feat(pdfengines): add embed feature

pkg/modules/pdfengines/multi.go

@@ -19,6 +19,7 @@ type multiPdfEngines struct {
 	readMetadataEngines  []gotenberg.PdfEngine
 	writeMetadataEngines []gotenberg.PdfEngine
 	passwordEngines      []gotenberg.PdfEngine
+	embedEngines         []gotenberg.PdfEngine
 }
 
 func newMultiPdfEngines(
@@ -28,7 +29,8 @@ func newMultiPdfEngines(
 	convertEngines,
 	readMetadataEngines,
 	writeMetadataEngines,
-	passwordEngines []gotenberg.PdfEngine,
+	passwordEngines,
+	embedEngines []gotenberg.PdfEngine,
 ) *multiPdfEngines {
 	return &multiPdfEngines{
 		mergeEngines:         mergeEngines,
@@ -38,6 +40,7 @@ func newMultiPdfEngines(
 		readMetadataEngines:  readMetadataEngines,
 		writeMetadataEngines: writeMetadataEngines,
 		passwordEngines:      passwordEngines,
+		embedEngines:         embedEngines,
 	}
 }
 
@@ -238,6 +241,31 @@ func (multi *multiPdfEngines) Encrypt(ctx context.Context, logger *zap.Logger, i
 	return fmt.Errorf("encrypt PDF using multi PDF engines: %w", err)
 }
 
+// EmbedFiles embeds files into a PDF using the first available
+// engine that supports file embedding.
+func (multi *multiPdfEngines) EmbedFiles(ctx context.Context, logger *zap.Logger, filePaths []string, inputPath string) error {
+	var err error
+	errChan := make(chan error, 1)
+
+	for _, engine := range multi.embedEngines {
+		go func(engine gotenberg.PdfEngine) {
+			errChan <- engine.EmbedFiles(ctx, logger, filePaths, inputPath)
+		}(engine)
+
+		select {
+		case embedErr := <-errChan:
+			errored := multierr.AppendInto(&err, embedErr)
+			if !errored {
+				return nil
+			}
+		case <-ctx.Done():
+			return ctx.Err()
+		}
+	}
+
+	return fmt.Errorf("embed files into PDF using multi PDF engines: %w", err)
+}
+
 // Interface guards.
 var (
 	_ gotenberg.PdfEngine = (*multiPdfEngines)(nil)