/**
 * Merge a ZUGFeRD / Factur-X CII XML into an existing PDF (the one iDempiere
 * generated) and return the new hybrid PDF buffer.
 *
 * Pragmatic v1 ("start pragmatic, harden later"): we do NOT convert the carrier
 * PDF to strict PDF/A-3. We attach `factur-x.xml` with the correct
 * AFRelationship (`Alternative`) and write the Factur-X XMP metadata packet so
 * common accounting software (DATEV, Lexware, sevDesk, …) detects and parses the
 * e-invoice. Strict PDF/A-3 conversion is a documented follow-up.
 *
 * Uses pdf-lib, already a project dependency (see invoices/batch-print.post.ts).
 */
import { PDFDocument, AFRelationship, PDFName } from 'pdf-lib'

const FACTURX_FILENAME = 'factur-x.xml'

// Full Factur-X XMP packet. The pdfaExtension "schemas" block is REQUIRED: without
// it, strict PDF/A-3 validators (portinvoice, veraPDF) don't recognise the custom
// fx: properties and report DocumentType/Version/ConformanceLevel as empty.
const buildXmpMetadata = (): string => `<?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
<x:xmpmeta xmlns:x="adobe:ns:meta/">
  <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
    <rdf:Description rdf:about="" xmlns:pdfaid="http://www.aiim.org/pdfa/ns/id/">
      <pdfaid:part>3</pdfaid:part>
      <pdfaid:conformance>B</pdfaid:conformance>
    </rdf:Description>
    <rdf:Description rdf:about="" xmlns:fx="urn:factur-x:pdfa:CrossIndustryDocument:invoice:1p0#">
      <fx:DocumentType>INVOICE</fx:DocumentType>
      <fx:DocumentFileName>${FACTURX_FILENAME}</fx:DocumentFileName>
      <fx:Version>1.0</fx:Version>
      <fx:ConformanceLevel>EN 16931</fx:ConformanceLevel>
    </rdf:Description>
    <rdf:Description rdf:about="" xmlns:pdfaExtension="http://www.aiim.org/pdfa/ns/extension/" xmlns:pdfaSchema="http://www.aiim.org/pdfa/ns/schema#" xmlns:pdfaProperty="http://www.aiim.org/pdfa/ns/property#">
      <pdfaExtension:schemas>
        <rdf:Bag>
          <rdf:li rdf:parseType="Resource">
            <pdfaSchema:schema>Factur-X PDFA Extension Schema</pdfaSchema:schema>
            <pdfaSchema:namespaceURI>urn:factur-x:pdfa:CrossIndustryDocument:invoice:1p0#</pdfaSchema:namespaceURI>
            <pdfaSchema:prefix>fx</pdfaSchema:prefix>
            <pdfaSchema:property>
              <rdf:Seq>
                <rdf:li rdf:parseType="Resource">
                  <pdfaProperty:name>DocumentFileName</pdfaProperty:name>
                  <pdfaProperty:valueType>Text</pdfaProperty:valueType>
                  <pdfaProperty:category>external</pdfaProperty:category>
                  <pdfaProperty:description>name of the embedded XML invoice file</pdfaProperty:description>
                </rdf:li>
                <rdf:li rdf:parseType="Resource">
                  <pdfaProperty:name>DocumentType</pdfaProperty:name>
                  <pdfaProperty:valueType>Text</pdfaProperty:valueType>
                  <pdfaProperty:category>external</pdfaProperty:category>
                  <pdfaProperty:description>INVOICE</pdfaProperty:description>
                </rdf:li>
                <rdf:li rdf:parseType="Resource">
                  <pdfaProperty:name>Version</pdfaProperty:name>
                  <pdfaProperty:valueType>Text</pdfaProperty:valueType>
                  <pdfaProperty:category>external</pdfaProperty:category>
                  <pdfaProperty:description>The actual version of the Factur-X XML schema</pdfaProperty:description>
                </rdf:li>
                <rdf:li rdf:parseType="Resource">
                  <pdfaProperty:name>ConformanceLevel</pdfaProperty:name>
                  <pdfaProperty:valueType>Text</pdfaProperty:valueType>
                  <pdfaProperty:category>external</pdfaProperty:category>
                  <pdfaProperty:description>The conformance level of the embedded Factur-X data</pdfaProperty:description>
                </rdf:li>
              </rdf:Seq>
            </pdfaSchema:property>
          </rdf:li>
        </rdf:Bag>
      </pdfaExtension:schemas>
    </rdf:Description>
  </rdf:RDF>
</x:xmpmeta>
<?xpacket end="w"?>`

/**
 * @param pdfBuffer  iDempiere's existing invoice PDF (already decoded from base64)
 * @param xmlString  the EN16931 CII XML from buildInvoiceXml()
 * @returns          a new PDF buffer with the XML embedded as factur-x.xml
 */
export const embedZugferdXml = async (pdfBuffer: Buffer, xmlString: string): Promise<Buffer> => {
  const pdfDoc = await PDFDocument.load(pdfBuffer)

  const now = new Date()
  await pdfDoc.attach(new TextEncoder().encode(xmlString), FACTURX_FILENAME, {
    mimeType: 'text/xml',
    description: 'Factur-X/ZUGFeRD invoice (EN16931)',
    creationDate: now,
    modificationDate: now,
    afRelationship: AFRelationship.Alternative,
  })

  // Write the Factur-X XMP metadata packet onto the catalog (uncompressed stream,
  // as PDF/A expects). pdf-lib has no first-class XMP API, so set it low-level.
  try {
    const xmp = buildXmpMetadata()
    const metadataStream = pdfDoc.context.stream(xmp, {
      Type: PDFName.of('Metadata'),
      Subtype: PDFName.of('XML'),
    })
    const metadataRef = pdfDoc.context.register(metadataStream)
    pdfDoc.catalog.set(PDFName.of('Metadata'), metadataRef)
  } catch (xmpErr) {
    // XMP is best-effort; the embedded file + AFRelationship are what matters most.
    console.error('[ZUGFeRD] Failed to set XMP metadata (continuing):', xmpErr)
  }

  const bytes = await pdfDoc.save({ useObjectStreams: false })
  return Buffer.from(bytes)
}

export default embedZugferdXml