feat: Rebrand Polkadot/Substrate references to PezkuwiChain

This commit systematically rebrands various references from Parity Technologies'
Polkadot/Substrate ecosystem to PezkuwiChain within the kurdistan-sdk.

Key changes include:
- Updated external repository URLs (zombienet-sdk, parity-db, parity-scale-codec, wasm-instrument) to point to pezkuwichain forks.
- Modified internal documentation and code comments to reflect PezkuwiChain naming and structure.
- Replaced direct references to  with  or specific paths within the  for XCM, Pezkuwi, and other modules.
- Cleaned up deprecated  issue and PR references in various  and  files, particularly in  and  modules.
- Adjusted image and logo URLs in documentation to point to PezkuwiChain assets.
- Removed or rephrased comments related to external Polkadot/Substrate PRs and issues.

This is a significant step towards fully customizing the SDK for the PezkuwiChain ecosystem.

bizinikiwi/pezframe/revive/src/storage/meter.rs

@@ -0,0 +1,792 @@
+// This file is part of Bizinikiwi.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! This module contains functions to meter the storage deposit.
+
+use crate::{
+	storage::ContractInfo, BalanceOf, Config, Error, ExecConfig, ExecOrigin as Origin, HoldReason,
+	Pallet, StorageDeposit as Deposit, LOG_TARGET,
+};
+use alloc::vec::Vec;
+use core::{fmt::Debug, marker::PhantomData};
+use pezframe_support::{traits::Get, DefaultNoBound, RuntimeDebugNoBound};
+use pezsp_runtime::{
+	traits::{Saturating, Zero},
+	DispatchError, DispatchResult, FixedPointNumber, FixedU128,
+};
+
+/// Deposit that uses the native fungible's balance type.
+pub type DepositOf<T> = Deposit<BalanceOf<T>>;
+
+/// A production root storage meter that actually charges from its origin.
+pub type Meter<T> = RawMeter<T, ReservingExt, Root>;
+
+/// A production nested storage meter that actually charges from its origin.
+pub type NestedMeter<T> = RawMeter<T, ReservingExt, Nested>;
+
+/// A production storage meter that actually charges from its origin.
+///
+/// This can be used where we want to be generic over the state (Root vs. Nested).
+pub type GenericMeter<T, S> = RawMeter<T, ReservingExt, S>;
+
+/// A trait that allows to decouple the metering from the charging of balance.
+///
+/// This mostly exists for testing so that the charging can be mocked.
+pub trait Ext<T: Config> {
+	/// This is called to inform the implementer that some balance should be charged due to
+	/// some interaction of the `origin` with a `contract`.
+	///
+	/// The balance transfer can either flow from `origin` to `contract` or the other way
+	/// around depending on whether `amount` constitutes a `Charge` or a `Refund`.
+	/// It will fail in case the `origin` has not enough balance to cover all storage deposits.
+	fn charge(
+		origin: &T::AccountId,
+		contract: &T::AccountId,
+		amount: &DepositOf<T>,
+		exec_config: &ExecConfig<T>,
+	) -> Result<(), DispatchError>;
+}
+
+/// This [`Ext`] is used for actual on-chain execution when balance needs to be charged.
+///
+/// It uses [`pezframe_support::traits::fungible::Mutate`] in order to do accomplish the reserves.
+pub enum ReservingExt {}
+
+/// Used to implement a type state pattern for the meter.
+///
+/// It is sealed and cannot be implemented outside of this module.
+pub trait State: private::Sealed {}
+
+/// State parameter that constitutes a meter that is in its root state.
+#[derive(Default, Debug)]
+pub struct Root;
+
+/// State parameter that constitutes a meter that is in its nested state.
+/// Its value indicates whether the nested meter has its own limit.
+#[derive(Default, Debug)]
+pub struct Nested;
+
+impl State for Root {}
+impl State for Nested {}
+
+/// A type that allows the metering of consumed or freed storage of a single contract call stack.
+#[derive(DefaultNoBound, RuntimeDebugNoBound)]
+pub struct RawMeter<T: Config, E, S: State + Default + Debug> {
+	/// The limit of how much balance this meter is allowed to consume.
+	limit: BalanceOf<T>,
+	/// The amount of balance that was used in this meter and all of its already absorbed children.
+	total_deposit: DepositOf<T>,
+	/// The amount of storage changes that were recorded in this meter alone.
