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use tokio::sync::mpsc;
use tokio::sync::oneshot;

use crate::error;
use crate::peer::Command;
use crate::Message;

/// A handle for a sent request.
///
/// The handle can be used to receive updates and the response from the remote peer,
/// and to send update messages to the remote peer.
pub struct SentRequest<Body> {
	request_id: u32,
	service_id: i32,
	incoming_rx: mpsc::UnboundedReceiver<Message<Body>>,
	command_tx: mpsc::UnboundedSender<Command<Body>>,
}

/// A handle for a received request.
///
/// The handle can be used to receive updates from the remote peer,
/// and to send updates and the response to the remote peer.
pub struct ReceivedRequest<Body> {
	request_id: u32,
	service_id: i32,
	body: Body,
	incoming_rx: mpsc::UnboundedReceiver<Message<Body>>,
	command_tx: mpsc::UnboundedSender<Command<Body>>,
}

/// An incoming request or stream message.
pub enum Incoming<Body> {
	/// An incoming request.
	Request(ReceivedRequest<Body>),

	/// An incoming stream message.
	Stream(Message<Body>),
}

/// An outgoing request or stream message.
pub enum Outgoing<Body> {
	/// An outgoing request.
	Request(SentRequest<Body>),

	/// An outgoing stream message.
	Stream(Message<Body>),
}

impl<Body> SentRequest<Body> {
	/// Create a new sent request.
	pub(crate) fn new(
		request_id: u32,
		service_id: i32,
		incoming_rx: mpsc::UnboundedReceiver<Message<Body>>,
		command_tx: mpsc::UnboundedSender<Command<Body>>,
	) -> Self {
		Self {
			request_id,
			service_id,
			incoming_rx,
			command_tx,
		}
	}

	/// Get the request ID of the sent request.
	pub fn request_id(&self) -> u32 {
		self.request_id
	}

	/// Get the service ID of the initial request message.
	pub fn service_id(&self) -> i32 {
		self.service_id
	}

	/// Receive the next message from the request.
	///
	/// This could be an update message or a response message.
	// TODO: change return type to eliminate impossible message types?
	pub async fn next_message(&mut self) -> Result<Message<Body>, error::NextMessageError> {
		Ok(self.incoming_rx.recv().await.ok_or_else(error::connection_aborted)?)
	}

	/// Send an update for the request.
	pub async fn send_update(&mut self, service_id: i32, body: impl Into<Body>) -> Result<(), error::WriteMessageError> {
		use crate::peer::SendRawMessage;
		let body = body.into();
		let (result_tx, result_rx) = oneshot::channel();
		let message = Message::requester_update(self.request_id, service_id, body);
		self.command_tx
			.send(SendRawMessage { message, result_tx }.into())
			.map_err(|_| error::connection_aborted())?;
		result_rx.await.map_err(|_| error::connection_aborted())?
	}
}

impl<Body> ReceivedRequest<Body> {
	/// Create a new received request.
	pub(crate) fn new(
		request_id: u32,
		service_id: i32,
		body: Body,
		incoming_rx: mpsc::UnboundedReceiver<Message<Body>>,
		command_tx: mpsc::UnboundedSender<Command<Body>>,
	) -> Self {
		Self {
			request_id,
			service_id,
			body,
			incoming_rx,
			command_tx,
		}
	}

	/// Get the request ID of the received request.
	pub fn request_id(&self) -> u32 {
		self.request_id
	}

	/// Get the service ID of the initial request message.
	pub fn service_id(&self) -> i32 {
		self.service_id
	}

	/// Get the body of the initial request message.
	pub fn body(&self) -> &Body {
		&self.body
	}

	/// Receive the next message from the request.
	///
	/// This can only be an update message.
	// TODO: change return type to eliminate impossible message types?
	pub async fn next_message(&mut self) -> Result<Message<Body>, error::ReadMessageError> {
		Ok(self.incoming_rx.recv().await.ok_or_else(error::connection_aborted)?)
	}

	/// Send an update for the request.
	pub async fn send_update(&mut self, service_id: i32, body: impl Into<Body>) -> Result<(), error::WriteMessageError> {
		let body = body.into();
		self.send_raw_message(Message::responder_update(self.request_id, service_id, body)).await
	}

	/// Send the final response.
	pub async fn send_response(mut self, service_id: i32, body: impl Into<Body>) -> Result<(), error::WriteMessageError> {
		let body = body.into();
		self.send_raw_message(Message::response(self.request_id, service_id, body)).await
	}

	/// Send the final response with an error message.
	pub async fn send_error_response(mut self, message: &str) -> Result<(), error::WriteMessageError>
	where
		Body: crate::Body,
	{
		self.send_raw_message(Message::error_response(self.request_id, message)).await
	}

	/// Send a raw message.
	async fn send_raw_message(&mut self, message: Message<Body>) -> Result<(), error::WriteMessageError> {
		use crate::peer::SendRawMessage;
		let (result_tx, result_rx) = oneshot::channel();
		self.command_tx
			.send(SendRawMessage { message, result_tx }.into())
			.map_err(|_| error::connection_aborted())?;
		result_rx.await.map_err(|_| error::connection_aborted())?
	}
}

impl<Body> std::fmt::Debug for SentRequest<Body> {
	fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
		// TODO: use finish_non_exhaustive when it hits stable.
		f.debug_struct("SentRequest")
			.field("request_id", &self.request_id)
			.field("service_id", &self.service_id)
			.finish()
	}
}

impl<Body> std::fmt::Debug for ReceivedRequest<Body> {
	fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
		// TODO: use finish_non_exhaustive when it hits stable.
		f.debug_struct("ReceivedRequest")
			.field("request_id", &self.request_id)
			.field("service_id", &self.service_id)
			.finish()
	}
}

impl<Body> std::fmt::Debug for Incoming<Body> {
	fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
		match self {
			Self::Request(x) => {
				write!(f, "ReceivedRequest(")?;
				x.fmt(f)?;
				write!(f, ")")?;
			},
			Self::Stream(x) => {
				write!(f, "Stream(")?;
				x.fmt(f)?;
				write!(f, ")")?;
			},
		}
		Ok(())
	}
}