lib.rs

		});
	}

	/// Start the execution of a particular block.
	pub fn initialize(
		number: &T::BlockNumber,
		parent_hash: &T::Hash,
		txs_root: &T::Hash,
		digest: &DigestOf<T>,
		kind: InitKind,
	) {
		// populate environment
		ExecutionPhase::put(Phase::Initialization);
		storage::unhashed::put(well_known_keys::EXTRINSIC_INDEX, &0u32);
		<Number<T>>::put(number);
		<Digest<T>>::put(digest);
		<ParentHash<T>>::put(parent_hash);
		<BlockHash<T>>::insert(*number - One::one(), parent_hash);
		<ExtrinsicsRoot<T>>::put(txs_root);

		if let InitKind::Full = kind {
			<Events<T>>::kill();
			EventCount::kill();
			<EventTopics<T>>::remove_all();
		}
	}

	/// Remove temporary "environment" entries in storage.
	pub fn finalize() -> T::Header {
		ExecutionPhase::kill();
		ExtrinsicCount::kill();
		AllExtrinsicsWeight::kill();
		AllExtrinsicsLen::kill();

		let number = <Number<T>>::take();
		let parent_hash = <ParentHash<T>>::take();
		let mut digest = <Digest<T>>::take();
		let extrinsics_root = <ExtrinsicsRoot<T>>::take();

		// move block hash pruning window by one block
		let block_hash_count = <T::BlockHashCount>::get();
		if number > block_hash_count {
			let to_remove = number - block_hash_count - One::one();

			// keep genesis hash
			if to_remove != Zero::zero() {
				<BlockHash<T>>::remove(to_remove);
			}
		}

		let storage_root = T::Hash::decode(&mut &sp_io::storage::root()[..])
			.expect("Node is configured to use the same hash; qed");
		let storage_changes_root = sp_io::storage::changes_root(&parent_hash.encode());

		// we can't compute changes trie root earlier && put it to the Digest
		// because it will include all currently existing temporaries.
		if let Some(storage_changes_root) = storage_changes_root {
			let item = generic::DigestItem::ChangesTrieRoot(
				T::Hash::decode(&mut &storage_changes_root[..])
					.expect("Node is configured to use the same hash; qed")
			);
			digest.push(item);
		}

		// The following fields
		//
		// - <Events<T>>
		// - <EventCount<T>>
		// - <EventTopics<T>>
		//
		// stay to be inspected by the client and will be cleared by `Self::initialize`.

		<T::Header as traits::Header>::new(number, extrinsics_root, storage_root, parent_hash, digest)
	}

	/// Deposits a log and ensures it matches the block's log data.
	///
	/// # <weight>
	/// - `O(1)`
	/// - 1 storage write (codec `O(1)`)
	/// # </weight>
	pub fn deposit_log(item: DigestItemOf<T>) {
		<Digest<T>>::append(item);
	}

	/// Get the basic externalities for this module, useful for tests.
	#[cfg(any(feature = "std", test))]
	pub fn externalities() -> TestExternalities {
		TestExternalities::new(sp_core::storage::Storage {
			top: map![
				<BlockHash<T>>::hashed_key_for(T::BlockNumber::zero()) => [69u8; 32].encode(),
				<Number<T>>::hashed_key().to_vec() => T::BlockNumber::one().encode(),
				<ParentHash<T>>::hashed_key().to_vec() => [69u8; 32].encode()
			],
			children_default: map![],
		})
	}

	/// Set the block number to something in particular. Can be used as an alternative to
	/// `initialize` for tests that don't need to bother with the other environment entries.
	#[cfg(any(feature = "std", feature = "runtime-benchmarks", test))]
	pub fn set_block_number(n: T::BlockNumber) {
		<Number<T>>::put(n);
	}

	/// Sets the index of extrinsic that is currently executing.
	#[cfg(any(feature = "std", test))]
	pub fn set_extrinsic_index(extrinsic_index: u32) {
		storage::unhashed::put(well_known_keys::EXTRINSIC_INDEX, &extrinsic_index)
	}

	/// Set the parent hash number to something in particular. Can be used as an alternative to
	/// `initialize` for tests that don't need to bother with the other environment entries.
	#[cfg(any(feature = "std", test))]
	pub fn set_parent_hash(n: T::Hash) {
		<ParentHash<T>>::put(n);
	}

	/// Set the current block weight. This should only be used in some integration tests.
	#[cfg(any(feature = "std", test))]
	pub fn set_block_limits(weight: Weight, len: usize) {
		AllExtrinsicsWeight::mutate(|current_weight| {
			current_weight.put(weight, DispatchClass::Normal)
		});
		AllExtrinsicsLen::put(len as u32);
	}

