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

library/src/main/java/org/mustangproject/Item.java

@@ -43,6 +43,8 @@ public class Item implements IZUGFeRDExportableItem {
 	protected ArrayList<IZUGFeRDAllowanceCharge> Charges = new ArrayList<>();
 	protected List<IncludedNote> includedNotes = null;
 	protected String accountingReference;
+	protected String parentLineID = null;
+	protected String lineStatusReasonCode = null;
 	//protected HashMap<String, String> attributes = new HashMap<>();
 
 	/***
@@ -91,9 +93,11 @@ public class Item implements IZUGFeRDExportableItem {
 
 
 		});
-		itemMap.getAsNodeMap("AssociatedDocumentLineDocument")
-			.flatMap(icnm -> icnm.getAsString("LineID"))
-			.ifPresent(this::setId);
+		itemMap.getAsNodeMap("AssociatedDocumentLineDocument").ifPresent(adld -> {
+			adld.getAsString("LineID").ifPresent(this::setId);
+			adld.getAsString("ParentLineID").ifPresent(this::setParentLineID);
+			adld.getAsString("LineStatusReasonCode").ifPresent(this::setLineStatusReasonCode);
+		});
 
 		itemMap.getAsNodeMap("Price").ifPresent(icnm -> {
 			// ubl
@@ -644,4 +648,34 @@ public class Item implements IZUGFeRDExportableItem {
 	public String getAccountingReference() {
 		return accountingReference;
 	}
+
+	@Override
+	public String getParentLineID() {
+		return parentLineID;
+	}
+
+	/***
+	 * for sub invoice lines: set the parent line ID
+	 * @param parentLineID the line ID of the parent line
+	 * @return fluent setter
+	 */
+	public Item setParentLineID(String parentLineID) {
+		this.parentLineID = parentLineID;
+		return this;
+	}
+
+	@Override
+	public String getLineStatusReasonCode() {
+		return lineStatusReasonCode;
+	}
+
+	/***
+	 * for sub invoice lines: set the status reason code (DETAIL, GROUP, INFORMATION)
+	 * @param lineStatusReasonCode the status reason code
+	 * @return fluent setter
+	 */
+	public Item setLineStatusReasonCode(String lineStatusReasonCode) {
+		this.lineStatusReasonCode = lineStatusReasonCode;
+		return this;
+	}
 }

library/src/main/java/org/mustangproject/ZUGFeRD/IZUGFeRDExportableItem.java

@@ -192,6 +192,36 @@ public interface IZUGFeRDExportableItem extends IAbsoluteValueProvider{
 		return null;
 	}
 
+	/***
+	 * for sub invoice lines in ZUGFeRD Extended: the line ID of the parent line
+	 * @return the parent line ID or null if this is a top-level line
+	 */
+	default String getParentLineID() {
+		return null;
+	}
+
+	/***
+	 * for sub invoice lines in ZUGFeRD Extended: the status reason code
+	 * determines if a line is relevant for calculation
+	 * @return DETAIL, GROUP, INFORMATION or null for standard lines
+	 */
+	default String getLineStatusReasonCode() {
+		return null;
+	}
+
+	/***
+	 * checks if this line should be included in sum calculation.
+	 * GROUP and INFORMATION lines are not calculation-relevant,
+	 * only DETAIL lines (or lines without status code) are.
+	 * @return true if the line should be included in calculation
+	 */
+	@com.fasterxml.jackson.annotation.JsonIgnore
+	default boolean isCalculationRelevant() {
+		String status = getLineStatusReasonCode();
+		// null means standard line (backwards compatible), DETAIL is explicitly relevant
+		return status == null || "DETAIL".equals(status);
+	}
+
 	/**
 	 * A grouping of business terms to indicate accounting-relevant free texts including a qualification of these.
 	 *

library/src/main/java/org/mustangproject/ZUGFeRD/TransactionCalculator.java

@@ -155,12 +155,15 @@ public class TransactionCalculator implements IAbsoluteValueProvider {
 
