// 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/>.

//! Runtime module which takes care of dispatching messages received over the bridge.
//!
//! The messages are interpreted directly as runtime `Call`. We attempt to decode
//! them and then dispatch as usual. To prevent compatibility issues, the Calls have
//! to include a `spec_version`. This will be checked before dispatch. In the case of
//! a successful dispatch an event is emitted.

#![cfg_attr(not(feature = "std"), no_std)]
#![warn(missing_docs)]
// Generated by `decl_event!`
#![allow(clippy::unused_unit)]

use bp_message_dispatch::{CallOrigin, MessageDispatch, MessagePayload, SpecVersion};
use bp_runtime::{
	derive_account_id,
	messages::{DispatchFeePayment, MessageDispatchResult},
	ChainId, SourceAccount,
};
use codec::Encode;
use frame_support::{
	dispatch::Dispatchable,
	ensure,
	traits::{Filter, Get},
	weights::{extract_actual_weight, GetDispatchInfo},
};
use frame_system::RawOrigin;
use sp_runtime::traits::{BadOrigin, Convert, IdentifyAccount, MaybeDisplay, Verify};
use sp_std::{fmt::Debug, prelude::*};

pub use pallet::*;

#[frame_support::pallet]
pub mod pallet {
	use super::*;
	use frame_support::pallet_prelude::*;
	use frame_system::pallet_prelude::*;

	#[pallet::config]
	pub trait Config<I: 'static = ()>: frame_system::Config {
		/// The overarching event type.
		type Event: From<Event<Self, I>> + IsType<<Self as frame_system::Config>::Event>;
		/// Id of the message. Whenever message is passed to the dispatch module, it emits
		/// event with this id + dispatch result. Could be e.g. (LaneId, MessageNonce) if
		/// it comes from the messages module.
		type MessageId: Parameter;
		/// Type of account ID on source chain.
		type SourceChainAccountId: Parameter + Member + MaybeSerializeDeserialize + Debug + MaybeDisplay + Ord + Default;
		/// Type of account public key on target chain.
		type TargetChainAccountPublic: Parameter + IdentifyAccount<AccountId = Self::AccountId>;
		/// Type of signature that may prove that the message has been signed by
		/// owner of `TargetChainAccountPublic`.
		type TargetChainSignature: Parameter + Verify<Signer = Self::TargetChainAccountPublic>;
		/// The overarching dispatch call type.
		type Call: Parameter
			+ GetDispatchInfo
			+ Dispatchable<
				Origin = <Self as frame_system::Config>::Origin,
				PostInfo = frame_support::dispatch::PostDispatchInfo,
			>;
		/// Pre-dispatch filter for incoming calls.
		///
		/// The pallet will filter all incoming calls right before they're dispatched. If this filter
		/// rejects the call, special event (`Event::MessageCallRejected`) is emitted.
		type CallFilter: Filter<<Self as Config<I>>::Call>;
		/// The type that is used to wrap the `Self::Call` when it is moved over bridge.
		///
		/// The idea behind this is to avoid `Call` conversion/decoding until we'll be sure
		/// that all other stuff (like `spec_version`) is ok. If we would try to decode
		/// `Call` which has been encoded using previous `spec_version`, then we might end
		/// up with decoding error, instead of `MessageVersionSpecMismatch`.
		type EncodedCall: Decode + Encode + Into<Result<<Self as Config<I>>::Call, ()>>;
		/// A type which can be turned into an AccountId from a 256-bit hash.
		///
		/// Used when deriving target chain AccountIds from source chain AccountIds.
		type AccountIdConverter: sp_runtime::traits::Convert<sp_core::hash::H256, Self::AccountId>;
	}

	type MessageIdOf<T, I> = <T as Config<I>>::MessageId;

	#[pallet::pallet]
	#[pallet::generate_store(pub(super) trait Store)]
	pub struct Pallet<T, I = ()>(PhantomData<(T, I)>);

	#[pallet::hooks]
	impl<T: Config<I>, I: 'static> Hooks<BlockNumberFor<T>> for Pallet<T, I> {}

