// Copyright 2019-2020 Parity Technologies (UK) Ltd.
// This file is part of Parity Bridges Common.

// Parity Bridges Common 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.

// Parity Bridges Common 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 Parity Bridges Common.  If not, see <http://www.gnu.org/licenses/>.

use codec::{Decode, Encode};
use ethereum_types::U256;
use finality_grandpa::voter_set::VoterSet;
use rialto_runtime::{Block, BlockNumber, Hash, Header as RuntimeHeader};
use sp_blockchain::Error as ClientError;
use sp_finality_grandpa::{AuthorityList, ConsensusLog, GRANDPA_ENGINE_ID};

/// Builtin errors.
#[derive(Debug)]
pub enum Error {
	/// Failed to decode block number.
	BlockNumberDecode,
	/// Failed to decode Substrate header.
	HeaderDecode(codec::Error),
	/// Failed to decode best voters set.
	BestSetDecode(codec::Error),
	/// Best voters set is invalid.
	InvalidBestSet,
	/// Failed to decode finality proof.
	FinalityProofDecode(codec::Error),
	/// Failed to verify justification.
	JustificationVerify(Box<ClientError>),
}

/// Substrate header.
#[derive(Debug, PartialEq)]
pub struct Header {
	/// Header hash.
	pub hash: Hash,
	/// Parent header hash.
	pub parent_hash: Hash,
	/// Header number.
	pub number: BlockNumber,
	/// GRANDPA validators change signal.
	pub signal: Option<ValidatorsSetSignal>,
}

/// GRANDPA validators set change signal.
#[derive(Debug, PartialEq)]
pub struct ValidatorsSetSignal {
	/// Signal delay.
	pub delay: BlockNumber,
	/// New validators set.
	pub validators: Vec<u8>,
}

/// Convert from U256 to BlockNumber. Fails if `U256` value isn't fitting within `BlockNumber`
/// limits (the runtime referenced by this module uses u32 as `BlockNumber`).
pub fn to_substrate_block_number(number: U256) -> Result<BlockNumber, Error> {
	let substrate_block_number = match number == number.low_u32().into() {
		true => Ok(number.low_u32()),
		false => Err(Error::BlockNumberDecode),
	};

	log::trace!(
		target: "bridge-builtin",
		"Parsed Substrate block number from {}: {:?}",
		number,
		substrate_block_number,
	);

	substrate_block_number
}

/// Convert from BlockNumber to U256.
pub fn from_substrate_block_number(number: BlockNumber) -> Result<U256, Error> {
	Ok(U256::from(number as u64))
}

/// Parse Substrate header.
pub fn parse_substrate_header(raw_header: &[u8]) -> Result<Header, Error> {
	let substrate_header = RuntimeHeader::decode(&mut &*raw_header)
		.map(|header| Header {
			hash: header.hash(),
			parent_hash: header.parent_hash,
			number: header.number,
			signal: sp_runtime::traits::Header::digest(&header)
				.log(|log| {
					log.as_consensus().and_then(|(engine_id, log)| {
						if engine_id == GRANDPA_ENGINE_ID {
							Some(log)
						} else {
							None
						}
					})
				})
				.and_then(|log| ConsensusLog::decode(&mut &*log).ok())
				.and_then(|log| match log {
					ConsensusLog::ScheduledChange(scheduled_change) => Some(ValidatorsSetSignal {
						delay: scheduled_change.delay,
						validators: scheduled_change.next_authorities.encode(),
					}),
					_ => None,
				}),
		})
		.map_err(Error::HeaderDecode);

	log::debug!(
		target: "bridge-builtin",
		"Parsed Substrate header {}: {:?}",
		if substrate_header.is_ok() {
			format!("<{}-bytes-blob>", raw_header.len())
		} else {
			hex::encode(raw_header)
		},
		substrate_header,
	);

	substrate_header
}

/// Verify GRANDPA finality proof.
pub fn verify_substrate_finality_proof(
	finality_target_number: BlockNumber,
	finality_target_hash: Hash,
	best_set_id: u64,
	raw_best_set: &[u8],
	raw_finality_proof: &[u8],
) -> Result<(), Error> {
	let best_set = AuthorityList::decode(&mut &*raw_best_set)
		.map_err(Error::BestSetDecode)
		.and_then(|authorities| VoterSet::new(authorities.into_iter()).ok_or(Error::InvalidBestSet));

	log::debug!(
		target: "bridge-builtin",
		"Parsed Substrate authorities set {}: {:?}",
		if best_set.is_ok() {
			format!("<{}-bytes-blob>", raw_best_set.len())
		} else {
			hex::encode(raw_best_set)
		},
		best_set,
	);

	let best_set = best_set?;

