// This file is part of Substrate.

// Copyright (C) 2020-2022 Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0

// This program 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.

// This program 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 this program. If not, see <https://www.gnu.org/licenses/>.

//! Helper for incoming light client requests.
//!
//! Handle (i.e. answer) incoming light client requests from a remote peer received via
//! `crate::request_responses::RequestResponsesBehaviour` with
//! [`LightClientRequestHandler`](handler::LightClientRequestHandler).

use crate::{
	chain::Client,
	config::ProtocolId,
	request_responses::{IncomingRequest, OutgoingResponse, ProtocolConfig},
	schema, PeerId,
};
use codec::{self, Decode, Encode};
use futures::{channel::mpsc, prelude::*};
use log::{debug, trace};
use prost::Message;
use sc_client_api::StorageProof;
use sc_peerset::ReputationChange;
use sp_core::{
	hexdisplay::HexDisplay,
	storage::{ChildInfo, ChildType, PrefixedStorageKey},
};
use sp_runtime::{generic::BlockId, traits::Block};
use std::sync::Arc;

const LOG_TARGET: &str = "light-client-request-handler";

/// Handler for incoming light client requests from a remote peer.
pub struct LightClientRequestHandler<B: Block> {
	request_receiver: mpsc::Receiver<IncomingRequest>,
	/// Blockchain client.
	client: Arc<dyn Client<B>>,
}

impl<B: Block> LightClientRequestHandler<B> {
	/// Create a new [`crate::block_request_handler::BlockRequestHandler`].
	pub fn new(protocol_id: &ProtocolId, client: Arc<dyn Client<B>>) -> (Self, ProtocolConfig) {
		// For now due to lack of data on light client request handling in production systems, this
		// value is chosen to match the block request limit.
		let (tx, request_receiver) = mpsc::channel(20);

		let mut protocol_config = super::generate_protocol_config(protocol_id);
		protocol_config.inbound_queue = Some(tx);

		(Self { client, request_receiver }, protocol_config)
	}

	/// Run [`LightClientRequestHandler`].
	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(peer, payload) {
				Ok(response_data) => {
					let response = OutgoingResponse {
						result: Ok(response_data),
						reputation_changes: Vec::new(),
						sent_feedback: None,
					};

					match pending_response.send(response) {
						Ok(()) => trace!(
							target: LOG_TARGET,
							"Handled light client request from {}.",
							peer,
						),
						Err(_) => debug!(
							target: LOG_TARGET,
							"Failed to handle light client request from {}: {}",
							peer,
							HandleRequestError::SendResponse,
						),
					};
				},
				Err(e) => {
					debug!(
						target: LOG_TARGET,
						"Failed to handle light client request from {}: {}", peer, e,
					);

					let reputation_changes = match e {
						HandleRequestError::BadRequest(_) => {
							vec![ReputationChange::new(-(1 << 12), "bad request")]
						},
						_ => Vec::new(),
					};

					let response = OutgoingResponse {
						result: Err(()),
						reputation_changes,
						sent_feedback: None,
					};

					if pending_response.send(response).is_err() {
						debug!(
							target: LOG_TARGET,
							"Failed to handle light client request from {}: {}",
							peer,
							HandleRequestError::SendResponse,
						);
					};
				},
			}
		}
	}

	fn handle_request(
		&mut self,
		peer: PeerId,
		payload: Vec<u8>,
	) -> Result<Vec<u8>, HandleRequestError> {
		let request = schema::v1::light::Request::decode(&payload[..])?;

		let response = match &request.request {
			Some(schema::v1::light::request::Request::RemoteCallRequest(r)) =>
				self.on_remote_call_request(&peer, r)?,
			Some(schema::v1::light::request::Request::RemoteReadRequest(r)) =>
				self.on_remote_read_request(&peer, r)?,
			Some(schema::v1::light::request::Request::RemoteHeaderRequest(_r)) =>
				return Err(HandleRequestError::BadRequest("Not supported.")),
			Some(schema::v1::light::request::Request::RemoteReadChildRequest(r)) =>
				self.on_remote_read_child_request(&peer, r)?,
			Some(schema::v1::light::request::Request::RemoteChangesRequest(_r)) =>
				return Err(HandleRequestError::BadRequest("Not supported.")),
			None =>
				return Err(HandleRequestError::BadRequest("Remote request without request data.")),
		};

		let mut data = Vec::new();
		response.encode(&mut data)?;