	#[pallet::call]
	impl<T: Config<I>, I: 'static> Pallet<T, I> {}

	#[pallet::event]
	#[pallet::generate_deposit(pub(super) fn deposit_event)]
	#[pallet::metadata(<T as frame_system::Config>::AccountId = "AccountId", MessageIdOf<T, I> = "MessageId")]
	pub enum Event<T: Config<I>, I: 'static = ()> {
		/// Message has been rejected before reaching dispatch.
		MessageRejected(ChainId, MessageIdOf<T, I>),
		/// Message has been rejected by dispatcher because of spec version mismatch.
		/// Last two arguments are: expected and passed spec version.
		MessageVersionSpecMismatch(ChainId, MessageIdOf<T, I>, SpecVersion, SpecVersion),
		/// Message has been rejected by dispatcher because of weight mismatch.
		/// Last two arguments are: expected and passed call weight.
		MessageWeightMismatch(ChainId, MessageIdOf<T, I>, Weight, Weight),
		/// Message signature mismatch.
		MessageSignatureMismatch(ChainId, MessageIdOf<T, I>),
		/// We have failed to decode Call from the message.
		MessageCallDecodeFailed(ChainId, MessageIdOf<T, I>),
		/// The call from the message has been rejected by the call filter.
		MessageCallRejected(ChainId, MessageIdOf<T, I>),
		/// The origin account has failed to pay fee for dispatching the message.
		MessageDispatchPaymentFailed(
			ChainId,
			MessageIdOf<T, I>,
			<T as frame_system::Config>::AccountId,
			Weight,
		),
		/// Message has been dispatched with given result.
		MessageDispatched(ChainId, MessageIdOf<T, I>, DispatchResult),
		/// Phantom member, never used. Needed to handle multiple pallet instances.
		_Dummy(PhantomData<I>),
	}
}

impl<T: Config<I>, I: 'static> MessageDispatch<T::AccountId, T::MessageId> for Pallet<T, I> {
	type Message =
		MessagePayload<T::SourceChainAccountId, T::TargetChainAccountPublic, T::TargetChainSignature, T::EncodedCall>;

	fn dispatch_weight(message: &Self::Message) -> bp_message_dispatch::Weight {
		message.weight
	}

	fn dispatch<P: FnOnce(&T::AccountId, bp_message_dispatch::Weight) -> Result<(), ()>>(
		source_chain: ChainId,
		target_chain: ChainId,
		id: T::MessageId,
		message: Result<Self::Message, ()>,
		pay_dispatch_fee: P,
	) -> MessageDispatchResult {
		// emit special even if message has been rejected by external component
		let message = match message {
			Ok(message) => message,
			Err(_) => {
				log::trace!(
					target: "runtime::bridge-dispatch",
					"Message {:?}/{:?}: rejected before actual dispatch",
					source_chain,
					id,
				);
				Self::deposit_event(Event::MessageRejected(source_chain, id));
				return MessageDispatchResult {
					dispatch_result: false,
					unspent_weight: 0,
					dispatch_fee_paid_during_dispatch: false,
				};
			}
		};

		// verify spec version
		// (we want it to be the same, because otherwise we may decode Call improperly)
		let mut dispatch_result = MessageDispatchResult {
			dispatch_result: false,
			unspent_weight: message.weight,
			dispatch_fee_paid_during_dispatch: false,
		};
		let expected_version = <T as frame_system::Config>::Version::get().spec_version;
		if message.spec_version != expected_version {
			log::trace!(
				"Message {:?}/{:?}: spec_version mismatch. Expected {:?}, got {:?}",
				source_chain,
				id,
				expected_version,
				message.spec_version,
			);
			Self::deposit_event(Event::MessageVersionSpecMismatch(
				source_chain,
				id,
				expected_version,
				message.spec_version,
			));
			return dispatch_result;
		}

		// now that we have spec version checked, let's decode the call
		let call = match message.call.into() {
			Ok(call) => call,
			Err(_) => {
				log::trace!(
					target: "runtime::bridge-dispatch",
					"Failed to decode Call from message {:?}/{:?}",
					source_chain,
					id,
				);
				Self::deposit_event(Event::MessageCallDecodeFailed(source_chain, id));
				return dispatch_result;
			}
		};