+	own_contribution: Contribution<T>,
+	/// List of charges that should be applied at the end of a contract stack execution.
+	///
+	/// We only have one charge per contract hence the size of this vector is
+	/// limited by the maximum call depth.
+	charges: Vec<Charge<T>>,
+	/// True if this is the root meter.
+	///
+	/// Sometimes we cannot know at compile time.
+	is_root: bool,
+	/// Type parameter only used in impls.
+	_phantom: PhantomData<(E, S)>,
+}
+
+/// This type is used to describe a storage change when charging from the meter.
+#[derive(Default, RuntimeDebugNoBound)]
+pub struct Diff {
+	/// How many bytes were added to storage.
+	pub bytes_added: u32,
+	/// How many bytes were removed from storage.
+	pub bytes_removed: u32,
+	/// How many storage items were added to storage.
+	pub items_added: u32,
+	/// How many storage items were removed from storage.
+	pub items_removed: u32,
+}
+
+impl Diff {
+	/// Calculate how much of a charge or refund results from applying the diff and store it
+	/// in the passed `info` if any.
+	///
+	/// # Note
+	///
+	/// In case `None` is passed for `info` only charges are calculated. This is because refunds
+	/// are calculated pro rata of the existing storage within a contract and hence need extract
+	/// this information from the passed `info`.
+	pub fn update_contract<T: Config>(&self, info: Option<&mut ContractInfo<T>>) -> DepositOf<T> {
+		let per_byte = T::DepositPerByte::get();
+		let per_item = T::DepositPerChildTrieItem::get();
+		let bytes_added = self.bytes_added.saturating_sub(self.bytes_removed);
+		let items_added = self.items_added.saturating_sub(self.items_removed);
+		let mut bytes_deposit = Deposit::Charge(per_byte.saturating_mul((bytes_added).into()));
+		let mut items_deposit = Deposit::Charge(per_item.saturating_mul((items_added).into()));
+
+		// Without any contract info we can only calculate diffs which add storage
+		let info = if let Some(info) = info {
+			info
+		} else {
+			return bytes_deposit.saturating_add(&items_deposit);
+		};
+
+		// Refunds are calculated pro rata based on the accumulated storage within the contract
+		let bytes_removed = self.bytes_removed.saturating_sub(self.bytes_added);
+		let items_removed = self.items_removed.saturating_sub(self.items_added);
+		let ratio = FixedU128::checked_from_rational(bytes_removed, info.storage_bytes)
+			.unwrap_or_default()
+			.min(FixedU128::from_u32(1));
+		bytes_deposit = bytes_deposit
+			.saturating_add(&Deposit::Refund(ratio.saturating_mul_int(info.storage_byte_deposit)));
+		let ratio = FixedU128::checked_from_rational(items_removed, info.storage_items)
+			.unwrap_or_default()
+			.min(FixedU128::from_u32(1));
+		items_deposit = items_deposit
+			.saturating_add(&Deposit::Refund(ratio.saturating_mul_int(info.storage_item_deposit)));
+
+		// We need to update the contract info structure with the new deposits
+		info.storage_bytes =
+			info.storage_bytes.saturating_add(bytes_added).saturating_sub(bytes_removed);
+		info.storage_items =
+			info.storage_items.saturating_add(items_added).saturating_sub(items_removed);
+		match &bytes_deposit {
+			Deposit::Charge(amount) =>
+				info.storage_byte_deposit = info.storage_byte_deposit.saturating_add(*amount),
+			Deposit::Refund(amount) =>
+				info.storage_byte_deposit = info.storage_byte_deposit.saturating_sub(*amount),
+		}
+		match &items_deposit {
+			Deposit::Charge(amount) =>
+				info.storage_item_deposit = info.storage_item_deposit.saturating_add(*amount),
+			Deposit::Refund(amount) =>
+				info.storage_item_deposit = info.storage_item_deposit.saturating_sub(*amount),
+		}
+
+		bytes_deposit.saturating_add(&items_deposit)
+	}
+}
+
+impl Diff {
+	fn saturating_add(&self, rhs: &Self) -> Self {
+		Self {
+			bytes_added: self.bytes_added.saturating_add(rhs.bytes_added),
+			bytes_removed: self.bytes_removed.saturating_add(rhs.bytes_removed),
+			items_added: self.items_added.saturating_add(rhs.items_added),
+			items_removed: self.items_removed.saturating_add(rhs.items_removed),
+		}
+	}
+}
+
+/// The state of a contract.
