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csharp-oop/Domain/Account.cs

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+namespace CsharpOop.Domain;
+
+/// Domain entity / aggregate root representing a bank account
+public sealed class Account : AggregateRoot<AccountId>
+{
+    public Money Balance { get; private set; }
+
+    // Often present to satisfy serializers / ORMs.
+    private Account()
+    {
+        Balance = new Money(0);
+    }
+
+    public Account(AccountId id, Money openingBalance)
+    {
+        if (openingBalance.Amount < 0)
+            throw new ArgumentOutOfRangeException(nameof(openingBalance));
+
+        Id = id;
+
+        Balance = openingBalance;
+    }
+
+    // Domain behaviour attached to the entity.
+    public void Withdraw(Money amount)
+    {
+        if (amount.Amount <= 0)
+            throw new InvalidOperationException("Withdrawal amount must be positive.");
+
+        if (Balance.Amount - amount.Amount < 0)
+            throw new InvalidOperationException("Balance cannot go below zero.");
+
+        Balance = Balance.Subtract(amount);
+    }
+}