		// prepare dispatch origin
		let origin_account = match message.origin {
			CallOrigin::SourceRoot => {
				let hex_id = derive_account_id::<T::SourceChainAccountId>(source_chain, SourceAccount::Root);
				let target_id = T::AccountIdConverter::convert(hex_id);
				log::trace!(target: "runtime::bridge-dispatch", "Root Account: {:?}", &target_id);
				target_id
			}
			CallOrigin::TargetAccount(source_account_id, target_public, target_signature) => {
				let digest = account_ownership_digest(
					&call,
					source_account_id,
					message.spec_version,
					source_chain,
					target_chain,
				);

				let target_account = target_public.into_account();
				if !target_signature.verify(&digest[..], &target_account) {
					log::trace!(
						target: "runtime::bridge-dispatch",
						"Message {:?}/{:?}: origin proof is invalid. Expected account: {:?} from signature: {:?}",
						source_chain,
						id,
						target_account,
						target_signature,
					);
					Self::deposit_event(Event::MessageSignatureMismatch(source_chain, id));
					return dispatch_result;
				}

				log::trace!(target: "runtime::bridge-dispatch", "Target Account: {:?}", &target_account);
				target_account
			}
			CallOrigin::SourceAccount(source_account_id) => {
				let hex_id = derive_account_id(source_chain, SourceAccount::Account(source_account_id));
				let target_id = T::AccountIdConverter::convert(hex_id);
				log::trace!(target: "runtime::bridge-dispatch", "Source Account: {:?}", &target_id);
				target_id
			}
		};

		// filter the call
		if !T::CallFilter::filter(&call) {
			log::trace!(
				target: "runtime::bridge-dispatch",
				"Message {:?}/{:?}: the call ({:?}) is rejected by filter",
				source_chain,
				id,
				call,
			);
			Self::deposit_event(Event::MessageCallRejected(source_chain, id));
			return dispatch_result;
		}

		// verify weight
		// (we want passed weight to be at least equal to pre-dispatch weight of the call
		// because otherwise Calls may be dispatched at lower price)
		let dispatch_info = call.get_dispatch_info();
		let expected_weight = dispatch_info.weight;
		if message.weight < expected_weight {
			log::trace!(
				target: "runtime::bridge-dispatch",
				"Message {:?}/{:?}: passed weight is too low. Expected at least {:?}, got {:?}",
				source_chain,
				id,
				expected_weight,
				message.weight,
			);
			Self::deposit_event(Event::MessageWeightMismatch(
				source_chain,
				id,
				expected_weight,
				message.weight,
			));
			return dispatch_result;
		}

		// pay dispatch fee right before dispatch
		let pay_dispatch_fee_at_target_chain = message.dispatch_fee_payment == DispatchFeePayment::AtTargetChain;
		if pay_dispatch_fee_at_target_chain && pay_dispatch_fee(&origin_account, message.weight).is_err() {
			log::trace!(
				target: "runtime::bridge-dispatch",
				"Failed to pay dispatch fee for dispatching message {:?}/{:?} with weight {}",
				source_chain,
				id,
				message.weight,
			);
			Self::deposit_event(Event::MessageDispatchPaymentFailed(
				source_chain,
				id,
				origin_account,
				message.weight,
			));
			return dispatch_result;
		}
		dispatch_result.dispatch_fee_paid_during_dispatch = pay_dispatch_fee_at_target_chain;

		// finally dispatch message
		let origin = RawOrigin::Signed(origin_account).into();

		log::trace!(target: "runtime::bridge-dispatch", "Message being dispatched is: {:.4096?}", &call);
		let result = call.dispatch(origin);
		let actual_call_weight = extract_actual_weight(&result, &dispatch_info);
		dispatch_result.dispatch_result = result.is_ok();
		dispatch_result.unspent_weight = message.weight.saturating_sub(actual_call_weight);

		log::trace!(
			target: "runtime::bridge-dispatch",
			"Message {:?}/{:?} has been dispatched. Weight: {} of {}. Result: {:?}. Call dispatch result: {:?}",
			source_chain,
			id,
			actual_call_weight,
			message.weight,
			dispatch_result,
			result,
		);

