// Copyright 2019-2020 Parity Technologies (UK) Ltd.
//
// Permission is hereby granted, free of charge, to any
// person obtaining a copy of this software and associated
// documentation files (the "Software"), to deal in the
// Software without restriction, including without
// limitation the rights to use, copy, modify, merge,
// publish, distribute, sublicense, and/or sell copies of
// the Software, and to permit persons to whom the Software
// is furnished to do so, subject to the following
// conditions:
//
// The above copyright notice and this permission notice
// shall be included in all copies or substantial portions
// of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
// ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
// TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
// PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
// SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
// CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
// IN background_task WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.

use futures_channel::mpsc;
use futures_util::io::{BufReader, BufWriter};
use futures_util::stream::StreamExt;
use jsonrpsee_types::TEN_MB_SIZE_BYTES;
use soketto::handshake::{server::Response, Server as SokettoServer};
use std::{net::SocketAddr, sync::Arc};
use tokio::net::{TcpListener, ToSocketAddrs};
use tokio_stream::wrappers::TcpListenerStream;
use tokio_util::compat::TokioAsyncReadCompatExt;

use jsonrpsee_types::error::Error;
use jsonrpsee_types::v2::error::JsonRpcErrorCode;
use jsonrpsee_types::v2::params::Id;
use jsonrpsee_types::v2::request::{JsonRpcInvalidRequest, JsonRpcRequest};
use jsonrpsee_utils::server::helpers::{collect_batch_response, send_error};
use jsonrpsee_utils::server::rpc_module::{ConnectionId, Methods, RpcModule};

/// Default maximum connections allowed.
const MAX_CONNECTIONS: u64 = 100;

/// A WebSocket JSON RPC server.
#[derive(Debug)]
pub struct Server {
	methods: Methods,
	listener: TcpListener,
	cfg: Settings,
}

impl Server {
	/// Register all methods from a [`Methods`] of provided [`RpcModule`] on this server.
	/// In case a method already is registered with the same name, no method is added and a [`Error::MethodAlreadyRegistered`]
	/// is returned. Note that the [`RpcModule`] is consumed after this call.
	pub fn register_module<Context>(&mut self, module: RpcModule<Context>) -> Result<(), Error> {
		self.methods.merge(module.into_methods())?;
		Ok(())
	}

	/// Returns a `Vec` with all the method names registered on this server.
	pub fn method_names(&self) -> Vec<&'static str> {
		self.methods.method_names()
	}

	/// Returns socket address to which the server is bound.
	pub fn local_addr(&self) -> Result<SocketAddr, Error> {
		self.listener.local_addr().map_err(Into::into)
	}

	/// Start responding to connections requests. This will block current thread until the server is stopped.
	pub async fn start(self) {
		let mut incoming = TcpListenerStream::new(self.listener);
		let methods = self.methods;
		let conn_counter = Arc::new(());
		let cfg = self.cfg;
		let mut id = 0;

		while let Some(socket) = incoming.next().await {
			if let Ok(socket) = socket {
				socket.set_nodelay(true).unwrap_or_else(|e| panic!("Could not set NODELAY on socket: {:?}", e));

				if Arc::strong_count(&conn_counter) > self.cfg.max_connections as usize {
					log::warn!("Too many connections. Try again in a while");
					continue;
				}
				let methods = methods.clone();
				let counter = conn_counter.clone();

				tokio::spawn(async move {
					let r = background_task(socket, id, methods, cfg).await;
					drop(counter);
					r
				});

				id += 1;
			}
		}
	}
}

async fn background_task(
	socket: tokio::net::TcpStream,
	conn_id: ConnectionId,
	methods: Methods,
	cfg: Settings,
) -> Result<(), Error> {
	// For each incoming background_task we perform a handshake.
	let mut server = SokettoServer::new(BufReader::new(BufWriter::new(socket.compat())));

	let websocket_key = {
		let req = server.receive_request().await?;
		req.into_key()
	};

	// Here we accept the client unconditionally.
	let accept = Response::Accept { key: &websocket_key, protocol: None };
	server.send_response(&accept).await?;

