[Bug][SubscriptionBilling] Enforce Subscription Line Start Date change rules on all edit paths

src/Apps/W1/Subscription Billing/App/Billing/Tables/BillingLine.Table.al

@@ -470,6 +470,11 @@ table 8061 "Billing Line"
         Rec.SetRange("Subscription Contract Line No.", ContractLineNo);
     end;
 
+    internal procedure FilterBillingLineOnServiceCommitment(ServiceCommitmentEntryNo: Integer)
+    begin
+        Rec.SetRange("Subscription Line Entry No.", ServiceCommitmentEntryNo);
+    end;
+
     local procedure RecalculateCustomerContractHarmonizedBillingFields()
     var
         CustomerContract: Record "Customer Subscription Contract";

src/Apps/W1/Subscription Billing/App/Billing/Tables/BillingLineArchive.Table.al

@@ -199,6 +199,9 @@ table 8064 "Billing Line Archive"
         key(SK1; "Subscription Contract No.", "Subscription Contract Line No.", "Billing from")
         {
         }
+        key(SK2; "Subscription Line Entry No.")
+        {
+        }
     }
 
     fieldgroups

src/Apps/W1/Subscription Billing/App/Service Commitments/Tables/SubscriptionLine.Table.al

@@ -56,6 +56,7 @@ table 8059 "Subscription Line"
 
             trigger OnValidate()
             begin
+                CheckSubscriptionLineStartDateChangeAllowed();
                 DateFormulaManagement.ErrorIfDateEmpty("Subscription Line Start Date", FieldCaption("Subscription Line Start Date"));
                 UpdateNextBillingDate("Subscription Line Start Date" - 1);
                 CheckServiceDates();
@@ -1022,11 +1023,7 @@ table 8059 "Subscription Line"
                     FieldNo("Invoicing Item No."):
                         Validate("Invoicing Item No.", "Invoicing Item No.");
                     FieldNo("Subscription Line Start Date"):
-                        begin
-                            Rec.ErrorIfBillingLineArchiveForServiceCommitmentExist();
-                            Rec.ErrorIfBillingLineForServiceCommitmentExist();
-                            Validate("Subscription Line Start Date", "Subscription Line Start Date");
-                        end;
+                        Validate("Subscription Line Start Date", "Subscription Line Start Date");
                     FieldNo("Subscription Line End Date"):
                         Validate("Subscription Line End Date", "Subscription Line End Date");
                     FieldNo(Quantity):
@@ -1475,11 +1472,42 @@ table 8059 "Subscription Line"
     end;
 
     internal procedure ErrorIfBillingLineForServiceCommitmentExist()
+    var
+        BillingLine: Record "Billing Line";
     begin
-        if BillingLineExists() then
+        BillingLine.FilterBillingLineOnServiceCommitment(Rec."Entry No.");
+        if not BillingLine.IsEmpty() then
             Error(BillingLineForServiceCommitmentExistErr);
     end;
 
+    /// <summary>
+    /// Checks whether the Subscription Line Start Date may still be changed.
+    /// The change is allowed as long as no billing has taken place for the Subscription Line, or as long as the
+    /// Next Billing Date is still on the Subscription Line Start Date, which is the state after a cancellation
+    /// or a credit memo and the case in which the billing period legitimately has to be corrected.
+    /// </summary>
+    local procedure CheckSubscriptionLineStartDateChangeAllowed()
+    begin
+        CheckBillingStateAllowsSubscriptionLineStartDateChange();
+        OnAfterCheckSubscriptionLineStartDateChangeAllowed(Rec);
+    end;
+
+    local procedure CheckBillingStateAllowsSubscriptionLineStartDateChange()
+    var
+        SubscriptionLine: Record "Subscription Line";
+    begin
+        if Rec.IsTemporary() then
+            exit;
+        SubscriptionLine.SetLoadFields("Subscription Line Start Date", "Next Billing Date");
+        if not SubscriptionLine.Get(Rec."Entry No.") then
+            exit;
+        if SubscriptionLine."Next Billing Date" = SubscriptionLine."Subscription Line Start Date" then
+            exit;
+
+        ErrorIfBillingLineArchiveForServiceCommitmentExist();
+        ErrorIfBillingLineForServiceCommitmentExist();
+    end;
+
     internal procedure GetPartnerNoFromContract(): Code[20]
     var
         CustomerContract: Record "Customer Subscription Contract";
@@ -1504,8 +1532,7 @@ table 8059 "Subscription Line"
         BillingLineArchive: Record "Billing Line Archive";
     begin
         BillingLineArchive.FilterBillingLineArchiveOnServiceCommitment(Rec."Entry No.");
-        BillingLineArchive.CalcSums(Amount);
-        if BillingLineArchive.Amount <> 0 then
+        if not BillingLineArchive.IsEmpty() then
             Error(BillingLineArchiveForServiceCommitmentExistErr);
     end;
 