		Self::deposit_event(Event::MessageDispatched(
			source_chain,
			id,
			result.map(drop).map_err(|e| e.error),
		));

		dispatch_result
	}
}

/// Check if the message is allowed to be dispatched on the target chain given the sender's origin
/// on the source chain.
///
/// For example, if a message is sent from a "regular" account on the source chain it will not be
/// allowed to be dispatched as Root on the target chain. This is a useful check to do on the source
/// chain _before_ sending a message whose dispatch will be rejected on the target chain.
pub fn verify_message_origin<SourceChainAccountId, TargetChainAccountPublic, TargetChainSignature, Call>(
	sender_origin: &RawOrigin<SourceChainAccountId>,
	message: &MessagePayload<SourceChainAccountId, TargetChainAccountPublic, TargetChainSignature, Call>,
) -> Result<Option<SourceChainAccountId>, BadOrigin>
where
	SourceChainAccountId: PartialEq + Clone,
{
	match message.origin {
		CallOrigin::SourceRoot => {
			ensure!(sender_origin == &RawOrigin::Root, BadOrigin);
			Ok(None)
		}
		CallOrigin::TargetAccount(ref source_account_id, _, _) => {
			ensure!(
				sender_origin == &RawOrigin::Signed(source_account_id.clone()),
				BadOrigin
			);
			Ok(Some(source_account_id.clone()))
		}
		CallOrigin::SourceAccount(ref source_account_id) => {
			ensure!(
				sender_origin == &RawOrigin::Signed(source_account_id.clone()) || sender_origin == &RawOrigin::Root,
				BadOrigin
			);
			Ok(Some(source_account_id.clone()))
		}
	}
}

/// Target account ownership digest from the source chain.
///
/// The byte vector returned by this function will be signed with a target chain account
/// private key. This way, the owner of `source_account_id` on the source chain proves that
/// the target chain account private key is also under his control.
pub fn account_ownership_digest<Call, AccountId, SpecVersion>(
	call: &Call,
	source_account_id: AccountId,
	target_spec_version: SpecVersion,
	source_chain_id: ChainId,
	target_chain_id: ChainId,
) -> Vec<u8>
where
	Call: Encode,
	AccountId: Encode,
	SpecVersion: Encode,
{
	let mut proof = Vec::new();
	call.encode_to(&mut proof);
	source_account_id.encode_to(&mut proof);
	target_spec_version.encode_to(&mut proof);
	source_chain_id.encode_to(&mut proof);
	target_chain_id.encode_to(&mut proof);

	proof
}

#[cfg(test)]
mod tests {
	// From construct_runtime macro
	#![allow(clippy::from_over_into)]

	use super::*;
	use codec::Decode;
	use frame_support::{parameter_types, weights::Weight};
	use frame_system::{EventRecord, Phase};
	use sp_core::H256;
	use sp_runtime::{
		testing::Header,
		traits::{BlakeTwo256, IdentityLookup},
		Perbill,
	};

	type AccountId = u64;
	type MessageId = [u8; 4];

	const SOURCE_CHAIN_ID: ChainId = *b"srce";
	const TARGET_CHAIN_ID: ChainId = *b"trgt";

	#[derive(Debug, Encode, Decode, Clone, PartialEq, Eq)]
	pub struct TestAccountPublic(AccountId);

	impl IdentifyAccount for TestAccountPublic {
		type AccountId = AccountId;

		fn into_account(self) -> AccountId {
			self.0
		}
	}

	#[derive(Debug, Encode, Decode, Clone, PartialEq, Eq)]
	pub struct TestSignature(AccountId);

	impl Verify for TestSignature {
		type Signer = TestAccountPublic;

		fn verify<L: sp_runtime::traits::Lazy<[u8]>>(&self, _msg: L, signer: &AccountId) -> bool {
			self.0 == *signer
		}
	}

	pub struct AccountIdConverter;

	impl sp_runtime::traits::Convert<H256, AccountId> for AccountIdConverter {
		fn convert(hash: H256) -> AccountId {
			hash.to_low_u64_ne()
		}
	}

	type Block = frame_system::mocking::MockBlock<TestRuntime>;
	type UncheckedExtrinsic = frame_system::mocking::MockUncheckedExtrinsic<TestRuntime>;

	use crate as call_dispatch;

	frame_support::construct_runtime! {
		pub enum TestRuntime where
			Block = Block,
			NodeBlock = Block,
			UncheckedExtrinsic = UncheckedExtrinsic,
		{
			System: frame_system::{Pallet, Call, Config, Storage, Event<T>},
			Dispatch: call_dispatch::{Pallet, Call, Event<T>},
		}
	}

	parameter_types! {
		pub const BlockHashCount: u64 = 250;
		pub const MaximumBlockWeight: Weight = 1024;
		pub const MaximumBlockLength: u32 = 2 * 1024;
		pub const AvailableBlockRatio: Perbill = Perbill::one();
	}