	/// Return the chain's current runtime version.
	pub fn runtime_version() -> RuntimeVersion { T::Version::get() }

	/// Retrieve the account transaction counter from storage.
	pub fn account_nonce(who: impl EncodeLike<T::AccountId>) -> T::Index {
		Account::<T>::get(who).nonce
	}

	/// Increment a particular account's nonce by 1.
	pub fn inc_account_nonce(who: impl EncodeLike<T::AccountId>) {
		Account::<T>::mutate(who, |a| a.nonce += T::Index::one());
	}

	/// Note what the extrinsic data of the current extrinsic index is. If this
	/// is called, then ensure `derive_extrinsics` is also called before
	/// block-building is completed.
	///
	/// NOTE: This function is called only when the block is being constructed locally.
	/// `execute_block` doesn't note any extrinsics.
	pub fn note_extrinsic(encoded_xt: Vec<u8>) {
		ExtrinsicData::insert(Self::extrinsic_index().unwrap_or_default(), encoded_xt);
	}

	/// To be called immediately after an extrinsic has been applied.
	pub fn note_applied_extrinsic(r: &DispatchOutcome, _encoded_len: u32, info: DispatchInfo) {
		Self::deposit_event(
			match r {
				Ok(()) => RawEvent::ExtrinsicSuccess(info),
				Err(err) => {
					sp_runtime::print(err);
					RawEvent::ExtrinsicFailed(err.clone(), info)
				},
			}
		);

		let next_extrinsic_index = Self::extrinsic_index().unwrap_or_default() + 1u32;

		storage::unhashed::put(well_known_keys::EXTRINSIC_INDEX, &next_extrinsic_index);
		ExecutionPhase::put(Phase::ApplyExtrinsic(next_extrinsic_index));
	}

	/// To be called immediately after `note_applied_extrinsic` of the last extrinsic of the block
	/// has been called.
	pub fn note_finished_extrinsics() {
		let extrinsic_index: u32 = storage::unhashed::take(well_known_keys::EXTRINSIC_INDEX)
			.unwrap_or_default();
		ExtrinsicCount::put(extrinsic_index);
		ExecutionPhase::put(Phase::Finalization);
	}

	/// To be called immediately after finishing the initialization of the block
	/// (e.g., called `on_initialize` for all modules).
	pub fn note_finished_initialize() {
		ExecutionPhase::put(Phase::ApplyExtrinsic(0))
	}

	/// Remove all extrinsic data and save the extrinsics trie root.
	pub fn derive_extrinsics() {
		let extrinsics = (0..ExtrinsicCount::get().unwrap_or_default())
			.map(ExtrinsicData::take).collect();
		let xts_root = extrinsics_data_root::<T::Hashing>(extrinsics);
		<ExtrinsicsRoot<T>>::put(xts_root);
	}

	/// An account is being created.
	pub fn on_created_account(who: T::AccountId) {
		T::OnNewAccount::on_new_account(&who);
		Self::deposit_event(RawEvent::NewAccount(who));
	}

	/// Do anything that needs to be done after an account has been killed.
	fn on_killed_account(who: T::AccountId) {
		T::OnKilledAccount::on_killed_account(&who);
		Self::deposit_event(RawEvent::KilledAccount(who));
	}

	/// Remove an account from storage. This should only be done when its refs are zero or you'll
	/// get storage leaks in other modules. Nonetheless we assume that the calling logic knows best.
	///
	/// This is a no-op if the account doesn't already exist. If it does then it will ensure
	/// cleanups (those in `on_killed_account`) take place.
	fn kill_account(who: &T::AccountId) {
		if Account::<T>::contains_key(who) {
			let account = Account::<T>::take(who);
			if account.refcount > 0 {
				debug::debug!(
					target: "system",
					"WARNING: Referenced account deleted. This is probably a bug."
				);
			}
			Module::<T>::on_killed_account(who.clone());
		}
	}

	/// Determine whether or not it is possible to update the code.
	///
	/// This function has no side effects and is idempotent, but is fairly
	/// heavy. It is automatically called by `set_code`; in most cases,
	/// a direct call to `set_code` is preferable. It is useful to call
	/// `can_set_code` when it is desirable to perform the appropriate
	/// runtime checks without actually changing the code yet.
	pub fn can_set_code(origin: T::Origin, code: &[u8]) -> Result<(), sp_runtime::DispatchError> {
		ensure_root(origin)?;

		let current_version = T::Version::get();
		let new_version = sp_io::misc::runtime_version(&code)
			.and_then(|v| RuntimeVersion::decode(&mut &v[..]).ok())
			.ok_or_else(|| Error::<T>::FailedToExtractRuntimeVersion)?;

		if new_version.spec_name != current_version.spec_name {
			Err(Error::<T>::InvalidSpecName)?
		}

		if new_version.spec_version <= current_version.spec_version {
			Err(Error::<T>::SpecVersionNeedsToIncrease)?
		}

