Add SubInvoiceLine support for ZUGFeRD Extended profile

- Parse ParentLineID and LineStatusReasonCode from XML
  - Filter GROUP/INFORMATION lines from calculation (only DETAIL counts)
  - Add hierarchy validation for GROUP line totals
  - Add tests for sub invoice line import and validation

validator/src/main/java/org/mustangproject/validator/XMLValidator.java

@@ -5,6 +5,7 @@ import java.io.PrintWriter;
 import java.io.StringReader;
 import java.io.StringWriter;
 import java.io.UncheckedIOException;
+import java.math.BigDecimal;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Paths;
@@ -24,6 +25,8 @@ import javax.xml.xpath.XPathFactory;
 
 import org.mustangproject.CalculatedInvoice;
 import org.mustangproject.XMLTools;
+import org.mustangproject.ZUGFeRD.IZUGFeRDExportableItem;
+import org.mustangproject.ZUGFeRD.LineCalculator;
 import org.mustangproject.ZUGFeRD.ZUGFeRDInvoiceImporter;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -454,6 +457,9 @@ public class XMLValidator extends Validator {
 			CalculatedInvoice ci=new CalculatedInvoice();
 			zi.extractInto(ci);
 
+			// check sub invoice line hierarchy if present
+			checkSubInvoiceLineHierarchy(ci, context);
+
 		} catch ( ArithmeticException e) {
 			try {
 				context.addResultItem(new ValidationResultItem(ESeverity.warning, "Arithmetical issue:"+e.getMessage()).setSection(10));
@@ -469,6 +475,77 @@ public class XMLValidator extends Validator {
 
 	}
 
+	/***
+	 * validates that GROUP line totals match the sum of their DETAIL child lines
+	 */
+	private void checkSubInvoiceLineHierarchy(CalculatedInvoice invoice, ValidationContext context) {
+		IZUGFeRDExportableItem[] items = invoice.getZFItems();
+		if (items == null || items.length == 0) {
+			return;
+		}
+
+		// check if we have any sub invoice lines at all
+		boolean hasSubInvoiceLines = false;
+		for (IZUGFeRDExportableItem item : items) {
+			if (item.getLineStatusReasonCode() != null) {
+				hasSubInvoiceLines = true;
+				break;
+			}
+		}
+		if (!hasSubInvoiceLines) {
+			return;
+		}
+
+		// build a map of line ID to item for quick lookup
+		java.util.HashMap<String, IZUGFeRDExportableItem> itemMap = new java.util.HashMap<>();
+		for (IZUGFeRDExportableItem item : items) {
+			if (item.getId() != null) {
+				itemMap.put(item.getId(), item);
+			}
+		}
+
+		// for each GROUP line, sum up the DETAIL children and compare
+		for (IZUGFeRDExportableItem item : items) {
+			if ("GROUP".equals(item.getLineStatusReasonCode())) {
+				String groupId = item.getId();
+				if (groupId == null) {
+					continue;
+				}
+
+				// sum up direct DETAIL children
+				BigDecimal childSum = BigDecimal.ZERO;
+				for (IZUGFeRDExportableItem child : items) {
+					if (groupId.equals(child.getParentLineID()) && "DETAIL".equals(child.getLineStatusReasonCode())) {
+						LineCalculator lc = child.getCalculation();
+						childSum = childSum.add(lc.getItemTotalNetAmount());
+					}
+				}
+
+				// also sum up nested GROUP children (their totals should already include their DETAIL children)
+				for (IZUGFeRDExportableItem child : items) {
+					if (groupId.equals(child.getParentLineID()) && "GROUP".equals(child.getLineStatusReasonCode())) {
+						LineCalculator lc = child.getCalculation();
+						childSum = childSum.add(lc.getItemTotalNetAmount());
+					}
+				}
+
+				// compare with GROUP total
+				LineCalculator groupLc = item.getCalculation();
+				BigDecimal groupTotal = groupLc.getItemTotalNetAmount();
+				if (childSum.compareTo(groupTotal) != 0) {
+					try {
+						context.addResultItem(new ValidationResultItem(ESeverity.warning,
+							"Sub invoice line hierarchy mismatch: GROUP line " + groupId +
+							" has total " + groupTotal + " but sum of child lines is " + childSum)
+							.setSection(10));
+					} catch (IrrecoverableValidationError ie) {
+						LOGGER.error(ie.getMessage(), ie);
+					}
+				}
+			}
+		}
+	}
+
 	public void validateXR(String xml, ESeverity errorImpact) throws IrrecoverableValidationError {
 
 		//Guideline ID=urn:cen.eu:en16931:2017#compliant#urn:xoev-de:kosit:standard:xrechnung_1.2  or

validator/src/test/java/org/mustangproject/validator/XMLValidatorTest.java

@@ -373,4 +373,28 @@ public class XMLValidatorTest extends ResourceCase {
 
 	}
 
+	public void testSubInvoiceLineHierarchy() {
+		final ValidationContext ctx = new ValidationContext(null);
+		final XMLValidator xv = new XMLValidator(ctx);
+		final XPathEngine xpath = new JAXPXPathEngine();
+
+		// test invalid hierarchy: GROUP sum does not match DETAIL children sum
+		// GROUP 01 has LineTotalAmount=999, but children sum to 1050 (600+450)
+		File tempFile = getResourceAsFile("invalidSubInvoiceLineHierarchy.xml");
+		try {
+			xv.setFilename(tempFile.getAbsolutePath());
+			xv.validate();
+
+			String s = "<validation>" + xv.getXMLResult() + "</validation>";
+			// hierarchy mismatch should produce at least one warning
+			assertThat(s).valueByXPath("count(//warning)")
+				.asInt()
+				.isGreaterThanOrEqualTo(1);
+
+		} catch (final IrrecoverableValidationError e) {
+			// ignore, will be in XML output anyway
+		}
+
+	}
+
 }