feat(validation): Implement EN16931 compliance validation types and VAT categories

- Added validation types for EN16931 compliance in `validation.types.ts`, including interfaces for `ValidationResult`, `ValidationOptions`, and `ValidationReport`.
- Introduced `VATCategoriesValidator` in `vat-categories.validator.ts` to validate VAT categories according to EN16931 rules, including detailed checks for standard, zero-rated, exempt, reverse charge, intra-community, export, and out-of-scope services.
- Enhanced `IEInvoiceMetadata` interface in `en16931-metadata.ts` to include additional fields required for full standards compliance, such as delivery information, payment information, allowances, and charges.
- Implemented helper methods for VAT calculations and validation logic to ensure accurate compliance with EN16931 standards.

ts/einvoice.ts

@@ -27,6 +27,14 @@ import { PDFExtractor } from './formats/pdf/pdf.extractor.js';
 // Import format detector
 import { FormatDetector } from './formats/utils/format.detector.js';
 
+// Import enhanced validators
+import { EN16931BusinessRulesValidator } from './formats/validation/en16931.business-rules.validator.js';
+import { CodeListValidator } from './formats/validation/codelist.validator.js';
+import type { ValidationOptions } from './formats/validation/validation.types.js';
+
+// Import EN16931 metadata interface
+import type { IEInvoiceMetadata } from './interfaces/en16931-metadata.js';
+
 /**
  * Main class for working with electronic invoices.
  * Supports various invoice formats including Factur-X, ZUGFeRD, UBL, and XRechnung
@@ -169,13 +177,7 @@ export class EInvoice implements TInvoice {
   }
 
   // EInvoice specific properties
-  public metadata?: {
-    format?: InvoiceFormat;
-    version?: string;
-    profile?: string;
-    customizationId?: string;
-    extensions?: Record<string, any>;
-  };
+  public metadata?: IEInvoiceMetadata;
   
   private xmlString: string = '';
   private detectedFormat: InvoiceFormat = InvoiceFormat.UNKNOWN;
@@ -430,17 +432,64 @@ export class EInvoice implements TInvoice {
    * @param level The validation level to use
    * @returns The validation result
    */
-  public async validate(level: ValidationLevel = ValidationLevel.BUSINESS): Promise<ValidationResult> {
+  public async validate(level: ValidationLevel = ValidationLevel.BUSINESS, options?: ValidationOptions): Promise<ValidationResult> {
     try {
-      const format = this.detectedFormat || InvoiceFormat.UNKNOWN;
-      if (format === InvoiceFormat.UNKNOWN) {
-        throw new EInvoiceValidationError('Cannot validate: format unknown', []);
-      }
-
-      const validator = ValidatorFactory.createValidator(this.xmlString);
-      const result = validator.validate(level);
+      // For programmatically created invoices without XML, skip XML-based validation
+      let result: ValidationResult;
       
+      if (this.xmlString && this.detectedFormat !== InvoiceFormat.UNKNOWN) {
+        // Use existing validator for XML-based validation
+        const validator = ValidatorFactory.createValidator(this.xmlString);
+        result = validator.validate(level);
+      } else {
+        // Create a basic result for programmatically created invoices
+        result = {
+          valid: true,
+          errors: [],
+          warnings: [],
+          level: level
+        };
+      }
+      
+      // Enhanced validation with feature flags
+      if (options?.featureFlags?.includes('EN16931_BUSINESS_RULES')) {
+        const businessRulesValidator = new EN16931BusinessRulesValidator();
+        const businessResults = businessRulesValidator.validate(this, options);
+        
+        // Merge results
+        result.errors = result.errors.concat(
+          businessResults
+            .filter(r => r.severity === 'error')
+            .map(r => ({ code: r.ruleId, message: r.message, field: r.field }))
+        );
+        
+        // Add warnings if not in report-only mode
+        if (!options.reportOnly) {
+          result.warnings = (result.warnings || []).concat(
+            businessResults
+              .filter(r => r.severity === 'warning')
+              .map(r => ({ code: r.ruleId, message: r.message, field: r.field }))
+          );
+        }
+      }
+      
+      // Code list validation with feature flag
+      if (options?.featureFlags?.includes('CODE_LIST_VALIDATION')) {
+        const codeListValidator = new CodeListValidator();
+        const codeListResults = codeListValidator.validate(this);
+        
+        // Merge results
+        result.errors = result.errors.concat(
+          codeListResults
+            .filter(r => r.severity === 'error')
+            .map(r => ({ code: r.ruleId, message: r.message, field: r.field }))
+        );
+      }
+      
+      // Update validation status
       this.validationErrors = result.errors;
+      result.valid = result.errors.length === 0 || options?.reportOnly === true;
+      
       return result;
     } catch (error) {
       if (error instanceof EInvoiceError) {