		Ok(())
	}
}

/// Event handler which calls on_created_account when it happens.
pub struct CallOnCreatedAccount<T>(PhantomData<T>);
impl<T: Trait> Happened<T::AccountId> for CallOnCreatedAccount<T> {
	fn happened(who: &T::AccountId) {
		Module::<T>::on_created_account(who.clone());
	}
}

/// Event handler which calls kill_account when it happens.
pub struct CallKillAccount<T>(PhantomData<T>);
impl<T: Trait> Happened<T::AccountId> for CallKillAccount<T> {
	fn happened(who: &T::AccountId) {
		Module::<T>::kill_account(who)
	}
}

// Implement StoredMap for a simple single-item, kill-account-on-remove system. This works fine for
// storing a single item which is required to not be empty/default for the account to exist.
// Anything more complex will need more sophisticated logic.
impl<T: Trait> StoredMap<T::AccountId, T::AccountData> for Module<T> {
	fn get(k: &T::AccountId) -> T::AccountData {
		Account::<T>::get(k).data
	}
	fn is_explicit(k: &T::AccountId) -> bool {
		Account::<T>::contains_key(k)
	}
	fn insert(k: &T::AccountId, data: T::AccountData) {
		let existed = Account::<T>::contains_key(k);
		Account::<T>::mutate(k, |a| a.data = data);
		if !existed {
			Self::on_created_account(k.clone());
		}
	}
	fn remove(k: &T::AccountId) {
		Self::kill_account(k)
	}
	fn mutate<R>(k: &T::AccountId, f: impl FnOnce(&mut T::AccountData) -> R) -> R {
		let existed = Account::<T>::contains_key(k);
		let r = Account::<T>::mutate(k, |a| f(&mut a.data));
		if !existed {
			Self::on_created_account(k.clone());
		}
		r
	}
	fn mutate_exists<R>(k: &T::AccountId, f: impl FnOnce(&mut Option<T::AccountData>) -> R) -> R {
		Self::try_mutate_exists(k, |x| -> Result<R, Infallible> { Ok(f(x)) }).expect("Infallible; qed")
	}
	fn try_mutate_exists<R, E>(k: &T::AccountId, f: impl FnOnce(&mut Option<T::AccountData>) -> Result<R, E>) -> Result<R, E> {
		Account::<T>::try_mutate_exists(k, |maybe_value| {
			let existed = maybe_value.is_some();
			let (maybe_prefix, mut maybe_data) = split_inner(
				maybe_value.take(),
				|account| ((account.nonce, account.refcount), account.data)
			);
			f(&mut maybe_data).map(|result| {
				*maybe_value = maybe_data.map(|data| {
					let (nonce, refcount) = maybe_prefix.unwrap_or_default();
					AccountInfo { nonce, refcount, data }
				});
				(existed, maybe_value.is_some(), result)
			})
		}).map(|(existed, exists, v)| {
			if !existed && exists {
				Self::on_created_account(k.clone());
			} else if existed && !exists {
				Self::on_killed_account(k.clone());
			}
			v
		})
	}
}

/// Split an `option` into two constituent options, as defined by a `splitter` function.
pub fn split_inner<T, R, S>(option: Option<T>, splitter: impl FnOnce(T) -> (R, S))
	-> (Option<R>, Option<S>)
{
	match option {
		Some(inner) => {
			let (r, s) = splitter(inner);
			(Some(r), Some(s))
		}
		None => (None, None),
	}
}

/// resource limit check.
#[derive(Encode, Decode, Clone, Eq, PartialEq)]
pub struct CheckWeight<T: Trait + Send + Sync>(PhantomData<T>);

impl<T: Trait + Send + Sync> CheckWeight<T> where
	T::Call: Dispatchable<Info=DispatchInfo, PostInfo=PostDispatchInfo>
{
	/// Get the quota ratio of each dispatch class type. This indicates that all operational and mandatory
	/// dispatches can use the full capacity of any resource, while user-triggered ones can consume
	/// a portion.
	fn get_dispatch_limit_ratio(class: DispatchClass) -> Perbill {
		match class {
			DispatchClass::Operational | DispatchClass::Mandatory
				=> <Perbill as sp_runtime::PerThing>::one(),
			DispatchClass::Normal => T::AvailableBlockRatio::get(),
		}
	}

