use std::fmt;
use std::marker::PhantomData;
use std::sync::Arc;

use bytes::{BufMut, Bytes, BytesMut};
use serde::{Deserialize, Serialize};

use futures::stream::StreamExt;

use crate::error::*;
use crate::stream::*;
use crate::util::*;

/// Priority of a request (click to read more about priorities).
///
/// This priority value is used to priorize messages
/// in the send queue of the client, and their responses in the send queue of the
/// server. Lower values mean higher priority.
///
/// This mechanism is usefull for messages bigger than the maximum chunk size
/// (set at `0x4000` bytes), such as large file transfers.
/// In such case, all of the messages in the send queue with the highest priority
/// will take turns to send individual chunks, in a round-robin fashion.
/// Once all highest priority messages are sent successfully, the messages with
/// the next highest priority will begin being sent in the same way.
///
/// The same priority value is given to a request and to its associated response.
pub type RequestPriority = u8;

/// Priority class: high
pub const PRIO_HIGH: RequestPriority = 0x20;
/// Priority class: normal
pub const PRIO_NORMAL: RequestPriority = 0x40;
/// Priority class: background
pub const PRIO_BACKGROUND: RequestPriority = 0x80;
/// Priority: primary among given class
pub const PRIO_PRIMARY: RequestPriority = 0x00;
/// Priority: secondary among given class (ex: `PRIO_HIGH | PRIO_SECONDARY`)
pub const PRIO_SECONDARY: RequestPriority = 0x01;

// ----

/// This trait should be implemented by all messages your application
/// wants to handle
pub trait Message: Serialize + for<'de> Deserialize<'de> + Send + Sync {
	type Response: Serialize + for<'de> Deserialize<'de> + Send + Sync;
}

// ----

/// The Req<M> is a helper object used to create requests and attach them
/// a stream of data. If the stream is a fixed Bytes and not a ByteStream,
/// Req<M> is cheaply clonable to allow the request to be sent to different
/// peers (Clone will panic if the stream is a ByteStream).
pub struct Req<M: Message> {
	pub(crate) _phantom: PhantomData<M>,
	pub(crate) msg: Arc<M>,
	pub(crate) msg_ser: Option<Bytes>,
	pub(crate) stream: AttachedStream,
}

impl<M: Message> Req<M> {
	pub fn with_stream_from_buffer(self, b: Bytes) -> Self {
		Self {
			stream: AttachedStream::Fixed(b),
			..self
		}
	}

	pub fn with_stream(self, b: ByteStream) -> Self {
		Self {
			stream: AttachedStream::Stream(b),
			..self
		}
	}

	pub fn msg(&self) -> &M {
		&self.msg
	}

	pub fn take_stream(&mut self) -> Option<ByteStream> {
		std::mem::replace(&mut self.stream, AttachedStream::None).into_stream()
	}

	pub(crate) fn into_enc(
		self,
		prio: RequestPriority,
		path: Bytes,
		telemetry_id: Bytes,
	) -> ReqEnc {
		ReqEnc {
			prio,
			path,
			telemetry_id,
			msg: self.msg_ser.unwrap(),
			stream: self.stream.into_stream(),
		}
	}

	pub(crate) fn from_enc(enc: ReqEnc) -> Result<Self, rmp_serde::decode::Error> {
		let msg = rmp_serde::decode::from_read_ref(&enc.msg)?;
		Ok(Req {
			_phantom: Default::default(),
			msg: Arc::new(msg),
			msg_ser: Some(enc.msg),
			stream: enc
				.stream
				.map(AttachedStream::Stream)
				.unwrap_or(AttachedStream::None),
		})
	}
}

pub trait IntoReq<M: Message> {
	fn into_req(self) -> Result<Req<M>, rmp_serde::encode::Error>;
	fn into_req_local(self) -> Req<M>;
}

impl<M: Message> IntoReq<M> for M {
	fn into_req(self) -> Result<Req<M>, rmp_serde::encode::Error> {
		let msg_ser = rmp_to_vec_all_named(&self)?;
		Ok(Req {
			_phantom: Default::default(),
			msg: Arc::new(self),
			msg_ser: Some(Bytes::from(msg_ser)),
			stream: AttachedStream::None,
		})
	}
	fn into_req_local(self) -> Req<M> {
		Req {
			_phantom: Default::default(),
			msg: Arc::new(self),
			msg_ser: None,
			stream: AttachedStream::None,
		}
	}
}

