lib.rs

	pub fn account_exists(who: &T::AccountId) -> bool {
		Account::<T>::contains_key(who)
	}

	/// Write code to the storage and emit related events and digest items.
	///
	/// Note this function almost never should be used directly. It is exposed
	/// for `OnSetCode` implementations that defer actual code being written to
	/// the storage (for instance in case of parachains).
	pub fn update_code_in_storage(code: &[u8]) -> DispatchResult {
		storage::unhashed::put_raw(well_known_keys::CODE, code);
		Self::deposit_log(generic::DigestItem::RuntimeEnvironmentUpdated);
		Self::deposit_event(Event::CodeUpdated);
		Ok(())
	}

	/// Increment the reference counter on an account.
	#[deprecated = "Use `inc_consumers` instead"]
	pub fn inc_ref(who: &T::AccountId) {
		let _ = Self::inc_consumers(who);
	}

	/// Decrement the reference counter on an account. This *MUST* only be done once for every time
	/// you called `inc_consumers` on `who`.
	#[deprecated = "Use `dec_consumers` instead"]
	pub fn dec_ref(who: &T::AccountId) {
		let _ = Self::dec_consumers(who);
	}

	/// The number of outstanding references for the account `who`.
	#[deprecated = "Use `consumers` instead"]
	pub fn refs(who: &T::AccountId) -> RefCount {
		Self::consumers(who)
	}

	/// True if the account has no outstanding references.
	#[deprecated = "Use `!is_provider_required` instead"]
	pub fn allow_death(who: &T::AccountId) -> bool {
		!Self::is_provider_required(who)
	}

	/// Increment the provider reference counter on an account.
	pub fn inc_providers(who: &T::AccountId) -> IncRefStatus {
		Account::<T>::mutate(who, |a| {
			if a.providers == 0 && a.sufficients == 0 {
				// Account is being created.
				a.providers = 1;
				Self::on_created_account(who.clone(), a);
				IncRefStatus::Created
			} else {
				a.providers = a.providers.saturating_add(1);
				IncRefStatus::Existed
			}
		})
	}

	/// Decrement the provider reference counter on an account.
	///
	/// This *MUST* only be done once for every time you called `inc_providers` on `who`.
	pub fn dec_providers(who: &T::AccountId) -> Result<DecRefStatus, DispatchError> {
		Account::<T>::try_mutate_exists(who, |maybe_account| {
			if let Some(mut account) = maybe_account.take() {
				if account.providers == 0 {
					// Logic error - cannot decrement beyond zero.
					log::error!(
						target: LOG_TARGET,
						"Logic error: Unexpected underflow in reducing provider",
					);
					account.providers = 1;
				}
				match (account.providers, account.consumers, account.sufficients) {
					(1, 0, 0) => {
						// No providers left (and no consumers) and no sufficients. Account dead.

						Pallet::<T>::on_killed_account(who.clone());
						Ok(DecRefStatus::Reaped)
					},
					(1, c, _) if c > 0 => {
						// Cannot remove last provider if there are consumers.
						Err(DispatchError::ConsumerRemaining)
					},
					(x, _, _) => {
						// Account will continue to exist as there is either > 1 provider or
						// > 0 sufficients.
						account.providers = x - 1;
						*maybe_account = Some(account);
						Ok(DecRefStatus::Exists)
					},
				}
			} else {
				log::error!(
					target: LOG_TARGET,
					"Logic error: Account already dead when reducing provider",
				);
				Ok(DecRefStatus::Reaped)
			}
		})
	}

	/// Increment the self-sufficient reference counter on an account.
	pub fn inc_sufficients(who: &T::AccountId) -> IncRefStatus {
		Account::<T>::mutate(who, |a| {
			if a.providers + a.sufficients == 0 {
				// Account is being created.
				a.sufficients = 1;
				Self::on_created_account(who.clone(), a);
				IncRefStatus::Created
			} else {
				a.sufficients = a.sufficients.saturating_add(1);
				IncRefStatus::Existed
			}
		})
	}