+#[derive(RuntimeDebugNoBound, Clone, PartialEq, Eq)]
+pub enum ContractState<T: Config> {
+	Alive { amount: DepositOf<T> },
+	Terminated,
+}
+
+/// Records information to charge or refund a plain account.
+///
+/// All the charges are deferred to the end of a whole call stack. Reason is that by doing
+/// this we can do all the refunds before doing any charge. This way a plain account can use
+/// more deposit than it has balance as along as it is covered by a refund. This
+/// essentially makes the order of storage changes irrelevant with regard to the deposit system.
+/// The only exception is when a special (tougher) deposit limit is specified for a cross-contract
+/// call. In that case the limit is enforced once the call is returned, rolling it back if
+/// exhausted.
+#[derive(RuntimeDebugNoBound, Clone)]
+struct Charge<T: Config> {
+	contract: T::AccountId,
+	state: ContractState<T>,
+}
+
+/// Records the storage changes of a storage meter.
+#[derive(RuntimeDebugNoBound)]
+enum Contribution<T: Config> {
+	/// The contract the meter belongs to is alive and accumulates changes using a [`Diff`].
+	Alive(Diff),
+	/// The meter was checked against its limit using [`RawMeter::enforce_limit`] at the end of
+	/// its execution. In this process the [`Diff`] was converted into a [`Deposit`].
+	Checked(DepositOf<T>),
+}
+
+impl<T: Config> Contribution<T> {
+	/// See [`Diff::update_contract`].
+	fn update_contract(&self, info: Option<&mut ContractInfo<T>>) -> DepositOf<T> {
+		match self {
+			Self::Alive(diff) => diff.update_contract::<T>(info),
+			Self::Checked(deposit) => deposit.clone(),
+		}
+	}
+}
+
+impl<T: Config> Default for Contribution<T> {
+	fn default() -> Self {
+		Self::Alive(Default::default())
+	}
+}
+
+/// Functions that apply to all states.
+impl<T, E, S> RawMeter<T, E, S>
+where
+	T: Config,
+	E: Ext<T>,
+	S: State + Default + Debug,
+{
+	/// Create a new child that has its `limit`.
+	///
+	/// This is called whenever a new subcall is initiated in order to track the storage
+	/// usage for this sub call separately. This is necessary because we want to exchange balance
+	/// with the current contract we are interacting with.
+	pub fn nested(&self, limit: BalanceOf<T>) -> RawMeter<T, E, Nested> {
+		RawMeter { limit: self.available().min(limit), ..Default::default() }
+	}
+
+	/// Absorb a child that was spawned to handle a sub call.
+	///
+	/// This should be called whenever a sub call comes to its end and it is **not** reverted.
+	/// This does the actual balance transfer from/to `origin` and `contract` based on the
+	/// overall storage consumption of the call. It also updates the supplied contract info.
+	///
+	/// In case a contract reverted the child meter should just be dropped in order to revert
+	/// any changes it recorded.
+	///
+	/// # Parameters
+	///
+	/// - `absorbed`: The child storage meter that should be absorbed.
+	/// - `origin`: The origin that spawned the original root meter.
+	/// - `contract`: The contract's account that this sub call belongs to.
+	/// - `info`: The info of the contract in question. `None` if the contract was terminated.
+	pub fn absorb(
+		&mut self,
+		absorbed: RawMeter<T, E, Nested>,
+		contract: &T::AccountId,
+		info: Option<&mut ContractInfo<T>>,
+	) {
+		let own_deposit = absorbed.own_contribution.update_contract(info);
+		self.total_deposit = self
+			.total_deposit
+			.saturating_add(&absorbed.total_deposit)
+			.saturating_add(&own_deposit);
+		self.charges.extend_from_slice(&absorbed.charges);
+
+		if !own_deposit.is_zero() {
+			self.charges.push(Charge {
+				contract: contract.clone(),
+				state: ContractState::Alive { amount: own_deposit },
+			});
+		}
+	}
+
+	/// Record a charge that has taken place externally.
+	///
+	/// This will not perform a charge. It just records it to reflect it in the
+	/// total amount of storage required for a transaction.