@@ -2111,6 +2138,16 @@ table 8059 "Subscription Line"
     begin
     end;
 
+    /// <summary>
+    /// Raised after the Subscription Line Start Date change has passed the billing state check.
+    /// Subscribers can only tighten the rule, by raising an error of their own.
+    /// </summary>
+    /// <param name="SubscriptionLine">The Subscription Line carrying the new Subscription Line Start Date.</param>
+    [IntegrationEvent(false, false)]
+    local procedure OnAfterCheckSubscriptionLineStartDateChangeAllowed(SubscriptionLine: Record "Subscription Line")
+    begin
+    end;
+
     [IntegrationEvent(false, false)]
     local procedure OnAfterCalculateServiceAmount(var SubscriptionLine: Record "Subscription Line"; CalledByFieldNo: Integer)
     begin

src/Apps/W1/Subscription Billing/Test/Service Commitments/ServiceCommitmentTest.Codeunit.al

@@ -29,6 +29,8 @@ codeunit 148156 "Service Commitment Test"
         DiscountCanBeInvoicedViaContractErr: Label 'Recurring discounts can only be granted for Invoicing via Contract.', Locked = true;
         DiscountCannotBeAssignedErr: Label 'Subscription Package Lines, which are discounts, can only be assigned to Subscription Items.', Locked = true;
         RecurringDiscountCannotBeGrantedErr: Label 'Recurring discounts cannot be granted in conjunction with Usage Based Billing', Locked = true;
+        BillingLineForServiceCommitmentExistErr: Label 'The contract line is in the current billing. Delete the billing line to be able to adjust the Subscription Line start date.', Locked = true;
+        BillingLineArchiveForServiceCommitmentExistErr: Label 'The contract line has already been billed. The Subscription Line start date can no longer be changed.', Locked = true;
 
     #region Tests
 
@@ -597,6 +599,139 @@ codeunit 148156 "Service Commitment Test"
         Assert.ExpectedError(RecurringDiscountCannotBeGrantedErr);
     end;
 