 	/***
 	 * returns the total net value of all items, without document level
-	 * charges/allowances
+	 * charges/allowances. For sub invoice lines only DETAIL lines are summed,
+	 * GROUP and INFORMATION lines are ignored.
 	 *
 	 * @return item sum
 	 */
 	protected BigDecimal getTotal() {
-		BigDecimal dec = Stream.of(trans.getZFItems()).map(LineCalculator::new)
+		BigDecimal dec = Stream.of(trans.getZFItems())
+			.filter(IZUGFeRDExportableItem::isCalculationRelevant)
+			.map(LineCalculator::new)
 			.map(LineCalculator::getItemTotalNetAmount).reduce(ZERO, BigDecimal::add);
 		return dec;
 	}
@@ -190,6 +193,10 @@ public class TransactionCalculator implements IAbsoluteValueProvider {
 		final String vatDueDateTypeCode = trans.getVATDueDateTypeCode();
 
 		for (IZUGFeRDExportableItem currentItem : trans.getZFItems()) {
+			// skip GROUP and INFORMATION lines for sub invoice lines
+			if (!currentItem.isCalculationRelevant()) {
+				continue;
+			}
 			BigDecimal percent = null;
 			if (currentItem.getProduct() != null) {
 				percent = currentItem.getProduct().getVATPercent();
@@ -258,6 +265,10 @@ public class TransactionCalculator implements IAbsoluteValueProvider {
 		final String vatDueDateTypeCode = this.trans.getVATDueDateTypeCode();
 		for (final IZUGFeRDExportableItem currentItem : this.trans.getZFItems())
 		{
+			// skip GROUP and INFORMATION lines for sub invoice lines
+			if (!currentItem.isCalculationRelevant()) {
+				continue;
+			}
 			BigDecimal percent = null;
 			if (currentItem.getProduct() != null)
 			{

