Creating a Journal Reversal handler.

wolverine/a-frame-architecture/FinancialApi.Application/ApplyFeeHandler.cs

@@ -8,9 +8,11 @@ public record ApplyFeeCommand(int AccountId, decimal Amount);
 
 public record FeeAppliedEvent(int AccountId, decimal Amount);
 
+public record FeePair(Account Source, Account Destination);
+
 public static class ApplyFeeHandler
 {
-    public static async Task<(Account, Account)> LoadAsync(
+    public static async Task<FeePair> LoadAsync(
         ApplyFeeCommand cmd,
         IAccountQuery query)
     {
@@ -20,7 +22,7 @@ public static class ApplyFeeHandler
         {
             throw new InvalidOperationException($"Cannot process transfer. Account(s) not found.");
         }
-        return (source, dest);
+        return new FeePair(source, dest);
     }
 
     public static (
@@ -31,12 +33,11 @@ public static class ApplyFeeHandler
         )
         Handle(
             ApplyFeeCommand cmd,
-            Account source,
-            Account dest
+            FeePair pair
         )
     {
-        var updatedSource = source.ApplyPosting(cmd.Amount, EntryType.Debit);
-        var updatedRevenue = dest.ApplyPosting(cmd.Amount, EntryType.Credit);
+        var updatedSource = pair.Source.ApplyPosting(cmd.Amount, EntryType.Debit);
+        var updatedRevenue = pair.Destination.ApplyPosting(cmd.Amount, EntryType.Credit);
         var lines = new List<JournalLine>
         {
             new(updatedSource.Id, cmd.Amount, EntryType.Debit),

wolverine/a-frame-architecture/FinancialApi.Application/ReverseJournalHandler.cs

@@ -0,0 +1,52 @@
+using FinancialApi.Domain;
+using Wolverine.Persistence;
+
+namespace FinancialApi.Application;
+
+public record ReverseJournalCommand(Guid OriginalJournalId, string Reason);
+
+public record JournalReversedEvent(Guid OriginalJournalId, Guid ReversalJournalId);
+
+public record ReversalData(JournalEntry OriginalJournalEntry, IReadOnlyList<Account> AffectedAccounts);
+
+public interface IReversalQuery
+{
+    Task<ReversalData?> GetReversalDataAsync(Guid journalEntryId);
+}
+
+public static class ReverseJournalHandler
+{
+    public static async Task<ReversalData?> LoadAsync(ReverseJournalCommand cmd, IReversalQuery query)
+    {
+        var data = await query.GetReversalDataAsync(cmd.OriginalJournalId);
+        if (data == null)
+        {
+            throw new InvalidOperationException($"Journal Entry {cmd.OriginalJournalId} does not exist");
+        }
+
+        return data;
+    }
+
+    public static (
+        IStorageAction<JournalEntry> ReversalWrite,
+        IStorageAction<Account>[] AccountWrites,
+        JournalReversedEvent Event) Handle(ReverseJournalCommand cmd, ReversalData data)
+    {
+        var reversalJournal =
+            BalancedJournal.CreateReversal(data.OriginalJournalEntry, cmd.Reason, DateTimeOffset.UtcNow);
+        var accountState = data.AffectedAccounts.ToDictionary(a => a.Id);
+
+        reversalJournal.Entry.Lines.ForEach(l =>
+        {
+            var currentAccount = accountState[l.AccountId];
+            accountState[l.AccountId] = currentAccount.ApplyPosting(l.Amount, l.Type);
+        });
+
+        var accountWrites = accountState.Values.Select(a => (IStorageAction<Account>)Storage.Update(a)).ToArray();
+        return (
+            Storage.Insert(reversalJournal.Entry),
+            accountWrites,
+            new JournalReversedEvent(cmd.OriginalJournalId, reversalJournal.Entry.Id)
+        );
+    }
+}

wolverine/a-frame-architecture/FinancialApi.Domain/BalancedJournal.cs

@@ -20,4 +20,13 @@ public record BalancedJournal
 
         return new(new JournalEntry(id, description, createdAt, lines));
     }
+
+    public static BalancedJournal CreateReversal(JournalEntry original, string reason, DateTimeOffset now)
+    {
+        var reversedLines = original.Lines.Select(l =>
+                l with { Type = l.Type == EntryType.Debit ? EntryType.Credit : EntryType.Debit })
+            .ToList();
+
+        return Create(Guid.NewGuid(), reason, now, reversedLines);
+    }
 }

wolverine/a-frame-architecture/FinancialApi.Domain/JournalEntry.cs

@@ -7,6 +7,10 @@ public record JournalEntry
     public DateTimeOffset CreatedAt { get; init; }
     public List<JournalLine> Lines { get; init; } = [];
 
+    internal JournalEntry()
+    {
+    }
+
     internal JournalEntry(Guid id, string description, DateTimeOffset createdAt, List<JournalLine> lines)
     {
         Lines = lines;

wolverine/a-frame-architecture/FinancialApi.Infrastructure/ReversalQuery.cs

@@ -0,0 +1,33 @@
+using FinancialApi.Application;
+using Microsoft.EntityFrameworkCore;
+
+namespace FinancialApi.Infrastructure;
+
+public class ReversalQuery : IReversalQuery
+{
+    private readonly AccountDbContext _db;
+
+    public ReversalQuery(AccountDbContext db) => _db = db;
+
+    public async Task<ReversalData?> GetReversalDataAsync(Guid journalEntryId)
+    {
+        var entry = await _db.JournalEntries
+            .Include(x => x.Lines)
+            .AsNoTracking()
+            .FirstOrDefaultAsync(x => x.Id == journalEntryId);
+
+        if (entry == null)
+        {
+            return null;
+        }
+
+        var accountIds = entry.Lines.Select(l => l.AccountId).Distinct().ToList();
+
+        var accounts = await _db.Accounts
+            .AsNoTracking()
+            .Where(a => accountIds.Contains(a.Id))
+            .ToListAsync();
+
+        return new ReversalData(entry, accounts);
+    }
+}

wolverine/a-frame-architecture/FinancialApi/FinancialApi.http

@@ -24,3 +24,13 @@ Content-Type: application/json
   "destinationAccountId": 2,
   "amount": 3000.00
 }
+
+### Reverse a Journal Entry
+
+POST {{FinancialApi_HostAddress}}/journal/reverse
+Content-Type: application/json
+
+{
+  "originalJournalId": "AD4FC011-9979-4364-A0D4-2CCD922ECB5E",
+  "reason": "Incorrect Account"
+}

wolverine/a-frame-architecture/FinancialApi/Program.cs

@@ -21,6 +21,7 @@ builder.Services.AddDbContext<AccountDbContext>(options =>
     options.UseSqlite(connectionString));
 
 builder.Services.AddScoped<IAccountQuery, AccountQuery>();
+builder.Services.AddScoped<IReversalQuery, ReversalQuery>();
 
 // Add services to the container.
 // Learn more about configuring OpenAPI at https://aka.ms/aspnet/openapi
@@ -67,4 +68,10 @@ app.MapPost("/accounts/transfer", async (TransferFundsCommand cmd, IMessageBus b
     return Results.Accepted();
 });
 
+app.MapPost("/journal/reverse", async (ReverseJournalCommand cmd, IMessageBus bus) =>
+{
+    await bus.InvokeAsync(cmd); 
+    return Results.Accepted();
+});
+
 app.Run();