Loans: Add multiple triggers for write-off (#1314)

* ideas from Jeroen at multiple-cashflows branch

* trigger refactor working

* rename state to rule

* simplify policy rule search

* organize find rule method

* add test

* minor coments

* minor fixes

* fixed strum issue

* added migration

* reorganize migrations

* remove old altair migrations

* minor simplification

* fix migration condition

* minor fix

* protected agains same triggers with different values

* write off to its own module

* added migration to development

* added migration test

* fix clippy

* solve review comments

pallets/loans-ref/Cargo.toml

@@ -24,6 +24,8 @@ cfg-primitives = { path = "../../libs/primitives", default-features = false }
 cfg-traits = { path = "../../libs/traits", default-features = false }
 cfg-types = { path = "../../libs/types", default-features = false }
 
+strum = { version = "0.24", default-features = false, features = ["derive"] }
+
 # Optionals for benchamarking
 frame-benchmarking = { git = "https://github.com/paritytech/substrate", default-features = false, optional = true, branch = "polkadot-v0.9.37" }
 
@@ -57,6 +59,7 @@ std = [
   "cfg-types/std",
   "frame-benchmarking/std",
   "sp-io/std",
+  "strum/std",
 ]
 runtime-benchmarks = [
   "frame-benchmarking",

pallets/loans-ref/src/benchmarking.rs

@@ -5,9 +5,12 @@ use cfg_types::{
 	permissions::{PermissionScope, PoolRole, Role},
 };
 use frame_benchmarking::{account, benchmarks, impl_benchmark_test_suite};
-use frame_support::traits::{
-	tokens::nonfungibles::{Create, Mutate},
-	UnixTime,
+use frame_support::{
+	storage::bounded_vec::BoundedVec,
+	traits::{
+		tokens::nonfungibles::{Create, Mutate},
+		UnixTime,
+	},
 };
 use frame_system::RawOrigin;
 use sp_arithmetic::FixedPointNumber;
@@ -16,8 +19,9 @@ use sp_std::{time::Duration, vec};
 
 use super::{
 	pallet::*,
-	types::{LoanInfo, MaxBorrowAmount, WriteOffState},
+	types::{LoanInfo, MaxBorrowAmount},
 	valuation::{DiscountedCashFlow, ValuationMethod},
+	write_off::{WriteOffRule, WriteOffTrigger},
 };
 
 const OFFSET: Duration = Duration::from_secs(120);
@@ -77,7 +81,7 @@ where
 		T::NonFungible::create_collection(&COLLECION_ID.into(), &borrower, &borrower).unwrap();
 		T::Permissions::add(
 			PermissionScope::Pool(pool_id),
-			borrower.clone(),
+			borrower,
 			Role::PoolRole(PoolRole::Borrower),
 		)
 		.unwrap();
@@ -134,31 +138,27 @@ where
 		.unwrap();
 	}
 
+	// Worst case policy where you need to iterate for the whole policy.
+	fn create_policy() -> BoundedVec<WriteOffRule<T::Rate>, T::MaxWriteOffPolicySize> {
+		vec![
+			WriteOffRule::new(
+				[WriteOffTrigger::PrincipalOverdueDays(0)],
+				T::Rate::zero(),
+				T::Rate::zero(),
+			);
+			T::MaxWriteOffPolicySize::get() as usize
+		]
+		.try_into()
+		.unwrap()
+	}
+
 	fn set_policy(pool_id: PoolIdOf<T>) {
 		let pool_admin = account::<T::AccountId>("pool_admin", 0, 0);
 
-		// Worst case policy where you need to iterate for the whole policy.
-		let policy = [
-			vec![
-				WriteOffState {
-					overdue_days: u32::MAX,
-					percentage: T::Rate::zero(),
-					penalty: T::Rate::zero(),
-				};
-				T::MaxWriteOffPolicySize::get() as usize - 1
-			],
-			vec![WriteOffState {
-				overdue_days: 0, // Last element is overdue
-				percentage: T::Rate::zero(),
-				penalty: T::Rate::zero(),
-			}],
-		]
-		.concat();
-
 		Pallet::<T>::update_write_off_policy(
 			RawOrigin::Signed(pool_admin).into(),
 			pool_id,
-			policy.try_into().unwrap(),
+			Self::create_policy(),
 		)
 		.unwrap();
 	}
@@ -263,15 +263,7 @@ benchmarks! {
 	update_write_off_policy {
 		let pool_admin = account("pool_admin", 0, 0);
 		let pool_id = Helper::<T>::prepare_benchmark();
-
-		let state = WriteOffState {
-			overdue_days: 0,
-			percentage: T::Rate::zero(),
-			penalty: T::Rate::zero(),
-		};
-		let policy = vec![state; T::MaxWriteOffPolicySize::get() as usize]
-			.try_into()
-			.unwrap();
+		let policy = Helper::<T>::create_policy();
 
 	}: _(RawOrigin::Signed(pool_admin), pool_id, policy)
 

pallets/loans-ref/src/lib.rs

@@ -36,9 +36,14 @@
 //! The whole pallet is optimized for the more expensive extrinsic that is
 //! [`Pallet::update_portfolio_valuation()`] that should go through all active loans.
 
