pezkuwi-subxt/bridges/bin/runtime-common/src/messages.rs

// Copyright 2019-2021 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/>.

//! Types that allow runtime to act as a source/target endpoint of message lanes.
//!
//! Messages are assumed to be encoded `Call`s of the target chain. Call-dispatch
//! pallet is used to dispatch incoming messages. Message identified by a tuple
//! of to elements - message lane id and message nonce.

use bp_messages::{
	source_chain::LaneMessageVerifier,
	target_chain::{DispatchMessage, MessageDispatch, ProvedLaneMessages, ProvedMessages},
	InboundLaneData, LaneId, Message, MessageData, MessageKey, MessageNonce, OutboundLaneData,
};
use bp_polkadot_core::parachains::{ParaHash, ParaHasher, ParaId};
use bp_runtime::{messages::MessageDispatchResult, ChainId, Size, StorageProofChecker};
use codec::{Decode, DecodeLimit, Encode, MaxEncodedLen};
use frame_support::{traits::Get, weights::Weight, RuntimeDebug};
use hash_db::Hasher;
use scale_info::TypeInfo;
use sp_runtime::{
	traits::{AtLeast32BitUnsigned, CheckedAdd, CheckedDiv, CheckedMul, Header as HeaderT},
	FixedPointNumber, FixedPointOperand, FixedU128,
};
use sp_std::{cmp::PartialOrd, convert::TryFrom, fmt::Debug, marker::PhantomData, vec::Vec};
use sp_trie::StorageProof;
use xcm::latest::prelude::*;

/// Bidirectional message bridge.
pub trait MessageBridge {
	/// Relayer interest (in percents).
	const RELAYER_FEE_PERCENT: u32;

	/// Identifier of this chain.
	const THIS_CHAIN_ID: ChainId;
	/// Identifier of the Bridged chain.
	const BRIDGED_CHAIN_ID: ChainId;
	/// Name of the paired messages pallet instance at the Bridged chain.
	///
	/// Should be the name that is used in the `construct_runtime!()` macro.
	const BRIDGED_MESSAGES_PALLET_NAME: &'static str;

	/// This chain in context of message bridge.
	type ThisChain: ThisChainWithMessages;
	/// Bridged chain in context of message bridge.
	type BridgedChain: BridgedChainWithMessages;

	/// Convert Bridged chain balance into This chain balance.
	fn bridged_balance_to_this_balance(
		bridged_balance: BalanceOf<BridgedChain<Self>>,
		bridged_to_this_conversion_rate_override: Option<FixedU128>,
	) -> BalanceOf<ThisChain<Self>>;
}

/// Chain that has `pallet-bridge-messages` and `dispatch` modules.
pub trait ChainWithMessages {
	/// Hash used in the chain.
	type Hash: Decode;
	/// Accound id on the chain.
	type AccountId: Encode + Decode + MaxEncodedLen;
	/// Public key of the chain account that may be used to verify signatures.
	type Signer: Encode + Decode;
	/// Signature type used on the chain.
	type Signature: Encode + Decode;
	/// Type of weight that is used on the chain. This would almost always be a regular
	/// `frame_support::weight::Weight`. But since the meaning of weight on different chains
	/// may be different, the `WeightOf<>` construct is used to avoid confusion between
	/// different weights.
	type Weight: From<frame_support::weights::Weight> + PartialOrd;
	/// Type of balances that is used on the chain.
	type Balance: Encode
		+ Decode
		+ CheckedAdd
		+ CheckedDiv
		+ CheckedMul
		+ PartialOrd
		+ From<u32>
		+ Copy;
}

/// Message related transaction parameters estimation.
#[derive(RuntimeDebug)]
pub struct MessageTransaction<Weight> {
	/// The estimated dispatch weight of the transaction.
	pub dispatch_weight: Weight,
	/// The estimated size of the encoded transaction.
	pub size: u32,
}

/// Helper trait for estimating the size and weight of a single message delivery confirmation
/// transaction.
pub trait ConfirmationTransactionEstimation<Weight> {
	// Estimate size and weight of single message delivery confirmation transaction.
	fn estimate_delivery_confirmation_transaction() -> MessageTransaction<Weight>;
}

/// Default implementation for `ConfirmationTransactionEstimation`.
pub struct BasicConfirmationTransactionEstimation<
	AccountId: MaxEncodedLen,
	const MAX_CONFIRMATION_TX_WEIGHT: Weight,
	const EXTRA_STORAGE_PROOF_SIZE: u32,
	const TX_EXTRA_BYTES: u32,
>(PhantomData<AccountId>);

impl<
		AccountId: MaxEncodedLen,
		const MAX_CONFIRMATION_TX_WEIGHT: Weight,
		const EXTRA_STORAGE_PROOF_SIZE: u32,
		const TX_EXTRA_BYTES: u32,
	> ConfirmationTransactionEstimation<Weight>
	for BasicConfirmationTransactionEstimation<
		AccountId,
		MAX_CONFIRMATION_TX_WEIGHT,
		EXTRA_STORAGE_PROOF_SIZE,
		TX_EXTRA_BYTES,
	>
{
	fn estimate_delivery_confirmation_transaction() -> MessageTransaction<Weight> {
		let inbound_data_size = InboundLaneData::<AccountId>::encoded_size_hint_u32(1, 1);
		MessageTransaction {
			dispatch_weight: MAX_CONFIRMATION_TX_WEIGHT,
			size: inbound_data_size
				.saturating_add(EXTRA_STORAGE_PROOF_SIZE)
				.saturating_add(TX_EXTRA_BYTES),
		}
	}
}

/// This chain that has `pallet-bridge-messages` and `dispatch` modules.
pub trait ThisChainWithMessages: ChainWithMessages {
	/// Call origin on the chain.
	type Origin;
	/// Call type on the chain.
	type Call: Encode + Decode;
	/// Helper for estimating the size and weight of a single message delivery confirmation
	/// transaction at this chain.
	type ConfirmationTransactionEstimation: ConfirmationTransactionEstimation<WeightOf<Self>>;

	/// Do we accept message sent by given origin to given lane?
	fn is_message_accepted(origin: &Self::Origin, lane: &LaneId) -> bool;

	/// Maximal number of pending (not yet delivered) messages at This chain.
	///
	/// Any messages over this limit, will be rejected.
	fn maximal_pending_messages_at_outbound_lane() -> MessageNonce;

	/// Estimate size and weight of single message delivery confirmation transaction at This chain.
	fn estimate_delivery_confirmation_transaction() -> MessageTransaction<WeightOf<Self>> {
		Self::ConfirmationTransactionEstimation::estimate_delivery_confirmation_transaction()
	}

	/// Returns minimal transaction fee that must be paid for given transaction at This chain.
	fn transaction_payment(transaction: MessageTransaction<WeightOf<Self>>) -> BalanceOf<Self>;
}

/// Bridged chain that has `pallet-bridge-messages` and `dispatch` modules.
pub trait BridgedChainWithMessages: ChainWithMessages {
	/// Maximal extrinsic size at Bridged chain.
	fn maximal_extrinsic_size() -> u32;

	/// Returns `true` if message dispatch weight is withing expected limits. `false` means
	/// that the message is too heavy to be sent over the bridge and shall be rejected.
	fn verify_dispatch_weight(message_payload: &[u8]) -> bool;

	/// Estimate size and weight of single message delivery transaction at the Bridged chain.
	fn estimate_delivery_transaction(
		message_payload: &[u8],
		include_pay_dispatch_fee_cost: bool,
		message_dispatch_weight: WeightOf<Self>,
	) -> MessageTransaction<WeightOf<Self>>;

	/// Returns minimal transaction fee that must be paid for given transaction at the Bridged
	/// chain.
	fn transaction_payment(transaction: MessageTransaction<WeightOf<Self>>) -> BalanceOf<Self>;
}

/// This chain in context of message bridge.
pub type ThisChain<B> = <B as MessageBridge>::ThisChain;
/// Bridged chain in context of message bridge.
pub type BridgedChain<B> = <B as MessageBridge>::BridgedChain;
/// Hash used on the chain.
pub type HashOf<C> = <C as ChainWithMessages>::Hash;
/// Account id used on the chain.
pub type AccountIdOf<C> = <C as ChainWithMessages>::AccountId;
/// Public key of the chain account that may be used to verify signature.
pub type SignerOf<C> = <C as ChainWithMessages>::Signer;
/// Signature type used on the chain.
pub type SignatureOf<C> = <C as ChainWithMessages>::Signature;
/// Type of weight that used on the chain.
pub type WeightOf<C> = <C as ChainWithMessages>::Weight;
/// Type of balances that is used on the chain.
pub type BalanceOf<C> = <C as ChainWithMessages>::Balance;
/// Type of origin that is used on the chain.
pub type OriginOf<C> = <C as ThisChainWithMessages>::Origin;
/// Type of call that is used on this chain.
pub type CallOf<C> = <C as ThisChainWithMessages>::Call;