impl<M: Message> IntoReq<M> for Req<M> {
	fn into_req(self) -> Result<Req<M>, rmp_serde::encode::Error> {
		Ok(self)
	}
	fn into_req_local(self) -> Req<M> {
		self
	}
}

impl<M: Message> Clone for Req<M> {
	fn clone(&self) -> Self {
		let stream = match &self.stream {
			AttachedStream::None => AttachedStream::None,
			AttachedStream::Fixed(b) => AttachedStream::Fixed(b.clone()),
			AttachedStream::Stream(_) => {
				panic!("Cannot clone a Req<_> with a non-buffer attached stream")
			}
		};
		Self {
			_phantom: Default::default(),
			msg: self.msg.clone(),
			msg_ser: self.msg_ser.clone(),
			stream,
		}
	}
}

impl<M> fmt::Debug for Req<M>
where
	M: Message + fmt::Debug,
{
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
		write!(f, "Req[{:?}", self.msg)?;
		match &self.stream {
			AttachedStream::None => write!(f, "]"),
			AttachedStream::Fixed(b) => write!(f, "; stream=buf:{}]", b.len()),
			AttachedStream::Stream(_) => write!(f, "; stream]"),
		}
	}
}

// ----

/// The Resp<M> represents a full response from a RPC that may have
/// an attached stream.
pub struct Resp<M: Message> {
	pub(crate) _phantom: PhantomData<M>,
	pub(crate) msg: M::Response,
	pub(crate) stream: AttachedStream,
}

impl<M: Message> Resp<M> {
	pub fn new(v: M::Response) -> Self {
		Resp {
			_phantom: Default::default(),
			msg: v,
			stream: AttachedStream::None,
		}
	}

	pub fn with_stream_from_buffer(self, b: Bytes) -> Self {
		Self {
			stream: AttachedStream::Fixed(b),
			..self
		}
	}

	pub fn with_stream(self, b: ByteStream) -> Self {
		Self {
			stream: AttachedStream::Stream(b),
			..self
		}
	}

	pub fn msg(&self) -> &M::Response {
		&self.msg
	}

	pub fn into_msg(self) -> M::Response {
		self.msg
	}

	pub fn into_parts(self) -> (M::Response, Option<ByteStream>) {
		(self.msg, self.stream.into_stream())
	}

	pub(crate) fn into_enc(self) -> Result<RespEnc, rmp_serde::encode::Error> {
		Ok(RespEnc::Success {
			msg: rmp_to_vec_all_named(&self.msg)?.into(),
			stream: self.stream.into_stream(),
		})
	}

	pub(crate) fn from_enc(enc: RespEnc) -> Result<Self, Error> {
		match enc {
			RespEnc::Success { msg, stream } => {
				let msg = rmp_serde::decode::from_read_ref(&msg)?;
				Ok(Self {
					_phantom: Default::default(),
					msg,
					stream: stream
						.map(AttachedStream::Stream)
						.unwrap_or(AttachedStream::None),
				})
			}
			RespEnc::Error { code, message } => Err(Error::Remote(code, message)),
		}
	}
}

impl<M> fmt::Debug for Resp<M>
where
	M: Message,
	<M as Message>::Response: fmt::Debug,
{
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
		write!(f, "Resp[{:?}", self.msg)?;
		match &self.stream {
			AttachedStream::None => write!(f, "]"),
			AttachedStream::Fixed(b) => write!(f, "; stream=buf:{}]", b.len()),
			AttachedStream::Stream(_) => write!(f, "; stream]"),
		}
	}
}

// ----

pub(crate) enum AttachedStream {
	None,
	Fixed(Bytes),
	Stream(ByteStream),
}

impl AttachedStream {
	pub fn into_stream(self) -> Option<ByteStream> {
		match self {
			AttachedStream::None => None,
			AttachedStream::Fixed(b) => Some(Box::pin(futures::stream::once(async move { Ok(b) }))),
			AttachedStream::Stream(s) => Some(s),
		}
	}
}