	/// Checks if the current extrinsic can fit into the block with respect to block weight limits.
	///
	/// Upon successes, it returns the new block weight as a `Result`.
	fn check_weight(
		info: &DispatchInfoOf<T::Call>,
	) -> Result<ExtrinsicsWeight, TransactionValidityError> {
		let maximum_weight = T::MaximumBlockWeight::get();
		let mut all_weight = Module::<T>::all_extrinsics_weight();
		match info.class {
			// If we have a dispatch that must be included in the block, it ignores all the limits.
			DispatchClass::Mandatory => {
				let extrinsic_weight = info.weight.saturating_add(T::ExtrinsicBaseWeight::get());
				all_weight.add(extrinsic_weight, DispatchClass::Mandatory);
				Ok(all_weight)
			},
			// If we have a normal dispatch, we follow all the normal rules and limits.
			DispatchClass::Normal => {
				let normal_limit = Self::get_dispatch_limit_ratio(DispatchClass::Normal) * maximum_weight;
				let extrinsic_weight = info.weight.checked_add(T::ExtrinsicBaseWeight::get())
					.ok_or(InvalidTransaction::ExhaustsResources)?;
				all_weight.checked_add(extrinsic_weight, DispatchClass::Normal)
					.map_err(|_| InvalidTransaction::ExhaustsResources)?;
				if all_weight.get(DispatchClass::Normal) > normal_limit {
					Err(InvalidTransaction::ExhaustsResources.into())
				} else {
					Ok(all_weight)
				}
			},
			// If we have an operational dispatch, allow it if we have not used our full
			// "operational space" (independent of existing fullness).
			DispatchClass::Operational => {
				let operational_limit = Self::get_dispatch_limit_ratio(DispatchClass::Operational) * maximum_weight;
				let normal_limit = Self::get_dispatch_limit_ratio(DispatchClass::Normal) * maximum_weight;
				let operational_space = operational_limit.saturating_sub(normal_limit);

				let extrinsic_weight = info.weight.checked_add(T::ExtrinsicBaseWeight::get())
					.ok_or(InvalidTransaction::ExhaustsResources)?;
				all_weight.checked_add(extrinsic_weight, DispatchClass::Operational)
					.map_err(|_| InvalidTransaction::ExhaustsResources)?;

				// If it would fit in normally, its okay
				if all_weight.total() <= maximum_weight ||
				// If we have not used our operational space
				all_weight.get(DispatchClass::Operational) <= operational_space {
					Ok(all_weight)
				} else {
					Err(InvalidTransaction::ExhaustsResources.into())
				}
			}
		}
	}

	/// Checks if the current extrinsic can fit into the block with respect to block length limits.
	///
	/// Upon successes, it returns the new block length as a `Result`.
	fn check_block_length(
		info: &DispatchInfoOf<T::Call>,
		len: usize,
	) -> Result<u32, TransactionValidityError> {
		let current_len = Module::<T>::all_extrinsics_len();
		let maximum_len = T::MaximumBlockLength::get();
		let limit = Self::get_dispatch_limit_ratio(info.class) * maximum_len;
		let added_len = len as u32;
		let next_len = current_len.saturating_add(added_len);
		if next_len > limit {
			Err(InvalidTransaction::ExhaustsResources.into())
		} else {
			Ok(next_len)
		}
	}

	/// get the priority of an extrinsic denoted by `info`.
	fn get_priority(info: &DispatchInfoOf<T::Call>) -> TransactionPriority {
		match info.class {
			DispatchClass::Normal => info.weight.into(),
			DispatchClass::Operational => Bounded::max_value(),
			// Mandatory extrinsics are only for inherents; never transactions.
			DispatchClass::Mandatory => Bounded::min_value(),
		}
	}

	/// Creates new `SignedExtension` to check weight of the extrinsic.
	pub fn new() -> Self {
		Self(PhantomData)
	}

	/// Do the pre-dispatch checks. This can be applied to both signed and unsigned.
	///
	/// It checks and notes the new weight and length.
	fn do_pre_dispatch(
		info: &DispatchInfoOf<T::Call>,
		len: usize,
	) -> Result<(), TransactionValidityError> {
		let next_len = Self::check_block_length(info, len)?;
		let next_weight = Self::check_weight(info)?;
		AllExtrinsicsLen::put(next_len);
		AllExtrinsicsWeight::put(next_weight);
		Ok(())
	}

	/// Do the validate checks. This can be applied to both signed and unsigned.
	///
	/// It only checks that the block weight and length limit will not exceed.
	fn do_validate(
		info: &DispatchInfoOf<T::Call>,
		len: usize,
	) -> TransactionValidity {
		// ignore the next weight and length. If they return `Ok`, then it is below the limit.
		let _ = Self::check_block_length(info, len)?;
		let _ = Self::check_weight(info)?;