/// Raw storage proof type (just raw trie nodes).
pub type RawStorageProof = Vec<Vec<u8>>;

/// Compute fee of transaction at runtime where regular transaction payment pallet is being used.
///
/// The value of `multiplier` parameter is the expected value of
/// `pallet_transaction_payment::NextFeeMultiplier` at the moment when transaction is submitted. If
/// you're charging this payment in advance (and that's what happens with delivery and confirmation
/// transaction in this crate), then there's a chance that the actual fee will be larger than what
/// is paid in advance. So the value must be chosen carefully.
pub fn transaction_payment<Balance: AtLeast32BitUnsigned + FixedPointOperand>(
	base_extrinsic_weight: Weight,
	per_byte_fee: Balance,
	multiplier: FixedU128,
	weight_to_fee: impl Fn(Weight) -> Balance,
	transaction: MessageTransaction<Weight>,
) -> Balance {
	// base fee is charged for every tx
	let base_fee = weight_to_fee(base_extrinsic_weight);

	// non-adjustable per-byte fee
	let len_fee = per_byte_fee.saturating_mul(Balance::from(transaction.size));

	// the adjustable part of the fee
	let unadjusted_weight_fee = weight_to_fee(transaction.dispatch_weight);
	let adjusted_weight_fee = multiplier.saturating_mul_int(unadjusted_weight_fee);

	base_fee.saturating_add(len_fee).saturating_add(adjusted_weight_fee)
}

/// Sub-module that is declaring types required for processing This -> Bridged chain messages.
pub mod source {
	use super::*;

	/// Message payload for This -> Bridged chain messages.
	pub type FromThisChainMessagePayload = Vec<u8>;

	/// Maximal size of outbound message payload.
	pub struct FromThisChainMaximalOutboundPayloadSize<B>(PhantomData<B>);

	impl<B: MessageBridge> Get<u32> for FromThisChainMaximalOutboundPayloadSize<B> {
		fn get() -> u32 {
			maximal_message_size::<B>()
		}
	}

	/// Messages delivery proof from bridged chain:
	///
	/// - hash of finalized header;
	/// - storage proof of inbound lane state;
	/// - lane id.
	#[derive(Clone, Decode, Encode, Eq, PartialEq, RuntimeDebug, TypeInfo)]
	pub struct FromBridgedChainMessagesDeliveryProof<BridgedHeaderHash> {
		/// Hash of the bridge header the proof is for.
		pub bridged_header_hash: BridgedHeaderHash,
		/// Storage trie proof generated for [`Self::bridged_header_hash`].
		pub storage_proof: RawStorageProof,
		/// Lane id of which messages were delivered and the proof is for.
		pub lane: LaneId,
	}

	impl<BridgedHeaderHash> Size for FromBridgedChainMessagesDeliveryProof<BridgedHeaderHash> {
		fn size(&self) -> u32 {
			u32::try_from(
				self.storage_proof
					.iter()
					.fold(0usize, |sum, node| sum.saturating_add(node.len())),
			)
			.unwrap_or(u32::MAX)
		}
	}

	/// 'Parsed' message delivery proof - inbound lane id and its state.
	pub type ParsedMessagesDeliveryProofFromBridgedChain<B> =
		(LaneId, InboundLaneData<AccountIdOf<ThisChain<B>>>);

	/// Message verifier that is doing all basic checks.
	///
	/// This verifier assumes following:
	///
	/// - all message lanes are equivalent, so all checks are the same;
	///
	/// Following checks are made:
	///
	/// - message is rejected if its lane is currently blocked;
	/// - message is rejected if there are too many pending (undelivered) messages at the outbound
	///   lane;
	/// - check that the sender has rights to dispatch the call on target chain using provided
	///   dispatch origin;
	/// - check that the sender has paid enough funds for both message delivery and dispatch.
	#[derive(RuntimeDebug)]
	pub struct FromThisChainMessageVerifier<B>(PhantomData<B>);

	/// The error message returned from LaneMessageVerifier when outbound lane is disabled.
	pub const MESSAGE_REJECTED_BY_OUTBOUND_LANE: &str =
		"The outbound message lane has rejected the message.";
	/// The error message returned from LaneMessageVerifier when too many pending messages at the
	/// lane.
	pub const TOO_MANY_PENDING_MESSAGES: &str = "Too many pending messages at the lane.";
	/// The error message returned from LaneMessageVerifier when call origin is mismatch.
	pub const BAD_ORIGIN: &str = "Unable to match the source origin to expected target origin.";
	/// The error message returned from LaneMessageVerifier when the message fee is too low.
	pub const TOO_LOW_FEE: &str = "Provided fee is below minimal threshold required by the lane.";

	impl<B>
		LaneMessageVerifier<
			OriginOf<ThisChain<B>>,
			AccountIdOf<ThisChain<B>>,
			FromThisChainMessagePayload,
			BalanceOf<ThisChain<B>>,
		> for FromThisChainMessageVerifier<B>
	where
		B: MessageBridge,
		// matches requirements from the `frame_system::Config::Origin`
		OriginOf<ThisChain<B>>: Clone
			+ Into<Result<frame_system::RawOrigin<AccountIdOf<ThisChain<B>>>, OriginOf<ThisChain<B>>>>,
		AccountIdOf<ThisChain<B>>: PartialEq + Clone,
	{
		type Error = &'static str;

		fn verify_message(
			submitter: &OriginOf<ThisChain<B>>,
			delivery_and_dispatch_fee: &BalanceOf<ThisChain<B>>,
			lane: &LaneId,
			lane_outbound_data: &OutboundLaneData,
			payload: &FromThisChainMessagePayload,
		) -> Result<(), Self::Error> {
			// reject message if lane is blocked
			if !ThisChain::<B>::is_message_accepted(submitter, lane) {
				return Err(MESSAGE_REJECTED_BY_OUTBOUND_LANE)
			}

			// reject message if there are too many pending messages at this lane
			let max_pending_messages = ThisChain::<B>::maximal_pending_messages_at_outbound_lane();
			let pending_messages = lane_outbound_data
				.latest_generated_nonce
				.saturating_sub(lane_outbound_data.latest_received_nonce);
			if pending_messages > max_pending_messages {
				return Err(TOO_MANY_PENDING_MESSAGES)
			}

			let minimal_fee_in_this_tokens = estimate_message_dispatch_and_delivery_fee::<B>(
				payload,
				B::RELAYER_FEE_PERCENT,
				None,
			)?;

			// compare with actual fee paid
			if *delivery_and_dispatch_fee < minimal_fee_in_this_tokens {
				return Err(TOO_LOW_FEE)
			}

			Ok(())
		}
	}

	/// Return maximal message size of This -> Bridged chain message.
	pub fn maximal_message_size<B: MessageBridge>() -> u32 {
		super::target::maximal_incoming_message_size(BridgedChain::<B>::maximal_extrinsic_size())
	}

	/// Do basic Bridged-chain specific verification of This -> Bridged chain message.
	///
	/// Ok result from this function means that the delivery transaction with this message
	/// may be 'mined' by the target chain. But the lane may have its own checks (e.g. fee
	/// check) that would reject message (see `FromThisChainMessageVerifier`).
	pub fn verify_chain_message<B: MessageBridge>(
		payload: &FromThisChainMessagePayload,
	) -> Result<(), &'static str> {
		if !BridgedChain::<B>::verify_dispatch_weight(payload) {
			return Err("Incorrect message weight declared")
		}

		// The maximal size of extrinsic at Substrate-based chain depends on the
		// `frame_system::Config::MaximumBlockLength` and
		// `frame_system::Config::AvailableBlockRatio` constants. This check is here to be sure that
		// the lane won't stuck because message is too large to fit into delivery transaction.
		//
		// **IMPORTANT NOTE**: the delivery transaction contains storage proof of the message, not
		// the message itself. The proof is always larger than the message. But unless chain state
		// is enormously large, it should be several dozens/hundreds of bytes. The delivery
		// transaction also contains signatures and signed extensions. Because of this, we reserve
		// 1/3 of the the maximal extrinsic weight for this data.
		if payload.len() > maximal_message_size::<B>() as usize {
			return Err("The message is too large to be sent over the lane")
		}

		Ok(())
	}

	/// Estimate delivery and dispatch fee that must be paid for delivering a message to the Bridged
	/// chain.
	///
	/// The fee is paid in This chain Balance, but we use Bridged chain balance to avoid additional
	/// conversions. Returns `None` if overflow has happened.
	pub fn estimate_message_dispatch_and_delivery_fee<B: MessageBridge>(
		payload: &FromThisChainMessagePayload,
		relayer_fee_percent: u32,
		bridged_to_this_conversion_rate: Option<FixedU128>,
	) -> Result<BalanceOf<ThisChain<B>>, &'static str> {
		// the fee (in Bridged tokens) of all transactions that are made on the Bridged chain
		//
		// if we're going to pay dispatch fee at the target chain, then we don't include weight
		// of the message dispatch in the delivery transaction cost
		let delivery_transaction =
			BridgedChain::<B>::estimate_delivery_transaction(&payload.encode(), true, 0.into());
		let delivery_transaction_fee = BridgedChain::<B>::transaction_payment(delivery_transaction);