library/src/test/java/org/mustangproject/ZUGFeRD/ZF2ZInvoiceImporterTest.java

@@ -895,4 +895,117 @@ public class ZF2ZInvoiceImporterTest extends ResourceCase {
 		assertNull(invoice.getDespatchAdviceReferencedDocumentID());
 		assertNull(invoice.getInvoiceReferencedDocumentID());
 	}
+
+	@Test
+	public void testSubInvoiceLinesImport() throws FileNotFoundException, XPathExpressionException, ParseException {
+		// test import of sub invoice lines with GROUP and DETAIL lines
+		File inputFile = getResourceAsFile("subinvoicelines/Extended_SubInvoiceLines_Hardware_Bsp2.xml");
+		ZUGFeRDInvoiceImporter zii = new ZUGFeRDInvoiceImporter();
+		zii.setInputStream(new FileInputStream(inputFile));
+
+		Invoice invoice = zii.extractInvoice();
+		assertEquals(6, invoice.getZFItems().length);
+
+		// find GROUP and DETAIL lines and verify LineStatusReasonCode and ParentLineID
+		Item group01 = findItemById(invoice, "01");
+		assertNotNull(group01);
+		assertEquals("GROUP", group01.getLineStatusReasonCode());
+		assertNull(group01.getParentLineID());
+		assertFalse(group01.isCalculationRelevant());
+
+		Item detail0101 = findItemById(invoice, "0101");
+		assertNotNull(detail0101);
+		assertEquals("DETAIL", detail0101.getLineStatusReasonCode());
+		assertEquals("01", detail0101.getParentLineID());
+		assertTrue(detail0101.isCalculationRelevant());
+
+		Item detail0102 = findItemById(invoice, "0102");
+		assertNotNull(detail0102);
+		assertEquals("DETAIL", detail0102.getLineStatusReasonCode());
+		assertEquals("01", detail0102.getParentLineID());
+		assertTrue(detail0102.isCalculationRelevant());
+
+		// verify that only DETAIL lines are summed (not GROUP lines)
+		// DETAIL lines: 0101=600, 0102=450, 0201=360, 0202=90 = 1500
+		// GROUP lines should NOT be added: 01=1050, 02=450
+		TransactionCalculator tc = new TransactionCalculator(invoice);
+		assertEquals(new BigDecimal("1500.00"), tc.getTotal().setScale(2));
+		assertEquals(new BigDecimal("1785.00"), tc.getGrandTotal().setScale(2));
+	}
+
+	@Test
+	public void testSubInvoiceLinesNestedImport() throws FileNotFoundException, XPathExpressionException, ParseException {
+		// test import of nested sub invoice lines (GROUP containing GROUP containing DETAIL)
+		File inputFile = getResourceAsFile("subinvoicelines/Extended___SubInvoiceLines_Kaffee_Bundle_Set_Bsp4__.xml");
+		ZUGFeRDInvoiceImporter zii = new ZUGFeRDInvoiceImporter();
+		zii.setInputStream(new FileInputStream(inputFile));
+
+		Invoice invoice = zii.extractInvoice();
+
+		// find nested structure: 1 (GROUP) -> 1.3 (GROUP) -> 1.3.1 (DETAIL)
+		Item group1 = findItemById(invoice, "1");
+		assertNotNull(group1);
+		assertEquals("GROUP", group1.getLineStatusReasonCode());
+
+		Item group13 = findItemById(invoice, "1.3");
+		assertNotNull(group13);
+		assertEquals("GROUP", group13.getLineStatusReasonCode());
+		assertEquals("1", group13.getParentLineID());
+
+		Item detail131 = findItemById(invoice, "1.3.1");
+		assertNotNull(detail131);
+		assertEquals("DETAIL", detail131.getLineStatusReasonCode());
+		assertEquals("1.3", detail131.getParentLineID());
+
+		// verify calculation only includes DETAIL lines
+		// DETAIL: 1.1=30, 1.2=60, 1.3.1=90, 1.3.2=36 = 216
+		TransactionCalculator tc = new TransactionCalculator(invoice);
+		assertEquals(new BigDecimal("216.00"), tc.getTotal().setScale(2));
+	}
+
+	@Test
+	public void testSubInvoiceLinesWithDiscounts() throws FileNotFoundException, XPathExpressionException, ParseException {
+		// test sub invoice lines with negative amounts (discounts)
+		File inputFile = getResourceAsFile("subinvoicelines/Extended___SubInvoiceLines_Buero_Material_Bsp3__.xml");
+		ZUGFeRDInvoiceImporter zii = new ZUGFeRDInvoiceImporter();
+		zii.setInputStream(new FileInputStream(inputFile));
+
+		Invoice invoice = zii.extractInvoice();
+
+		// verify calculation handles negative DETAIL lines correctly
+		// GROUP 01: 600 + 450 - 50 = 1000
+		// GROUP 02: 360 + 90 - 45 = 405
+		// Total DETAIL: 1405
+		TransactionCalculator tc = new TransactionCalculator(invoice);
+		assertEquals(new BigDecimal("1405.00"), tc.getTotal().setScale(2));
+	}
+
+	@Test
+	public void testSubInvoiceLinesInformation() throws FileNotFoundException, XPathExpressionException, ParseException {
+		// test INFORMATION lines (should have price 0 and not affect calculation)
+		File inputFile = getResourceAsFile("subinvoicelines/Extended_Fallschutz-Set_SubInvoiceLine_Bsp5.xml");
+		ZUGFeRDInvoiceImporter zii = new ZUGFeRDInvoiceImporter();
+		zii.setInputStream(new FileInputStream(inputFile));
+
+		Invoice invoice = zii.extractInvoice();
+
+		// find INFORMATION lines
+		Item info0101 = findItemById(invoice, "01.01");
+		assertNotNull(info0101);
+		assertEquals("INFORMATION", info0101.getLineStatusReasonCode());
+		assertFalse(info0101.isCalculationRelevant());
+
+		// DETAIL line 01 = 45000
+		TransactionCalculator tc = new TransactionCalculator(invoice);
+		assertEquals(new BigDecimal("45000.00"), tc.getTotal().setScale(2));
+	}
+
+	private Item findItemById(Invoice invoice, String id) {
+		for (IZUGFeRDExportableItem item : invoice.getZFItems()) {
+			if (item instanceof Item && id.equals(((Item) item).getId())) {
+				return (Item) item;
+			}
+		}
+		return null;
+	}
 }

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
+		}
+
+	}
+
 }