simplify negative interest

simontreanor · Apr 12, 2024 · 8db73fb · 8db73fb
1 parent 9c5665c
commit 8db73fb
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Showing 14 changed files with 16 additions and 102 deletions.
diff --git a/docs/exampleAmortisation.fsx b/docs/exampleAmortisation.fsx
@@ -53,9 +53,7 @@ let scheduleParameters =
             AprMethod = Apr.CalculationMethod.UnitedKingdom 3
             RoundingOptions = RoundingOptions.recommended
             MinimumPayment = DeferOrWriteOff 50L<Cent>
-            PaymentTimeout = 3<DurationDay>
-            NegativeInterestOption = ApplyNegativeInterest
-        }
+            PaymentTimeout = 3<DurationDay>        }
     }
 
 let actualPayments = [|

diff --git a/docs/examplePaymentSchedule.fsx b/docs/examplePaymentSchedule.fsx
@@ -54,7 +54,6 @@ let scheduleParameters =
             RoundingOptions = RoundingOptions.recommended
             MinimumPayment = DeferOrWriteOff 50L<Cent>
             PaymentTimeout = 3<DurationDay>
-            NegativeInterestOption = ApplyNegativeInterest
         }
     }
 let schedule = scheduleParameters |> calculate AroundZero

diff --git a/src/Amortisation.fs b/src/Amortisation.fs
@@ -174,12 +174,12 @@ module Amortisation =
 
             let newInterest =
                 if si.PrincipalBalance <= 0L<Cent> then
-                    match sp.Calculation.NegativeInterestOption with
-                    | ApplyNegativeInterest ->
+                    match sp.Interest.RateOnNegativeBalance with
+                    | ValueSome _ ->
                         dailyInterestRates si.OffsetDay ap.AppliedPaymentDay
                         |> Array.map(fun dr -> { dr with InterestRate = sp.Interest.RateOnNegativeBalance |> ValueOption.defaultValue Interest.Rate.Zero })
                         |> Interest.calculate (si.PrincipalBalance + si.FeesBalance) ValueNone (ValueSome sp.Calculation.RoundingOptions.InterestRounding)
-                    | DoNotApplyNegativeInterest ->
+                    | ValueNone ->
                         0m<Cent>
                 else
                     dailyInterestRates si.OffsetDay ap.AppliedPaymentDay

diff --git a/src/Calculation.fs b/src/Calculation.fs
@@ -27,14 +27,6 @@ module Calculation =
         /// intended just for information, e.g. to view the current status of a loan
         | Statement
 
-    /// whether to apply interest on a negative balance (i.e. while a refund is owing)
-    [<Struct>]
-    type NegativeInterestOption =
-        /// apply negative interest (e.g. statutory interest on outstanding refunds)
-        | ApplyNegativeInterest
-        /// do not apply negative interest (e.g. if the customer has volutarily overpaid)
-        | DoNotApplyNegativeInterest
-
     /// holds the result of a devision, separated into quotient and remainder
     [<Struct>]
     type DivisionResult = {

diff --git a/src/PaymentSchedule.fs b/src/PaymentSchedule.fs
@@ -71,8 +71,6 @@ module PaymentSchedule =
         AprMethod: Apr.CalculationMethod
         /// which rounding method to use
         RoundingOptions: RoundingOptions
-        /// how to handle interest on negative principal balances
-        NegativeInterestOption: NegativeInterestOption
         /// the minimum payment that can be taken and how to handle it
         MinimumPayment: MinimumPayment
         /// the duration after which a pending payment is considered a missed payment

diff --git a/src/Rescheduling.fs b/src/Rescheduling.fs
@@ -23,7 +23,7 @@ module Rescheduling =
         /// whether the plan is autogenerated or a manual plan provided
         PaymentSchedule: CustomerPaymentSchedule
         /// how to handle interest on negative principal balances
-        NegativeInterestOption: NegativeInterestOption
+        RateOnNegativeBalance: Interest.Rate voption
         /// any promotional or introductory offers during which a different interest rate is applicable
         PromotionalInterestRates: Interest.PromotionalRate array
         /// any period during which charges are not payable
@@ -70,8 +70,12 @@ module Rescheduling =
                     ScheduleType = PaymentSchedule.ScheduleType.Rescheduled rp.OriginalFinalPaymentDay
                     PaymentSchedule = [| oldPaymentSchedule; newPaymentSchedule |] |> Array.concat |> IrregularSchedule
                     FeesAndCharges = { sp.FeesAndCharges with ChargesHolidays = rp.ChargesHolidays }
-                    Interest = { sp.Interest with InitialGracePeriod = 0<DurationDay>; PromotionalRates = rp.PromotionalInterestRates }
-                    Calculation = { sp.Calculation with NegativeInterestOption = rp.NegativeInterestOption }
+                    Interest =
+                        { sp.Interest with
+                            InitialGracePeriod = 0<DurationDay>
+                            PromotionalRates = rp.PromotionalInterestRates
+                            RateOnNegativeBalance = rp.RateOnNegativeBalance
+                        }
                 }
             // create the new amortiation schedule
             let intendedPurpose =

diff --git a/tests/ActualPaymentTests.fs b/tests/ActualPaymentTests.fs
@@ -86,7 +86,6 @@ module ActualPaymentTests =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         }
 