	impl frame_system::Config for TestRuntime {
		type Origin = Origin;
		type Index = u64;
		type Call = Call;
		type BlockNumber = u64;
		type Hash = H256;
		type Hashing = BlakeTwo256;
		type AccountId = AccountId;
		type Lookup = IdentityLookup<Self::AccountId>;
		type Header = Header;
		type Event = Event;
		type BlockHashCount = BlockHashCount;
		type Version = ();
		type PalletInfo = PalletInfo;
		type AccountData = ();
		type OnNewAccount = ();
		type OnKilledAccount = ();
		type BaseCallFilter = ();
		type SystemWeightInfo = ();
		type BlockWeights = ();
		type BlockLength = ();
		type DbWeight = ();
		type SS58Prefix = ();
		type OnSetCode = ();
	}

	impl Config for TestRuntime {
		type Event = Event;
		type MessageId = MessageId;
		type SourceChainAccountId = AccountId;
		type TargetChainAccountPublic = TestAccountPublic;
		type TargetChainSignature = TestSignature;
		type Call = Call;
		type CallFilter = TestCallFilter;
		type EncodedCall = EncodedCall;
		type AccountIdConverter = AccountIdConverter;
	}

	#[derive(Decode, Encode)]
	pub struct EncodedCall(Vec<u8>);

	impl From<EncodedCall> for Result<Call, ()> {
		fn from(call: EncodedCall) -> Result<Call, ()> {
			Call::decode(&mut &call.0[..]).map_err(drop)
		}
	}

	pub struct TestCallFilter;

	impl Filter<Call> for TestCallFilter {
		fn filter(call: &Call) -> bool {
			!matches!(*call, Call::System(frame_system::Call::fill_block(_)))
		}
	}

	const TEST_SPEC_VERSION: SpecVersion = 0;
	const TEST_WEIGHT: Weight = 1_000_000_000;

	fn new_test_ext() -> sp_io::TestExternalities {
		let t = frame_system::GenesisConfig::default()
			.build_storage::<TestRuntime>()
			.unwrap();
		sp_io::TestExternalities::new(t)
	}

	fn prepare_message(
		origin: CallOrigin<AccountId, TestAccountPublic, TestSignature>,
		call: Call,
	) -> <Pallet<TestRuntime> as MessageDispatch<AccountId, <TestRuntime as Config>::MessageId>>::Message {
		MessagePayload {
			spec_version: TEST_SPEC_VERSION,
			weight: TEST_WEIGHT,
			origin,
			dispatch_fee_payment: DispatchFeePayment::AtSourceChain,
			call: EncodedCall(call.encode()),
		}
	}

	fn prepare_root_message(
		call: Call,
	) -> <Pallet<TestRuntime> as MessageDispatch<AccountId, <TestRuntime as Config>::MessageId>>::Message {
		prepare_message(CallOrigin::SourceRoot, call)
	}

	fn prepare_target_message(
		call: Call,
	) -> <Pallet<TestRuntime> as MessageDispatch<AccountId, <TestRuntime as Config>::MessageId>>::Message {
		let origin = CallOrigin::TargetAccount(1, TestAccountPublic(1), TestSignature(1));
		prepare_message(origin, call)
	}

	fn prepare_source_message(
		call: Call,
	) -> <Pallet<TestRuntime> as MessageDispatch<AccountId, <TestRuntime as Config>::MessageId>>::Message {
		let origin = CallOrigin::SourceAccount(1);
		prepare_message(origin, call)
	}

	#[test]
	fn should_fail_on_spec_version_mismatch() {
		new_test_ext().execute_with(|| {
			let id = [0; 4];

			const BAD_SPEC_VERSION: SpecVersion = 99;
			let mut message =
				prepare_root_message(Call::System(<frame_system::Call<TestRuntime>>::remark(vec![1, 2, 3])));
			let weight = message.weight;
			message.spec_version = BAD_SPEC_VERSION;

			System::set_block_number(1);
			let result = Dispatch::dispatch(SOURCE_CHAIN_ID, TARGET_CHAIN_ID, id, Ok(message), |_, _| unreachable!());
			assert_eq!(result.unspent_weight, weight);
			assert!(!result.dispatch_result);

			assert_eq!(
				System::events(),
				vec![EventRecord {
					phase: Phase::Initialization,
					event: Event::Dispatch(call_dispatch::Event::<TestRuntime>::MessageVersionSpecMismatch(
						SOURCE_CHAIN_ID,
						id,
						TEST_SPEC_VERSION,
						BAD_SPEC_VERSION
					)),
					topics: vec![],
				}],
			);
		});
	}