		Ok(ValidTransaction { priority: Self::get_priority(info), ..Default::default() })
	}
}

impl<T: Trait + Send + Sync> SignedExtension for CheckWeight<T> where
	T::Call: Dispatchable<Info=DispatchInfo, PostInfo=PostDispatchInfo>
{
	type AccountId = T::AccountId;
	type Call = T::Call;
	type AdditionalSigned = ();
	type Pre = ();
	const IDENTIFIER: &'static str = "CheckWeight";

	fn additional_signed(&self) -> sp_std::result::Result<(), TransactionValidityError> { Ok(()) }

	fn pre_dispatch(
		self,
		_who: &Self::AccountId,
		_call: &Self::Call,
		info: &DispatchInfoOf<Self::Call>,
		len: usize,
	) -> Result<(), TransactionValidityError> {
		if info.class == DispatchClass::Mandatory {
			Err(InvalidTransaction::MandatoryDispatch)?
		}
		Self::do_pre_dispatch(info, len)
	}

	fn validate(
		&self,
		_who: &Self::AccountId,
		_call: &Self::Call,
		info: &DispatchInfoOf<Self::Call>,
		len: usize,
	) -> TransactionValidity {
		if info.class == DispatchClass::Mandatory {
			Err(InvalidTransaction::MandatoryDispatch)?
		}
		Self::do_validate(info, len)
	}

	fn pre_dispatch_unsigned(
		_call: &Self::Call,
		info: &DispatchInfoOf<Self::Call>,
		len: usize,
	) -> Result<(), TransactionValidityError> {
		Self::do_pre_dispatch(info, len)
	}

	fn validate_unsigned(
		_call: &Self::Call,
		info: &DispatchInfoOf<Self::Call>,
		len: usize,
	) -> TransactionValidity {
		Self::do_validate(info, len)
	}

	fn post_dispatch(
		_pre: Self::Pre,
		info: &DispatchInfoOf<Self::Call>,
		post_info: &PostDispatchInfoOf<Self::Call>,
		_len: usize,
		result: &DispatchResult,
	) -> Result<(), TransactionValidityError> {
		// Since mandatory dispatched do not get validated for being overweight, we are sensitive
		// to them actually being useful. Block producers are thus not allowed to include mandatory
		// extrinsics that result in error.
		if info.class == DispatchClass::Mandatory && result.is_err() {
			Err(InvalidTransaction::BadMandatory)?
		}

		let unspent = post_info.calc_unspent(info);
		if unspent > 0 {
			AllExtrinsicsWeight::mutate(|current_weight| {
				current_weight.sub(unspent, info.class);
			})
		}

		Ok(())
	}
}

impl<T: Trait + Send + Sync> Debug for CheckWeight<T> {
	#[cfg(feature = "std")]
	fn fmt(&self, f: &mut sp_std::fmt::Formatter) -> sp_std::fmt::Result {
		write!(f, "CheckWeight")
	}

	#[cfg(not(feature = "std"))]
	fn fmt(&self, _: &mut sp_std::fmt::Formatter) -> sp_std::fmt::Result {
		Ok(())
	}
}

/// Nonce check and increment to give replay protection for transactions.
#[derive(Encode, Decode, Clone, Eq, PartialEq)]
pub struct CheckNonce<T: Trait>(#[codec(compact)] T::Index);

impl<T: Trait> CheckNonce<T> {
	/// utility constructor. Used only in client/factory code.
	pub fn from(nonce: T::Index) -> Self {
		Self(nonce)
	}
}

impl<T: Trait> Debug for CheckNonce<T> {
	#[cfg(feature = "std")]
	fn fmt(&self, f: &mut sp_std::fmt::Formatter) -> sp_std::fmt::Result {
		write!(f, "CheckNonce({})", self.0)
	}

	#[cfg(not(feature = "std"))]
	fn fmt(&self, _: &mut sp_std::fmt::Formatter) -> sp_std::fmt::Result {
		Ok(())
	}
}

impl<T: Trait> SignedExtension for CheckNonce<T> where
	T::Call: Dispatchable<Info=DispatchInfo>
{
	type AccountId = T::AccountId;
	type Call = T::Call;
	type AdditionalSigned = ();
	type Pre = ();
	const IDENTIFIER: &'static str = "CheckNonce";

	fn additional_signed(&self) -> sp_std::result::Result<(), TransactionValidityError> { Ok(()) }

	fn pre_dispatch(
		self,
		who: &Self::AccountId,
		_call: &Self::Call,
		_info: &DispatchInfoOf<Self::Call>,
		_len: usize,
	) -> Result<(), TransactionValidityError> {
		let mut account = Account::<T>::get(who);
		if self.0 != account.nonce {
			return Err(
				if self.0 < account.nonce {
					InvalidTransaction::Stale
				} else {
					InvalidTransaction::Future
				}.into()
			)
		}
		account.nonce += T::Index::one();
		Account::<T>::insert(who, account);
		Ok(())
	}