+	pub fn record_charge(&mut self, amount: &DepositOf<T>) -> DispatchResult {
+		let total_deposit = self.total_deposit.saturating_add(&amount);
+
+		// Limits are enforced at the end of each frame. But plain balance transfers
+		// do not sapwn a frame. This is specifically to enforce the limit for those.
+		if self.is_root && total_deposit.charge_or_zero() > self.limit {
+			log::debug!( target: LOG_TARGET, "Storage deposit limit exhausted: {:?} > {:?}", amount, self.limit);
+			return Err(<Error<T>>::StorageDepositLimitExhausted.into());
+		}
+
+		self.total_deposit = total_deposit;
+		Ok(())
+	}
+
+	/// The amount of balance that this meter has consumed.
+	///
+	/// This disregards any refunds pending in the current frame. This
+	/// is because we can calculate refunds only at the end of each frame.
+	pub fn consumed(&self) -> DepositOf<T> {
+		self.total_deposit.saturating_add(&self.own_contribution.update_contract(None))
+	}
+
+	/// The amount of balance still available from the current meter.
+	///
+	/// This includes charges from the current frame but no refunds.
+	pub fn available(&self) -> BalanceOf<T> {
+		self.consumed().available(&self.limit)
+	}
+}
+
+/// Functions that only apply to the root state.
+impl<T, E> RawMeter<T, E, Root>
+where
+	T: Config,
+	E: Ext<T>,
+{
+	/// Create new storage limiting storage deposits to the passed `limit`.
+	///
+	/// If the limit is larger than what the origin can afford we will just fail
+	/// when collecting the deposits in `try_into_deposit`.
+	pub fn new(limit: BalanceOf<T>) -> Self {
+		Self { limit, is_root: true, ..Default::default() }
+	}
+
+	/// The total amount of deposit that should change hands as result of the execution
+	/// that this meter was passed into. This will also perform all the charges accumulated
+	/// in the whole contract stack.
+	///
+	/// This drops the root meter in order to make sure it is only called when the whole
+	/// execution did finish.
+	pub fn try_into_deposit(
+		mut self,
+		origin: &Origin<T>,
+		exec_config: &ExecConfig<T>,
+	) -> Result<DepositOf<T>, DispatchError> {
+		// Only refund or charge deposit if the origin is not root.
+		let origin = match origin {
+			Origin::Root => return Ok(Deposit::Charge(Zero::zero())),
+			Origin::Signed(o) => o,
+		};
+
+		// Coalesce charges of the same contract
+		self.charges.sort_by(|a, b| a.contract.cmp(&b.contract));
+		self.charges = {
+			let mut coalesced: Vec<Charge<T>> = Vec::with_capacity(self.charges.len());
+			for mut ch in self.charges {
+				if let Some(last) = coalesced.last_mut() {
+					if last.contract == ch.contract {
+						match (&mut last.state, &mut ch.state) {
+							(
+								ContractState::Alive { amount: last_amount },
+								ContractState::Alive { amount: ch_amount },
+							) => {
+								*last_amount = last_amount.saturating_add(ch_amount);
+							},
+							(ContractState::Alive { amount }, ContractState::Terminated) |
+							(ContractState::Terminated, ContractState::Alive { amount }) => {
+								// undo all deposits made by a terminated contract
+								self.total_deposit = self.total_deposit.saturating_sub(amount);
+								last.state = ContractState::Terminated;
+							},
+							(ContractState::Terminated, ContractState::Terminated) => {
+								debug_assert!(
+									false,
+									"We never emit two terminates for the same contract."
+								)
+							},
+						}
+						continue;
+					}
+				}
+				coalesced.push(ch);
+			}
+			coalesced
+		};
+
+		// refunds first so origin is able to pay for the charges using the refunds
+		for charge in self.charges.iter() {
+			if let ContractState::Alive { amount: amount @ Deposit::Refund(_) } = &charge.state {
+				E::charge(origin, &charge.contract, amount, exec_config)?;
+			}
+		}
+		for charge in self.charges.iter() {
+			if let ContractState::Alive { amount: amount @ Deposit::Charge(_) } = &charge.state {
+				E::charge(origin, &charge.contract, amount, exec_config)?;
+			}
+		}
+
+		Ok(self.total_deposit)
+	}
+
+	/// Flag a `contract` as terminated.
+	///
+	/// This will signal to the meter to discard all charged and refunds incured by this
+	/// contract.