@@ -134,7 +133,6 @@ module ActualPaymentTests =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         }
 
@@ -182,7 +180,6 @@ module ActualPaymentTests =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         }
 
@@ -230,7 +227,6 @@ module ActualPaymentTests =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         }
 
@@ -302,7 +298,6 @@ module ActualPaymentTests =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         }
 
@@ -374,7 +369,6 @@ module ActualPaymentTests =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         }
 
@@ -451,7 +445,6 @@ module ActualPaymentTests =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         }
 
@@ -526,7 +519,6 @@ module ActualPaymentTests =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         }
 
@@ -602,7 +594,6 @@ module ActualPaymentTests =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         }
 
@@ -679,7 +670,6 @@ module ActualPaymentTests =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         }
 
@@ -755,7 +745,6 @@ module ActualPaymentTests =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         }
 
@@ -831,7 +820,6 @@ module ActualPaymentTests =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         }
 
@@ -909,7 +897,6 @@ module ActualPaymentTests =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         }
 
@@ -959,7 +946,6 @@ module ActualPaymentTests =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         }
 
@@ -1032,7 +1018,6 @@ module ActualPaymentTests =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         }
 
@@ -1082,7 +1067,6 @@ module ActualPaymentTests =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         }
 
@@ -1133,7 +1117,6 @@ module ActualPaymentTests =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         }
 
@@ -1185,7 +1168,6 @@ module ActualPaymentTests =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         }
 
@@ -1237,7 +1219,6 @@ module ActualPaymentTests =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         }
 
@@ -1286,7 +1267,6 @@ module ActualPaymentTests =
                 RoundingOptions = RoundingOptions.recommended
                 PaymentTimeout = 0<DurationDay>
                 MinimumPayment = NoMinimumPayment
-                NegativeInterestOption = ApplyNegativeInterest
             }
         }
 

diff --git a/tests/ActualPaymentTestsExtra.fs b/tests/ActualPaymentTestsExtra.fs
@@ -204,7 +204,6 @@ module ActualPaymentTestsExtra =
                     RoundingOptions = ro
                     MinimumPayment = DeferOrWriteOff 50L<Cent>
                     PaymentTimeout = 3<DurationDay>
-                    NegativeInterestOption = ApplyNegativeInterest
                 }
             }
             |> applyPayments
@@ -257,7 +256,6 @@ module ActualPaymentTestsExtra =
                     RoundingOptions = ro
                     MinimumPayment = DeferOrWriteOff 50L<Cent>
                     PaymentTimeout = 3<DurationDay>
-                    NegativeInterestOption = ApplyNegativeInterest
                 }
             }
         )))))))))))))))
@@ -349,7 +347,6 @@ module ActualPaymentTestsExtra =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         })
         let actual =
@@ -426,7 +423,6 @@ module ActualPaymentTestsExtra =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         })
         let actual =
@@ -505,7 +501,6 @@ module ActualPaymentTestsExtra =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         })
         let originalFinalPaymentDay = paymentDays sp.StartDate sp.PaymentSchedule |> Array.tryLast |> Option.defaultValue 0<OffsetDay>
@@ -518,8 +513,9 @@ module ActualPaymentTestsExtra =
                 let rp : RescheduleParameters = {
                     OriginalFinalPaymentDay = originalFinalPaymentDay'
                     FeesSettlement = Fees.SettlementRefund.ProRata
-                    PaymentSchedule = RegularFixedSchedule [| { UnitPeriodConfig = UnitPeriod.Config.Weekly(2, Date(2022, 9, 1)); PaymentCount = 155; PaymentAmount = 20_00L<Cent> } |]
-                    NegativeInterestOption = DoNotApplyNegativeInterest
+                    PaymentSchedule = RegularFixedSchedule [|
+                        { UnitPeriodConfig = UnitPeriod.Config.Weekly(2, Date(2022, 9, 1)); PaymentCount = 155; PaymentAmount = 20_00L<Cent> } |]
+                    RateOnNegativeBalance = ValueNone
                     PromotionalInterestRates = [||]
                     ChargesHolidays = [||]
                     FutureSettlementDay = ValueNone
@@ -591,7 +587,6 @@ module ActualPaymentTestsExtra =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         })
         let actual =
@@ -668,7 +663,6 @@ module ActualPaymentTestsExtra =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         })
         let actual =
@@ -745,7 +739,6 @@ module ActualPaymentTestsExtra =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         })
         let actual =
@@ -824,7 +817,6 @@ module ActualPaymentTestsExtra =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         })
         let originalFinalPaymentDay = paymentDays sp.StartDate sp.PaymentSchedule |> Array.tryLast |> Option.defaultValue 0<OffsetDay>
@@ -909,7 +901,6 @@ module ActualPaymentTestsExtra =
                 RoundingOptions = RoundingOptions.recommended
                 MinimumPayment = DeferOrWriteOff 50L<Cent>
                 PaymentTimeout = 3<DurationDay>
-                NegativeInterestOption = ApplyNegativeInterest
             }
         })
         let originalFinalPaymentDay = paymentDays sp.StartDate sp.PaymentSchedule |> Array.tryLast |> Option.defaultValue 0<OffsetDay>