	fn validate(
		&self,
		who: &Self::AccountId,
		_call: &Self::Call,
		info: &DispatchInfoOf<Self::Call>,
		_len: usize,
	) -> TransactionValidity {
		// check index
		let account = Account::<T>::get(who);
		if self.0 < account.nonce {
			return InvalidTransaction::Stale.into()
		}

		let provides = vec![Encode::encode(&(who, self.0))];
		let requires = if account.nonce < self.0 {
			vec![Encode::encode(&(who, self.0 - One::one()))]
		} else {
			vec![]
		};

		Ok(ValidTransaction {
			priority: info.weight as TransactionPriority,
			requires,
			provides,
			longevity: TransactionLongevity::max_value(),
			propagate: true,
		})
	}
}

impl<T: Trait> IsDeadAccount<T::AccountId> for Module<T> {
	fn is_dead_account(who: &T::AccountId) -> bool {
		!Account::<T>::contains_key(who)
	}
}

/// Check for transaction mortality.
#[derive(Encode, Decode, Clone, Eq, PartialEq)]
pub struct CheckEra<T: Trait + Send + Sync>(Era, sp_std::marker::PhantomData<T>);

impl<T: Trait + Send + Sync> CheckEra<T> {
	/// utility constructor. Used only in client/factory code.
	pub fn from(era: Era) -> Self {
		Self(era, sp_std::marker::PhantomData)
	}
}

impl<T: Trait + Send + Sync> Debug for CheckEra<T> {
	#[cfg(feature = "std")]
	fn fmt(&self, f: &mut sp_std::fmt::Formatter) -> sp_std::fmt::Result {
		write!(f, "CheckEra({:?})", self.0)
	}

	#[cfg(not(feature = "std"))]
	fn fmt(&self, _: &mut sp_std::fmt::Formatter) -> sp_std::fmt::Result {
		Ok(())
	}
}

impl<T: Trait + Send + Sync> SignedExtension for CheckEra<T> {
	type AccountId = T::AccountId;
	type Call = T::Call;
	type AdditionalSigned = T::Hash;
	type Pre = ();
	const IDENTIFIER: &'static str = "CheckEra";

	fn validate(
		&self,
		_who: &Self::AccountId,
		_call: &Self::Call,
		_info: &DispatchInfoOf<Self::Call>,
		_len: usize,
	) -> TransactionValidity {
		let current_u64 = <Module<T>>::block_number().saturated_into::<u64>();
		let valid_till = self.0.death(current_u64);
		Ok(ValidTransaction {
			longevity: valid_till.saturating_sub(current_u64),
			..Default::default()
		})
	}

	fn additional_signed(&self) -> Result<Self::AdditionalSigned, TransactionValidityError> {
		let current_u64 = <Module<T>>::block_number().saturated_into::<u64>();
		let n = self.0.birth(current_u64).saturated_into::<T::BlockNumber>();
		if !<BlockHash<T>>::contains_key(n) {
			Err(InvalidTransaction::AncientBirthBlock.into())
		} else {
			Ok(<Module<T>>::block_hash(n))
		}
	}
}

/// Nonce check and increment to give replay protection for transactions.
#[derive(Encode, Decode, Clone, Eq, PartialEq)]
pub struct CheckGenesis<T: Trait + Send + Sync>(sp_std::marker::PhantomData<T>);

impl<T: Trait + Send + Sync> Debug for CheckGenesis<T> {
	#[cfg(feature = "std")]
	fn fmt(&self, f: &mut sp_std::fmt::Formatter) -> sp_std::fmt::Result {
		write!(f, "CheckGenesis")
	}

	#[cfg(not(feature = "std"))]
	fn fmt(&self, _: &mut sp_std::fmt::Formatter) -> sp_std::fmt::Result {
		Ok(())
	}
}

impl<T: Trait + Send + Sync> CheckGenesis<T> {
	/// Creates new `SignedExtension` to check genesis hash.
	pub fn new() -> Self {
		Self(sp_std::marker::PhantomData)
	}
}

impl<T: Trait + Send + Sync> SignedExtension for CheckGenesis<T> {
	type AccountId = T::AccountId;
	type Call = <T as Trait>::Call;
	type AdditionalSigned = T::Hash;
	type Pre = ();
	const IDENTIFIER: &'static str = "CheckGenesis";

	fn additional_signed(&self) -> Result<Self::AdditionalSigned, TransactionValidityError> {
		Ok(<Module<T>>::block_hash(T::BlockNumber::zero()))
	}
}