	#[test]
	fn should_fail_on_weight_mismatch() {
		new_test_ext().execute_with(|| {
			let id = [0; 4];
			let call = Call::System(<frame_system::Call<TestRuntime>>::remark(vec![1, 2, 3]));
			let call_weight = call.get_dispatch_info().weight;
			let mut message = prepare_root_message(call);
			message.weight = 7;
			assert!(
				call_weight != 7,
				"needed for test to actually trigger a weight mismatch"
			);

			System::set_block_number(1);
			let result = Dispatch::dispatch(SOURCE_CHAIN_ID, TARGET_CHAIN_ID, id, Ok(message), |_, _| unreachable!());
			assert_eq!(result.unspent_weight, 7);
			assert!(!result.dispatch_result);

			assert_eq!(
				System::events(),
				vec![EventRecord {
					phase: Phase::Initialization,
					event: Event::Dispatch(call_dispatch::Event::<TestRuntime>::MessageWeightMismatch(
						SOURCE_CHAIN_ID,
						id,
						call_weight,
						7,
					)),
					topics: vec![],
				}],
			);
		});
	}

	#[test]
	fn should_fail_on_signature_mismatch() {
		new_test_ext().execute_with(|| {
			let id = [0; 4];

			let call_origin = CallOrigin::TargetAccount(1, TestAccountPublic(1), TestSignature(99));
			let message = prepare_message(
				call_origin,
				Call::System(<frame_system::Call<TestRuntime>>::remark(vec![1, 2, 3])),
			);
			let weight = message.weight;

			System::set_block_number(1);
			let result = Dispatch::dispatch(SOURCE_CHAIN_ID, TARGET_CHAIN_ID, id, Ok(message), |_, _| unreachable!());
			assert_eq!(result.unspent_weight, weight);
			assert!(!result.dispatch_result);

			assert_eq!(
				System::events(),
				vec![EventRecord {
					phase: Phase::Initialization,
					event: Event::Dispatch(call_dispatch::Event::<TestRuntime>::MessageSignatureMismatch(
						SOURCE_CHAIN_ID,
						id
					)),
					topics: vec![],
				}],
			);
		});
	}

	#[test]
	fn should_emit_event_for_rejected_messages() {
		new_test_ext().execute_with(|| {
			let id = [0; 4];

			System::set_block_number(1);
			Dispatch::dispatch(SOURCE_CHAIN_ID, TARGET_CHAIN_ID, id, Err(()), |_, _| unreachable!());

			assert_eq!(
				System::events(),
				vec![EventRecord {
					phase: Phase::Initialization,
					event: Event::Dispatch(call_dispatch::Event::<TestRuntime>::MessageRejected(
						SOURCE_CHAIN_ID,
						id
					)),
					topics: vec![],
				}],
			);
		});
	}

	#[test]
	fn should_fail_on_call_decode() {
		new_test_ext().execute_with(|| {
			let id = [0; 4];

			let mut message =
				prepare_root_message(Call::System(<frame_system::Call<TestRuntime>>::remark(vec![1, 2, 3])));
			let weight = message.weight;
			message.call.0 = vec![];

			System::set_block_number(1);
			let result = Dispatch::dispatch(SOURCE_CHAIN_ID, TARGET_CHAIN_ID, id, Ok(message), |_, _| unreachable!());
			assert_eq!(result.unspent_weight, weight);
			assert!(!result.dispatch_result);

			assert_eq!(
				System::events(),
				vec![EventRecord {
					phase: Phase::Initialization,
					event: Event::Dispatch(call_dispatch::Event::<TestRuntime>::MessageCallDecodeFailed(
						SOURCE_CHAIN_ID,
						id
					)),
					topics: vec![],
				}],
			);
		});
	}

	#[test]
	fn should_emit_event_for_rejected_calls() {
		new_test_ext().execute_with(|| {
			let id = [0; 4];

			let call = Call::System(<frame_system::Call<TestRuntime>>::fill_block(Perbill::from_percent(75)));
			let weight = call.get_dispatch_info().weight;
			let mut message = prepare_root_message(call);
			message.weight = weight;