	let verify_result = sc_finality_grandpa::GrandpaJustification::<Block>::decode_and_verify_finalizes(
		&raw_finality_proof,
		(finality_target_hash, finality_target_number),
		best_set_id,
		&best_set,
	)
	.map_err(Box::new)
	.map_err(Error::JustificationVerify)
	.map(|_| ());

	log::debug!(
		target: "bridge-builtin",
		"Verified Substrate finality proof {}: {:?}",
		if verify_result.is_ok() {
			format!("<{}-bytes-blob>", raw_finality_proof.len())
		} else {
			hex::encode(raw_finality_proof)
		},
		verify_result,
	);

	verify_result
}

#[cfg(test)]
mod tests {
	use super::*;
	use rialto_runtime::DigestItem;
	use sp_core::crypto::Public;
	use sp_finality_grandpa::{AuthorityId, ScheduledChange};
	use sp_runtime::generic::Digest;

	#[test]
	fn to_substrate_block_number_succeeds() {
		assert_eq!(to_substrate_block_number(U256::zero()).unwrap(), 0);
		assert_eq!(
			to_substrate_block_number(U256::from(std::u32::MAX as u64)).unwrap(),
			0xFFFFFFFF
		);
	}

	#[test]
	fn to_substrate_block_number_fails() {
		assert!(matches!(
			to_substrate_block_number(U256::from(std::u32::MAX as u64 + 1)),
			Err(Error::BlockNumberDecode)
		));
	}

	#[test]
	fn from_substrate_block_number_succeeds() {
		assert_eq!(from_substrate_block_number(0).unwrap(), U256::zero());
		assert_eq!(
			from_substrate_block_number(std::u32::MAX).unwrap(),
			U256::from(std::u32::MAX)
		);
	}

	#[test]
	fn substrate_header_without_signal_parsed() {
		let raw_header = RuntimeHeader {
			parent_hash: [0u8; 32].into(),
			number: 0,
			state_root: "b2fc47904df5e355c6ab476d89fbc0733aeddbe302f0b94ba4eea9283f7e89e7"
				.parse()
				.unwrap(),
			extrinsics_root: "03170a2e7597b7b7e3d84c05391d139a62b157e78786d8c082f29dcf4c111314"
				.parse()
				.unwrap(),
			digest: Default::default(),
		}
		.encode();
		assert_eq!(
			raw_header,
			hex::decode("000000000000000000000000000000000000000000000000000000000000000000b2fc47904df5e355c6ab476d89fbc0733aeddbe302f0b94ba4eea9283f7e89e703170a2e7597b7b7e3d84c05391d139a62b157e78786d8c082f29dcf4c11131400").unwrap(),
		);

		assert_eq!(
			parse_substrate_header(&raw_header).unwrap(),
			Header {
				hash: "afbbeb92bf6ff14f60bdef0aa89f043dd403659ae82665238810ace0d761f6d0"
					.parse()
					.unwrap(),
				parent_hash: Default::default(),
				number: 0,
				signal: None,
			},
		);
	}

	#[test]
	fn substrate_header_with_signal_parsed() {
		let authorities = vec![
			(AuthorityId::from_slice(&[1; 32]), 101),
			(AuthorityId::from_slice(&[3; 32]), 103),
		];
		let mut digest = Digest::default();
		digest.push(DigestItem::Consensus(
			GRANDPA_ENGINE_ID,
			ConsensusLog::ScheduledChange(ScheduledChange {
				next_authorities: authorities.clone(),
				delay: 8,
			})
			.encode(),
		));

		let raw_header = RuntimeHeader {
			parent_hash: "c0ac300d4005141ea690f3df593e049739c227316eb7f05052f3ee077388b68b"
				.parse()
				.unwrap(),
			number: 8,
			state_root: "822d6b412033aa9ac8e1722918eec5f25633529225754b3d4149982f5cacd4aa"
				.parse()
				.unwrap(),
			extrinsics_root: "e7b07c0ce2799416ce7877b9cefc7f596bea5e8813bb2a0abf760414073ca928"
				.parse()
				.unwrap(),
			digest,
		}
		.encode();
		assert_eq!(
			raw_header,
			hex::decode("c0ac300d4005141ea690f3df593e049739c227316eb7f05052f3ee077388b68b20822d6b412033aa9ac8e1722918eec5f25633529225754b3d4149982f5cacd4aae7b07c0ce2799416ce7877b9cefc7f596bea5e8813bb2a0abf760414073ca928040446524e4b59010108010101010101010101010101010101010101010101010101010101010101010165000000000000000303030303030303030303030303030303030303030303030303030303030303670000000000000008000000").unwrap(),
		);

		assert_eq!(
			parse_substrate_header(&raw_header).unwrap(),
			Header {
				hash: "3dfebb280bd87a4640f89d7f2adecd62b88148747bff5b63af6e1634ee37a56e"
					.parse()
					.unwrap(),
				parent_hash: "c0ac300d4005141ea690f3df593e049739c227316eb7f05052f3ee077388b68b"
					.parse()
					.unwrap(),
				number: 8,
				signal: Some(ValidatorsSetSignal {
					delay: 8,
					validators: authorities.encode(),
				}),
			},
		);
	}

