use std::{
	collections::HashMap,
	convert::TryFrom,
};

use chrono::{DateTime, Utc};
use dashmap::DashMap;
use tokio::sync::{
	Mutex,
	RwLock,
	oneshot,
	watch,
};

use crate::{
	Body,
	Config,
	RelayError,
	ShuttingDownError,
};

use ptth_core::http_serde;

/*

Here's what we need to handle:

When a request comes in:

- Park the client in response_rendezvous
- Look up the server ID in request_rendezvous
- If a server is parked, unpark it and send the request
- Otherwise, queue the request

When a server comes to listen:

- Look up the server ID in request_rendezvous
- Either return all pending requests, or park the server

When a server comes to respond:

- Look up the parked client in response_rendezvous
- Unpark the client and begin streaming

So we need these lookups to be fast:

- Server IDs, where (1 server) or (0 or many clients)
can be parked
- Request IDs, where 1 client is parked

*/

pub enum RequestRendezvous {
	ParkedClients (Vec <http_serde::WrappedRequest>),
	ParkedServer (oneshot::Sender <Result <http_serde::WrappedRequest, ShuttingDownError>>),
}

type ResponseRendezvous = oneshot::Sender <Result <(http_serde::ResponseParts, Body), ShuttingDownError>>;

#[derive (Clone)]
pub struct ServerStatus {
	pub last_seen: DateTime <Utc>,
}

impl Default for ServerStatus {
	fn default () -> Self {
		Self {
			last_seen: Utc::now (),
		}
	}
}

pub struct RelayState {
	pub config: RwLock <Config>,
	
	// Key: Server ID
	pub request_rendezvous: Mutex <HashMap <String, RequestRendezvous>>,
	pub server_status: Mutex <HashMap <String, ServerStatus>>,
	
	// Key: Request ID
	pub response_rendezvous: RwLock <DashMap <String, ResponseRendezvous>>,
	
	pub shutdown_watch_tx: watch::Sender <bool>,
	pub shutdown_watch_rx: watch::Receiver <bool>,
}

impl TryFrom <Config> for RelayState {
	type Error = RelayError;
	
	fn try_from (config: Config) -> Result <Self, Self::Error> {
		let (shutdown_watch_tx, shutdown_watch_rx) = watch::channel (false);
		
		Ok (Self {
			config: config.into (),
			request_rendezvous: Default::default (),
			server_status: Default::default (),
			response_rendezvous: Default::default (),
			shutdown_watch_tx,
			shutdown_watch_rx,
		})
	}
}

impl RelayState {
	pub async fn list_servers (&self) -> Vec <String> {
		self.request_rendezvous.lock ().await.iter ()
		.map (|(k, _)| (*k).clone ())
		.collect ()
	}
}