			System::set_block_number(1);
			let result = Dispatch::dispatch(SOURCE_CHAIN_ID, TARGET_CHAIN_ID, id, Ok(message), |_, _| unreachable!());
			assert_eq!(result.unspent_weight, weight);
			assert!(!result.dispatch_result);

			assert_eq!(
				System::events(),
				vec![EventRecord {
					phase: Phase::Initialization,
					event: Event::Dispatch(call_dispatch::Event::<TestRuntime>::MessageCallRejected(
						SOURCE_CHAIN_ID,
						id
					)),
					topics: vec![],
				}],
			);
		});
	}

	#[test]
	fn should_emit_event_for_unpaid_calls() {
		new_test_ext().execute_with(|| {
			let id = [0; 4];

			let mut message =
				prepare_root_message(Call::System(<frame_system::Call<TestRuntime>>::remark(vec![1, 2, 3])));
			let weight = message.weight;
			message.dispatch_fee_payment = DispatchFeePayment::AtTargetChain;

			System::set_block_number(1);
			let result = Dispatch::dispatch(SOURCE_CHAIN_ID, TARGET_CHAIN_ID, id, Ok(message), |_, _| Err(()));
			assert_eq!(result.unspent_weight, weight);
			assert!(!result.dispatch_result);

			assert_eq!(
				System::events(),
				vec![EventRecord {
					phase: Phase::Initialization,
					event: Event::Dispatch(call_dispatch::Event::<TestRuntime>::MessageDispatchPaymentFailed(
						SOURCE_CHAIN_ID,
						id,
						AccountIdConverter::convert(derive_account_id::<AccountId>(
							SOURCE_CHAIN_ID,
							SourceAccount::Root
						)),
						TEST_WEIGHT,
					)),
					topics: vec![],
				}],
			);
		});
	}

	#[test]
	fn should_dispatch_calls_paid_at_target_chain() {
		new_test_ext().execute_with(|| {
			let id = [0; 4];

			let mut message =
				prepare_root_message(Call::System(<frame_system::Call<TestRuntime>>::remark(vec![1, 2, 3])));
			message.dispatch_fee_payment = DispatchFeePayment::AtTargetChain;

			System::set_block_number(1);
			let result = Dispatch::dispatch(SOURCE_CHAIN_ID, TARGET_CHAIN_ID, id, Ok(message), |_, _| Ok(()));
			assert!(result.dispatch_fee_paid_during_dispatch);
			assert!(result.dispatch_result);

			assert_eq!(
				System::events(),
				vec![EventRecord {
					phase: Phase::Initialization,
					event: Event::Dispatch(call_dispatch::Event::<TestRuntime>::MessageDispatched(
						SOURCE_CHAIN_ID,
						id,
						Ok(())
					)),
					topics: vec![],
				}],
			);
		});
	}

	#[test]
	fn should_return_dispatch_failed_flag_if_dispatch_happened_but_failed() {
		new_test_ext().execute_with(|| {
			let id = [0; 4];

			let call = Call::System(<frame_system::Call<TestRuntime>>::set_heap_pages(1));
			let message = prepare_target_message(call);

			System::set_block_number(1);
			let result = Dispatch::dispatch(SOURCE_CHAIN_ID, TARGET_CHAIN_ID, id, Ok(message), |_, _| unreachable!());
			assert!(!result.dispatch_fee_paid_during_dispatch);
			assert!(!result.dispatch_result);

			assert_eq!(
				System::events(),
				vec![EventRecord {
					phase: Phase::Initialization,
					event: Event::Dispatch(call_dispatch::Event::<TestRuntime>::MessageDispatched(
						SOURCE_CHAIN_ID,
						id,
						Err(sp_runtime::DispatchError::BadOrigin)
					)),
					topics: vec![],
				}],
			);
		})
	}

	#[test]
	fn should_dispatch_bridge_message_from_root_origin() {
		new_test_ext().execute_with(|| {
			let id = [0; 4];
			let message = prepare_root_message(Call::System(<frame_system::Call<TestRuntime>>::remark(vec![1, 2, 3])));

