Add OPC UA array element write integration test

src/ZB.MOM.WW.LmxOpcUa.Host/OpcUa/LmxNodeManager.cs

@@ -363,7 +363,20 @@ namespace ZB.MOM.WW.LmxOpcUa.Host.OpcUa
                 {
                     try
                     {
-                        var value = nodesToWrite[i].Value.WrappedValue.Value;
+                        var writeValue = nodesToWrite[i];
+                        var value = writeValue.Value.WrappedValue.Value;
+
+                        if (!string.IsNullOrWhiteSpace(writeValue.IndexRange))
+                        {
+                            if (!TryApplyArrayElementWrite(tagRef, value, writeValue.IndexRange, out var updatedArray))
+                            {
+                                errors[i] = new ServiceResult(StatusCodes.BadIndexRangeInvalid);
+                                continue;
+                            }
+
+                            value = updatedArray;
+                        }
+
                         var success = _mxAccessClient.WriteAsync(tagRef, value).GetAwaiter().GetResult();
                         errors[i] = success ? ServiceResult.Good : new ServiceResult(StatusCodes.BadInternalError);
                     }
@@ -376,6 +389,53 @@ namespace ZB.MOM.WW.LmxOpcUa.Host.OpcUa
             }
         }
 
+        private bool TryApplyArrayElementWrite(string tagRef, object? writeValue, string indexRange, out object updatedArray)
+        {
+            updatedArray = null!;
+
+            if (!int.TryParse(indexRange, out var index) || index < 0)
+                return false;
+
+            var currentValue = _mxAccessClient.ReadAsync(tagRef).GetAwaiter().GetResult().Value;
+            if (currentValue is not Array currentArray || currentArray.Rank != 1 || index >= currentArray.Length)
+                return false;
+
+            var nextArray = (Array)currentArray.Clone();
+            var elementType = currentArray.GetType().GetElementType();
+            if (elementType == null)
+                return false;
+
+            var normalizedValue = NormalizeIndexedWriteValue(writeValue);
+            nextArray.SetValue(ConvertArrayElementValue(normalizedValue, elementType), index);
+            updatedArray = nextArray;
+            return true;
+        }
+
+        private static object? NormalizeIndexedWriteValue(object? value)
+        {
+            if (value is Array array && array.Length == 1)
+                return array.GetValue(0);
+            return value;
+        }
+
+        private static object? ConvertArrayElementValue(object? value, Type elementType)
+        {
+            if (value == null)
+            {
+                if (elementType.IsValueType)
+                    return Activator.CreateInstance(elementType);
+                return null;
+            }
+
+            if (elementType.IsInstanceOfType(value))
+                return value;
+
+            if (elementType == typeof(string))
+                return value.ToString();
+
+            return Convert.ChangeType(value, elementType);
+        }
+
         #endregion
 
         #region Subscription Delivery