add csharp-es sample

2026-04-27 23:09:38 +01:00
parent cb06d80d6a
commit d785852c1c
8 changed files with 509 additions and 0 deletions
@@ -0,0 +1,108 @@
+using System.Collections.Immutable;
+using CsharpEs.Domain;
+using CsharpEs.Library;
+
+namespace CsharpEs.Infrastructure;
+
+public abstract record ReadModelError
+{
+    public sealed record AccountDetailsNotFound : ReadModelError;
+}
+
+public sealed record AccountBalanceReadModel(
+    Func<AccountEvent, Result<AccountDetails, ReadModelError>> Project,
+    Func<Result<KeyValuePair<Guid, AccountDetails>[], ReadModelError>> Query
+);
+
+[Flags]
+public enum AccountFlags
+{
+    None = 0,
+    InOverdraft = 1,
+}
+
+public sealed record AccountDetails(Money Balance, AccountFlags Flags);
+
+public static class AccountBalanceReadModelModule
+{
+    public static Result<AccountBalanceReadModel, ReadModelError> Create()
+    {
+        // This is our read-model specific "persistent" storage
+        var modelData = ImmutableDictionary<Guid, AccountDetails>.Empty;
+
+        Result<AccountDetails, ReadModelError> Project(AccountEvent @event)
+        {
+            Logging.Output("rm", "Projecting event", @event);
+            switch (@event)
+            {
+                case AccountEvent.AccountOpened e:
+                    modelData = modelData.SetItem(
+                        e.AccountId,
+                        new AccountDetails(e.OpeningBalance, AccountFlags.None)
+                    );
+                    break;
+
+                case AccountEvent.MoneyWithdrawn e:
+                    {
+                        if (modelData.TryGetValue(e.AccountId, out var oldDetails))
+                        {
+                            var newBalance = new Money(oldDetails.Balance.Amount - e.Amount.Amount);
+                            modelData = modelData.SetItem(
+                                e.AccountId,
+                                oldDetails with
+                                {
+                                    Balance = newBalance,
+                                    Flags = CalcAccountFlags(newBalance, oldDetails),
+                                }
+                            );
+                        }
+                        else
+                            return Result<AccountDetails, ReadModelError>.Fail(
+                                new ReadModelError.AccountDetailsNotFound()
+                            );
+                    }
+                    break;
+
+                case AccountEvent.MoneyDeposited e:
+                    {
+                        if (modelData.TryGetValue(e.AccountId, out var oldDetails))
+                        {
+                            var newBalance = new Money(oldDetails.Balance.Amount + e.Amount.Amount);
+                            modelData = modelData.SetItem(
+                                e.AccountId,
+                                oldDetails with
+                                {
+                                    Balance = newBalance,
+                                    Flags = CalcAccountFlags(newBalance, oldDetails),
+                                }
+                            );
+                        }
+                        else
+                            return Result<AccountDetails, ReadModelError>.Fail(
+                                new ReadModelError.AccountDetailsNotFound()
+                            );
+                    }
+                    break;
+            }
+
+            // Read model-side "project" may not normally return any data, but for demo
+            // purposes we return the affected data directly to save us modeling a separate
+            // query side.
+            return Result<AccountDetails, ReadModelError>.Ok(modelData[@event.AccountId]);
+        }
+
+        Result<KeyValuePair<Guid, AccountDetails>[], ReadModelError> Query() =>
+            Result<KeyValuePair<Guid, AccountDetails>[], ReadModelError>.Ok(modelData.ToArray());
+
+        return Result<AccountBalanceReadModel, ReadModelError>.Ok(
+            new AccountBalanceReadModel(Project, Query)
+        );
+    }
+
+    private static AccountFlags CalcAccountFlags(Money newBalance, AccountDetails oldDetails)
+    {
+        return newBalance.Amount < 0
+            ? oldDetails.Flags | AccountFlags.InOverdraft
+            : oldDetails.Flags & ~AccountFlags.InOverdraft;
+    }
+}