+    [Test]
+    [HandlerFunctions('CreateCustomerBillingDocsPageHandler,ExchangeRateSelectionModalPageHandler,MessageHandler')]
+    procedure PreventStartDateChangeOnSubscriptionLinesPageAfterBilling()
+    var
+        BillingLine: Record "Billing Line";
+        BillingTemplate: Record "Billing Template";
+        SalesHeader: Record "Sales Header";
+        SubscriptionLine: Record "Subscription Line";
+        ServiceCommitmentsPage: TestPage "Service Commitments";
+    begin
+        // [SCENARIO] The Subscription Line Start Date can no longer be changed on the Subscription Lines page after the Subscription Line has been billed
+
+        // [GIVEN] A Customer Subscription Contract with a Subscription Line for which an invoice has been posted
+        Initialize();
+        BillContractAndPostInvoice(BillingTemplate, BillingLine, SalesHeader);
+        SubscriptionLine.Get(BillingLine."Subscription Line Entry No.");
+        Assert.AreNotEqual(SubscriptionLine."Subscription Line Start Date", SubscriptionLine."Next Billing Date", 'The Subscription Line should have been billed.');
+        Commit(); // retain data after asserterror
+
+        // [WHEN] The Subscription Line Start Date is changed on the Subscription Lines page
+        ServiceCommitmentsPage.OpenEdit();
+        ServiceCommitmentsPage.GoToRecord(SubscriptionLine);
+
+        // [THEN] The change is rejected with the same error as on the contract line list
+        asserterror ServiceCommitmentsPage."Service Start Date".SetValue(GetDifferentDateAllowedByLicense(SubscriptionLine."Subscription Line Start Date"));
+        Assert.ExpectedError(BillingLineArchiveForServiceCommitmentExistErr);
+    end;
+
+    [Test]
+    procedure UT_PreventStartDateChangeWhenBilledSubscriptionLineHasZeroAmount()
+    var
+        SubscriptionLine: Record "Subscription Line";
+    begin
+        // [SCENARIO] The Subscription Line Start Date can no longer be changed for a Subscription Line which has been billed at zero value
+
+        // [GIVEN] A billed Subscription Line whose archived billing lines add up to zero
+        Initialize();
+        MockBilledSubscriptionLine(SubscriptionLine);
+        MockBillingLineArchive(SubscriptionLine."Entry No.", 0);
+
+        // [WHEN] The Subscription Line Start Date is changed
+        // [THEN] The change is rejected
+        asserterror SubscriptionLine.Validate("Subscription Line Start Date", CalcDate('<+2M>', SubscriptionLine."Subscription Line Start Date"));
+        Assert.ExpectedError(BillingLineArchiveForServiceCommitmentExistErr);
+    end;
+
+    [Test]
+    procedure UT_PreventStartDateChangeWhenSubscriptionLineIsInCurrentBilling()
+    var
+        SubscriptionLine: Record "Subscription Line";
+    begin
+        // [SCENARIO] The Subscription Line Start Date cannot be changed as long as the Subscription Line is part of the current billing
+
+        // [GIVEN] A Subscription Line with an open Billing Line
+        Initialize();
+        MockBilledSubscriptionLine(SubscriptionLine);
+        MockBillingLine(SubscriptionLine."Entry No.");
+
+        // [WHEN] The Subscription Line Start Date is changed
+        // [THEN] The change is rejected
+        asserterror SubscriptionLine.Validate("Subscription Line Start Date", CalcDate('<+2M>', SubscriptionLine."Subscription Line Start Date"));
+        Assert.ExpectedError(BillingLineForServiceCommitmentExistErr);
+    end;
+
+    [Test]
+    procedure UT_AllowStartDateChangeWhenNextBillingDateIsOnStartDate()
+    var
+        SubscriptionLine: Record "Subscription Line";
+        NewStartDate: Date;
+    begin
+        // [SCENARIO] The Subscription Line Start Date may be corrected as long as the Next Billing Date is back on the Subscription Line Start Date
+
+        // [GIVEN] A billed Subscription Line whose Next Billing Date has been reset to the Subscription Line Start Date by a credit memo
+        Initialize();
+        MockBilledSubscriptionLine(SubscriptionLine);
+        MockBillingLineArchive(SubscriptionLine."Entry No.", LibraryRandom.RandDec(100, 2));
+        SubscriptionLine."Next Billing Date" := SubscriptionLine."Subscription Line Start Date";
+        SubscriptionLine.Modify(false);
+
+        // [WHEN] The Subscription Line Start Date is changed
+        NewStartDate := CalcDate('<+2M>', SubscriptionLine."Subscription Line Start Date");
+        SubscriptionLine.Validate("Subscription Line Start Date", NewStartDate);
+
+        // [THEN] The change is accepted and the Next Billing Date follows the new Subscription Line Start Date
+        SubscriptionLine.TestField("Subscription Line Start Date", NewStartDate);
+        SubscriptionLine.TestField("Next Billing Date", NewStartDate);
+    end;
+
+    [Test]
+    procedure UT_AllowStartDateChangeWhenSubscriptionLineHasNotBeenBilled()
+    var
+        SubscriptionLine: Record "Subscription Line";
+        NewStartDate: Date;
+    begin
+        // [SCENARIO] The Subscription Line Start Date may be changed as long as no billing has been performed for the Subscription Line
+
+        // [GIVEN] A Subscription Line without any Billing Line and without any Billing Line Archive
+        Initialize();
+        MockBilledSubscriptionLine(SubscriptionLine);
+
+        // [WHEN] The Subscription Line Start Date is changed
+        NewStartDate := CalcDate('<+2M>', SubscriptionLine."Subscription Line Start Date");
+        SubscriptionLine.Validate("Subscription Line Start Date", NewStartDate);
+
+        // [THEN] The change is accepted and the Next Billing Date follows the new Subscription Line Start Date
+        SubscriptionLine.TestField("Subscription Line Start Date", NewStartDate);
+        SubscriptionLine.TestField("Next Billing Date", NewStartDate);
+    end;
+
+    [Test]
+    procedure UT_AllowStartDateChangeOnTemporarySubscriptionLine()
+    var
+        SubscriptionLine: Record "Subscription Line";
+        TempSubscriptionLine: Record "Subscription Line" temporary;
+        NewStartDate: Date;
+    begin
+        // [SCENARIO] Buffering a billed Subscription Line in a temporary record, as the contract renewal does, is not blocked by the start date check
+
+        // [GIVEN] A billed Subscription Line and a temporary Subscription Line carrying its Entry No.
+        Initialize();
+        MockBilledSubscriptionLine(SubscriptionLine);
+        MockBillingLineArchive(SubscriptionLine."Entry No.", LibraryRandom.RandDec(100, 2));
+        TempSubscriptionLine.Init();
+        TempSubscriptionLine."Entry No." := SubscriptionLine."Entry No.";
+
+        // [WHEN] The Subscription Line Start Date is set on the temporary record
+        NewStartDate := CalcDate('<+2M>', SubscriptionLine."Subscription Line Start Date");
+        TempSubscriptionLine.Validate("Subscription Line Start Date", NewStartDate);
+
+        // [THEN] The value is accepted
+        TempSubscriptionLine.TestField("Subscription Line Start Date", NewStartDate);
+    end;
+
     #endregion Tests
 
