Implement UID check

Elwig/Helpers/Validator.cs

@@ -247,20 +247,72 @@ namespace Elwig.Helpers {
             }
 
             // https://statistik.at/fileadmin/shared/QM/Standarddokumentationen/RW/std_r_land-forstw_register.pdf#page=41
-            int s = 0;
+            int s = 0, v = 0;
             for (int i = 0; i < 6; i++)
                 s += (input.Text[i] - '0') * (7 - i);
-            s = (11 - (s % 11)) % 10;
+            v = (11 - (s % 11)) % 10;
 
-            if (s != (input.Text[6] - '0'))
+            if (v != (input.Text[6] - '0'))
                 return new(false, "Prüfsumme der Betriebsnummer ist falsch");
 
             return new(true, null);
         }
 
         public static ValidationResult CheckUstId(TextBox input, bool required) {
-            // TODO
+            string text = "";
-            return new(true, "Not implemented yet");
+            int pos = input.CaretIndex;
+            for (int i = 0, v = 0; i < input.Text.Length; i++) {
+                char ch = input.Text[i];
+                if (v < 2 && char.IsAscii(ch) && char.IsLetter(ch)) {
+                    v++;
+                    text += char.ToUpper(ch);
+                } else if (v >= 2 && char.IsAscii(ch) && char.IsLetterOrDigit(ch)) {
+                    if (text.StartsWith("AT")) {
+                        if (v == 2 && (ch == 'u' || ch == 'U')) {
+                            v++;
+                            text += 'U';
+                        } else if (v > 2 && char.IsDigit(ch)) {
+                            v++;
+                            text += ch;
+                        }
+                    } else {
+                        v++;
+                        text += char.ToUpper(ch);
+                    }
+                }
+
+                if (i == input.CaretIndex - 1) {
+                    pos = text.Length;
+                } else if (v >= 14) {
+                    break;
+                } else if (text.StartsWith("AT") && v >= 11) {
+                    break;
+                }
+            }
+
+            input.Text = text;
+            input.CaretIndex = pos;
+
+            if (text.Length == 0)
+                return required ? new(false, "UID ist nicht optional") : new(true, null);
+
+            if (text.StartsWith("AT")) {
+                if (text.Length != 11 || text[2] != 'U')
+                    return new(false, "UID ist ungültig");
+
+                // http://www.pruefziffernberechnung.de/U/USt-IdNr.shtml
+                int s = 0, v = 0;
+                for (int i = 0; i < 8; i++)
+                    s += ((text[i + 3] - '0') * (i % 2 + 1)).ToString().Select(ch => ch - '0').Sum();
+                v = (96 - s) % 10;
+
+                if (v != (text[10] - '0'))
+                    return new(false, "Prüfsumme der UID ist falsch");
+            } else {
+                return new(false, "Not implemented yet");
+            }
+
+            return new(true, null);
         }
 
         public static ValidationResult CheckMgNr(TextBox input, bool required, AppDbContext ctx, Member? m) {