+	pub fn terminate(&mut self, contract: T::AccountId, refunded: BalanceOf<T>) {
+		self.total_deposit = self.total_deposit.saturating_add(&Deposit::Refund(refunded));
+		self.charges.push(Charge { contract, state: ContractState::Terminated });
+	}
+}
+
+/// Functions that only apply to the nested state.
+impl<T: Config, E: Ext<T>> RawMeter<T, E, Nested> {
+	/// Charges `diff` from the meter.
+	pub fn charge(&mut self, diff: &Diff) {
+		match &mut self.own_contribution {
+			Contribution::Alive(own) => *own = own.saturating_add(diff),
+			_ => panic!("Charge is never called after termination; qed"),
+		};
+	}
+
+	/// Adds a charge without recording it in the contract info.
+	///
+	/// Use this method instead of [`Self::charge`] when the charge is not the result of a storage
+	/// change within the contract's child trie. This is the case when when the `code_hash` is
+	/// updated. [`Self::charge`] cannot be used here because we keep track of the deposit charge
+	/// separately from the storage charge.
+	///
+	/// If this functions is used the amount of the charge has to be stored by the caller somewhere
+	/// alese in order to be able to refund it.
+	pub fn charge_deposit(&mut self, contract: T::AccountId, amount: DepositOf<T>) {
+		// will not fail in a nested meter
+		self.record_charge(&amount).ok();
+		self.charges.push(Charge { contract, state: ContractState::Alive { amount } });
+	}
+
+	/// [`Self::charge`] does not enforce the storage limit since we want to do this check as late
+	/// as possible to allow later refunds to offset earlier charges.
+	pub fn enforce_limit(
+		&mut self,
+		info: Option<&mut ContractInfo<T>>,
+	) -> Result<(), DispatchError> {
+		let deposit = self.own_contribution.update_contract(info);
+		let total_deposit = self.total_deposit.saturating_add(&deposit);
+		self.own_contribution = Contribution::Checked(deposit);
+		if let Deposit::Charge(amount) = total_deposit {
+			if amount > self.limit {
+				log::debug!( target: LOG_TARGET, "Storage deposit limit exhausted: {:?} > {:?}", amount, self.limit);
+				return Err(<Error<T>>::StorageDepositLimitExhausted.into());
+			}
+		}
+		Ok(())
+	}
+}
+
+impl<T: Config> Ext<T> for ReservingExt {
+	fn charge(
+		origin: &T::AccountId,
+		contract: &T::AccountId,
+		amount: &DepositOf<T>,
+		exec_config: &ExecConfig<T>,
+	) -> Result<(), DispatchError> {
+		match amount {
+			Deposit::Charge(amount) | Deposit::Refund(amount) if amount.is_zero() => (),
+			Deposit::Charge(amount) => {
+				<Pallet<T>>::charge_deposit(
+					Some(HoldReason::StorageDepositReserve),
+					origin,
+					contract,
+					*amount,
+					exec_config,
+				)?;
+			},
+			Deposit::Refund(amount) => {
+				<Pallet<T>>::refund_deposit(
+					HoldReason::StorageDepositReserve,
+					contract,
+					origin,
+					*amount,
+					Some(exec_config),
+				)?;
+			},
+		}
+		Ok(())
+	}
+}
+
+mod private {
+	pub trait Sealed {}
+	impl Sealed for super::Root {}
+	impl Sealed for super::Nested {}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+	use crate::{exec::AccountIdOf, test_utils::*, tests::Test};
+	use pezframe_support::parameter_types;
+	use pretty_assertions::assert_eq;
+
+	type TestMeter = RawMeter<Test, TestExt, Root>;
+
+	parameter_types! {
+		static TestExtTestValue: TestExt = Default::default();
+	}
+
+	#[derive(Debug, PartialEq, Eq, Clone)]
+	struct Charge {
+		origin: AccountIdOf<Test>,
+		contract: AccountIdOf<Test>,
+		amount: DepositOf<Test>,
+	}
+
+	#[derive(Default, Debug, PartialEq, Eq, Clone)]
+	pub struct TestExt {