		// the fee (in This tokens) of all transactions that are made on This chain
		let confirmation_transaction = ThisChain::<B>::estimate_delivery_confirmation_transaction();
		let confirmation_transaction_fee =
			ThisChain::<B>::transaction_payment(confirmation_transaction);

		// minimal fee (in This tokens) is a sum of all required fees
		let minimal_fee = B::bridged_balance_to_this_balance(
			delivery_transaction_fee,
			bridged_to_this_conversion_rate,
		)
		.checked_add(&confirmation_transaction_fee);

		// before returning, add extra fee that is paid to the relayer (relayer interest)
		minimal_fee
			.and_then(|fee|
			// having message with fee that is near the `Balance::MAX_VALUE` of the chain is
			// unlikely and should be treated as an error
			// => let's do multiplication first
			fee
				.checked_mul(&relayer_fee_percent.into())
				.and_then(|interest| interest.checked_div(&100u32.into()))
				.and_then(|interest| fee.checked_add(&interest)))
			.ok_or("Overflow when computing minimal required message delivery and dispatch fee")
	}

	/// Verify proof of This -> Bridged chain messages delivery.
	///
	/// This function is used when Bridged chain is directly using GRANDPA finality. For Bridged
	/// parachains, please use the `verify_messages_delivery_proof_from_parachain`.
	pub fn verify_messages_delivery_proof<B: MessageBridge, ThisRuntime, GrandpaInstance: 'static>(
		proof: FromBridgedChainMessagesDeliveryProof<HashOf<BridgedChain<B>>>,
	) -> Result<ParsedMessagesDeliveryProofFromBridgedChain<B>, &'static str>
	where
		ThisRuntime: pallet_bridge_grandpa::Config<GrandpaInstance>,
		HashOf<BridgedChain<B>>: Into<
			bp_runtime::HashOf<
				<ThisRuntime as pallet_bridge_grandpa::Config<GrandpaInstance>>::BridgedChain,
			>,
		>,
	{
		let FromBridgedChainMessagesDeliveryProof { bridged_header_hash, storage_proof, lane } =
			proof;
		pallet_bridge_grandpa::Pallet::<ThisRuntime, GrandpaInstance>::parse_finalized_storage_proof(
			bridged_header_hash.into(),
			StorageProof::new(storage_proof),
			|storage| do_verify_messages_delivery_proof::<
				B,
				bp_runtime::HasherOf<
					<ThisRuntime as pallet_bridge_grandpa::Config<GrandpaInstance>>::BridgedChain,
				>,
			>(lane, storage),
		)
		.map_err(<&'static str>::from)?
	}

	/// Verify proof of This -> Bridged chain messages delivery.
	///
	/// This function is used when Bridged chain is using parachain finality. For Bridged
	/// chains with direct GRANDPA finality, please use the `verify_messages_delivery_proof`.
	///
	/// This function currently only supports parachains, which are using header type that
	/// implements `sp_runtime::traits::Header` trait.
	pub fn verify_messages_delivery_proof_from_parachain<
		B,
		BridgedHeader,
		ThisRuntime,
		ParachainsInstance: 'static,
	>(
		bridged_parachain: ParaId,
		proof: FromBridgedChainMessagesDeliveryProof<HashOf<BridgedChain<B>>>,
	) -> Result<ParsedMessagesDeliveryProofFromBridgedChain<B>, &'static str>
	where
		B: MessageBridge,
		B::BridgedChain: ChainWithMessages<Hash = ParaHash>,
		BridgedHeader: HeaderT<Hash = HashOf<BridgedChain<B>>>,
		ThisRuntime: pallet_bridge_parachains::Config<ParachainsInstance>,
	{
		let FromBridgedChainMessagesDeliveryProof { bridged_header_hash, storage_proof, lane } =
			proof;
		pallet_bridge_parachains::Pallet::<ThisRuntime, ParachainsInstance>::parse_finalized_storage_proof(
			bridged_parachain,
			bridged_header_hash,
			StorageProof::new(storage_proof),
			|para_head| BridgedHeader::decode(&mut &para_head.0[..]).ok().map(|h| *h.state_root()),
			|storage| do_verify_messages_delivery_proof::<B, ParaHasher>(lane, storage),
		)
		.map_err(<&'static str>::from)?
	}

	/// The essense of This -> Bridged chain messages delivery proof verification.
	fn do_verify_messages_delivery_proof<B: MessageBridge, H: Hasher>(
		lane: LaneId,
		storage: bp_runtime::StorageProofChecker<H>,
	) -> Result<ParsedMessagesDeliveryProofFromBridgedChain<B>, &'static str> {
		// Messages delivery proof is just proof of single storage key read => any error
		// is fatal.
		let storage_inbound_lane_data_key = bp_messages::storage_keys::inbound_lane_data_key(
			B::BRIDGED_MESSAGES_PALLET_NAME,
			&lane,
		);
		let raw_inbound_lane_data = storage
			.read_value(storage_inbound_lane_data_key.0.as_ref())
			.map_err(|_| "Failed to read inbound lane state from storage proof")?
			.ok_or("Inbound lane state is missing from the messages proof")?;
		let inbound_lane_data = InboundLaneData::decode(&mut &raw_inbound_lane_data[..])
			.map_err(|_| "Failed to decode inbound lane state from the proof")?;

		Ok((lane, inbound_lane_data))
	}

	/// XCM bridge.
	pub trait XcmBridge {
		/// Runtime message bridge configuration.
		type MessageBridge: MessageBridge;
		/// Runtime message sender adapter.
		type MessageSender: bp_messages::source_chain::MessagesBridge<
			OriginOf<ThisChain<Self::MessageBridge>>,
			AccountIdOf<ThisChain<Self::MessageBridge>>,
			BalanceOf<ThisChain<Self::MessageBridge>>,
			FromThisChainMessagePayload,
		>;

		/// Our location within the Consensus Universe.
		fn universal_location() -> InteriorMultiLocation;
		/// Verify that the adapter is responsible for handling given XCM destination.
		fn verify_destination(dest: &MultiLocation) -> bool;
		/// Build route from this chain to the XCM destination.
		fn build_destination() -> MultiLocation;
		/// Return message lane used to deliver XCM messages.
		fn xcm_lane() -> LaneId;
	}

	/// XCM bridge adapter for `bridge-messages` pallet.
	pub struct XcmBridgeAdapter<T>(PhantomData<T>);

	impl<T: XcmBridge> SendXcm for XcmBridgeAdapter<T>
	where
		BalanceOf<ThisChain<T::MessageBridge>>: Into<Fungibility>,
		OriginOf<ThisChain<T::MessageBridge>>: From<pallet_xcm::Origin>,
	{
		type Ticket = (BalanceOf<ThisChain<T::MessageBridge>>, FromThisChainMessagePayload);

		fn validate(
			dest: &mut Option<MultiLocation>,
			msg: &mut Option<Xcm<()>>,
		) -> SendResult<Self::Ticket> {
			let d = dest.take().ok_or(SendError::MissingArgument)?;
			if !T::verify_destination(&d) {
				*dest = Some(d);
				return Err(SendError::NotApplicable)
			}

			let route = T::build_destination();
			let msg = (route, msg.take().ok_or(SendError::MissingArgument)?).encode();

			let fee = estimate_message_dispatch_and_delivery_fee::<T::MessageBridge>(
				&msg,
				T::MessageBridge::RELAYER_FEE_PERCENT,
				None,
			);
			let fee = match fee {
				Ok(fee) => fee,
				Err(e) => {
					log::trace!(
						target: "runtime::bridge",
						"Failed to comupte fee for XCM message to {:?}: {:?}",
						T::MessageBridge::BRIDGED_CHAIN_ID,
						e,
					);
					*dest = Some(d);
					return Err(SendError::Transport(e))
				},
			};
			let fee_assets = MultiAssets::from((Here, fee));

			Ok(((fee, msg), fee_assets))
		}

		fn deliver(ticket: Self::Ticket) -> Result<XcmHash, SendError> {
			use bp_messages::source_chain::MessagesBridge;

			let lane = T::xcm_lane();
			let (fee, msg) = ticket;
			let result = T::MessageSender::send_message(
				pallet_xcm::Origin::from(MultiLocation::from(T::universal_location())).into(),
				lane,
				msg,
				fee,
			);
			result
				.map(|artifacts| {
					let hash = (lane, artifacts.nonce).using_encoded(sp_io::hashing::blake2_256);
					log::debug!(
						target: "runtime::bridge",
						"Sent XCM message {:?}/{} to {:?}: {:?}",
						lane,
						artifacts.nonce,
						T::MessageBridge::BRIDGED_CHAIN_ID,
						hash,
					);
					hash
				})
				.map_err(|e| {
					log::debug!(
						target: "runtime::bridge",
						"Failed to send XCM message over lane {:?} to {:?}: {:?}",
						lane,
						T::MessageBridge::BRIDGED_CHAIN_ID,
						e,
					);
					SendError::Transport("Bridge has rejected the message")
				})
		}
	}
}

