use std::cell::Cell;
use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll};
use futures_signals::signal::{MutableSignalRef, ReadOnlyMutable, Signal};
use futures_util::future::BoxFuture;
use crate::resources::state::State;

mod shelly;

pub trait Actor {
    fn apply(&mut self, state: State) -> BoxFuture<'static, ()>;
}

fn loader<S: Signal<Item = State>>(cell: &Cell<Option<S>>) -> Option<S> {
    cell.take()
}

pub struct ActorDriver<S: 'static> {
    signal: S,

    actor: Box<dyn Actor + Send + Sync>,
    future: Option<BoxFuture<'static, ()>>,
}

impl<S: Signal<Item = State>> ActorDriver<S>
{
    pub fn new(signal: S, actor: Box<dyn Actor + Send + Sync>)
        -> Self
    {
        Self {
            signal,
            actor,
            future: None,
        }
    }
}


impl<S> Future for ActorDriver<S>
    where S: Signal<Item=State> + Unpin + Send,
{
    type Output = ();

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
        // Work until there is no more work to do.
        loop {

            // Poll the `apply` future. And ensure it's completed before the next one is started
            match self.future.as_mut()
                .map(|future| Future::poll(Pin::new(future), cx))
            {
                // Skip and poll for a new future to do
                None => { }

                // This apply future is done, get a new one
                Some(Poll::Ready(_)) => self.future = None,

                // This future would block so we return to continue work another time
                Some(Poll::Pending) => return Poll::Pending,
            }

            // Poll the signal and apply any change that happen to the inner Actuator
            match Pin::new(&mut self.signal).poll_change(cx)
            {
                Poll::Pending => return Poll::Pending,
                Poll::Ready(None) => return Poll::Pending,
                Poll::Ready(Some(state)) => {
                    // This future MUST be polled before we exit from the Actor::poll because if we
                    // do not do that it will not register the dependency and thus NOT BE POLLED.
                    let f = self.actor.apply(state);
                    self.future.replace(f);
                }
            }
        }
    }
}