//! Message passing things
use super::*;
use tokio::{
    sync::{
	watch,
    },
};
use std::{
    task::{Poll, Context},
    pin::Pin,
    fmt,
    error,
};
use futures::{
    future::Future,
};

#[derive(Debug)]
pub struct InitError;
#[derive(Debug)]
pub struct InitWaitError;

impl error::Error for InitError{}
impl fmt::Display for InitError
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
    {
	write!(f, "failed to set init value")
    }
}

impl error::Error for InitWaitError{}
impl fmt::Display for InitWaitError
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
    {
	write!(f, "failed to receive init value")
    }
}

#[derive(Clone, Debug)]
pub struct Initialiser
{
    tx: Arc<watch::Sender<bool>>,
    rx: watch::Receiver<bool>
}

impl Initialiser
{
    pub fn new() -> Self
    {
	let (tx, rx) = watch::channel(false);
	Self {
	    tx: Arc::new(tx),
	    rx,
	}
    }

    pub fn new_set() -> Self
    {
	let (tx, rx) = watch::channel(true);
	Self {
	    tx: Arc::new(tx),
	    rx,
	}
    }

    pub async fn wait(&mut self) -> Result<(), InitWaitError>
    {
	if !*self.rx.borrow() {
	    self.rx.recv().await
		.ok_or_else(|| InitWaitError)
		.and_then(|x| if x {Ok(())} else {Err(InitWaitError)})
	} else {
	    Ok(())
	}
    }

    pub fn is_set(&self) -> bool
    {
	*self.rx.borrow()
    }
    
    pub fn set(self) -> Result<(), InitError>
    {
	if !*self.rx.borrow() {
	    self.tx.broadcast(true).map_err(|_| InitError)
	} else {
	    Ok(())
	}
    }
}

impl Future for Initialiser
{
    type Output = Result<(), InitWaitError>;
    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
	
	if !*self.rx.borrow() {
	    let rx = self.rx.recv();
	    tokio::pin!(rx);
	    rx.poll(cx).map(|x| x.ok_or_else(|| InitWaitError)
			    .and_then(|x| if x {Ok(())} else {Err(InitWaitError)}))
	} else {
	    Poll::Ready(Ok(()))
	}
    }
}