	/// Decrement the sufficients reference counter on an account.
	///
	/// This *MUST* only be done once for every time you called `inc_sufficients` on `who`.
	pub fn dec_sufficients(who: &T::AccountId) -> DecRefStatus {
		Account::<T>::mutate_exists(who, |maybe_account| {
			if let Some(mut account) = maybe_account.take() {
				if account.sufficients == 0 {
					// Logic error - cannot decrement beyond zero.
					log::error!(
						target: LOG_TARGET,
						"Logic error: Unexpected underflow in reducing sufficients",
					);
				}
				match (account.sufficients, account.providers) {
					(0, 0) | (1, 0) => {
						Pallet::<T>::on_killed_account(who.clone());
						DecRefStatus::Reaped
					},
					(x, _) => {
						account.sufficients = x - 1;
						*maybe_account = Some(account);
						DecRefStatus::Exists
					},
				}
			} else {
				log::error!(
					target: LOG_TARGET,
					"Logic error: Account already dead when reducing provider",
				);
				DecRefStatus::Reaped
			}
		})
	}

	/// The number of outstanding provider references for the account `who`.
	pub fn providers(who: &T::AccountId) -> RefCount {
		Account::<T>::get(who).providers
	}

	/// The number of outstanding sufficient references for the account `who`.
	pub fn sufficients(who: &T::AccountId) -> RefCount {
		Account::<T>::get(who).sufficients
	}

	/// The number of outstanding provider and sufficient references for the account `who`.
	pub fn reference_count(who: &T::AccountId) -> RefCount {
		let a = Account::<T>::get(who);
		a.providers + a.sufficients
	}

	/// Increment the reference counter on an account.
	///
	/// The account `who`'s `providers` must be non-zero and the current number of consumers must
	/// be less than `MaxConsumers::max_consumers()` or this will return an error.
	pub fn inc_consumers(who: &T::AccountId) -> Result<(), DispatchError> {
		Account::<T>::try_mutate(who, |a| {
			if a.providers > 0 {
				if a.consumers < T::MaxConsumers::max_consumers() {
					a.consumers = a.consumers.saturating_add(1);
					Ok(())
				} else {
					Err(DispatchError::TooManyConsumers)
				}
			} else {
				Err(DispatchError::NoProviders)
			}
		})
	}

	/// Increment the reference counter on an account, ignoring the `MaxConsumers` limits.
	///
	/// The account `who`'s `providers` must be non-zero or this will return an error.
	pub fn inc_consumers_without_limit(who: &T::AccountId) -> Result<(), DispatchError> {
		Account::<T>::try_mutate(who, |a| {
			if a.providers > 0 {
				a.consumers = a.consumers.saturating_add(1);
				Ok(())
			} else {
				Err(DispatchError::NoProviders)
			}
		})
	}

	/// Decrement the reference counter on an account. This *MUST* only be done once for every time
	/// you called `inc_consumers` on `who`.
	pub fn dec_consumers(who: &T::AccountId) {
		Account::<T>::mutate(who, |a| {
			if a.consumers > 0 {
				a.consumers -= 1;
			} else {
				log::error!(
					target: LOG_TARGET,
					"Logic error: Unexpected underflow in reducing consumer",
				);
			}
		})
	}

	/// The number of outstanding references for the account `who`.
	pub fn consumers(who: &T::AccountId) -> RefCount {
		Account::<T>::get(who).consumers
	}

	/// True if the account has some outstanding consumer references.
	pub fn is_provider_required(who: &T::AccountId) -> bool {
		Account::<T>::get(who).consumers != 0
	}

	/// True if the account has no outstanding consumer references or more than one provider.
	pub fn can_dec_provider(who: &T::AccountId) -> bool {
		let a = Account::<T>::get(who);
		a.consumers == 0 || a.providers > 1
	}

