import { Invoice } from '../types/invoice.types';
import fs from 'fs';
import path from 'path';

export interface ValidationError {
  field: string;
  message: string;
  value?: any;
}

export interface ValidationResult {
  isValid: boolean;
  errors: ValidationError[];
}

/**
 * Validates invoice data against business rules
 */
export function validateInvoice(invoice: Invoice): ValidationResult {
  const errors: ValidationError[] = [];

  // Required fields validation
  if (!invoice.sender?.name) {
    errors.push({ field: 'sender.name', message: 'Sender name is required' });
  }

  if (!invoice.sender?.address?.street) {
    errors.push({ field: 'sender.address.street', message: 'Sender street is required' });
  }

  if (!invoice.sender?.contactInfo?.email) {
    errors.push({ field: 'sender.contactInfo.email', message: 'Sender email is required' });
  }

  if (!invoice.recipient?.name) {
    errors.push({ field: 'recipient.name', message: 'Recipient name is required' });
  }

  if (!invoice.details?.invoiceNumber) {
    errors.push({ field: 'details.invoiceNumber', message: 'Invoice number is required' });
  }

  if (!invoice.details?.invoiceDate) {
    errors.push({ field: 'details.invoiceDate', message: 'Invoice date is required' });
  }

  // Items validation
  if (!invoice.items || invoice.items.length === 0) {
    errors.push({ field: 'items', message: 'At least one item is required' });
  } else {
    invoice.items.forEach((item, index) => {
      if (!item.description) {
        errors.push({ field: `items[${index}].description`, message: 'Item description is required' });
      }
      if (item.quantity <= 0) {
        errors.push({ field: `items[${index}].quantity`, message: 'Item quantity must be greater than 0' });
      }
      if (item.unitPrice <= 0) {
        errors.push({ field: `items[${index}].unitPrice`, message: 'Item unit price must be greater than 0' });
      }
    });
  }

  // Totals validation
  if (!invoice.totals?.grossAmount || invoice.totals.grossAmount <= 0) {
    errors.push({ field: 'totals.grossAmount', message: 'Gross amount must be greater than 0' });
  }

  // Payment info validation
  if (!invoice.paymentInfo?.iban) {
    errors.push({ field: 'paymentInfo.iban', message: 'IBAN is required' });
  }

  if (!invoice.paymentInfo?.bic) {
    errors.push({ field: 'paymentInfo.bic', message: 'BIC is required' });
  }

  // VAT validation for German invoices
  if (invoice.sender?.vatId && !invoice.sender.vatId.startsWith('DE')) {
    errors.push({ field: 'sender.vatId', message: 'German VAT ID must start with DE' });
  }

  return {
    isValid: errors.length === 0,
    errors
  };
}

/**
 * Validates email format
 */
export function validateEmail(email: string): boolean {
  const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
  return emailRegex.test(email);
}

/**
 * Validates IBAN format (basic validation)
 */
export function validateIBAN(iban: string): boolean {
  // Remove spaces and convert to uppercase
  const cleanIBAN = iban.replace(/\s/g, '').toUpperCase();
  
  // Basic IBAN format validation
  const ibanRegex = /^[A-Z]{2}[0-9]{2}[A-Z0-9]{4}[0-9]{7}([A-Z0-9]?){0,16}$/;
  return ibanRegex.test(cleanIBAN);
}

/**
 * Validates BIC/SWIFT format
 */
export function validateBIC(bic: string): boolean {
  const bicRegex = /^[A-Z]{6}[A-Z2-9][A-NP-Z0-9]([A-Z0-9]{3})?$/;
  return bicRegex.test(bic.toUpperCase());
}

/**
 * Loads and validates invoice from JSON file
 */
export function loadAndValidateInvoice(jsonPath: string): { invoice: Invoice; validation: ValidationResult } {
  if (!fs.existsSync(jsonPath)) {
    throw new Error(`Invoice file not found: ${jsonPath}`);
  }

  const jsonContent = fs.readFileSync(jsonPath, 'utf8');
  let invoice: Invoice;

  try {
    invoice = JSON.parse(jsonContent);
  } catch (error) {
    throw new Error(`Invalid JSON format: ${error}`);
  }

  const validation = validateInvoice(invoice);

  return { invoice, validation };
}