/// Sub-module that is declaring types required for processing Bridged -> This chain messages.
pub mod target {
	use super::*;

	/// Decoded Bridged -> This message payload.
	#[derive(RuntimeDebug, PartialEq, Eq)]
	pub struct FromBridgedChainMessagePayload<Call> {
		/// Data that is actually sent over the wire.
		pub xcm: (xcm::v3::MultiLocation, xcm::v3::Xcm<Call>),
		/// Weight of the message, computed by the weigher. Unknown initially.
		pub weight: Option<Weight>,
	}

	impl<Call: Decode> Decode for FromBridgedChainMessagePayload<Call> {
		fn decode<I: codec::Input>(input: &mut I) -> Result<Self, codec::Error> {
			let _: codec::Compact<u32> = Decode::decode(input)?;
			type XcmPairType<Call> = (xcm::v3::MultiLocation, xcm::v3::Xcm<Call>);
			Ok(FromBridgedChainMessagePayload {
				xcm: XcmPairType::<Call>::decode_with_depth_limit(
					sp_api::MAX_EXTRINSIC_DEPTH,
					input,
				)?,
				weight: None,
			})
		}
	}

	impl<Call> From<(xcm::v3::MultiLocation, xcm::v3::Xcm<Call>)>
		for FromBridgedChainMessagePayload<Call>
	{
		fn from(xcm: (xcm::v3::MultiLocation, xcm::v3::Xcm<Call>)) -> Self {
			FromBridgedChainMessagePayload { xcm, weight: None }
		}
	}

	/// Messages proof from bridged chain:
	///
	/// - hash of finalized header;
	/// - storage proof of messages and (optionally) outbound lane state;
	/// - lane id;
	/// - nonces (inclusive range) of messages which are included in this proof.
	#[derive(Clone, Decode, Encode, Eq, PartialEq, RuntimeDebug, TypeInfo)]
	pub struct FromBridgedChainMessagesProof<BridgedHeaderHash> {
		/// Hash of the finalized bridged header the proof is for.
		pub bridged_header_hash: BridgedHeaderHash,
		/// A storage trie proof of messages being delivered.
		pub storage_proof: RawStorageProof,
		/// Messages in this proof are sent over this lane.
		pub lane: LaneId,
		/// Nonce of the first message being delivered.
		pub nonces_start: MessageNonce,
		/// Nonce of the last message being delivered.
		pub nonces_end: MessageNonce,
	}

	impl<BridgedHeaderHash> Size for FromBridgedChainMessagesProof<BridgedHeaderHash> {
		fn size(&self) -> u32 {
			u32::try_from(
				self.storage_proof
					.iter()
					.fold(0usize, |sum, node| sum.saturating_add(node.len())),
			)
			.unwrap_or(u32::MAX)
		}
	}

	/// Dispatching Bridged -> This chain messages.
	#[derive(RuntimeDebug, Clone, Copy)]
	pub struct FromBridgedChainMessageDispatch<B, XcmExecutor, XcmWeigher, WeightCredit> {
		_marker: PhantomData<(B, XcmExecutor, XcmWeigher, WeightCredit)>,
	}

	impl<B: MessageBridge, XcmExecutor, XcmWeigher, WeightCredit>
		MessageDispatch<AccountIdOf<ThisChain<B>>, BalanceOf<BridgedChain<B>>>
		for FromBridgedChainMessageDispatch<B, XcmExecutor, XcmWeigher, WeightCredit>
	where
		XcmExecutor: xcm::v3::ExecuteXcm<CallOf<ThisChain<B>>>,
		XcmWeigher: xcm_executor::traits::WeightBounds<CallOf<ThisChain<B>>>,
		WeightCredit: Get<Weight>,
	{
		type DispatchPayload = FromBridgedChainMessagePayload<CallOf<ThisChain<B>>>;

		fn dispatch_weight(
			message: &mut DispatchMessage<Self::DispatchPayload, BalanceOf<BridgedChain<B>>>,
		) -> frame_support::weights::Weight {
			match message.data.payload {
				Ok(ref mut payload) => {
					// I have no idea why this method takes `&mut` reference and there's nothing
					// about that in documentation. Hope it'll only mutate iff error is returned.
					let weight = XcmWeigher::weight(&mut payload.xcm.1);
					let weight = weight.unwrap_or_else(|e| {
						log::debug!(
							target: "runtime::bridge-dispatch",
							"Failed to compute dispatch weight of incoming XCM message {:?}/{}: {:?}",
							message.key.lane_id,
							message.key.nonce,
							e,
						);

						// we shall return 0 and then the XCM executor will fail to execute XCM
						// if we'll return something else (e.g. maximal value), the lane may stuck
						0
					});

					payload.weight = Some(weight);
					weight
				},
				_ => 0,
			}
		}

		fn dispatch(
			_relayer_account: &AccountIdOf<ThisChain<B>>,
			message: DispatchMessage<Self::DispatchPayload, BalanceOf<BridgedChain<B>>>,
		) -> MessageDispatchResult {
			let message_id = (message.key.lane_id, message.key.nonce);
			let do_dispatch = move || -> sp_std::result::Result<Outcome, codec::Error> {
				let FromBridgedChainMessagePayload { xcm: (location, xcm), weight: weight_limit } =
					message.data.payload?;
				log::trace!(
					target: "runtime::bridge-dispatch",
					"Going to execute message {:?} (weight limit: {:?}): {:?} {:?}",
					message_id,
					weight_limit,
					location,
					xcm,
				);
				let hash = message_id.using_encoded(sp_io::hashing::blake2_256);

				// if this cod will end up in production, this most likely needs to be set to zero
				let weight_credit = WeightCredit::get();

				let xcm_outcome = XcmExecutor::execute_xcm_in_credit(
					location,
					xcm,
					hash,
					weight_limit.unwrap_or(0),
					weight_credit,
				);
				Ok(xcm_outcome)
			};

			let xcm_outcome = do_dispatch();
			log::trace!(target: "runtime::bridge-dispatch", "Incoming message {:?} dispatched with result: {:?}", message_id, xcm_outcome);
			MessageDispatchResult {
				dispatch_result: true,
				unspent_weight: 0,
				dispatch_fee_paid_during_dispatch: false,
			}
		}
	}

	/// Return maximal dispatch weight of the message we're able to receive.
	pub fn maximal_incoming_message_dispatch_weight(maximal_extrinsic_weight: Weight) -> Weight {
		maximal_extrinsic_weight / 2
	}

	/// Return maximal message size given maximal extrinsic size.
	pub fn maximal_incoming_message_size(maximal_extrinsic_size: u32) -> u32 {
		maximal_extrinsic_size / 3 * 2
	}

	/// Verify proof of Bridged -> This chain messages.
	///
	/// This function is used when Bridged chain is directly using GRANDPA finality. For Bridged
	/// parachains, please use the `verify_messages_proof_from_parachain`.
	///
	/// The `messages_count` argument verification (sane limits) is supposed to be made
	/// outside of this function. This function only verifies that the proof declares exactly
	/// `messages_count` messages.
	pub fn verify_messages_proof<B: MessageBridge, ThisRuntime, GrandpaInstance: 'static>(
		proof: FromBridgedChainMessagesProof<HashOf<BridgedChain<B>>>,
		messages_count: u32,
	) -> Result<ProvedMessages<Message<BalanceOf<BridgedChain<B>>>>, &'static str>
	where
		ThisRuntime: pallet_bridge_grandpa::Config<GrandpaInstance>,
		HashOf<BridgedChain<B>>: Into<
			bp_runtime::HashOf<
				<ThisRuntime as pallet_bridge_grandpa::Config<GrandpaInstance>>::BridgedChain,
			>,
		>,
	{
		verify_messages_proof_with_parser::<B, _, _>(
			proof,
			messages_count,
			|bridged_header_hash, bridged_storage_proof| {
				pallet_bridge_grandpa::Pallet::<ThisRuntime, GrandpaInstance>::parse_finalized_storage_proof(
					bridged_header_hash.into(),
					StorageProof::new(bridged_storage_proof),
					|storage_adapter| storage_adapter,
				)
				.map(|storage| StorageProofCheckerAdapter::<_, B> {
					storage,
					_dummy: Default::default(),
				})
				.map_err(|err| MessageProofError::Custom(err.into()))
			},
		)
		.map_err(Into::into)
	}