	/// True if the account has at least one provider reference.
	pub fn can_inc_consumer(who: &T::AccountId) -> bool {
		let a = Account::<T>::get(who);
		a.providers > 0 && a.consumers < T::MaxConsumers::max_consumers()
	}

	/// Deposits an event into this block's event record.
	///
	/// NOTE: Events not registered at the genesis block and quietly omitted.
	pub fn deposit_event(event: impl Into<T::RuntimeEvent>) {
		Self::deposit_event_indexed(&[], event.into());
	}

	/// Deposits an event into this block's event record adding this event
	/// to the corresponding topic indexes.
	///
	/// This will update storage entries that correspond to the specified topics.
	/// It is expected that light-clients could subscribe to this topics.
	///
	/// NOTE: Events not registered at the genesis block and quietly omitted.
	pub fn deposit_event_indexed(topics: &[T::Hash], event: T::RuntimeEvent) {
		let block_number = Self::block_number();
		// Don't populate events on genesis.
		if block_number.is_zero() {
			return
		}

		let phase = ExecutionPhase::<T>::get().unwrap_or_default();
		let event = EventRecord { phase, event, topics: topics.to_vec() };

		// Index of the to be added event.
		let event_idx = {
			let old_event_count = EventCount::<T>::get();
			let new_event_count = match old_event_count.checked_add(1) {
				// We've reached the maximum number of events at this block, just
				// don't do anything and leave the event_count unaltered.
				None => return,
				Some(nc) => nc,
			};
			EventCount::<T>::put(new_event_count);
			old_event_count
		};

		Events::<T>::append(event);

		for topic in topics {
			<EventTopics<T>>::append(topic, &(block_number, event_idx));
		}
	}

	/// Gets the index of extrinsic that is currently executing.
	pub fn extrinsic_index() -> Option<u32> {
		storage::unhashed::get(well_known_keys::EXTRINSIC_INDEX)
	}

	/// Gets extrinsics count.
	pub fn extrinsic_count() -> u32 {
		ExtrinsicCount::<T>::get().unwrap_or_default()
	}

	pub fn all_extrinsics_len() -> u32 {
		AllExtrinsicsLen::<T>::get().unwrap_or_default()
	}

	/// Inform the system pallet of some additional weight that should be accounted for, in the
	/// current block.
	///
	/// NOTE: use with extra care; this function is made public only be used for certain pallets
	/// that need it. A runtime that does not have dynamic calls should never need this and should
	/// stick to static weights. A typical use case for this is inner calls or smart contract calls.
	/// Furthermore, it only makes sense to use this when it is presumably  _cheap_ to provide the
	/// argument `weight`; In other words, if this function is to be used to account for some
	/// unknown, user provided call's weight, it would only make sense to use it if you are sure you
	/// can rapidly compute the weight of the inner call.
	///
	/// Even more dangerous is to note that this function does NOT take any action, if the new sum
	/// of block weight is more than the block weight limit. This is what the _unchecked_.
	///
	/// Another potential use-case could be for the `on_initialize` and `on_finalize` hooks.
	pub fn register_extra_weight_unchecked(weight: Weight, class: DispatchClass) {
		BlockWeight::<T>::mutate(|current_weight| {
			current_weight.accrue(weight, class);
		});
	}

	/// Start the execution of a particular block.
	pub fn initialize(number: &T::BlockNumber, parent_hash: &T::Hash, digest: &generic::Digest) {
		// populate environment
		ExecutionPhase::<T>::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);

