import { PDFDocument, PDFDict, PDFName, PDFRawStream, PDFArray, PDFString } from 'pdf-lib';
import { BaseXMLExtractor } from './base.extractor.js';

/**
 * Associated files extractor for PDF/A-3 documents
 * Extracts XML from associated files (AF entry in the catalog)
 * Particularly useful for ZUGFeRD v1 and some Factur-X documents
 */
export class AssociatedFilesExtractor extends BaseXMLExtractor {
  /**
   * Extract XML from a PDF buffer using associated files
   * @param pdfBuffer PDF buffer
   * @returns XML content or null if not found
   */
  public async extractXml(pdfBuffer: Uint8Array | Buffer): Promise<string | null> {
    try {
      const pdfDoc = await PDFDocument.load(pdfBuffer);
      
      // Try to find associated files via the AF entry in the catalog
      const afArray = pdfDoc.catalog.lookup(PDFName.of('AF'));
      if (!(afArray instanceof PDFArray)) {
        console.warn('No AF (Associated Files) entry found in PDF catalog');
        return null;
      }
      
      // Process each associated file
      for (let i = 0; i < afArray.size(); i++) {
        const fileSpec = afArray.lookup(i);
        if (!(fileSpec instanceof PDFDict)) {
          continue;
        }
        
        // Get the file name
        const fileNameObj = fileSpec.lookup(PDFName.of('F')) || fileSpec.lookup(PDFName.of('UF'));
        if (!(fileNameObj instanceof PDFString)) {
          continue;
        }
        
        const fileName = fileNameObj.decodeText();
        
        // Check if it's a known invoice XML file name
        const isKnownFileName = this.knownFileNames.some(
          knownName => fileName.toLowerCase() === knownName.toLowerCase()
        );
        
        // Check if it's any XML file or has invoice-related keywords
        const isXmlFile = fileName.toLowerCase().endsWith('.xml') || 
                          fileName.toLowerCase().includes('zugferd') ||
                          fileName.toLowerCase().includes('factur-x') ||
                          fileName.toLowerCase().includes('xrechnung') ||
                          fileName.toLowerCase().includes('invoice');
        
        if (isKnownFileName || isXmlFile) {
          // Get the embedded file dictionary
          const efDict = fileSpec.lookup(PDFName.of('EF'));
          if (!(efDict instanceof PDFDict)) {
            continue;
          }
          
          // Get the file stream
          const fileStream = efDict.lookup(PDFName.of('F'));
          if (fileStream instanceof PDFRawStream) {
            const xmlContent = await this.extractXmlFromStream(fileStream, fileName);
            if (xmlContent) {
              return xmlContent;
            }
          }
        }
      }
      
      console.warn('No valid XML found in associated files');
      return null;
    } catch (error) {
      console.error('Error in associated files extraction:', error);
      return null;
    }
  }
}