	/// Verify proof of Bridged -> This chain messages.
	///
	/// This function is used when Bridged chain is using parachain finality. For Bridged
	/// chains with direct GRANDPA finality, please use the `verify_messages_proof`.
	///
	/// The `messages_count` argument verification (sane limits) is supposed to be made
	/// outside of this function. This function only verifies that the proof declares exactly
	/// `messages_count` messages.
	///
	/// This function currently only supports parachains, which are using header type that
	/// implements `sp_runtime::traits::Header` trait.
	pub fn verify_messages_proof_from_parachain<
		B,
		BridgedHeader,
		ThisRuntime,
		ParachainsInstance: 'static,
	>(
		bridged_parachain: ParaId,
		proof: FromBridgedChainMessagesProof<HashOf<BridgedChain<B>>>,
		messages_count: u32,
	) -> Result<ProvedMessages<Message<BalanceOf<BridgedChain<B>>>>, &'static str>
	where
		B: MessageBridge,
		B::BridgedChain: ChainWithMessages<Hash = ParaHash>,
		BridgedHeader: HeaderT<Hash = HashOf<BridgedChain<B>>>,
		ThisRuntime: pallet_bridge_parachains::Config<ParachainsInstance>,
	{
		verify_messages_proof_with_parser::<B, _, _>(
			proof,
			messages_count,
			|bridged_header_hash, bridged_storage_proof| {
				pallet_bridge_parachains::Pallet::<ThisRuntime, ParachainsInstance>::parse_finalized_storage_proof(
					bridged_parachain,
					bridged_header_hash,
					StorageProof::new(bridged_storage_proof),
					|para_head| BridgedHeader::decode(&mut &para_head.0[..]).ok().map(|h| *h.state_root()),
					|storage_adapter| storage_adapter,
				)
				.map(|storage| StorageProofCheckerAdapter::<_, B> {
					storage,
					_dummy: Default::default(),
				})
				.map_err(|err| MessageProofError::Custom(err.into()))
			},
		)
		.map_err(Into::into)
	}

	#[derive(Debug, PartialEq, Eq)]
	pub(crate) enum MessageProofError {
		Empty,
		MessagesCountMismatch,
		MissingRequiredMessage,
		FailedToDecodeMessage,
		FailedToDecodeOutboundLaneState,
		Custom(&'static str),
	}

	impl From<MessageProofError> for &'static str {
		fn from(err: MessageProofError) -> &'static str {
			match err {
				MessageProofError::Empty => "Messages proof is empty",
				MessageProofError::MessagesCountMismatch =>
					"Declared messages count doesn't match actual value",
				MessageProofError::MissingRequiredMessage => "Message is missing from the proof",
				MessageProofError::FailedToDecodeMessage =>
					"Failed to decode message from the proof",
				MessageProofError::FailedToDecodeOutboundLaneState =>
					"Failed to decode outbound lane data from the proof",
				MessageProofError::Custom(err) => err,
			}
		}
	}

	pub(crate) trait MessageProofParser {
		fn read_raw_outbound_lane_data(&self, lane_id: &LaneId) -> Option<Vec<u8>>;
		fn read_raw_message(&self, message_key: &MessageKey) -> Option<Vec<u8>>;
	}

	struct StorageProofCheckerAdapter<H: Hasher, B> {
		storage: StorageProofChecker<H>,
		_dummy: sp_std::marker::PhantomData<B>,
	}

	impl<H, B> MessageProofParser for StorageProofCheckerAdapter<H, B>
	where
		H: Hasher,
		B: MessageBridge,
	{
		fn read_raw_outbound_lane_data(&self, lane_id: &LaneId) -> Option<Vec<u8>> {
			let storage_outbound_lane_data_key = bp_messages::storage_keys::outbound_lane_data_key(
				B::BRIDGED_MESSAGES_PALLET_NAME,
				lane_id,
			);
			self.storage.read_value(storage_outbound_lane_data_key.0.as_ref()).ok()?
		}

		fn read_raw_message(&self, message_key: &MessageKey) -> Option<Vec<u8>> {
			let storage_message_key = bp_messages::storage_keys::message_key(
				B::BRIDGED_MESSAGES_PALLET_NAME,
				&message_key.lane_id,
				message_key.nonce,
			);
			self.storage.read_value(storage_message_key.0.as_ref()).ok()?
		}
	}

	/// Verify proof of Bridged -> This chain messages using given message proof parser.
	pub(crate) fn verify_messages_proof_with_parser<B: MessageBridge, BuildParser, Parser>(
		proof: FromBridgedChainMessagesProof<HashOf<BridgedChain<B>>>,
		messages_count: u32,
		build_parser: BuildParser,
	) -> Result<ProvedMessages<Message<BalanceOf<BridgedChain<B>>>>, MessageProofError>
	where
		BuildParser:
			FnOnce(HashOf<BridgedChain<B>>, RawStorageProof) -> Result<Parser, MessageProofError>,
		Parser: MessageProofParser,
	{
		let FromBridgedChainMessagesProof {
			bridged_header_hash,
			storage_proof,
			lane,
			nonces_start,
			nonces_end,
		} = proof;

		// receiving proofs where end < begin is ok (if proof includes outbound lane state)
		let messages_in_the_proof =
			if let Some(nonces_difference) = nonces_end.checked_sub(nonces_start) {
				// let's check that the user (relayer) has passed correct `messages_count`
				// (this bounds maximal capacity of messages vec below)
				let messages_in_the_proof = nonces_difference.saturating_add(1);
				if messages_in_the_proof != MessageNonce::from(messages_count) {
					return Err(MessageProofError::MessagesCountMismatch)
				}

				messages_in_the_proof
			} else {
				0
			};

		let parser = build_parser(bridged_header_hash, storage_proof)?;

		// Read messages first. All messages that are claimed to be in the proof must
		// be in the proof. So any error in `read_value`, or even missing value is fatal.
		//
		// Mind that we allow proofs with no messages if outbound lane state is proved.
		let mut messages = Vec::with_capacity(messages_in_the_proof as _);
		for nonce in nonces_start..=nonces_end {
			let message_key = MessageKey { lane_id: lane, nonce };
			let raw_message_data = parser
				.read_raw_message(&message_key)
				.ok_or(MessageProofError::MissingRequiredMessage)?;
			let message_data =
				MessageData::<BalanceOf<BridgedChain<B>>>::decode(&mut &raw_message_data[..])
					.map_err(|_| MessageProofError::FailedToDecodeMessage)?;
			messages.push(Message { key: message_key, data: message_data });
		}

		// Now let's check if proof contains outbound lane state proof. It is optional, so we
		// simply ignore `read_value` errors and missing value.
		let mut proved_lane_messages = ProvedLaneMessages { lane_state: None, messages };
		let raw_outbound_lane_data = parser.read_raw_outbound_lane_data(&lane);
		if let Some(raw_outbound_lane_data) = raw_outbound_lane_data {
			proved_lane_messages.lane_state = Some(
				OutboundLaneData::decode(&mut &raw_outbound_lane_data[..])
					.map_err(|_| MessageProofError::FailedToDecodeOutboundLaneState)?,
			);
		}

		// Now we may actually check if the proof is empty or not.
		if proved_lane_messages.lane_state.is_none() && proved_lane_messages.messages.is_empty() {
			return Err(MessageProofError::Empty)
		}

		// We only support single lane messages in this generated_schema
		let mut proved_messages = ProvedMessages::new();
		proved_messages.insert(lane, proved_lane_messages);

		Ok(proved_messages)
	}
}

pub use xcm_copy::*;

// copy of private types from xcm-builder/src/universal_exports.rs
pub mod xcm_copy {
	use codec::{Decode, Encode};
	use frame_support::{ensure, traits::Get};
	use sp_std::{convert::TryInto, marker::PhantomData, prelude::*};
	use xcm::prelude::*;
	use xcm_executor::traits::ExportXcm;

	pub trait DispatchBlob {
		/// Dispatches an incoming blob and returns the unexpectable weight consumed by the
		/// dispatch.
		fn dispatch_blob(blob: Vec<u8>) -> Result<(), DispatchBlobError>;
	}

	pub trait HaulBlob {
		/// Sends a blob over some point-to-point link. This will generally be implemented by a
		/// bridge.
		fn haul_blob(blob: Vec<u8>);
	}