		// Remove previous block data from storage
		BlockWeight::<T>::kill();
	}

	/// Remove temporary "environment" entries in storage, compute the storage root and return the
	/// resulting header for this block.
	pub fn finalize() -> T::Header {
		log::debug!(
			target: LOG_TARGET,
			"[{:?}] {} extrinsics, length: {} (normal {}%, op: {}%, mandatory {}%) / normal weight:\
			 {} ({}%) op weight {} ({}%) / mandatory weight {} ({}%)",
			Self::block_number(),
			Self::extrinsic_index().unwrap_or_default(),
			Self::all_extrinsics_len(),
			sp_runtime::Percent::from_rational(
				Self::all_extrinsics_len(),
				*T::BlockLength::get().max.get(DispatchClass::Normal)
			).deconstruct(),
			sp_runtime::Percent::from_rational(
				Self::all_extrinsics_len(),
				*T::BlockLength::get().max.get(DispatchClass::Operational)
			).deconstruct(),
			sp_runtime::Percent::from_rational(
				Self::all_extrinsics_len(),
				*T::BlockLength::get().max.get(DispatchClass::Mandatory)
			).deconstruct(),
			Self::block_weight().get(DispatchClass::Normal),
			sp_runtime::Percent::from_rational(
				Self::block_weight().get(DispatchClass::Normal).ref_time(),
				T::BlockWeights::get().get(DispatchClass::Normal).max_total.unwrap_or(Bounded::max_value()).ref_time()
			).deconstruct(),
			Self::block_weight().get(DispatchClass::Operational),
			sp_runtime::Percent::from_rational(
				Self::block_weight().get(DispatchClass::Operational).ref_time(),
				T::BlockWeights::get().get(DispatchClass::Operational).max_total.unwrap_or(Bounded::max_value()).ref_time()
			).deconstruct(),
			Self::block_weight().get(DispatchClass::Mandatory),
			sp_runtime::Percent::from_rational(
				Self::block_weight().get(DispatchClass::Mandatory).ref_time(),
				T::BlockWeights::get().get(DispatchClass::Mandatory).max_total.unwrap_or(Bounded::max_value()).ref_time()
			).deconstruct(),
		);
		ExecutionPhase::<T>::kill();
		AllExtrinsicsLen::<T>::kill();

		// The following fields
		//
		// - <Events<T>>
		// - <EventCount<T>>
		// - <EventTopics<T>>
		// - <Number<T>>
		// - <ParentHash<T>>
		// - <Digest<T>>
		//
		// stay to be inspected by the client and will be cleared by `Self::initialize`.
		let number = <Number<T>>::get();
		let parent_hash = <ParentHash<T>>::get();
		let digest = <Digest<T>>::get();

		let extrinsics = (0..ExtrinsicCount::<T>::take().unwrap_or_default())
			.map(ExtrinsicData::<T>::take)
			.collect();
		let extrinsics_root = extrinsics_data_root::<T::Hashing>(extrinsics);

		// move block hash pruning window by one block
		let block_hash_count = T::BlockHashCount::get();
		let to_remove = number.saturating_sub(block_hash_count).saturating_sub(One::one());

		// keep genesis hash
		if !to_remove.is_zero() {
			<BlockHash<T>>::remove(to_remove);
		}

		let version = T::Version::get().state_version();
		let storage_root = T::Hash::decode(&mut &sp_io::storage::root(version)[..])
			.expect("Node is configured to use the same hash; qed");

		<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.
	///
	/// ## Complexity
	/// - `O(1)`
	pub fn deposit_log(item: generic::DigestItem) {
		<Digest<T>>::append(item);
	}

	/// Get the basic externalities for this pallet, 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![],
		})
	}

	/// Get the current events deposited by the runtime.
	///
	/// NOTE: This should only be used in tests. Reading events from the runtime can have a large
	/// impact on the PoV size of a block. Users should use alternative and well bounded storage
	/// items for any behavior like this.
	///
	/// NOTE: Events not registered at the genesis block and quietly omitted.
	#[cfg(any(feature = "std", feature = "runtime-benchmarks", test))]
	pub fn events() -> Vec<EventRecord<T::RuntimeEvent, T::Hash>> {
		debug_assert!(
			!Self::block_number().is_zero(),
			"events not registered at the genesis block"
		);
		// Dereferencing the events here is fine since we are not in the
		// memory-restricted runtime.
		Self::read_events_no_consensus().map(|e| *e).collect()
	}