	/// Number of the example block with justification.
	const EXAMPLE_JUSTIFIED_BLOCK_NUMBER: u32 = 8;
	/// Hash of the example block with justification.
	const EXAMPLE_JUSTIFIED_BLOCK_HASH: &str = "a2f45892db86b2ad133ce57d81b7e4375bb7035ce9883e6b68c358164f343775";
	/// Id of authorities set that have generated example justification. Could be computed by tracking
	/// every set change in canonized headers.
	const EXAMPLE_AUTHORITIES_SET_ID: u64 = 0;
	/// Encoded authorities set that has generated example justification. Could be fetched from `ScheduledChange`
	/// digest of the block that has scheduled this set OR by calling `GrandpaApi::grandpa_authorities()` at
	/// appropriate block.
	const EXAMPLE_AUTHORITIES_SET: &str = "1488dc3417d5058ec4b4503e0c12ea1a0a89be200fe98922423d4334014fa6b0ee0100000000000000d17c2d7823ebf260fd138f2d7e27d114c0145d968b5ff5006125f2414fadae690100000000000000439660b36c6c03afafca027b910b4fecf99801834c62a5e6006f27d978de234f01000000000000005e639b43e0052c47447dac87d6fd2b6ec50bdd4d0f614e4299c665249bbd09d901000000000000001dfe3e22cc0d45c70779c1095f7489a8ef3cf52d62fbd8c2fa38c9f1723502b50100000000000000";
	/// Example justification. Could be fetched by calling 'chain_getBlock' RPC.
	const EXAMPLE_JUSTIFICATION: &str = "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";

	#[test]
	fn substrate_header_parse_fails() {
		assert!(matches!(parse_substrate_header(&[]), Err(_)));
	}

	#[test]
	fn verify_substrate_finality_proof_succeeds() {
		verify_substrate_finality_proof(
			EXAMPLE_JUSTIFIED_BLOCK_NUMBER,
			EXAMPLE_JUSTIFIED_BLOCK_HASH.parse().unwrap(),
			EXAMPLE_AUTHORITIES_SET_ID,
			&hex::decode(EXAMPLE_AUTHORITIES_SET).unwrap(),
			&hex::decode(EXAMPLE_JUSTIFICATION).unwrap(),
		)
		.unwrap();
	}

	#[test]
	fn verify_substrate_finality_proof_fails_when_wrong_block_is_finalized() {
		verify_substrate_finality_proof(
			4,
			Default::default(),
			EXAMPLE_AUTHORITIES_SET_ID,
			&hex::decode(EXAMPLE_AUTHORITIES_SET).unwrap(),
			&hex::decode(EXAMPLE_JUSTIFICATION).unwrap(),
		)
		.unwrap_err();
	}

	#[test]
	fn verify_substrate_finality_proof_fails_when_wrong_set_is_provided() {
		verify_substrate_finality_proof(
			EXAMPLE_JUSTIFIED_BLOCK_NUMBER,
			EXAMPLE_JUSTIFIED_BLOCK_HASH.parse().unwrap(),
			EXAMPLE_AUTHORITIES_SET_ID,
			&hex::decode("deadbeef").unwrap(),
			&hex::decode(EXAMPLE_JUSTIFICATION).unwrap(),
		)
		.unwrap_err();
	}

	#[test]
	fn verify_substrate_finality_proof_fails_when_wrong_set_id_is_provided() {
		verify_substrate_finality_proof(
			EXAMPLE_JUSTIFIED_BLOCK_NUMBER,
			EXAMPLE_JUSTIFIED_BLOCK_HASH.parse().unwrap(),
			42,
			&hex::decode(EXAMPLE_AUTHORITIES_SET).unwrap(),
			&hex::decode(EXAMPLE_JUSTIFICATION).unwrap(),
		)
		.unwrap_err();
	}

	#[test]
	fn verify_substrate_finality_proof_fails_when_wrong_proof_is_provided() {
		verify_substrate_finality_proof(
			EXAMPLE_JUSTIFIED_BLOCK_NUMBER,
			EXAMPLE_JUSTIFIED_BLOCK_HASH.parse().unwrap(),
			0,
			&hex::decode(EXAMPLE_AUTHORITIES_SET).unwrap(),
			&hex::decode("deadbeef").unwrap(),
		)
		.unwrap_err();
	}
}