// ---- ----

/// Encoding for requests into a ByteStream:
/// - priority: u8
/// - path length: u8
/// - path: [u8; path length]
/// - telemetry id length: u8
/// - telemetry id: [u8; telemetry id length]
/// - msg len: u32
/// - msg [u8; ..]
/// - the attached stream as the rest of the encoded stream
pub(crate) struct ReqEnc {
	pub(crate) prio: RequestPriority,
	pub(crate) path: Bytes,
	pub(crate) telemetry_id: Bytes,
	pub(crate) msg: Bytes,
	pub(crate) stream: Option<ByteStream>,
}

impl ReqEnc {
	pub(crate) fn encode(self) -> ByteStream {
		let mut buf = BytesMut::with_capacity(
			self.path.len() + self.telemetry_id.len() + self.msg.len() + 16,
		);

		buf.put_u8(self.prio);

		buf.put_u8(self.path.len() as u8);
		buf.put(self.path);

		buf.put_u8(self.telemetry_id.len() as u8);
		buf.put(&self.telemetry_id[..]);

		buf.put_u32(self.msg.len() as u32);

		let header = buf.freeze();

		if let Some(stream) = self.stream {
			Box::pin(futures::stream::iter([Ok(header), Ok(self.msg)]).chain(stream))
		} else {
			Box::pin(futures::stream::iter([Ok(header), Ok(self.msg)]))
		}
	}

	pub(crate) async fn decode(stream: ByteStream) -> Result<Self, Error> {
		Self::decode_aux(stream).await.map_err(|_| Error::Framing)
	}

	pub(crate) async fn decode_aux(stream: ByteStream) -> Result<Self, ReadExactError> {
		let mut reader = ByteStreamReader::new(stream);

		let prio = reader.read_u8().await?;

		let path_len = reader.read_u8().await?;
		let path = reader.read_exact(path_len as usize).await?;

		let telemetry_id_len = reader.read_u8().await?;
		let telemetry_id = reader.read_exact(telemetry_id_len as usize).await?;

		let msg_len = reader.read_u32().await?;
		let msg = reader.read_exact(msg_len as usize).await?;

		Ok(Self {
			prio,
			path,
			telemetry_id,
			msg,
			stream: Some(reader.into_stream()),
		})
	}
}

/// Encoding for responses into a ByteStream:
/// IF SUCCESS:
/// - 0: u8
/// - msg len: u32
/// - msg [u8; ..]
/// - the attached stream as the rest of the encoded stream
/// IF ERROR:
/// - message length + 1: u8
/// - error code: u8
/// - message: [u8; message_length]
pub(crate) enum RespEnc {
	Error {
		code: u8,
		message: String,
	},
	Success {
		msg: Bytes,
		stream: Option<ByteStream>,
	},
}

impl RespEnc {
	pub(crate) fn from_err(e: Error) -> Self {
		RespEnc::Error {
			code: e.code(),
			message: format!("{}", e),
		}
	}

	pub(crate) fn encode(self) -> ByteStream {
		match self {
			RespEnc::Success { msg, stream } => {
				let mut buf = BytesMut::with_capacity(msg.len() + 8);

				buf.put_u8(0);
				buf.put_u32(msg.len() as u32);

				let header = buf.freeze();

				if let Some(stream) = stream {
					Box::pin(futures::stream::iter([Ok(header), Ok(msg)]).chain(stream))
				} else {
					Box::pin(futures::stream::iter([Ok(header), Ok(msg)]))
				}
			}
			RespEnc::Error { code, message } => {
				let mut buf = BytesMut::with_capacity(message.len() + 8);
				buf.put_u8(1 + message.len() as u8);
				buf.put_u8(code);
				buf.put(message.as_bytes());
				let header = buf.freeze();
				Box::pin(futures::stream::once(async move { Ok(header) }))
			}
		}
	}

	pub(crate) async fn decode(stream: ByteStream) -> Result<Self, Error> {
		Self::decode_aux(stream).await.map_err(|_| Error::Framing)
	}

	pub(crate) async fn decode_aux(stream: ByteStream) -> Result<Self, ReadExactError> {
		let mut reader = ByteStreamReader::new(stream);

		let is_err = reader.read_u8().await?;

		if is_err > 0 {
			let code = reader.read_u8().await?;
			let message = reader.read_exact(is_err as usize - 1).await?;
			let message = String::from_utf8(message.to_vec()).unwrap_or_default();
			Ok(RespEnc::Error { code, message })
		} else {
			let msg_len = reader.read_u32().await?;
			let msg = reader.read_exact(msg_len as usize).await?;

			Ok(RespEnc::Success {
				msg,
				stream: Some(reader.into_stream()),
			})
		}
	}
}