-pub mod migrations;
+pub mod migrations {
+	pub mod nuke;
+	pub mod v1;
+}
+
 pub mod types;
 pub mod valuation;
+pub mod write_off;
 
 #[cfg(test)]
 mod mock;
@@ -82,10 +87,12 @@ pub mod pallet {
 		traits::{BadOrigin, One, Zero},
 		ArithmeticError, FixedPointOperand,
 	};
+	use sp_std::vec::Vec;
 	use types::{
 		self, ActiveLoan, AssetOf, BorrowLoanError, CloseLoanError, CreateLoanError, LoanInfoOf,
-		PortfolioValuationUpdateType, WriteOffState, WriteOffStatus, WrittenOffError,
+		PortfolioValuationUpdateType, WrittenOffError,
 	};
+	use write_off::{WriteOffRule, WriteOffStatus};
 
 	use super::*;
 
@@ -94,7 +101,7 @@ pub mod pallet {
 		<T as Config>::CurrencyId,
 	>>::PoolId;
 
-	const STORAGE_VERSION: StorageVersion = StorageVersion::new(0);
+	const STORAGE_VERSION: StorageVersion = StorageVersion::new(1);
 
 	#[pallet::pallet]
 	#[pallet::generate_store(pub(super) trait Store)]
@@ -237,7 +244,7 @@ pub mod pallet {
 		_,
 		Blake2_128Concat,
 		PoolIdOf<T>,
-		BoundedVec<WriteOffState<T::Rate>, T::MaxWriteOffPolicySize>,
+		BoundedVec<WriteOffRule<T::Rate>, T::MaxWriteOffPolicySize>,
 		ValueQuery,
 	>;
 
@@ -293,7 +300,7 @@ pub mod pallet {
 		},
 		WriteOffPolicyUpdated {
 			pool_id: PoolIdOf<T>,
-			policy: BoundedVec<WriteOffState<T::Rate>, T::MaxWriteOffPolicySize>,
+			policy: BoundedVec<WriteOffRule<T::Rate>, T::MaxWriteOffPolicySize>,
 		},
 	}
 
@@ -305,9 +312,9 @@ pub mod pallet {
 		LoanNotFound,
 		/// Emits when a loan exist but it's not active
 		LoanNotActive,
-		/// Emits when a write-off state is not found in a policy for a specific loan.
+		/// Emits when a write-off rule is not found in a policy for a specific loan.
 		/// It happens when there is no policy or the loan is not overdue.
-		NoValidWriteOffState,
+		NoValidWriteOffRule,
 		/// Emits when the NFT owner is not found
 		NFTOwnerNotFound,
 		/// Emits when NFT owner doesn't match the expected owner
@@ -473,8 +480,8 @@ pub mod pallet {
 		/// - Write off by admin with percentage 0.5 and penalty 0.2
 		/// - Time passes and the policy can be applied.
 		/// - Write of with a policy that says: percentage 0.3, penaly 0.4
-		/// - The loan is written off with the maximum between the policy and the current state:
-		///   percentage 0.5, penaly 0.4
+		/// - The loan is written off with the maximum between the policy and the current rule:
+		///   percentage 0.5, penalty 0.4
 		///
 		/// No special permisions are required to this call.
 		/// The portfolio valuation of the pool is updated to reflect the new present value of the loan.
@@ -488,8 +495,9 @@ pub mod pallet {
 			ensure_signed(origin)?;
 
 			let (status, _count) = Self::update_active_loan(pool_id, loan_id, |loan| {
-				let state = Self::find_write_off_state(pool_id, loan.maturity_date())?;
-				let limit = state.status().max(loan.write_off_status());
+				let rule = Self::find_write_off_rule(pool_id, loan)?
+					.ok_or(Error::<T>::NoValidWriteOffRule)?;
+				let limit = rule.status.compose_max(loan.write_off_status());
 
 				loan.write_off(&limit, &limit)?;
 
@@ -532,10 +540,11 @@ pub mod pallet {
 			};
 
 			let _count = Self::update_active_loan(pool_id, loan_id, |loan| {
-				let state = Self::find_write_off_state(pool_id, loan.maturity_date());
-				let limit = state.map(|s| s.status()).unwrap_or_else(|_| status.clone());
+				let rule = Self::find_write_off_rule(pool_id, loan)?;
+				let limit = rule.map(|r| r.status).unwrap_or_else(|| status.clone());
 
-				loan.write_off(&limit, &status)
+				loan.write_off(&limit, &status)?;
+				Ok(limit)
 			})?;
 
