use serde::{Serialize, Deserialize};
use std::{
    io::{BufWriter, BufReader, prelude::*},
    process::{Child, ChildStdin, Command, Stdio},
    sync::mpsc::{channel, Receiver},
    time::{Duration},
};
use serde_block_tree::{self, write_to, read_from};
use log::{error};

#[derive(Serialize, Deserialize)]
pub enum Message {
    /// An echo request. This should elicit an identical reply.
    Echo(String),
    /// Orders the node to halt.
    Halt,
}

pub struct Node {
    child: Child,
    stdin: BufWriter<ChildStdin>,
    message_rx: Receiver<Message>,
}

impl Node {
    pub fn new() -> Result<Node, std::io::Error> {
        let mut child = Command::new("btnode")
            .stdin(Stdio::piped())
            .stdout(Stdio::piped())
            .stderr(Stdio::inherit())
            .spawn()?;
        let stdin = BufWriter::new(child.stdin.take().unwrap());
        let mut stdout = BufReader::new(child.stdout.take().unwrap());
        let (message_tx, message_rx) = channel();
        std::thread::spawn(move ||  loop {
            match read_from(&mut stdout) {
                Ok(msg) => {
                    match message_tx.send(msg) {
                        Ok(_) => (),
                        // Break if the receiver is dead.
                        Err(_) => break,
                    }
                },
                // Break if the child is has exited.
                Err(serde_block_tree::Error::Eof) => break,
                Err(serde_block_tree::Error::Io(io_err)) => {
                    match io_err.kind() {
                        std::io::ErrorKind::UnexpectedEof => break,
                        _ => error!("IO error ocurred: {:?}", io_err),
                    }
                },
                Err(err) => error!("Failed to deserialize child message {:?}", err),
            };
        });
        Ok(Node { child, stdin, message_rx })
    }

    pub fn send(&mut self, msg: &Message) -> serde_block_tree::Result<()> {
        write_to(&msg, &mut self.stdin)?;
        self.stdin.flush().map_err(serde_block_tree::Error::Io)?;
        Ok(())
    }

    pub fn receive(&mut self, timeout: Duration) -> Option<Message> {
        match self.message_rx.recv_timeout(timeout) {
            Ok(msg) => Some(msg),
            Err(err) => {
                eprintln!("Failed to receive message from thread. Error: {:?}", err);
                None
            }
        }
    }

    pub fn halt(mut self) -> Result<(), NodeHaltError> {
        self.send(&Message::Halt).unwrap();
        match self.child.wait() {
            Ok(status) => {
                let code = status.code();
                if code == Some(0) {
                    Ok(())
                }
                else {
                    Err(NodeHaltError::NonZeroExitCode(code))
                }
            },
            Err(err) => Err(NodeHaltError::Io(err)),
        }
    }
}

#[derive(Debug)]
pub enum NodeHaltError {
    /// The node exited with a non-zero or non-existent status code.
    NonZeroExitCode(Option<i32>),
    /// An IO error was encountered.
    Io(std::io::Error),
}

impl Drop for Node {
    fn drop(&mut self) {
        let _ = self.child.kill();
    }
}

#[cfg(test)]
mod test {
    use super::*;
    use ctor::ctor;
    use log::info;

    #[ctor]
    fn test_init() {
        use env_logger::{self, Env};
        env_logger::init_from_env(Env::default().default_filter_or("debug"));
        info!("Using cargo to install btnode...");
        let success = Command::new("cargo")
            .args(["install", "--path", "../btnode"])
            .status()
            .expect("failed to invoke cargo")
            .success();
        assert!(success, "failed to build btnode");
    }

    #[test]
    fn message_echo() {
        let mut node = Node::new().unwrap();
        for k in 0..7 {
            let expected = format!("Rep number {}", k);
            node.send(&Message::Echo(expected.clone())).unwrap();
            let reply = node.receive(Duration::from_millis(100)).unwrap();
            let reply_payload = match reply {
                Message::Echo(actual) => Some(actual),
                _ => None,
            };
            assert_eq!(Some(expected), reply_payload);
        }
    }

    #[test]
    fn message_halt() {
        let node = Node::new().unwrap();
        node.halt().unwrap();
    }
}