	#[derive(Clone, Encode, Decode)]
	pub struct BridgeMessage {
		/// The message destination as a *Universal Location*. This means it begins with a
		/// `GlobalConsensus` junction describing the network under which global consensus happens.
		/// If this does not match our global consensus then it's a fatal error.
		universal_dest: VersionedInteriorMultiLocation,
		message: VersionedXcm<()>,
	}

	pub enum DispatchBlobError {
		Unbridgable,
		InvalidEncoding,
		UnsupportedLocationVersion,
		UnsupportedXcmVersion,
		RoutingError,
		NonUniversalDestination,
		WrongGlobal,
	}

	pub struct BridgeBlobDispatcher<Router, OurPlace>(PhantomData<(Router, OurPlace)>);
	impl<Router: SendXcm, OurPlace: Get<InteriorMultiLocation>> DispatchBlob
		for BridgeBlobDispatcher<Router, OurPlace>
	{
		fn dispatch_blob(blob: Vec<u8>) -> Result<(), DispatchBlobError> {
			let our_universal = OurPlace::get();
			let our_global =
				our_universal.global_consensus().map_err(|()| DispatchBlobError::Unbridgable)?;
			let BridgeMessage { universal_dest, message } =
				Decode::decode(&mut &blob[..]).map_err(|_| DispatchBlobError::InvalidEncoding)?;
			let universal_dest: InteriorMultiLocation = universal_dest
				.try_into()
				.map_err(|_| DispatchBlobError::UnsupportedLocationVersion)?;
			// `universal_dest` is the desired destination within the universe: first we need to
			// check we're in the right global consensus.
			let intended_global = universal_dest
				.global_consensus()
				.map_err(|()| DispatchBlobError::NonUniversalDestination)?;
			ensure!(intended_global == our_global, DispatchBlobError::WrongGlobal);
			let dest = universal_dest.relative_to(&our_universal);
			let message: Xcm<()> =
				message.try_into().map_err(|_| DispatchBlobError::UnsupportedXcmVersion)?;
			send_xcm::<Router>(dest, message).map_err(|_| DispatchBlobError::RoutingError)?;
			Ok(())
		}
	}

	pub struct HaulBlobExporter<Bridge, BridgedNetwork, Price>(
		PhantomData<(Bridge, BridgedNetwork, Price)>,
	);
	impl<Bridge: HaulBlob, BridgedNetwork: Get<NetworkId>, Price: Get<MultiAssets>> ExportXcm
		for HaulBlobExporter<Bridge, BridgedNetwork, Price>
	{
		type Ticket = (Vec<u8>, XcmHash);

		fn validate(
			network: NetworkId,
			_channel: u32,
			destination: &mut Option<InteriorMultiLocation>,
			message: &mut Option<Xcm<()>>,
		) -> Result<((Vec<u8>, XcmHash), MultiAssets), SendError> {
			let bridged_network = BridgedNetwork::get();
			ensure!(network == bridged_network, SendError::NotApplicable);
			// We don't/can't use the `channel` for this adapter.
			let dest = destination.take().ok_or(SendError::MissingArgument)?;
			let universal_dest = match dest.pushed_front_with(GlobalConsensus(bridged_network)) {
				Ok(d) => d.into(),
				Err((dest, _)) => {
					*destination = Some(dest);
					return Err(SendError::NotApplicable)
				},
			};
			let message = VersionedXcm::from(message.take().ok_or(SendError::MissingArgument)?);
			let hash = message.using_encoded(sp_io::hashing::blake2_256);
			let blob = BridgeMessage { universal_dest, message }.encode();
			Ok(((blob, hash), Price::get()))
		}

		fn deliver((blob, hash): (Vec<u8>, XcmHash)) -> Result<XcmHash, SendError> {
			Bridge::haul_blob(blob);
			Ok(hash)
		}
	}
}

#[cfg(test)]
mod tests {
	use super::*;
	use codec::{Decode, Encode};
	use frame_support::weights::Weight;
	use std::ops::RangeInclusive;

	const DELIVERY_TRANSACTION_WEIGHT: Weight = 100;
	const DELIVERY_CONFIRMATION_TRANSACTION_WEIGHT: Weight = 100;
	const THIS_CHAIN_WEIGHT_TO_BALANCE_RATE: Weight = 2;
	const BRIDGED_CHAIN_WEIGHT_TO_BALANCE_RATE: Weight = 4;
	const BRIDGED_CHAIN_TO_THIS_CHAIN_BALANCE_RATE: u32 = 6;
	const BRIDGED_CHAIN_MIN_EXTRINSIC_WEIGHT: usize = 5;
	const BRIDGED_CHAIN_MAX_EXTRINSIC_WEIGHT: usize = 2048;
	const BRIDGED_CHAIN_MAX_EXTRINSIC_SIZE: u32 = 1024;

	/// Bridge that is deployed on ThisChain and allows sending/receiving messages to/from
	/// BridgedChain;
	#[derive(Debug, PartialEq, Eq)]
	struct OnThisChainBridge;

	impl MessageBridge for OnThisChainBridge {
		const RELAYER_FEE_PERCENT: u32 = 10;
		const THIS_CHAIN_ID: ChainId = *b"this";
		const BRIDGED_CHAIN_ID: ChainId = *b"brdg";
		const BRIDGED_MESSAGES_PALLET_NAME: &'static str = "";

		type ThisChain = ThisChain;
		type BridgedChain = BridgedChain;

		fn bridged_balance_to_this_balance(
			bridged_balance: BridgedChainBalance,
			bridged_to_this_conversion_rate_override: Option<FixedU128>,
		) -> ThisChainBalance {
			let conversion_rate = bridged_to_this_conversion_rate_override
				.map(|r| r.to_float() as u32)
				.unwrap_or(BRIDGED_CHAIN_TO_THIS_CHAIN_BALANCE_RATE);
			ThisChainBalance(bridged_balance.0 * conversion_rate)
		}
	}

	/// Bridge that is deployed on BridgedChain and allows sending/receiving messages to/from
	/// ThisChain;
	#[derive(Debug, PartialEq, Eq)]
	struct OnBridgedChainBridge;

	impl MessageBridge for OnBridgedChainBridge {
		const RELAYER_FEE_PERCENT: u32 = 20;
		const THIS_CHAIN_ID: ChainId = *b"brdg";
		const BRIDGED_CHAIN_ID: ChainId = *b"this";
		const BRIDGED_MESSAGES_PALLET_NAME: &'static str = "";

		type ThisChain = BridgedChain;
		type BridgedChain = ThisChain;

		fn bridged_balance_to_this_balance(
			_this_balance: ThisChainBalance,
			_bridged_to_this_conversion_rate_override: Option<FixedU128>,
		) -> BridgedChainBalance {
			unreachable!()
		}
	}

	#[derive(Debug, PartialEq, Eq, Decode, Encode, Clone, MaxEncodedLen)]
	struct ThisChainAccountId(u32);
	#[derive(Debug, PartialEq, Eq, Decode, Encode)]
	struct ThisChainSigner(u32);
	#[derive(Debug, PartialEq, Eq, Decode, Encode)]
	struct ThisChainSignature(u32);
	#[derive(Debug, PartialEq, Eq, Decode, Encode)]
	enum ThisChainCall {
		#[codec(index = 42)]
		Transfer,
		#[codec(index = 84)]
		Mint,
	}
	#[derive(Clone, Debug)]
	struct ThisChainOrigin(Result<frame_system::RawOrigin<ThisChainAccountId>, ()>);

	impl From<ThisChainOrigin>
		for Result<frame_system::RawOrigin<ThisChainAccountId>, ThisChainOrigin>
	{
		fn from(
			origin: ThisChainOrigin,
		) -> Result<frame_system::RawOrigin<ThisChainAccountId>, ThisChainOrigin> {
			origin.clone().0.map_err(|_| origin)
		}
	}

	#[derive(Debug, PartialEq, Eq, Decode, Encode, MaxEncodedLen)]
	struct BridgedChainAccountId(u32);
	#[derive(Debug, PartialEq, Eq, Decode, Encode)]
	struct BridgedChainSigner(u32);
	#[derive(Debug, PartialEq, Eq, Decode, Encode)]
	struct BridgedChainSignature(u32);
	#[derive(Debug, PartialEq, Eq, Decode, Encode)]
	enum BridgedChainCall {}
	#[derive(Clone, Debug)]
	struct BridgedChainOrigin;

	impl From<BridgedChainOrigin>
		for Result<frame_system::RawOrigin<BridgedChainAccountId>, BridgedChainOrigin>
	{
		fn from(
			_origin: BridgedChainOrigin,
		) -> Result<frame_system::RawOrigin<BridgedChainAccountId>, BridgedChainOrigin> {
			unreachable!()
		}
	}

	macro_rules! impl_wrapped_balance {
		($name:ident) => {
			#[derive(Debug, PartialEq, Eq, Decode, Encode, Clone, Copy)]
			struct $name(u32);

			impl From<u32> for $name {
				fn from(balance: u32) -> Self {
					Self(balance)
				}
			}

			impl sp_std::ops::Add for $name {
				type Output = $name;

				fn add(self, other: Self) -> Self {
					Self(self.0 + other.0)
				}
			}

			impl sp_std::ops::Div for $name {
				type Output = $name;

				fn div(self, other: Self) -> Self {
					Self(self.0 / other.0)
				}
			}

			impl sp_std::ops::Mul for $name {
				type Output = $name;

