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/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;
+	}
 }