	/// Get the current events deposited by the runtime.
	///
	/// Should only be called if you know what you are doing and outside of the runtime block
	/// execution else it can have a large impact on the PoV size of a block.
	pub fn read_events_no_consensus(
	) -> impl sp_std::iter::Iterator<Item = Box<EventRecord<T::RuntimeEvent, T::Hash>>> {
		Events::<T>::stream_iter()
	}

	/// 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_consumed_resources(weight: Weight, len: usize) {
		BlockWeight::<T>::mutate(|current_weight| {
			current_weight.set(weight, DispatchClass::Normal)
		});
		AllExtrinsicsLen::<T>::put(len as u32);
	}

	/// Reset events.
	///
	/// This needs to be used in prior calling [`initialize`](Self::initialize) for each new block
	/// to clear events from previous block.
	pub fn reset_events() {
		<Events<T>>::kill();
		EventCount::<T>::kill();
		let _ = <EventTopics<T>>::clear(u32::max_value(), None);
	}

	/// Assert the given `event` exists.
	///
	/// NOTE: Events not registered at the genesis block and quietly omitted.
	#[cfg(any(feature = "std", feature = "runtime-benchmarks", test))]
	pub fn assert_has_event(event: T::RuntimeEvent) {
		let events = Self::events();
		assert!(
			events.iter().any(|record| record.event == event),
			"expected event {event:?} not found in events {events:?}",
		);
	}

	/// Assert the last event equal to the given `event`.
	///
	/// NOTE: Events not registered at the genesis block and quietly omitted.
	#[cfg(any(feature = "std", feature = "runtime-benchmarks", test))]
	pub fn assert_last_event(event: T::RuntimeEvent) {
		let last_event = Self::events().last().expect("events expected").event.clone();
		assert_eq!(
			last_event, event,
			"expected event {event:?} is not equal to the last event {last_event:?}",
		);
	}

	/// 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.
	///
	/// This is required to be called before applying an extrinsic. The data will used
	/// in [`Self::finalize`] to calculate the correct extrinsics root.
	pub fn note_extrinsic(encoded_xt: Vec<u8>) {
		ExtrinsicData::<T>::insert(Self::extrinsic_index().unwrap_or_default(), encoded_xt);
	}

	/// To be called immediately after an extrinsic has been applied.
	///
	/// Emits an `ExtrinsicSuccess` or `ExtrinsicFailed` event depending on the outcome.
	/// The emitted event contains the post-dispatch corrected weight including
	/// the base-weight for its dispatch class.
	pub fn note_applied_extrinsic(r: &DispatchResultWithPostInfo, mut info: DispatchInfo) {
		info.weight = extract_actual_weight(r, &info)
			.saturating_add(T::BlockWeights::get().get(info.class).base_extrinsic);
		info.pays_fee = extract_actual_pays_fee(r, &info);

		Self::deposit_event(match r {
			Ok(_) => Event::ExtrinsicSuccess { dispatch_info: info },
			Err(err) => {
				log::trace!(
					target: LOG_TARGET,
					"Extrinsic failed at block({:?}): {:?}",
					Self::block_number(),
					err,
				);
				Event::ExtrinsicFailed { dispatch_error: err.error, dispatch_info: info }
			},
		});

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

		storage::unhashed::put(well_known_keys::EXTRINSIC_INDEX, &next_extrinsic_index);
		ExecutionPhase::<T>::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::<T>::put(extrinsic_index);
		ExecutionPhase::<T>::put(Phase::Finalization);
	}

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

	/// An account is being created.
	pub fn on_created_account(who: T::AccountId, _a: &mut AccountInfo<T::Index, T::AccountData>) {
		T::OnNewAccount::on_new_account(&who);
		Self::deposit_event(Event::NewAccount { account: 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(Event::KilledAccount { account: who });
	}

	/// Determine whether or not it is possible to update the code.
	///
	/// Checks the given code if it is a valid runtime wasm blob by instantianting
	/// it and extracting the runtime version of it. It checks that the runtime version
	/// of the old and new runtime has the same spec name and that the spec version is increasing.
	pub fn can_set_code(code: &[u8]) -> Result<(), sp_runtime::DispatchError> {
		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(Error::<T>::FailedToExtractRuntimeVersion)?;