 			Self::deposit_event(Event::<T>::WrittenOff {
@@ -584,7 +593,7 @@ pub mod pallet {
 			Ok(())
 		}
 
-		/// Updates the write off policy.
+		/// Updates the write off policy with write off rules.
 		///
 		/// The write off policy is used to automatically set a write off minimum value to the
 		/// loan.
@@ -593,7 +602,7 @@ pub mod pallet {
 		pub fn update_write_off_policy(
 			origin: OriginFor<T>,
 			pool_id: PoolIdOf<T>,
-			policy: BoundedVec<WriteOffState<T::Rate>, T::MaxWriteOffPolicySize>,
+			policy: BoundedVec<WriteOffRule<T::Rate>, T::MaxWriteOffPolicySize>,
 		) -> DispatchResult {
 			let who = ensure_signed(origin)?;
 			Self::ensure_role(pool_id, &who, PoolRole::PoolAdmin)?;
@@ -679,16 +688,38 @@ pub mod pallet {
 			})
 		}
 
-		fn find_write_off_state(
+		/// From all overdue write off rules, it returns the one with the highest percentage
+		/// (or highest penalty, if same percentage) that can be applied.
+		///
+		/// Suppose a policy with the following rules:
+		/// - overdue_days: 5,   percentage 10%
+		/// - overdue_days: 10,  percentage 30%
+		/// - overdue_days: 15,  percentage 20%
+		///
+		/// If the loan is not overdue, it will not return any rule.
+		/// If the loan is overdue by 4 days, it will not return any rule.
+		/// If the loan is overdue by 9 days, it will return the first rule.
+		/// If the loan is overdue by 60 days, it will return the second rule
+		/// (because it has a higher percetage).
+		fn find_write_off_rule(
 			pool_id: PoolIdOf<T>,
-			maturity_date: Moment,
-		) -> Result<WriteOffState<T::Rate>, DispatchError> {
-			WriteOffState::find_best(
-				WriteOffPolicy::<T>::get(pool_id).into_iter(),
-				maturity_date,
-				T::Time::now().as_secs(),
-			)
-			.ok_or_else(|| Error::<T>::NoValidWriteOffState.into())
+			loan: &ActiveLoan<T>,
+		) -> Result<Option<WriteOffRule<T::Rate>>, DispatchError> {
+			Ok(WriteOffPolicy::<T>::get(pool_id)
+				.into_iter()
+				.filter_map(|rule| {
+					rule.triggers
+						.iter()
+						.map(|trigger| loan.check_write_off_trigger(&trigger.0))
+						.find(|e| match e {
+							Ok(value) => *value,
+							Err(_) => true,
+						})
+						.map(|result| result.map(|_| rule))
+				})
+				.collect::<Result<Vec<_>, _>>()? // This exits if error before getting the maximum
+				.into_iter()
+				.max_by(|r1, r2| r1.status.cmp(&r2.status)))
 		}
 
 		fn update_portfolio_valuation_with_pv(

pallets/loans-ref/src/migrations.rs → pallets/loans-ref/src/migrations/nuke.rs

@@ -12,7 +12,7 @@ use sp_std::vec::Vec;
 
 use crate::*;
 
-mod v0 {
+mod old {
 	use super::*;
 
 	/// This storage comes from the previous pallet loans.
@@ -24,9 +24,9 @@ mod v0 {
 }
 
 /// This migration nukes all storages from the pallet individually.
-pub struct NukeMigration<T>(sp_std::marker::PhantomData<T>);
+pub struct Migration<T>(sp_std::marker::PhantomData<T>);
 
-impl<T: Config> OnRuntimeUpgrade for NukeMigration<T> {
+impl<T: Config> OnRuntimeUpgrade for Migration<T> {
 	#[cfg(feature = "try-runtime")]
 	fn pre_upgrade() -> Result<Vec<u8>, &'static str> {
 		ensure!(
@@ -35,15 +35,15 @@ impl<T: Config> OnRuntimeUpgrade for NukeMigration<T> {
 		);
 
 		ensure!(
-			v0::NextLoanId::<T>::iter_values().count() == 1,
+			old::NextLoanId::<T>::iter_values().count() == 1,
 			"Pallet loans contains doesn't contain old data"
 		);
 
 		Ok(Vec::new())
 	}
 
 	fn on_runtime_upgrade() -> Weight {
-		let old_values = v0::NextLoanId::<T>::iter_values().count();
+		let old_values = old::NextLoanId::<T>::iter_values().count();
 		if old_values > 0 {
 			let result = storage::unhashed::clear_prefix(&loan_prefix(), None, None);
 
@@ -69,7 +69,7 @@ impl<T: Config> OnRuntimeUpgrade for NukeMigration<T> {
 		);
 
 		ensure!(
-			v0::NextLoanId::<T>::iter_values().count() == 0,
+			old::NextLoanId::<T>::iter_values().count() == 0,
 			"Pallet loans still contains old data"
 		);