			System::set_block_number(1);
			let result = Dispatch::dispatch(SOURCE_CHAIN_ID, TARGET_CHAIN_ID, id, Ok(message), |_, _| unreachable!());
			assert!(!result.dispatch_fee_paid_during_dispatch);
			assert!(result.dispatch_result);

			assert_eq!(
				System::events(),
				vec![EventRecord {
					phase: Phase::Initialization,
					event: Event::Dispatch(call_dispatch::Event::<TestRuntime>::MessageDispatched(
						SOURCE_CHAIN_ID,
						id,
						Ok(())
					)),
					topics: vec![],
				}],
			);
		});
	}

	#[test]
	fn should_dispatch_bridge_message_from_target_origin() {
		new_test_ext().execute_with(|| {
			let id = [0; 4];

			let call = Call::System(<frame_system::Call<TestRuntime>>::remark(vec![]));
			let message = prepare_target_message(call);

			System::set_block_number(1);
			let result = Dispatch::dispatch(SOURCE_CHAIN_ID, TARGET_CHAIN_ID, id, Ok(message), |_, _| unreachable!());
			assert!(!result.dispatch_fee_paid_during_dispatch);
			assert!(result.dispatch_result);

			assert_eq!(
				System::events(),
				vec![EventRecord {
					phase: Phase::Initialization,
					event: Event::Dispatch(call_dispatch::Event::<TestRuntime>::MessageDispatched(
						SOURCE_CHAIN_ID,
						id,
						Ok(())
					)),
					topics: vec![],
				}],
			);
		})
	}

	#[test]
	fn should_dispatch_bridge_message_from_source_origin() {
		new_test_ext().execute_with(|| {
			let id = [0; 4];

			let call = Call::System(<frame_system::Call<TestRuntime>>::remark(vec![]));
			let message = prepare_source_message(call);

			System::set_block_number(1);
			let result = Dispatch::dispatch(SOURCE_CHAIN_ID, TARGET_CHAIN_ID, id, Ok(message), |_, _| unreachable!());
			assert!(!result.dispatch_fee_paid_during_dispatch);
			assert!(result.dispatch_result);

			assert_eq!(
				System::events(),
				vec![EventRecord {
					phase: Phase::Initialization,
					event: Event::Dispatch(call_dispatch::Event::<TestRuntime>::MessageDispatched(
						SOURCE_CHAIN_ID,
						id,
						Ok(())
					)),
					topics: vec![],
				}],
			);
		})
	}

	#[test]
	fn origin_is_checked_when_verifying_sending_message_using_source_root_account() {
		let call = Call::System(<frame_system::Call<TestRuntime>>::remark(vec![]));
		let message = prepare_root_message(call);

		// When message is sent by Root, CallOrigin::SourceRoot is allowed
		assert!(matches!(verify_message_origin(&RawOrigin::Root, &message), Ok(None)));

		// when message is sent by some real account, CallOrigin::SourceRoot is not allowed
		assert!(matches!(
			verify_message_origin(&RawOrigin::Signed(1), &message),
			Err(BadOrigin)
		));
	}

	#[test]
	fn origin_is_checked_when_verifying_sending_message_using_target_account() {
		let call = Call::System(<frame_system::Call<TestRuntime>>::remark(vec![]));
		let message = prepare_target_message(call);

		// When message is sent by Root, CallOrigin::TargetAccount is not allowed
		assert!(matches!(
			verify_message_origin(&RawOrigin::Root, &message),
			Err(BadOrigin)
		));

		// When message is sent by some other account, it is rejected
		assert!(matches!(
			verify_message_origin(&RawOrigin::Signed(2), &message),
			Err(BadOrigin)
		));

		// When message is sent by a real account, it is allowed to have origin
		// CallOrigin::TargetAccount
		assert!(matches!(
			verify_message_origin(&RawOrigin::Signed(1), &message),
			Ok(Some(1))
		));
	}

	#[test]
	fn origin_is_checked_when_verifying_sending_message_using_source_account() {
		let call = Call::System(<frame_system::Call<TestRuntime>>::remark(vec![]));
		let message = prepare_source_message(call);

		// Sending a message from the expected origin account works
		assert!(matches!(
			verify_message_origin(&RawOrigin::Signed(1), &message),
			Ok(Some(1))
		));

		// If we send a message from a different account, it is rejected
		assert!(matches!(
			verify_message_origin(&RawOrigin::Signed(2), &message),
			Err(BadOrigin)
		));

		// The Root account is allowed to assume any expected origin account
		assert!(matches!(verify_message_origin(&RawOrigin::Root, &message), Ok(Some(1))));
	}
}