/// Ensure the transaction version registered in the transaction is the same as at present.
#[derive(Encode, Decode, Clone, Eq, PartialEq)]
pub struct CheckTxVersion<T: Trait + Send + Sync>(sp_std::marker::PhantomData<T>);

impl<T: Trait + Send + Sync> Debug for CheckTxVersion<T> {
	#[cfg(feature = "std")]
	fn fmt(&self, f: &mut sp_std::fmt::Formatter) -> sp_std::fmt::Result {
		write!(f, "CheckTxVersion")
	}

	#[cfg(not(feature = "std"))]
	fn fmt(&self, _: &mut sp_std::fmt::Formatter) -> sp_std::fmt::Result {
		Ok(())
	}
}

impl<T: Trait + Send + Sync> CheckTxVersion<T> {
	/// Create new `SignedExtension` to check transaction version.
	pub fn new() -> Self {
		Self(sp_std::marker::PhantomData)
	}
}

impl<T: Trait + Send + Sync> SignedExtension for CheckTxVersion<T> {
	type AccountId = T::AccountId;
	type Call = <T as Trait>::Call;
	type AdditionalSigned = u32;
	type Pre = ();
	const IDENTIFIER: &'static str = "CheckTxVersion";

	fn additional_signed(&self) -> Result<Self::AdditionalSigned, TransactionValidityError> {
		Ok(<Module<T>>::runtime_version().transaction_version)
	}
}

/// Ensure the runtime version registered in the transaction is the same as at present.
#[derive(Encode, Decode, Clone, Eq, PartialEq)]
pub struct CheckSpecVersion<T: Trait + Send + Sync>(sp_std::marker::PhantomData<T>);

impl<T: Trait + Send + Sync> Debug for CheckSpecVersion<T> {
	#[cfg(feature = "std")]
	fn fmt(&self, f: &mut sp_std::fmt::Formatter) -> sp_std::fmt::Result {
		write!(f, "CheckSpecVersion")
	}

	#[cfg(not(feature = "std"))]
	fn fmt(&self, _: &mut sp_std::fmt::Formatter) -> sp_std::fmt::Result {
		Ok(())
	}
}

impl<T: Trait + Send + Sync> CheckSpecVersion<T> {
	/// Create new `SignedExtension` to check runtime version.
	pub fn new() -> Self {
		Self(sp_std::marker::PhantomData)
	}
}

impl<T: Trait + Send + Sync> SignedExtension for CheckSpecVersion<T> {
	type AccountId = T::AccountId;
	type Call = <T as Trait>::Call;
	type AdditionalSigned = u32;
	type Pre = ();
	const IDENTIFIER: &'static str = "CheckSpecVersion";

	fn additional_signed(&self) -> Result<Self::AdditionalSigned, TransactionValidityError> {
		Ok(<Module<T>>::runtime_version().spec_version)
	}
}

pub struct ChainContext<T>(sp_std::marker::PhantomData<T>);
impl<T> Default for ChainContext<T> {
	fn default() -> Self {
		ChainContext(sp_std::marker::PhantomData)
	}
}

impl<T: Trait> Lookup for ChainContext<T> {
	type Source = <T::Lookup as StaticLookup>::Source;
	type Target = <T::Lookup as StaticLookup>::Target;

	fn lookup(&self, s: Self::Source) -> Result<Self::Target, LookupError> {
		<T::Lookup as StaticLookup>::lookup(s)
	}
}

#[cfg(test)]
pub(crate) mod tests {
	use super::*;
	use sp_std::cell::RefCell;
	use sp_core::H256;
	use sp_runtime::{traits::{BlakeTwo256, IdentityLookup, SignedExtension}, testing::Header, DispatchError};
	use frame_support::{impl_outer_origin, parameter_types, assert_ok, assert_noop};

	impl_outer_origin! {
		pub enum Origin for Test where system = super {}
	}

	#[derive(Clone, Eq, PartialEq, Debug)]
	pub struct Test;

	parameter_types! {
		pub const BlockHashCount: u64 = 10;
		pub const MaximumBlockWeight: Weight = 1024;
		pub const AvailableBlockRatio: Perbill = Perbill::from_percent(75);
		pub const MaximumBlockLength: u32 = 1024;
		pub const Version: RuntimeVersion = RuntimeVersion {
			spec_name: sp_version::create_runtime_str!("test"),
			impl_name: sp_version::create_runtime_str!("system-test"),
			authoring_version: 1,
			spec_version: 1,
			impl_version: 1,
			apis: sp_version::create_apis_vec!([]),
			transaction_version: 1,
		};
		pub const BlockExecutionWeight: Weight = 10;
		pub const ExtrinsicBaseWeight: Weight = 5;
		pub const DbWeight: RuntimeDbWeight = RuntimeDbWeight {
			read: 10,
			write: 100,
		};
	}

	thread_local!{
		pub static KILLED: RefCell<Vec<u64>> = RefCell::new(vec![]);
	}

	pub struct RecordKilled;
	impl OnKilledAccount<u64> for RecordKilled {
		fn on_killed_account(who: &u64) { KILLED.with(|r| r.borrow_mut().push(*who)) }
	}

