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/interfaces/common.ts

@@ -44,6 +44,7 @@ export interface ValidationError {
 export interface ValidationResult {
   valid: boolean; // Overall validation result
   errors: ValidationError[]; // List of validation errors
+  warnings?: ValidationError[]; // List of validation warnings (optional)
   level: ValidationLevel; // The level that was validated
 }
 

ts/interfaces/en16931-metadata.ts

@@ -0,0 +1,97 @@
+/**
+ * EN16931-compliant metadata interface for EInvoice
+ * Contains all additional fields required for full standards compliance
+ */
+
+import type { business } from '@tsclass/tsclass';
+import type { InvoiceFormat } from './common.js';
+
+/**
+ * Extended metadata for EN16931 compliance
+ */
+export interface IEInvoiceMetadata {
+  // Format identification
+  format?: InvoiceFormat;
+  version?: string;
+  profile?: string;
+  customizationId?: string;
+  
+  // EN16931 Business Terms
+  vatAccountingCurrency?: string;                // BT-6
+  documentTypeCode?: string;                     // BT-3
+  paymentMeansCode?: string;                     // BT-81
+  paidAmount?: number;                          // BT-113
+  amountDue?: number;                           // BT-115
+  
+  // Delivery information (BG-13)
+  deliveryAddress?: {
+    streetName?: string;
+    houseNumber?: string;
+    city?: string;
+    postalCode?: string;
+    countryCode?: string;                      // BT-80
+    countrySubdivision?: string;
+  };
+  
+  // Payment information (BG-16)
+  paymentAccount?: {
+    iban?: string;                             // BT-84
+    accountName?: string;                      // BT-85
+    bankId?: string;                          // BT-86
+  };
+  
+  // Allowances and charges (BG-20, BG-21)
+  allowances?: Array<{
+    amount: number;                            // BT-92
+    baseAmount?: number;                      // BT-93
+    percentage?: number;                      // BT-94
+    vatCategoryCode?: string;                 // BT-95
+    vatRate?: number;                         // BT-96
+    reason?: string;                           // BT-97
+    reasonCode?: string;                       // BT-98
+  }>;
+  
+  charges?: Array<{
+    amount: number;                            // BT-99
+    baseAmount?: number;                      // BT-100
+    percentage?: number;                       // BT-101
+    vatCategoryCode?: string;                 // BT-102
+    vatRate?: number;                         // BT-103
+    reason?: string;                           // BT-104
+    reasonCode?: string;                       // BT-105
+  }>;
+  
+  // Extensions for specific standards
+  extensions?: Record<string, any>;
+}
+
+/**
+ * Extended item metadata for EN16931 compliance
+ */
+export interface IItemMetadata {
+  vatCategoryCode?: string;                     // BT-151
+  priceBaseQuantity?: number;                  // BT-149
+  exemptionReason?: string;                    // BT-120 (for exempt categories)
+  originCountryCode?: string;                  // BT-159
+  commodityCode?: string;                      // BT-158
+  
+  // Item attributes (BG-32)
+  attributes?: Array<{
+    name: string;                              // BT-160
+    value: string;                             // BT-161
+  }>;
+}
+
+/**
+ * Extended accounting document item with metadata
+ */
+export interface IExtendedAccountingDocItem {
+  position: number;
+  name: string;
+  articleNumber?: string;
+  unitType: string;
+  unitQuantity: number;
+  unitNetPrice: number;
+  vatPercentage: number;
+  metadata?: IItemMetadata;
+}