	// And we can finally transition to a websocket background_task.
	let (mut sender, mut receiver) = server.into_builder().finish();
	let (tx, mut rx) = mpsc::unbounded::<String>();

	// Send results back to the client.
	tokio::spawn(async move {
		while let Some(response) = rx.next().await {
			log::debug!("send: {}", response);
			let _ = sender.send_text(response).await;
			let _ = sender.flush().await;
		}
	});

	// Buffer for incoming data.
	let mut data = Vec::with_capacity(100);

	loop {
		data.clear();

		receiver.receive_data(&mut data).await?;

		if data.len() > cfg.max_request_body_size as usize {
			log::warn!("Request is too big ({} bytes, max is {})", data.len(), cfg.max_request_body_size);
			send_error(Id::Null, &tx, JsonRpcErrorCode::OversizedRequest.into());
			continue;
		}

		// For reasons outlined [here](https://github.com/serde-rs/json/issues/497), `RawValue` can't be used with
		// untagged enums at the moment. This means we can't use an `SingleOrBatch` untagged enum here and have to try
		// each case individually: first the single request case, then the batch case and lastly the error. For the
		// worst case – unparseable input – we make three calls to [`serde_json::from_slice`] which is pretty annoying.
		// Our [issue](https://github.com/paritytech/jsonrpsee/issues/296).
		if let Ok(req) = serde_json::from_slice::<JsonRpcRequest>(&data) {
			log::debug!("recv: {:?}", req);
			methods.execute(&tx, req, conn_id).await;
		} else if let Ok(batch) = serde_json::from_slice::<Vec<JsonRpcRequest>>(&data) {
			if !batch.is_empty() {
				// Batch responses must be sent back as a single message so we read the results from each request in the
				// batch and read the results off of a new channel, `rx_batch`, and then send the complete batch response
				// back to the client over `tx`.
				let (tx_batch, mut rx_batch) = mpsc::unbounded::<String>();
				for req in batch {
					methods.execute(&tx_batch, req, conn_id).await;
				}
				// Closes the receiving half of a channel without dropping it. This prevents any further messages from
				// being sent on the channel.
				rx_batch.close();
				let results = collect_batch_response(rx_batch).await;
				if let Err(err) = tx.unbounded_send(results) {
					log::error!("Error sending batch response to the client: {:?}", err)
				}
			} else {
				send_error(Id::Null, &tx, JsonRpcErrorCode::InvalidRequest.into());
			}
		} else {
			let (id, code) = match serde_json::from_slice::<JsonRpcInvalidRequest>(&data) {
				Ok(req) => (req.id, JsonRpcErrorCode::InvalidRequest),
				Err(_) => (Id::Null, JsonRpcErrorCode::ParseError),
			};

			send_error(id, &tx, code.into());
		}
	}
}

/// JSON-RPC Websocket server settings.
#[derive(Debug, Clone, Copy)]
struct Settings {
	/// Maximum size in bytes of a request.
	max_request_body_size: u32,
	/// Maximum number of incoming connections allowed.
	max_connections: u64,
}

impl Default for Settings {
	fn default() -> Self {
		Self { max_request_body_size: TEN_MB_SIZE_BYTES, max_connections: MAX_CONNECTIONS }
	}
}

/// Builder to configure and create a JSON-RPC Websocket server
#[derive(Debug)]
pub struct Builder {
	settings: Settings,
}

impl Builder {
	/// Set the maximum size of a request body in bytes. Default is 10 MiB.
	pub fn max_request_body_size(mut self, size: u32) -> Self {
		self.settings.max_request_body_size = size;
		self
	}

	/// Set the maximum number of connections allowed. Default is 100.
	pub fn max_connections(mut self, max: u64) -> Self {
		self.settings.max_connections = max;
		self
	}

	/// Finalize the configuration of the server. Consumes the [`Builder`].
	pub async fn build(self, addr: impl ToSocketAddrs) -> Result<Server, Error> {
		let listener = TcpListener::bind(addr).await?;
		Ok(Server { listener, methods: Methods::default(), cfg: self.settings })
	}
}

impl Default for Builder {
	fn default() -> Self {
		Self { settings: Settings::default() }
	}
}