// Copyright 2021 Parity Technologies (UK) Ltd.
// This file is part of Substrate.

// Substrate is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Substrate is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.

//! Helper for handling (i.e. answering) grandpa warp sync requests from a remote peer.

use crate::config::{IncomingRequest, OutgoingResponse, ProtocolId, RequestResponseConfig};
use codec::{Decode, Encode};
use futures::{
	channel::{mpsc, oneshot},
	stream::StreamExt,
};
use log::debug;
use sp_runtime::traits::Block as BlockT;
use std::{sync::Arc, time::Duration};

pub use sp_finality_grandpa::{AuthorityList, SetId};

/// Scale-encoded warp sync proof response.
pub struct EncodedProof(pub Vec<u8>);

/// Warp sync request
#[derive(Encode, Decode, Debug)]
pub struct Request<B: BlockT> {
	/// Start collecting proofs from this block.
	pub begin: B::Hash,
}

const MAX_RESPONSE_SIZE: u64 = 16 * 1024 * 1024;

/// Proof verification result.
pub enum VerificationResult<Block: BlockT> {
	/// Proof is valid, but the target was not reached.
	Partial(SetId, AuthorityList, Block::Hash),
	/// Target finality is proved.
	Complete(SetId, AuthorityList, Block::Header),
}

/// Warp sync backend. Handles retrieveing and verifying warp sync proofs.
pub trait WarpSyncProvider<B: BlockT>: Send + Sync {
	/// Generate proof starting at given block hash. The proof is accumulated until maximum proof
	/// size is reached.
	fn generate(
		&self,
		start: B::Hash,
	) -> Result<EncodedProof, Box<dyn std::error::Error + Send + Sync>>;
	/// Verify warp proof against current set of authorities.
	fn verify(
		&self,
		proof: &EncodedProof,
		set_id: SetId,
		authorities: AuthorityList,
	) -> Result<VerificationResult<B>, Box<dyn std::error::Error + Send + Sync>>;
	/// Get current list of authorities. This is supposed to be genesis authorities when starting
	/// sync.
	fn current_authorities(&self) -> AuthorityList;
}

/// Generates a [`RequestResponseConfig`] for the grandpa warp sync request protocol, refusing
/// incoming requests.
pub fn generate_request_response_config(protocol_id: ProtocolId) -> RequestResponseConfig {
	RequestResponseConfig {
		name: generate_protocol_name(protocol_id).into(),
		max_request_size: 32,
		max_response_size: MAX_RESPONSE_SIZE,
		request_timeout: Duration::from_secs(10),
		inbound_queue: None,
	}
}

/// Generate the grandpa warp sync protocol name from chain specific protocol identifier.
fn generate_protocol_name(protocol_id: ProtocolId) -> String {
	let mut s = String::new();
	s.push_str("/");
	s.push_str(protocol_id.as_ref());
	s.push_str("/sync/warp");
	s
}

/// Handler for incoming grandpa warp sync requests from a remote peer.
pub struct RequestHandler<TBlock: BlockT> {
	backend: Arc<dyn WarpSyncProvider<TBlock>>,
	request_receiver: mpsc::Receiver<IncomingRequest>,
}

impl<TBlock: BlockT> RequestHandler<TBlock> {
	/// Create a new [`RequestHandler`].
	pub fn new(
		protocol_id: ProtocolId,
		backend: Arc<dyn WarpSyncProvider<TBlock>>,
	) -> (Self, RequestResponseConfig) {
		let (tx, request_receiver) = mpsc::channel(20);

		let mut request_response_config = generate_request_response_config(protocol_id);
		request_response_config.inbound_queue = Some(tx);

		(Self { backend, request_receiver }, request_response_config)
	}

	fn handle_request(
		&self,
		payload: Vec<u8>,
		pending_response: oneshot::Sender<OutgoingResponse>,
	) -> Result<(), HandleRequestError> {
		let request = Request::<TBlock>::decode(&mut &payload[..])?;

		let EncodedProof(proof) = self
			.backend
			.generate(request.begin)
			.map_err(HandleRequestError::InvalidRequest)?;

		pending_response
			.send(OutgoingResponse {
				result: Ok(proof),
				reputation_changes: Vec::new(),
				sent_feedback: None,
			})
			.map_err(|_| HandleRequestError::SendResponse)
	}

	/// Run [`RequestHandler`].
	pub async fn run(mut self) {
		while let Some(request) = self.request_receiver.next().await {
			let IncomingRequest { peer, payload, pending_response } = request;

			match self.handle_request(payload, pending_response) {
				Ok(()) => {
					debug!(target: "sync", "Handled grandpa warp sync request from {}.", peer)
				},
				Err(e) => debug!(
					target: "sync",
					"Failed to handle grandpa warp sync request from {}: {}",
					peer, e,
				),
			}
		}
	}
}

#[derive(Debug, thiserror::Error)]
enum HandleRequestError {
	#[error("Failed to decode request: {0}.")]
	DecodeProto(#[from] prost::DecodeError),

	#[error("Failed to encode response: {0}.")]
	EncodeProto(#[from] prost::EncodeError),

	#[error("Failed to decode block hash: {0}.")]
	DecodeScale(#[from] codec::Error),

	#[error(transparent)]
	Client(#[from] sp_blockchain::Error),

	#[error("Invalid request {0}.")]
	InvalidRequest(#[from] Box<dyn std::error::Error + Send + Sync>),

	#[error("Failed to send response.")]
	SendResponse,
}
