    }

    pub trait Router {
        fn add_sender<S: Sender>(&mut self, sender: S) -> Result<()>;
        fn send(&mut self, msg: Msg) -> Result<()>;
    }

    trait TryClone<O> {
        fn try_clone(&self) -> Result<O>;
    }

    impl TryClone<PipeWriter> for PipeWriter {
        fn try_clone(&self) -> Result<PipeWriter> {
            Ok(PipeWriter::try_clone(self)?)
        }
    }

    pub struct WriteSender<W> {
        write: W,
        path: BlockPath,
    }

    impl<W: Write + Send> Sender for WriteSender<W> {
        fn send(&mut self, msg: Msg) -> Result<()> {
            Ok(write_to(&msg, &mut self.write)?)
        }

        fn path(&self) -> &BlockPath {
            &self.path
        }
    }

    impl<W: Write + TryClone<W>> TryClone<WriteSender<W>> for WriteSender<W> {
        fn try_clone(&self) -> Result<WriteSender<W>> {
            Ok(WriteSender {
                write: self.write.try_clone()?,
                path: self.path.clone(),
            })
        }
    }

    pub struct ReadReceiver<R> {
        read: R,
        path: BlockPath,
    }

    impl<R: Read> Receiver for ReadReceiver<R> {
        fn receive(&mut self) -> Result<Msg> {
            Ok(read_from(&mut self.read)?)
        }

        fn path(&self) -> &BlockPath {
            &self.path
        }
    }

    pub enum PipeChannel {}

    impl Channel for PipeChannel {
        type Sender = WriteSender<PipeWriter>;
        type Receiver = ReadReceiver<PipeReader>;

        fn new(path: BlockPath) -> Result<(Self::Sender, Self::Receiver)> {
            let (read, write) = os_pipe::pipe()?;
            let sender = WriteSender {
                path: path.clone(),
                write,
            };
            let receiver = ReadReceiver { path, read };
            Ok((sender, receiver))
        }
    }
}

#[cfg(test)]
mod tests {
    use crate::test_helpers;

    use super::*;

    #[test]
    fn ping_pong_via_pipes() {
        let ping_path = test_helpers::make_path(vec!["ping"]);
        let (mut ping_sender, mut ping_receiver) =
            PipeChannel::new(ping_path.clone()).expect("failed to create a ping channel");
        let pong_path = test_helpers::make_path(vec!["pong"]);
        let (mut pong_sender, mut pong_receiver) =
            PipeChannel::new(pong_path.clone()).expect("failed to create a pong channel");
        let pong = std::thread::spawn(move || loop {
            let msg = pong_receiver.receive().expect("pong receive failed");
            assert_eq!(pong_receiver.path(), msg.to());
            match msg.body() {
                MsgBody::Ping => ping_sender
                    .send_new(ping_path.clone(), MsgBody::Success)
                    .expect("send to ping failed"),
                MsgBody::Success => return,
                _ => panic!("unexpected message received by pong"),
            }
        });
        let mut iter = 5;
        while iter > 0 {
            pong_sender
                .send_new(pong_path.clone(), MsgBody::Ping)
                .expect("send to pong failed");
            let msg = ping_receiver.receive().expect("ping receive failed");
            assert_eq!(ping_receiver.path(), msg.to());
            match msg.body() {
                MsgBody::Success => iter -= 1,
                _ => panic!("unexpected message received by ping"),
            }
        }
        pong_sender
            .send_new(pong_path.clone(), MsgBody::Success)
            .expect("send success to pong failed");
        pong.join().expect("join failed");
    }
}