//! Commands for a service
use super::*;
use std::{any::Any, marker::{Send, Sync}};
use std::fmt;
use tokio::sync::{
    oneshot,
};

id_type!(pub CommandID: "ID of a sent command");

/// A response from the service for a sent command 
pub type Response = Box<dyn Any + Send + 'static>;

/// What kind of command to send to the service?
#[derive(Debug, PartialEq, Eq)]
pub enum CommandKind
{
    
}

/// A command to send to a running service.
///
/// Created when sending a `CommandKind` to a service. This is your handle for receiving the response.
#[derive(Debug)]
pub struct Command
{
    id: CommandID,
    //kind: CommandKind, // `CommandKind` -(sent to)> <running service> -(handle returned from send func)> `Command`

    resp: oneshot::Receiver<Option<Response>>,
}

impl fmt::Display for Command
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
    {
	write!(f, "CommandID<{}>", self.id.0.as_bytes().hex())
    }
}


impl Command
{
    /// The unique ID of this command
    #[inline] pub fn id(&self) -> &CommandID
    {
	&self.id
    }

    /// Prevent any response from being sent to this `Command` handle from the service.
    ///
    /// Indicates to the service we don't care about a response. This has the same effect as calling `ignore` but can be used in a builder-pattern way from a returned `Command` from a send.
    /// Example: `let comm = service.send_command(comm_kind).ignored();`
    #[inline(always)] pub fn ignored(mut self) -> Self
    {
	self.ignore();
	self
    }

    /// Close the response channel, indicating to the service that we don't care about the response.
    #[inline] pub fn ignore(&mut self)
    {
	self.resp.close();
    }

    /// Dispose of this `Command`, returning any `Response` that might've already been sent.
    #[inline] pub fn close(mut self) -> Option<Response>
    {
	use oneshot::error::TryRecvError;

	self.resp.close();
	self.resp.try_recv().ok().flatten()
    }

    /// Poll for a response. If none has been sent yet, then return `self` so it can be polled again.
    #[inline] pub fn try_into_response(mut self) -> Result<Option<Response>, Self>
    {
	use oneshot::error::TryRecvError;
	
	match self.resp.try_recv() {
	    Ok(v) => Ok(v),
	    Err(TryRecvError::Closed) => Ok(None),
	    Err(TryRecvError::Empty) => Err(self),
	}
    }

    /// Consume this instance into the response from the service.
    #[inline] pub async fn into_repsonse(self) -> Option<Response>
    {
	self.resp.await.ok().flatten()
    }
}

impl PartialEq for Command
{
    #[inline] fn eq(&self, other: &Self) -> bool
    {
	self.id == other.id
    }
}