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

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

use futures::stream::{Stream, StreamExt};

use crate::error::*;
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;
}

pub struct Req<M: Message> {
	pub(crate) _phantom: PhantomData<M>,
	pub(crate) msg: Arc<M>,
	pub(crate) msg_ser: Option<Bytes>,
	pub(crate) body: BodyData,
}

pub struct Resp<M: Message> {
	pub(crate) _phantom: PhantomData<M>,
	pub(crate) msg: M::Response,
	pub(crate) body: BodyData,
}

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

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

// ----

impl<M: Message> Req<M> {
	pub fn msg(&self) -> &M {
		&self.msg
	}

	pub fn with_fixed_body(self, b: Bytes) -> Self {
		Self {
			body: BodyData::Fixed(b),
			..self
		}
	}

	pub fn with_streaming_body(self, b: ByteStream) -> Self {
		Self {
			body: BodyData::Stream(b),
			..self
		}
	}
}

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)),
			body: BodyData::None,
		})
	}
	fn into_req_local(self) -> Req<M> {
		Req {
			_phantom: Default::default(),
			msg: Arc::new(self),
			msg_ser: None,
			body: BodyData::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 body = match &self.body {
			BodyData::None => BodyData::None,
			BodyData::Fixed(b) => BodyData::Fixed(b.clone()),
			BodyData::Stream(_) => panic!("Cannot clone a Req<_> with a stream body"),
		};
		Self {
			_phantom: Default::default(),
			msg: self.msg.clone(),
			msg_ser: self.msg_ser.clone(),
			body,
		}
	}
}

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.body {
			BodyData::None => write!(f, "]"),
			BodyData::Fixed(b) => write!(f, "; body={}]", b.len()),
			BodyData::Stream(_) => write!(f, "; body=stream]"),
		}
	}
}

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.body {
			BodyData::None => write!(f, "]"),
			BodyData::Fixed(b) => write!(f, "; body={}]", b.len()),
			BodyData::Stream(_) => write!(f, "; body=stream]"),
		}
	}
}

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

	pub fn with_fixed_body(self, b: Bytes) -> Self {
		Self {
			body: BodyData::Fixed(b),
			..self
		}
	}

	pub fn with_streaming_body(self, b: ByteStream) -> Self {
		Self {
			body: BodyData::Stream(b),
			..self
		}
	}

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

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

// ---- ----

pub(crate) struct QueryMessage<'a> {
	pub(crate) prio: RequestPriority,
	pub(crate) path: &'a [u8],
	pub(crate) telemetry_id: Option<Vec<u8>>,
	pub(crate) body: &'a [u8],
}

/// QueryMessage encoding:
/// - priority: u8
/// - path length: u8
/// - path: [u8; path length]
/// - telemetry id length: u8
/// - telemetry id: [u8; telemetry id length]
/// - body [u8; ..]
impl<'a> QueryMessage<'a> {
	pub(crate) fn encode(self) -> Vec<u8> {
		let tel_len = match &self.telemetry_id {
			Some(t) => t.len(),
			None => 0,
		};

		let mut ret = Vec::with_capacity(10 + self.path.len() + tel_len + self.body.len());

		ret.push(self.prio);

		ret.push(self.path.len() as u8);
		ret.extend_from_slice(self.path);

		if let Some(t) = self.telemetry_id {
			ret.push(t.len() as u8);
			ret.extend(t);
		} else {
			ret.push(0u8);
		}

		ret.extend_from_slice(self.body);

		ret
	}

	pub(crate) fn decode(bytes: &'a [u8]) -> Result<Self, Error> {
		if bytes.len() < 3 {
			return Err(Error::Message("Invalid protocol message".into()));
		}

		let path_length = bytes[1] as usize;
		if bytes.len() < 3 + path_length {
			return Err(Error::Message("Invalid protocol message".into()));
		}

		let telemetry_id_len = bytes[2 + path_length] as usize;
		if bytes.len() < 3 + path_length + telemetry_id_len {
			return Err(Error::Message("Invalid protocol message".into()));
		}

		let path = &bytes[2..2 + path_length];
		let telemetry_id = if telemetry_id_len > 0 {
			Some(bytes[3 + path_length..3 + path_length + telemetry_id_len].to_vec())
		} else {
			None
		};

		let body = &bytes[3 + path_length + telemetry_id_len..];

		Ok(Self {
			prio: bytes[0],
			path,
			telemetry_id,
			body,
		})
	}
}

// ---- ----

pub(crate) struct Framing {
	direct: Vec<u8>,
	stream: Option<ByteStream>,
}

impl Framing {
	pub fn new(direct: Vec<u8>, stream: Option<ByteStream>) -> Self {
		assert!(direct.len() <= u32::MAX as usize);
		Framing { direct, stream }
	}

	pub fn into_stream(self) -> ByteStream {
		use futures::stream;
		let len = self.direct.len() as u32;
		// required because otherwise the borrow-checker complains
		let Framing { direct, stream } = self;

		let res = stream::once(async move { Ok(u32::to_be_bytes(len).to_vec().into()) })
			.chain(stream::once(async move { Ok(direct.into()) }));

		if let Some(stream) = stream {
			Box::pin(res.chain(stream))
		} else {
			Box::pin(res)
		}
	}

	pub async fn from_stream<S: Stream<Item = Packet> + Unpin + Send + Sync + 'static>(
		mut stream: S,
	) -> Result<Self, Error> {
		let mut packet = stream
			.next()
			.await
			.ok_or(Error::Framing)?
			.map_err(|_| Error::Framing)?;
		if packet.len() < 4 {
			return Err(Error::Framing);
		}

		let mut len = [0; 4];
		len.copy_from_slice(&packet[..4]);
		let len = u32::from_be_bytes(len);
		packet = packet.slice(4..);

		let mut buffer = Vec::new();
		let len = len as usize;
		loop {
			let max_cp = std::cmp::min(len - buffer.len(), packet.len());

			buffer.extend_from_slice(&packet[..max_cp]);
			if buffer.len() == len {
				packet = packet.slice(max_cp..);
				break;
			}
			packet = stream
				.next()
				.await
				.ok_or(Error::Framing)?
				.map_err(|_| Error::Framing)?;
		}

		let stream: ByteStream = if packet.is_empty() {
			Box::pin(stream)
		} else {
			Box::pin(futures::stream::once(async move { Ok(packet) }).chain(stream))
		};

		Ok(Framing {
			direct: buffer,
			stream: Some(stream),
		})
	}

	pub fn into_parts(self) -> (Vec<u8>, ByteStream) {
		let Framing { direct, stream } = self;
		(direct, stream.unwrap_or(Box::pin(futures::stream::empty())))
	}
}