+		charges: Vec<Charge>,
+	}
+
+	impl TestExt {
+		fn clear(&mut self) {
+			self.charges.clear();
+		}
+	}
+
+	impl Ext<Test> for TestExt {
+		fn charge(
+			origin: &AccountIdOf<Test>,
+			contract: &AccountIdOf<Test>,
+			amount: &DepositOf<Test>,
+			_exec_config: &ExecConfig<Test>,
+		) -> Result<(), DispatchError> {
+			TestExtTestValue::mutate(|ext| {
+				ext.charges.push(Charge {
+					origin: origin.clone(),
+					contract: contract.clone(),
+					amount: amount.clone(),
+				})
+			});
+			Ok(())
+		}
+	}
+
+	fn clear_ext() {
+		TestExtTestValue::mutate(|ext| ext.clear())
+	}
+
+	struct ChargingTestCase {
+		origin: Origin<Test>,
+		deposit: DepositOf<Test>,
+		expected: TestExt,
+	}
+
+	#[derive(Default)]
+	struct StorageInfo {
+		bytes: u32,
+		items: u32,
+		bytes_deposit: BalanceOf<Test>,
+		items_deposit: BalanceOf<Test>,
+		immutable_data_len: u32,
+	}
+
+	fn new_info(info: StorageInfo) -> ContractInfo<Test> {
+		ContractInfo::<Test> {
+			trie_id: Default::default(),
+			code_hash: Default::default(),
+			storage_bytes: info.bytes,
+			storage_items: info.items,
+			storage_byte_deposit: info.bytes_deposit,
+			storage_item_deposit: info.items_deposit,
+			storage_base_deposit: Default::default(),
+			immutable_data_len: info.immutable_data_len,
+		}
+	}
+
+	#[test]
+	fn new_reserves_balance_works() {
+		clear_ext();
+
+		TestMeter::new(1_000);
+
+		assert_eq!(TestExtTestValue::get(), TestExt { ..Default::default() })
+	}
+
+	/// Previously, passing a limit of 0 meant unlimited storage for a nested call.
+	///
+	/// Now, a limit of 0 means the subcall will not be able to use any storage.
+	#[test]
+	fn nested_zero_limit_requested() {
+		clear_ext();
+
+		let meter = TestMeter::new(1_000);
+		assert_eq!(meter.available(), 1_000);
+		let nested0 = meter.nested(BalanceOf::<Test>::zero());
+		assert_eq!(nested0.available(), 0);
+	}
+
+	#[test]
+	fn nested_some_limit_requested() {
+		clear_ext();
+
+		let meter = TestMeter::new(1_000);
+		assert_eq!(meter.available(), 1_000);
+		let nested0 = meter.nested(500);
+		assert_eq!(nested0.available(), 500);
+	}
+
+	#[test]
+	fn nested_all_limit_requested() {
+		clear_ext();
+
+		let meter = TestMeter::new(1_000);
+		assert_eq!(meter.available(), 1_000);
+		let nested0 = meter.nested(1_000);
+		assert_eq!(nested0.available(), 1_000);
+	}
+
+	#[test]
+	fn nested_over_limit_requested() {
+		clear_ext();
+
+		let meter = TestMeter::new(1_000);
+		assert_eq!(meter.available(), 1_000);
+		let nested0 = meter.nested(2_000);
+		assert_eq!(nested0.available(), 1_000);
+	}
+
+	#[test]
+	fn empty_charge_works() {
+		clear_ext();
+
+		let mut meter = TestMeter::new(1_000);
+		assert_eq!(meter.available(), 1_000);
+
+		// an empty charge does not create a `Charge` entry
+		let mut nested0 = meter.nested(BalanceOf::<Test>::zero());
+		nested0.charge(&Default::default());
+		meter.absorb(nested0, &BOB, None);
+
+		assert_eq!(TestExtTestValue::get(), TestExt { ..Default::default() })
+	}
+
+	#[test]
+	fn charging_works() {
+		let test_cases = vec![
+			ChargingTestCase {
+				origin: Origin::<Test>::from_account_id(ALICE),
+				deposit: Deposit::Refund(28),
+				expected: TestExt {
+					charges: vec![
+						Charge { origin: ALICE, contract: CHARLIE, amount: Deposit::Refund(30) },
+						Charge { origin: ALICE, contract: BOB, amount: Deposit::Charge(2) },
+					],
+				},
+			},
+			ChargingTestCase {
+				origin: Origin::<Test>::Root,
+				deposit: Deposit::Charge(0),
+				expected: TestExt { charges: vec![] },
+			},
+		];