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

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

		Ok(())
	}
}

/// Event handler which registers a provider when created.
pub struct Provider<T>(PhantomData<T>);
impl<T: Config> HandleLifetime<T::AccountId> for Provider<T> {
	fn created(t: &T::AccountId) -> Result<(), DispatchError> {
		Pallet::<T>::inc_providers(t);
		Ok(())
	}
	fn killed(t: &T::AccountId) -> Result<(), DispatchError> {
		Pallet::<T>::dec_providers(t).map(|_| ())
	}
}

/// Event handler which registers a self-sufficient when created.
pub struct SelfSufficient<T>(PhantomData<T>);
impl<T: Config> HandleLifetime<T::AccountId> for SelfSufficient<T> {
	fn created(t: &T::AccountId) -> Result<(), DispatchError> {
		Pallet::<T>::inc_sufficients(t);
		Ok(())
	}
	fn killed(t: &T::AccountId) -> Result<(), DispatchError> {
		Pallet::<T>::dec_sufficients(t);
		Ok(())
	}
}

/// Event handler which registers a consumer when created.
pub struct Consumer<T>(PhantomData<T>);
impl<T: Config> HandleLifetime<T::AccountId> for Consumer<T> {
	fn created(t: &T::AccountId) -> Result<(), DispatchError> {
		Pallet::<T>::inc_consumers(t)
	}
	fn killed(t: &T::AccountId) -> Result<(), DispatchError> {
		Pallet::<T>::dec_consumers(t);
		Ok(())
	}
}

impl<T: Config> BlockNumberProvider for Pallet<T> {
	type BlockNumber = <T as Config>::BlockNumber;

	fn current_block_number() -> Self::BlockNumber {
		Pallet::<T>::block_number()
	}
}

fn is_providing<T: Default + Eq>(d: &T) -> bool {
	d != &T::default()
}

/// Implement StoredMap for a simple single-item, provide-when-not-default system. This works fine
/// for storing a single item which allows the account to continue existing as long as it's not
/// empty/default.
///
/// Anything more complex will need more sophisticated logic.
impl<T: Config> StoredMap<T::AccountId, T::AccountData> for Pallet<T> {
	fn get(k: &T::AccountId) -> T::AccountData {
		Account::<T>::get(k).data
	}

	fn try_mutate_exists<R, E: From<DispatchError>>(
		k: &T::AccountId,
		f: impl FnOnce(&mut Option<T::AccountData>) -> Result<R, E>,
	) -> Result<R, E> {
		let account = Account::<T>::get(k);
		let was_providing = is_providing(&account.data);
		let mut some_data = if was_providing { Some(account.data) } else { None };
		let result = f(&mut some_data)?;
		let is_providing = some_data.is_some();
		if !was_providing && is_providing {
			Self::inc_providers(k);
		} else if was_providing && !is_providing {
			match Self::dec_providers(k)? {
				DecRefStatus::Reaped => return Ok(result),
				DecRefStatus::Exists => {
					// Update value as normal...
				},
			}
		} else if !was_providing && !is_providing {
			return Ok(result)
		}
		Account::<T>::mutate(k, |a| a.data = some_data.unwrap_or_default());
		Ok(result)
	}
}

/// 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),
	}
}

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

impl<T: Config> 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)
	}
}

/// Prelude to be used alongside pallet macro, for ease of use.
pub mod pallet_prelude {
	pub use crate::{ensure_none, ensure_root, ensure_signed, ensure_signed_or_root};

	/// Type alias for the `Origin` associated type of system config.
	pub type OriginFor<T> = <T as crate::Config>::RuntimeOrigin;

	/// Type alias for the `BlockNumber` associated type of system config.
	pub type BlockNumberFor<T> = <T as crate::Config>::BlockNumber;
}