				fn mul(self, other: Self) -> Self {
					Self(self.0 * other.0)
				}
			}

			impl sp_std::cmp::PartialOrd for $name {
				fn partial_cmp(&self, other: &Self) -> Option<sp_std::cmp::Ordering> {
					self.0.partial_cmp(&other.0)
				}
			}

			impl CheckedAdd for $name {
				fn checked_add(&self, other: &Self) -> Option<Self> {
					self.0.checked_add(other.0).map(Self)
				}
			}

			impl CheckedDiv for $name {
				fn checked_div(&self, other: &Self) -> Option<Self> {
					self.0.checked_div(other.0).map(Self)
				}
			}

			impl CheckedMul for $name {
				fn checked_mul(&self, other: &Self) -> Option<Self> {
					self.0.checked_mul(other.0).map(Self)
				}
			}
		};
	}

	impl_wrapped_balance!(ThisChainBalance);
	impl_wrapped_balance!(BridgedChainBalance);

	struct ThisChain;

	impl ChainWithMessages for ThisChain {
		type Hash = ();
		type AccountId = ThisChainAccountId;
		type Signer = ThisChainSigner;
		type Signature = ThisChainSignature;
		type Weight = frame_support::weights::Weight;
		type Balance = ThisChainBalance;
	}

	impl ThisChainWithMessages for ThisChain {
		type Origin = ThisChainOrigin;
		type Call = ThisChainCall;
		type ConfirmationTransactionEstimation = BasicConfirmationTransactionEstimation<
			<ThisChain as ChainWithMessages>::AccountId,
			{ DELIVERY_CONFIRMATION_TRANSACTION_WEIGHT },
			0,
			0,
		>;

		fn is_message_accepted(_send_origin: &Self::Origin, lane: &LaneId) -> bool {
			lane == TEST_LANE_ID
		}

		fn maximal_pending_messages_at_outbound_lane() -> MessageNonce {
			MAXIMAL_PENDING_MESSAGES_AT_TEST_LANE
		}

		fn transaction_payment(transaction: MessageTransaction<WeightOf<Self>>) -> BalanceOf<Self> {
			ThisChainBalance(
				transaction.dispatch_weight as u32 * THIS_CHAIN_WEIGHT_TO_BALANCE_RATE as u32,
			)
		}
	}

	impl BridgedChainWithMessages for ThisChain {
		fn maximal_extrinsic_size() -> u32 {
			unreachable!()
		}

		fn verify_dispatch_weight(_message_payload: &[u8]) -> bool {
			unreachable!()
		}

		fn estimate_delivery_transaction(
			_message_payload: &[u8],
			_include_pay_dispatch_fee_cost: bool,
			_message_dispatch_weight: WeightOf<Self>,
		) -> MessageTransaction<WeightOf<Self>> {
			unreachable!()
		}

		fn transaction_payment(
			_transaction: MessageTransaction<WeightOf<Self>>,
		) -> BalanceOf<Self> {
			unreachable!()
		}
	}

	struct BridgedChain;

	impl ChainWithMessages for BridgedChain {
		type Hash = ();
		type AccountId = BridgedChainAccountId;
		type Signer = BridgedChainSigner;
		type Signature = BridgedChainSignature;
		type Weight = frame_support::weights::Weight;
		type Balance = BridgedChainBalance;
	}

	impl ThisChainWithMessages for BridgedChain {
		type Origin = BridgedChainOrigin;
		type Call = BridgedChainCall;
		type ConfirmationTransactionEstimation = BasicConfirmationTransactionEstimation<
			<BridgedChain as ChainWithMessages>::AccountId,
			0,
			0,
			0,
		>;

		fn is_message_accepted(_send_origin: &Self::Origin, _lane: &LaneId) -> bool {
			unreachable!()
		}

		fn maximal_pending_messages_at_outbound_lane() -> MessageNonce {
			unreachable!()
		}

		fn transaction_payment(
			_transaction: MessageTransaction<WeightOf<Self>>,
		) -> BalanceOf<Self> {
			unreachable!()
		}
	}

	impl BridgedChainWithMessages for BridgedChain {
		fn maximal_extrinsic_size() -> u32 {
			BRIDGED_CHAIN_MAX_EXTRINSIC_SIZE
		}

		fn verify_dispatch_weight(message_payload: &[u8]) -> bool {
			message_payload.len() >= BRIDGED_CHAIN_MIN_EXTRINSIC_WEIGHT &&
				message_payload.len() <= BRIDGED_CHAIN_MAX_EXTRINSIC_WEIGHT
		}

		fn estimate_delivery_transaction(
			_message_payload: &[u8],
			_include_pay_dispatch_fee_cost: bool,
			message_dispatch_weight: WeightOf<Self>,
		) -> MessageTransaction<WeightOf<Self>> {
			MessageTransaction {
				dispatch_weight: DELIVERY_TRANSACTION_WEIGHT + message_dispatch_weight,
				size: 0,
			}
		}

		fn transaction_payment(transaction: MessageTransaction<WeightOf<Self>>) -> BalanceOf<Self> {
			BridgedChainBalance(
				transaction.dispatch_weight as u32 * BRIDGED_CHAIN_WEIGHT_TO_BALANCE_RATE as u32,
			)
		}
	}

	fn test_lane_outbound_data() -> OutboundLaneData {
		OutboundLaneData::default()
	}

	const TEST_LANE_ID: &LaneId = b"test";
	const MAXIMAL_PENDING_MESSAGES_AT_TEST_LANE: MessageNonce = 32;

	fn regular_outbound_message_payload() -> source::FromThisChainMessagePayload {
		vec![42]
	}

	#[test]
	fn message_fee_is_checked_by_verifier() {
		const EXPECTED_MINIMAL_FEE: u32 = 2860;

		// payload of the This -> Bridged chain message
		let payload = regular_outbound_message_payload();

		// let's check if estimation matching hardcoded value
		assert_eq!(
			source::estimate_message_dispatch_and_delivery_fee::<OnThisChainBridge>(
				&payload,
				OnThisChainBridge::RELAYER_FEE_PERCENT,
				None,
			),
			Ok(ThisChainBalance(EXPECTED_MINIMAL_FEE)),
		);

		// and now check that the verifier checks the fee
		assert_eq!(
			source::FromThisChainMessageVerifier::<OnThisChainBridge>::verify_message(
				&ThisChainOrigin(Ok(frame_system::RawOrigin::Root)),
				&ThisChainBalance(1),
				TEST_LANE_ID,
				&test_lane_outbound_data(),
				&payload,
			),
			Err(source::TOO_LOW_FEE)
		);
		assert!(source::FromThisChainMessageVerifier::<OnThisChainBridge>::verify_message(
			&ThisChainOrigin(Ok(frame_system::RawOrigin::Root)),
			&ThisChainBalance(1_000_000),
			TEST_LANE_ID,
			&test_lane_outbound_data(),
			&payload,
		)
		.is_ok(),);
	}

	#[test]
	fn message_is_rejected_when_sent_using_disabled_lane() {
		assert_eq!(
			source::FromThisChainMessageVerifier::<OnThisChainBridge>::verify_message(
				&ThisChainOrigin(Ok(frame_system::RawOrigin::Root)),
				&ThisChainBalance(1_000_000),
				b"dsbl",
				&test_lane_outbound_data(),
				&regular_outbound_message_payload(),
			),
			Err(source::MESSAGE_REJECTED_BY_OUTBOUND_LANE)
		);
	}

	#[test]
	fn message_is_rejected_when_there_are_too_many_pending_messages_at_outbound_lane() {
		assert_eq!(
			source::FromThisChainMessageVerifier::<OnThisChainBridge>::verify_message(
				&ThisChainOrigin(Ok(frame_system::RawOrigin::Root)),
				&ThisChainBalance(1_000_000),
				TEST_LANE_ID,
				&OutboundLaneData {
					latest_received_nonce: 100,
					latest_generated_nonce: 100 + MAXIMAL_PENDING_MESSAGES_AT_TEST_LANE + 1,
					..Default::default()
				},
				&regular_outbound_message_payload(),
			),
			Err(source::TOO_MANY_PENDING_MESSAGES)
		);
	}

	#[test]
	fn verify_chain_message_rejects_message_with_too_small_declared_weight() {
		assert!(source::verify_chain_message::<OnThisChainBridge>(&vec![
			42;
			BRIDGED_CHAIN_MIN_EXTRINSIC_WEIGHT -
				1
		])
		.is_err());
	}

	#[test]
	fn verify_chain_message_rejects_message_with_too_large_declared_weight() {
		assert!(source::verify_chain_message::<OnThisChainBridge>(&vec![
			42;
			BRIDGED_CHAIN_MAX_EXTRINSIC_WEIGHT -
				1
		])
		.is_err());
	}

	#[test]
	fn verify_chain_message_rejects_message_too_large_message() {
		assert!(source::verify_chain_message::<OnThisChainBridge>(&vec![
			0;
			source::maximal_message_size::<OnThisChainBridge>()
				as usize + 1
		],)
		.is_err());
	}