	#[derive(Debug, codec::Encode, codec::Decode)]
	pub struct Call;

	impl Dispatchable for Call {
		type Origin = ();
		type Trait = ();
		type Info = DispatchInfo;
		type PostInfo = PostDispatchInfo;
		fn dispatch(self, _origin: Self::Origin)
			-> sp_runtime::DispatchResultWithInfo<Self::PostInfo> {
				panic!("Do not use dummy implementation for dispatch.");
		}
	}

	impl Trait for Test {
		type Origin = Origin;
		type Call = Call;
		type Index = u64;
		type BlockNumber = u64;
		type Hash = H256;
		type Hashing = BlakeTwo256;
		type AccountId = u64;
		type Lookup = IdentityLookup<Self::AccountId>;
		type Header = Header;
		type Event = u16;
		type BlockHashCount = BlockHashCount;
		type MaximumBlockWeight = MaximumBlockWeight;
		type DbWeight = DbWeight;
		type BlockExecutionWeight = BlockExecutionWeight;
		type ExtrinsicBaseWeight = ExtrinsicBaseWeight;
		type AvailableBlockRatio = AvailableBlockRatio;
		type MaximumBlockLength = MaximumBlockLength;
		type Version = Version;
		type ModuleToIndex = ();
		type AccountData = u32;
		type OnNewAccount = ();
		type OnKilledAccount = RecordKilled;
	}

	impl From<Event<Test>> for u16 {
		fn from(e: Event<Test>) -> u16 {
			match e {
				Event::<Test>::ExtrinsicSuccess(..) => 100,
				Event::<Test>::ExtrinsicFailed(..) => 101,
				Event::<Test>::CodeUpdated => 102,
				_ => 103,
			}
		}
	}

	type System = Module<Test>;

	const CALL: &<Test as Trait>::Call = &Call;

	fn new_test_ext() -> sp_io::TestExternalities {
		let mut ext: sp_io::TestExternalities = GenesisConfig::default().build_storage::<Test>().unwrap().into();
		// Add to each test the initial weight of a block
		ext.execute_with(|| System::register_extra_weight_unchecked(<Test as Trait>::BlockExecutionWeight::get(), DispatchClass::Mandatory));
		ext
	}

	fn normal_weight_limit() -> Weight {
		<Test as Trait>::AvailableBlockRatio::get() * <Test as Trait>::MaximumBlockWeight::get()
	}

	fn normal_length_limit() -> u32 {
		<Test as Trait>::AvailableBlockRatio::get() * <Test as Trait>::MaximumBlockLength::get()
	}

	#[test]
	fn origin_works() {
		let o = Origin::from(RawOrigin::<u64>::Signed(1u64));
		let x: Result<RawOrigin<u64>, Origin> = o.into();
		assert_eq!(x, Ok(RawOrigin::<u64>::Signed(1u64)));
	}

	#[test]
	fn stored_map_works() {
		new_test_ext().execute_with(|| {
			System::insert(&0, 42);
			assert!(System::allow_death(&0));

			System::inc_ref(&0);
			assert!(!System::allow_death(&0));

			System::insert(&0, 69);
			assert!(!System::allow_death(&0));

			System::dec_ref(&0);
			assert!(System::allow_death(&0));

			assert!(KILLED.with(|r| r.borrow().is_empty()));
			System::kill_account(&0);
			assert_eq!(KILLED.with(|r| r.borrow().clone()), vec![0u64]);
		});
	}

	#[test]
	fn deposit_event_should_work() {
		new_test_ext().execute_with(|| {
			System::initialize(
				&1,
				&[0u8; 32].into(),
				&[0u8; 32].into(),
				&Default::default(),
				InitKind::Full,
			);
			System::note_finished_extrinsics();
			System::deposit_event(1u16);
			System::finalize();
			assert_eq!(
				System::events(),
				vec![
					EventRecord {
						phase: Phase::Finalization,
						event: 1u16,
						topics: vec![],
					}
				]
			);

			System::initialize(
				&2,
				&[0u8; 32].into(),
				&[0u8; 32].into(),
				&Default::default(),
				InitKind::Full,
			);
			System::deposit_event(32u16);