		Ok(data)
	}

	fn on_remote_call_request(
		&mut self,
		peer: &PeerId,
		request: &schema::v1::light::RemoteCallRequest,
	) -> Result<schema::v1::light::Response, HandleRequestError> {
		trace!("Remote call request from {} ({} at {:?}).", peer, request.method, request.block,);

		let block = Decode::decode(&mut request.block.as_ref())?;

		let proof =
			match self
				.client
				.execution_proof(&BlockId::Hash(block), &request.method, &request.data)
			{
				Ok((_, proof)) => proof,
				Err(e) => {
					trace!(
						"remote call request from {} ({} at {:?}) failed with: {}",
						peer,
						request.method,
						request.block,
						e,
					);
					StorageProof::empty()
				},
			};

		let response = {
			let r = schema::v1::light::RemoteCallResponse { proof: proof.encode() };
			schema::v1::light::response::Response::RemoteCallResponse(r)
		};

		Ok(schema::v1::light::Response { response: Some(response) })
	}

	fn on_remote_read_request(
		&mut self,
		peer: &PeerId,
		request: &schema::v1::light::RemoteReadRequest,
	) -> Result<schema::v1::light::Response, HandleRequestError> {
		if request.keys.is_empty() {
			debug!("Invalid remote read request sent by {}.", peer);
			return Err(HandleRequestError::BadRequest("Remote read request without keys."))
		}

		trace!(
			"Remote read request from {} ({} at {:?}).",
			peer,
			fmt_keys(request.keys.first(), request.keys.last()),
			request.block,
		);

		let block = Decode::decode(&mut request.block.as_ref())?;

		let proof = match self
			.client
			.read_proof(&BlockId::Hash(block), &mut request.keys.iter().map(AsRef::as_ref))
		{
			Ok(proof) => proof,
			Err(error) => {
				trace!(
					"remote read request from {} ({} at {:?}) failed with: {}",
					peer,
					fmt_keys(request.keys.first(), request.keys.last()),
					request.block,
					error,
				);
				StorageProof::empty()
			},
		};

		let response = {
			let r = schema::v1::light::RemoteReadResponse { proof: proof.encode() };
			schema::v1::light::response::Response::RemoteReadResponse(r)
		};

		Ok(schema::v1::light::Response { response: Some(response) })
	}

	fn on_remote_read_child_request(
		&mut self,
		peer: &PeerId,
		request: &schema::v1::light::RemoteReadChildRequest,
	) -> Result<schema::v1::light::Response, HandleRequestError> {
		if request.keys.is_empty() {
			debug!("Invalid remote child read request sent by {}.", peer);
			return Err(HandleRequestError::BadRequest("Remove read child request without keys."))
		}

		trace!(
			"Remote read child request from {} ({} {} at {:?}).",
			peer,
			HexDisplay::from(&request.storage_key),
			fmt_keys(request.keys.first(), request.keys.last()),
			request.block,
		);

		let block = Decode::decode(&mut request.block.as_ref())?;

		let prefixed_key = PrefixedStorageKey::new_ref(&request.storage_key);
		let child_info = match ChildType::from_prefixed_key(prefixed_key) {
			Some((ChildType::ParentKeyId, storage_key)) => Ok(ChildInfo::new_default(storage_key)),
			None => Err(sp_blockchain::Error::InvalidChildStorageKey),
		};
		let proof = match child_info.and_then(|child_info| {
			self.client.read_child_proof(
				&BlockId::Hash(block),
				&child_info,
				&mut request.keys.iter().map(AsRef::as_ref),
			)
		}) {
			Ok(proof) => proof,
			Err(error) => {
				trace!(
					"remote read child request from {} ({} {} at {:?}) failed with: {}",
					peer,
					HexDisplay::from(&request.storage_key),
					fmt_keys(request.keys.first(), request.keys.last()),
					request.block,
					error,
				);
				StorageProof::empty()
			},
		};

		let response = {
			let r = schema::v1::light::RemoteReadResponse { proof: proof.encode() };
			schema::v1::light::response::Response::RemoteReadResponse(r)
		};

		Ok(schema::v1::light::Response { response: Some(response) })
	}
}

#[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 send response.")]
	SendResponse,
	/// A bad request has been received.
	#[error("bad request: {0}")]
	BadRequest(&'static str),
	/// Encoding or decoding of some data failed.
	#[error("codec error: {0}")]
	Codec(#[from] codec::Error),
}

fn fmt_keys(first: Option<&Vec<u8>>, last: Option<&Vec<u8>>) -> String {
	if let (Some(first), Some(last)) = (first, last) {
		if first == last {
			HexDisplay::from(first).to_string()
		} else {
			format!("{}..{}", HexDisplay::from(first), HexDisplay::from(last))
		}
	} else {
		String::from("n/a")
	}
}