	#[test]
	fn verify_chain_message_accepts_maximal_message() {
		assert_eq!(
			source::verify_chain_message::<OnThisChainBridge>(&vec![
				0;
				source::maximal_message_size::<OnThisChainBridge>()
					as _
			],),
			Ok(()),
		);
	}

	#[derive(Debug)]
	struct TestMessageProofParser {
		failing: bool,
		messages: RangeInclusive<MessageNonce>,
		outbound_lane_data: Option<OutboundLaneData>,
	}

	impl target::MessageProofParser for TestMessageProofParser {
		fn read_raw_outbound_lane_data(&self, _lane_id: &LaneId) -> Option<Vec<u8>> {
			if self.failing {
				Some(vec![])
			} else {
				self.outbound_lane_data.clone().map(|data| data.encode())
			}
		}

		fn read_raw_message(&self, message_key: &MessageKey) -> Option<Vec<u8>> {
			if self.failing {
				Some(vec![])
			} else if self.messages.contains(&message_key.nonce) {
				Some(
					MessageData::<BridgedChainBalance> {
						payload: message_key.nonce.encode(),
						fee: BridgedChainBalance(0),
					}
					.encode(),
				)
			} else {
				None
			}
		}
	}

	#[allow(clippy::reversed_empty_ranges)]
	fn no_messages_range() -> RangeInclusive<MessageNonce> {
		1..=0
	}

	fn messages_proof(nonces_end: MessageNonce) -> target::FromBridgedChainMessagesProof<()> {
		target::FromBridgedChainMessagesProof {
			bridged_header_hash: (),
			storage_proof: vec![],
			lane: Default::default(),
			nonces_start: 1,
			nonces_end,
		}
	}

	#[test]
	fn messages_proof_is_rejected_if_declared_less_than_actual_number_of_messages() {
		assert_eq!(
			target::verify_messages_proof_with_parser::<OnThisChainBridge, _, TestMessageProofParser>(
				messages_proof(10),
				5,
				|_, _| unreachable!(),
			),
			Err(target::MessageProofError::MessagesCountMismatch),
		);
	}

	#[test]
	fn messages_proof_is_rejected_if_declared_more_than_actual_number_of_messages() {
		assert_eq!(
			target::verify_messages_proof_with_parser::<OnThisChainBridge, _, TestMessageProofParser>(
				messages_proof(10),
				15,
				|_, _| unreachable!(),
			),
			Err(target::MessageProofError::MessagesCountMismatch),
		);
	}

	#[test]
	fn message_proof_is_rejected_if_build_parser_fails() {
		assert_eq!(
			target::verify_messages_proof_with_parser::<OnThisChainBridge, _, TestMessageProofParser>(
				messages_proof(10),
				10,
				|_, _| Err(target::MessageProofError::Custom("test")),
			),
			Err(target::MessageProofError::Custom("test")),
		);
	}

	#[test]
	fn message_proof_is_rejected_if_required_message_is_missing() {
		assert_eq!(
			target::verify_messages_proof_with_parser::<OnThisChainBridge, _, _>(
				messages_proof(10),
				10,
				|_, _| Ok(TestMessageProofParser {
					failing: false,
					messages: 1..=5,
					outbound_lane_data: None,
				}),
			),
			Err(target::MessageProofError::MissingRequiredMessage),
		);
	}

	#[test]
	fn message_proof_is_rejected_if_message_decode_fails() {
		assert_eq!(
			target::verify_messages_proof_with_parser::<OnThisChainBridge, _, _>(
				messages_proof(10),
				10,
				|_, _| Ok(TestMessageProofParser {
					failing: true,
					messages: 1..=10,
					outbound_lane_data: None,
				}),
			),
			Err(target::MessageProofError::FailedToDecodeMessage),
		);
	}

	#[test]
	fn message_proof_is_rejected_if_outbound_lane_state_decode_fails() {
		assert_eq!(
			target::verify_messages_proof_with_parser::<OnThisChainBridge, _, _>(
				messages_proof(0),
				0,
				|_, _| Ok(TestMessageProofParser {
					failing: true,
					messages: no_messages_range(),
					outbound_lane_data: Some(OutboundLaneData {
						oldest_unpruned_nonce: 1,
						latest_received_nonce: 1,
						latest_generated_nonce: 1,
					}),
				}),
			),
			Err(target::MessageProofError::FailedToDecodeOutboundLaneState),
		);
	}

	#[test]
	fn message_proof_is_rejected_if_it_is_empty() {
		assert_eq!(
			target::verify_messages_proof_with_parser::<OnThisChainBridge, _, _>(
				messages_proof(0),
				0,
				|_, _| Ok(TestMessageProofParser {
					failing: false,
					messages: no_messages_range(),
					outbound_lane_data: None,
				}),
			),
			Err(target::MessageProofError::Empty),
		);
	}

	#[test]
	fn non_empty_message_proof_without_messages_is_accepted() {
		assert_eq!(
			target::verify_messages_proof_with_parser::<OnThisChainBridge, _, _>(
				messages_proof(0),
				0,
				|_, _| Ok(TestMessageProofParser {
					failing: false,
					messages: no_messages_range(),
					outbound_lane_data: Some(OutboundLaneData {
						oldest_unpruned_nonce: 1,
						latest_received_nonce: 1,
						latest_generated_nonce: 1,
					}),
				}),
			),
			Ok(vec![(
				Default::default(),
				ProvedLaneMessages {
					lane_state: Some(OutboundLaneData {
						oldest_unpruned_nonce: 1,
						latest_received_nonce: 1,
						latest_generated_nonce: 1,
					}),
					messages: Vec::new(),
				},
			)]
			.into_iter()
			.collect()),
		);
	}

	#[test]
	fn non_empty_message_proof_is_accepted() {
		assert_eq!(
			target::verify_messages_proof_with_parser::<OnThisChainBridge, _, _>(
				messages_proof(1),
				1,
				|_, _| Ok(TestMessageProofParser {
					failing: false,
					messages: 1..=1,
					outbound_lane_data: Some(OutboundLaneData {
						oldest_unpruned_nonce: 1,
						latest_received_nonce: 1,
						latest_generated_nonce: 1,
					}),
				}),
			),
			Ok(vec![(
				Default::default(),
				ProvedLaneMessages {
					lane_state: Some(OutboundLaneData {
						oldest_unpruned_nonce: 1,
						latest_received_nonce: 1,
						latest_generated_nonce: 1,
					}),
					messages: vec![Message {
						key: MessageKey { lane_id: Default::default(), nonce: 1 },
						data: MessageData { payload: 1u64.encode(), fee: BridgedChainBalance(0) },
					}],
				},
			)]
			.into_iter()
			.collect()),
		);
	}

	#[test]
	fn verify_messages_proof_with_parser_does_not_panic_if_messages_count_mismatches() {
		assert_eq!(
			target::verify_messages_proof_with_parser::<OnThisChainBridge, _, _>(
				messages_proof(u64::MAX),
				0,
				|_, _| Ok(TestMessageProofParser {
					failing: false,
					messages: 0..=u64::MAX,
					outbound_lane_data: Some(OutboundLaneData {
						oldest_unpruned_nonce: 1,
						latest_received_nonce: 1,
						latest_generated_nonce: 1,
					}),
				}),
			),
			Err(target::MessageProofError::MessagesCountMismatch),
		);
	}

	#[test]
	fn transaction_payment_works_with_zero_multiplier() {
		use sp_runtime::traits::Zero;

		assert_eq!(
			transaction_payment(
				100,
				10,
				FixedU128::zero(),
				|weight| weight,
				MessageTransaction { size: 50, dispatch_weight: 777 },
			),
			100 + 50 * 10,
		);
	}

	#[test]
	fn transaction_payment_works_with_non_zero_multiplier() {
		use sp_runtime::traits::One;

		assert_eq!(
			transaction_payment(
				100,
				10,
				FixedU128::one(),
				|weight| weight,
				MessageTransaction { size: 50, dispatch_weight: 777 },
			),
			100 + 50 * 10 + 777,
		);
	}

	#[test]
	fn conversion_rate_override_works() {
		let payload = regular_outbound_message_payload();
		let regular_fee = source::estimate_message_dispatch_and_delivery_fee::<OnThisChainBridge>(
			&payload,
			OnThisChainBridge::RELAYER_FEE_PERCENT,
			None,
		);
		let overrided_fee = source::estimate_message_dispatch_and_delivery_fee::<OnThisChainBridge>(
			&payload,
			OnThisChainBridge::RELAYER_FEE_PERCENT,
			Some(FixedU128::from_float((BRIDGED_CHAIN_TO_THIS_CHAIN_BALANCE_RATE * 2) as f64)),
		);

		assert!(regular_fee < overrided_fee);
	}
}