added constructors and checks

api/Domain/Person.cs

@@ -2,10 +2,40 @@ namespace api.Domain;
 
 public sealed class Person
 {
-    public String Username { get; }
+    public string Username { get; }
 
-    public String RealName { get; }
+    public string RealName { get; }
 
     public DateOnly Birthday { get; }
 
+    private Person(string username, string realName, DateOnly birthday)
+    {
+        Username = username;
+        RealName = realName;
+        Birthday = birthday;
+    }
+
+    public static Person Create(string username, string realName, DateOnly birthday)
+    {
+        username = NormalizeUsername(username);
+        realName = realName.Trim();
+
+        // TODO: Error Handling
+        if (username.Length is < 3 or > 32) throw new Exception();
+        if (realName.Length == 0) throw new Exception();
+        if (birthday >= DateOnly.FromDateTime(DateTime.Today)) throw new Exception();
+        if (!IsAtLeast16(birthday)) throw new Exception();
+
+        return new Person(username, realName, birthday);
+    }
+
+    // Konstruktor zum Erzeugen von Nutzerobjekten aus der Datenbank
+    internal static Person FromStorage(string username, string realName, DateOnly birthday)
+        => new(username, realName, birthday);
+
+    public static string NormalizeUsername(string username)
+        => username.Trim().ToLowerInvariant();
+
+    public static bool IsAtLeast16(DateOnly birthday)
+        => birthday.AddYears(16) <= DateOnly.FromDateTime(DateTime.Today);
 }