+
+		for test_case in test_cases {
+			clear_ext();
+
+			let mut meter = TestMeter::new(100);
+			assert_eq!(meter.available(), 100);
+
+			let mut nested0_info = new_info(StorageInfo {
+				bytes: 100,
+				items: 5,
+				bytes_deposit: 100,
+				items_deposit: 10,
+				immutable_data_len: 0,
+			});
+			let mut nested0 = meter.nested(BalanceOf::<Test>::zero());
+			nested0.charge(&Diff {
+				bytes_added: 108,
+				bytes_removed: 5,
+				items_added: 1,
+				items_removed: 2,
+			});
+			nested0.charge(&Diff { bytes_removed: 99, ..Default::default() });
+
+			let mut nested1_info = new_info(StorageInfo {
+				bytes: 100,
+				items: 10,
+				bytes_deposit: 100,
+				items_deposit: 20,
+				immutable_data_len: 0,
+			});
+			let mut nested1 = nested0.nested(BalanceOf::<Test>::zero());
+			nested1.charge(&Diff { items_removed: 5, ..Default::default() });
+			nested0.absorb(nested1, &CHARLIE, Some(&mut nested1_info));
+
+			let mut nested2_info = new_info(StorageInfo {
+				bytes: 100,
+				items: 7,
+				bytes_deposit: 100,
+				items_deposit: 20,
+				immutable_data_len: 0,
+			});
+			let mut nested2 = nested0.nested(BalanceOf::<Test>::zero());
+			nested2.charge(&Diff { items_removed: 7, ..Default::default() });
+			nested0.absorb(nested2, &CHARLIE, Some(&mut nested2_info));
+
+			nested0.enforce_limit(Some(&mut nested0_info)).unwrap();
+			meter.absorb(nested0, &BOB, Some(&mut nested0_info));
+
+			assert_eq!(
+				meter
+					.try_into_deposit(&test_case.origin, &ExecConfig::new_bizinikiwi_tx())
+					.unwrap(),
+				test_case.deposit
+			);
+
+			assert_eq!(nested0_info.extra_deposit(), 112);
+			assert_eq!(nested1_info.extra_deposit(), 110);
+			assert_eq!(nested2_info.extra_deposit(), 100);
+
+			assert_eq!(TestExtTestValue::get(), test_case.expected)
+		}
+	}
+
+	#[test]
+	fn termination_works() {
+		let test_cases = vec![
+			ChargingTestCase {
+				origin: Origin::<Test>::from_account_id(ALICE),
+				deposit: Deposit::Refund(108),
+				expected: TestExt {
+					charges: vec![Charge {
+						origin: ALICE,
+						contract: BOB,
+						amount: Deposit::Charge(12),
+					}],
+				},
+			},
+			ChargingTestCase {
+				origin: Origin::<Test>::Root,
+				deposit: Deposit::Charge(0),
+				expected: TestExt { charges: vec![] },
+			},
+		];
+
+		for test_case in test_cases {
+			clear_ext();
+
+			let mut meter = TestMeter::new(1_000);
+			assert_eq!(meter.available(), 1_000);
+
+			let mut nested0 = meter.nested(BalanceOf::<Test>::max_value());
+			nested0.charge(&Diff {
+				bytes_added: 5,
+				bytes_removed: 1,
+				items_added: 3,
+				items_removed: 1,
+			});
+			nested0.charge(&Diff { items_added: 2, ..Default::default() });
+
+			let mut nested1_info = new_info(StorageInfo {
+				bytes: 100,
+				items: 10,
+				bytes_deposit: 100,
+				items_deposit: 20,
+				immutable_data_len: 0,
+			});
+			let mut nested1 = nested0.nested(BalanceOf::<Test>::max_value());
+			let total_deposit = nested1_info.total_deposit();
+			nested1.charge(&Diff { items_removed: 5, ..Default::default() });
+			nested1.charge(&Diff { bytes_added: 20, ..Default::default() });
+			nested0.enforce_limit(Some(&mut nested1_info)).unwrap();
+			nested0.absorb(nested1, &CHARLIE, None);
+
+			meter.absorb(nested0, &BOB, None);
+
+			meter.terminate(CHARLIE, total_deposit);
+
+			assert_eq!(
+				meter
+					.try_into_deposit(&test_case.origin, &ExecConfig::new_bizinikiwi_tx())
+					.unwrap(),
+				test_case.deposit
+			);
+			assert_eq!(TestExtTestValue::get(), test_case.expected)
+		}
+	}
+}