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use std::{
  ops::ControlFlow,
  thread::{self, JoinHandle}
};

use super::{channel, Client, MsgType, ReplyContext};

pub trait Handler<P, S, R, E, RV> {
  /// Optional initialization callback.
  ///
  /// This is called on the dispatcher thread before the main message
  /// processing loop is entered.
  #[allow(unused_variables)]
  fn init(&mut self, weak_client: ump_ng::WeakClient<P, S, R, E>) {}

  /// Post message processing callback.
  ///
  /// The callback must return `ControlFlow::Continue(())` to keep the
  /// dispatcher loop going.  Returning `ControlFlow::Break(RV)` will cause the
  /// dispatcher loop to abort and returns the value in `RV` from the thread.
  fn post(&mut self, msg: P) -> ControlFlow<RV, ()>;

  /// Request message processing callback.
  ///
  /// The callback must return `ControlFlow::Continue(())` to keep the
  /// dispatcher loop going.  Returning `ControlFlow::Break(RV)` will cause the
  /// dispatcher loop to abort and returns the value in `RV` from the thread.
  fn req(&mut self, msg: S, rctx: ReplyContext<R, E>) -> ControlFlow<RV, ()>;

  /// Optional termination callback.
  ///
  /// This is called on the dispatcher thread just after the main message
  /// processing loop has been terminbated.
  fn term(&mut self, rv: Option<RV>) -> Option<RV> {
    rv
  }
}

/// Launch a thread that will process incoming messages from an ump-ng server
/// end-point.
///
/// See top module's documentation for an overview of the [dispatch
/// loop](crate#dispatch-loop).
pub fn spawn<P, S, R, E, RV>(
  mut handler: impl Handler<P, S, R, E, RV> + Send + 'static
) -> (Client<P, S, R, E>, JoinHandle<Option<RV>>)
where
  P: 'static + Send,
  S: 'static + Send,
  R: 'static + Send,
  E: 'static + Send,
  RV: 'static + Send
{
  let (server, client) = channel();
  let weak_client = client.weak();
  let jh = thread::spawn(move || {
    handler.init(weak_client);
    let ret = loop {
      match server.wait() {
        Ok(msg) => match msg {
          MsgType::Put(m) => match handler.post(m) {
            ControlFlow::Continue(_) => {}
            ControlFlow::Break(rv) => break Some(rv)
          },
          MsgType::Request(m, rctx) => match handler.req(m, rctx) {
            ControlFlow::Continue(_) => {}
            ControlFlow::Break(rv) => break Some(rv)
          }
        },
        Err(_) => break None
      }
    };
    handler.term(ret)
  });

  (client, jh)
}

// vim: set ft=rust et sw=2 ts=2 sts=2 cinoptions=2 tw=79 :