     #region Procedures
@@ -637,6 +772,58 @@ codeunit 148156 "Service Commitment Test"
         until ServiceCommitment.Next() = 0;
     end;
 
+    local procedure BillContractAndPostInvoice(var BillingTemplate: Record "Billing Template"; var BillingLine: Record "Billing Line"; var SalesHeader: Record "Sales Header")
+    begin
+        ContractTestLibrary.CreateCustomerContractAndCreateContractLinesForItems(CustomerContract, ServiceObject, '');
+        ContractTestLibrary.DisableDeferralsForCustomerContract(CustomerContract, false);
+        ContractTestLibrary.CreateBillingProposal(BillingTemplate, Enum::"Service Partner"::Customer);
+        BillingLine.SetRange("Billing Template Code", BillingTemplate.Code);
+        BillingLine.SetRange(Partner, BillingLine.Partner::Customer);
+        Codeunit.Run(Codeunit::"Create Billing Documents", BillingLine);
+        BillingLine.FindLast();
+        SalesHeader.Get(SalesHeader."Document Type"::Invoice, BillingLine."Document No.");
+        LibrarySales.PostSalesDocument(SalesHeader, true, true);
+    end;
+
+    local procedure GetDifferentDateAllowedByLicense(ReferenceDate: Date) NewDate: Date
+    begin
+        // the date filter of the demo license only allows dates in November, December, January and February
+        NewDate := DMY2Date(1, 2, Date2DMY(ReferenceDate, 3));
+        if NewDate = ReferenceDate then
+            NewDate := DMY2Date(1, 1, Date2DMY(ReferenceDate, 3));
+    end;
+
+    local procedure MockBilledSubscriptionLine(var SubscriptionLine: Record "Subscription Line")
+    begin
+        SubscriptionLine.Init();
+        SubscriptionLine."Entry No." := 0;
+        SubscriptionLine."Invoicing via" := SubscriptionLine."Invoicing via"::Contract;
+        SubscriptionLine."Subscription Line Start Date" := WorkDate();
+        SubscriptionLine."Next Billing Date" := CalcDate('<+1M>', WorkDate());
+        SubscriptionLine.Insert(false);
+    end;
+
+    local procedure MockBillingLine(SubscriptionLineEntryNo: Integer)
+    var
+        BillingLine: Record "Billing Line";
+    begin
+        BillingLine.Init();
+        BillingLine."Entry No." := 0;
+        BillingLine."Subscription Line Entry No." := SubscriptionLineEntryNo;
+        BillingLine.Insert(false);
+    end;
+
+    local procedure MockBillingLineArchive(SubscriptionLineEntryNo: Integer; ArchivedAmount: Decimal)
+    var
+        BillingLineArchive: Record "Billing Line Archive";
+    begin
+        BillingLineArchive.Init();
+        BillingLineArchive."Entry No." := 0;
+        BillingLineArchive."Subscription Line Entry No." := SubscriptionLineEntryNo;
+        BillingLineArchive.Amount := ArchivedAmount;
+        BillingLineArchive.Insert(false);
+    end;
+
     local procedure MockSubscriptionLine(var SubscriptionLine: Record "Subscription Line")
     begin
         SubscriptionLine.Init();
@@ -681,6 +868,12 @@ codeunit 148156 "Service Commitment Test"
         Reply := true;
     end;
 
+    [ModalPageHandler]
+    procedure CreateCustomerBillingDocsPageHandler(var CreateCustomerBillingDocs: TestPage "Create Customer Billing Docs")
+    begin
+        CreateCustomerBillingDocs.OK().Invoke();
+    end;
+
     [ModalPageHandler]
     procedure ExchangeRateSelectionModalPageHandler(var ExchangeRateSelectionPage: TestPage "Exchange Rate Selection")
     begin