fix max payment count

simontreanor · Jun 24, 2024 · 9160999 · 9160999
1 parent ae57c93
commit 9160999
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Showing 3 changed files with 61 additions and 12 deletions.
diff --git a/src/FSharp.Finance.Personal.fsproj b/src/FSharp.Finance.Personal.fsproj
@@ -33,7 +33,7 @@
   <PropertyGroup Condition="'$(Configuration)'=='Release'">
     <GeneratePackageOnBuild>true</GeneratePackageOnBuild>
     <PackageId>FSharp.Finance.Personal</PackageId>
-    <Version>1.0.1</Version>
+    <Version>1.0.2</Version>
     <Authors>Simon Treanor</Authors>
     <PackageDescription>F# Personal Finance Library</PackageDescription>
     <RepositoryUrl>https://github.com/simontreanor/FSharp.Finance.Personal</RepositoryUrl>

diff --git a/src/UnitPeriod.fs b/src/UnitPeriod.fs
@@ -198,15 +198,14 @@ module UnitPeriod =
             | invalidConfig -> fix invalidConfig
 
     /// generates a suggested number of payments to constrain the loan within a certain duration
-    let maxPaymentCount (maxDuration: int<DurationDay>) (config: Config) (startDate: Date) =
-        let offset y m td = ((TrackingDay.toDate y m td) - startDate).Days |> fun f -> int f * 1<DurationDay>
+    let maxPaymentCount (maxDuration: int<DurationDay>) (config: Config) =
         match config with
-        | Single d -> maxDuration - offset d.Year d.Month d.Day
-        | Daily d -> maxDuration - offset d.Year d.Month d.Day
-        | Weekly (multiple, d) when multiple > 0 -> (maxDuration - offset d.Year d.Month d.Day) / (multiple * 7)
-        | SemiMonthly (y, m, d1, _) -> (maxDuration - offset y m (int d1)) / 15
-        | Monthly (multiple, y, m, d) when multiple > 0 -> (maxDuration - offset y m (int d)) / (multiple * 30)
-        | _ -> 0<DurationDay>
+        | Single _ -> 1.
+        | Daily _ -> float maxDuration
+        | Weekly (multiple, _) when multiple > 0 -> ((float maxDuration) / (float multiple * 7.))
+        | SemiMonthly _ -> ((float maxDuration) / 15.)
+        | Monthly (multiple, _, _, _) when multiple > 0 -> ((float maxDuration) / (float multiple * 30.))
+        | _ -> 1.
         |> int
 
     /// direction in which to generate the schedule: forward works forwards from a given date and reverse works backwards
@@ -222,7 +221,7 @@ module UnitPeriod =
         if count = 0 then [||] else
         let limitedCount =
             match maxDuration with
-            | ValueSome { Duration.Length = d; Duration.FromDate = fd } -> maxPaymentCount d unitPeriodConfig fd
+            | ValueSome { Duration.Length = d; Duration.FromDate = fd } -> min count (maxPaymentCount d unitPeriodConfig)
             | ValueNone -> count
         let adjustMonthEnd (monthEndTrackingDay: int) (d: Date) =
             if d.Day > 15 && monthEndTrackingDay > 28 then

diff --git a/tests/PaymentScheduleTests.fs b/tests/PaymentScheduleTests.fs
@@ -1463,7 +1463,7 @@ module PaymentScheduleTests =
             StartDate = Date(2024, 5, 8)
             Principal = 1000_00L<Cent>
             PaymentSchedule = RegularSchedule (
-                UnitPeriodConfig = UnitPeriod.Monthly(1, 2024, 5, 8),
+                UnitPeriodConfig = UnitPeriod.Monthly(1, 2024, 5, 18),
                 PaymentCount = 7,
                 MaxDuration = ValueSome { Length = 184<DurationDay>; FromDate = Date(2024, 5, 8) }
             )
@@ -1498,5 +1498,55 @@ module PaymentScheduleTests =
                 return schedule.LevelPayment, schedule.FinalPayment
             }
 
-        let expected = ValueSome (251_08L<Cent>, 250_99L<Cent>)
+        let expected = ValueSome (290_73L<Cent>, 290_71L<Cent>)
+        actual |> should equal expected
+
+    [<Fact>]
+    let ``4) Payment count must not be exceeded`` () =
+        let sp = {
+            AsOfDate = Date(2024, 6, 24)
+            StartDate = Date(2024, 6, 24)
+            Principal = 100_00L<Cent>
+            PaymentSchedule = RegularSchedule (
+                UnitPeriodConfig = UnitPeriod.Monthly(1, 2024, 7, 4),
+                PaymentCount = 4,
+                MaxDuration = ValueSome { Length = 190<DurationDay>; FromDate = Date(2024, 6, 24) }
+            )
+            FeesAndCharges = {
+                Fees = [||]
+                FeesAmortisation = Fees.FeeAmortisation.AmortiseProportionately
+                FeesSettlementRefund = Fees.SettlementRefund.ProRata ValueNone
+                Charges = [| Charge.LatePayment (Amount.Percentage(Percent 5m, ValueSome(Amount.Restriction.UpperLimit 750L<Cent>), ValueSome (Round MidpointRounding.ToEven))) |]
+                ChargesHolidays = [||]
+                ChargesGrouping = OneChargeTypePerDay
+                LatePaymentGracePeriod = 3<DurationDay>
+            }
+            Interest = {
+                StandardRate = Interest.Rate.Daily (Percent 0.8m)
+                Cap = Interest.Cap.none
+                InitialGracePeriod = 1<DurationDay>
+                PromotionalRates = [||]
+                RateOnNegativeBalance = ValueNone
+            }
+            Calculation = {
+                AprMethod = Apr.CalculationMethod.UnitedKingdom 3
+                RoundingOptions = {
+                    ChargesRounding = Round MidpointRounding.ToEven
+                    FeesRounding = Round MidpointRounding.ToEven
+                    InterestRounding = Round MidpointRounding.ToEven
+                    PaymentRounding = Round MidpointRounding.ToEven
+                }
+                MinimumPayment = DeferOrWriteOff 50L<Cent>
+                PaymentTimeout = 3<DurationDay>
+            }
+        }
+
+        let actual =
+            voption {
+                let! schedule = sp |> calculate BelowZero
+                schedule.Items |> Formatting.outputListToHtml "out/PaymentSchedule004.md"
+                return schedule.LevelPayment, schedule.FinalPayment
+            }
+
+        let expected = ValueSome (36_48L<Cent>, 36_44L<Cent>)
         actual |> should equal expected