feat: add solution for ex07

Author: tdelabro

exercises/ex07-imbalances/imbalances/src/lib.rs

@@ -62,13 +62,9 @@ pub mod pallet {
 		) -> DispatchResult {
 			ensure_root(origin)?;
 
-			// Here we add some tokens to the chain total_issuance
-			// If we do nothing more, those tokens will be removed when the `NegativeImbalance`
-			// contained in the `amount_to_distribute` variable will be drop
 			let amount_to_distribute = T::Currency::issue(amount);
-			// TODO
-			// We want to compensate this imbalance by increasing `benefeciary` balance by the
-			// corresponding amount
+			T::Currency::resolve_into_existing(&beneficiary, amount_to_distribute)
+				.map_err(|_| Error::<T>::AccountDoesNotExist)?;
 
 			Ok(())
 		}
@@ -81,10 +77,16 @@ pub mod pallet {
 		) -> DispatchResult {
 			ensure_root(origin)?;
 
-			// Todo: slash target
-			// Todo: give 1/3 of the slashed amount to the treasury and burn the rest
-			// Hint: use the `ration` method
-			// Hint: TreasuryAccount is defined as on l35 as a Config constant
+			let (negative_imbalance, _) = T::Currency::slash(&target, amount);
+			let (to_treasury, to_burn) = negative_imbalance.ration(1, 2);
+
+			T::Currency::resolve_creating(&T::TreasuryAccount::get(), to_treasury);
+			let amount_to_burn = to_burn.peek();
+			let burned = T::Currency::burn(amount_to_burn);
+			burned
+				.offset(to_burn)
+				.try_drop()
+				.map_err(|_| Error::<T>::ImbalanceOffsetFailed)?;
 
 			Ok(())
 		}
@@ -97,13 +99,30 @@ pub mod pallet {
 			beneficiary: T::AccountId,
 		) -> DispatchResult {
 			ensure_root(origin)?;
-
-			// Todo:
-			// Take as much as possible from each account in `sacked_accounts`,
-			// without removing them from existence
-			// and give it all to beneficiary
-			// except for the TreasuryFlatCut amount, that goes to the treasury for each sacked
-			// account Hint: there is a `split` method implemented on imbalances
+			let n_accounts = sacked_accounts.len();
+
+			let amount_collected = sacked_accounts.into_iter().try_fold(
+				NegativeBalanceOf::<T>::zero(),
+				|acc, account| {
+					let free_balance = T::Currency::free_balance(&account);
+					T::Currency::withdraw(
+						&account,
+						free_balance - T::Currency::minimum_balance(),
+						WithdrawReasons::TRANSFER,
+						ExistenceRequirement::KeepAlive,
+					)
+					.map(|v| acc.merge(v))
+				},
+			)?;
+
+			let amount_to_treasury = T::TreasuryFlatCut::get()
+				.checked_mul(&n_accounts.checked_into().ok_or(Error::<T>::Overflow)?)
+				.ok_or(Error::<T>::Overflow)?;
+
+			let (to_treasury, to_recipient) = amount_collected.split(amount_to_treasury);
+			T::Currency::resolve_creating(&T::TreasuryAccount::get(), to_treasury);
+			T::Currency::resolve_into_existing(&beneficiary, to_recipient)
+				.map_err(|_| Error::<T>::AccountDoesNotExist)?;
 
 			Ok(())
 		}