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 +1,93 @@
+using CsharpEs.Library;
+
+namespace CsharpEs.Domain;
+
+public sealed record AccountState(Guid Id);
+
+public abstract record AccountCommand
+{
+    public sealed record OpenAccount(Guid AccountId, Money OpeningBalance) : AccountCommand;
+
+    public sealed record WithdrawMoney(Guid AccountId, Money Amount) : AccountCommand;
+
+    public sealed record DepositMoney(Guid AccountId, Money Amount) : AccountCommand;
+}
+
+public abstract record AccountEvent(Guid AccountId)
+{
+    public sealed record AccountOpened(Guid AccountId, Money OpeningBalance)
+        : AccountEvent(AccountId);
+
+    public sealed record MoneyWithdrawn(Guid AccountId, Money Amount) : AccountEvent(AccountId);
+
+    public sealed record MoneyDeposited(Guid AccountId, Money Amount) : AccountEvent(AccountId);
+}
+
+public abstract record AccountError
+{
+    public sealed record AccountNotFound : AccountError;
+
+    public sealed record AccountOpenAlready : AccountError;
+
+    public sealed record OpeningBalanceMustBeNonNegative : AccountError;
+
+    public sealed record InnerException(Exception exception) : AccountError;
+}
+
+public static class AccountDecider
+{
+    public static Result<AccountEvent, AccountError> Decide(
+        AccountState? state,
+        AccountCommand command
+    ) =>
+        Result<AccountEvent, AccountError>.Catch(
+            () =>
+                (state, command) switch
+                {
+                    // if this is a new account, check for valid opening balance
+                    (null, AccountCommand.OpenAccount c) when c.OpeningBalance.Amount < 0m =>
+                        Result<AccountEvent, AccountError>.Fail(
+                            new AccountError.OpeningBalanceMustBeNonNegative()
+                        ),
+
+                    // still a new account, now we can open it
+                    (null, AccountCommand.OpenAccount c) => Result<AccountEvent, AccountError>.Ok(
+                        new AccountEvent.AccountOpened(c.AccountId, c.OpeningBalance)
+                    ),
+
+                    // if we have an account already, you can't open it
+                    (not null, AccountCommand.OpenAccount c) => Result<
+                        AccountEvent,
+                        AccountError
+                    >.Fail(new AccountError.AccountOpenAlready()),
+
+                    (null, _) => Result<AccountEvent, AccountError>.Fail(
+                        new AccountError.AccountNotFound()
+                    ),
+
+                    (_, AccountCommand.WithdrawMoney c) => Result<AccountEvent, AccountError>.Ok(
+                        new AccountEvent.MoneyWithdrawn(c.AccountId, c.Amount)
+                    ),
+
+                    (_, AccountCommand.DepositMoney c) => Result<AccountEvent, AccountError>.Ok(
+                        new AccountEvent.MoneyDeposited(c.AccountId, c.Amount)
+                    ),
+
+                    _ => throw new InvalidOperationException("Unknown command."),
+                },
+            e => new AccountError.InnerException(e)
+        );
+
+    public static Result<AccountState?, AccountError> Evolve(
+        AccountState? state,
+        AccountEvent @event
+    ) =>
+        (state, @event) switch
+        {
+            (null, AccountEvent.AccountOpened e) => Result<AccountState?, AccountError>.Ok(
+                new AccountState(e.AccountId)
+            ),
+
+            _ => Result<AccountState?, AccountError>.Ok(state),
+        };
+}