feat(pdfengines): add PDF/UA (#714)

pkg/gotenberg/pdfengine.go

@@ -8,45 +8,74 @@ import (
 )
 
 var (
-	// ErrPDFEngineMethodNotAvailable happens if a PDFEngine method is not
-	// available in the implementation.
-	ErrPDFEngineMethodNotAvailable = errors.New("method not available")
+	// ErrPdfEngineMethodNotSupported is returned when a specific method of the
+	// PdfEngine interface is not supported by its current implementation.
+	ErrPdfEngineMethodNotSupported = errors.New("method not supported")
 
-	// ErrPDFFormatNotAvailable happens if a PDFEngine Convert's method does
-	// not handle a specific format.
-	ErrPDFFormatNotAvailable = errors.New("PDF format not available")
+	// ErrPdfFormatNotSupported is returned when the Convert method of the
+	// PdfEngine interface does not support a requested PDF format conversion.
+	ErrPdfFormatNotSupported = errors.New("PDF format not supported")
 )
 
 const (
-	FormatPDFA1a string = "PDF/A-1a"
-	FormatPDFA1b string = "PDF/A-1b"
-	FormatPDFA2a string = "PDF/A-2a"
-	FormatPDFA2b string = "PDF/A-2b"
-	FormatPDFA2u string = "PDF/A-2u"
-	FormatPDFA3a string = "PDF/A-3a"
-	FormatPDFA3b string = "PDF/A-3b"
-	FormatPDFA3u string = "PDF/A-3u"
+	// PdfA1a represents the PDF/A-1a format.
+	PdfA1a string = "PDF/A-1a"
+
+	// PdfA1b represents the PDF/A-1b format.
+	PdfA1b string = "PDF/A-1b"
+
+	// PdfA2a represents the PDF/A-2a format.
+	PdfA2a string = "PDF/A-2a"
+
+	// PdfA2b represents the PDF/A-2b format.
+	PdfA2b string = "PDF/A-2b"
+
+	// PdfA2u represents the PDF/A-2u format.
+	PdfA2u string = "PDF/A-2u"
+
+	// PdfA3a represents the PDF/A-3a format.
+	PdfA3a string = "PDF/A-3a"
+
+	// PdfA3b represents the PDF/A-3b format.
+	PdfA3b string = "PDF/A-3b"
+
+	// PdfA3u represents the PDF/A-3u format.
+	PdfA3u string = "PDF/A-3u"
 )
 
-// PDFEngine is a module interface which exposes methods for manipulating one
-// or more PDFs. Implementations may abstract powerful tools like PDFtk, or
-// fulfill those methods contracts in Golang directly.
-type PDFEngine interface {
-	// Merge merges the given PDFs into a unique PDF. The pages' order reflects
-	// order of the given files.
+// PdfFormats specifies the target formats for a PDF conversion.
+type PdfFormats struct {
+	// PdfA denotes the PDF/A standard format (e.g., PDF/A-1a).
+	PdfA string
+
+	// PdfUa indicates whether the PDF should comply
+	// with the PDF/UA (Universal Accessibility) standard.
+	PdfUa bool
+}
+
+// PdfEngine provides an interface for operations on PDFs. Implementations
+// can utilize various tools like PDFtk, or implement functionality directly in
+// Go.
+type PdfEngine interface {
+	// Merge combines multiple PDFs into a single PDF. The resulting page order
+	// is determined by the order of files provided in inputPaths.
 	Merge(ctx context.Context, logger *zap.Logger, inputPaths []string, outputPath string) error
 
-	// Convert converts the given PDF to a specific PDF format.
-	Convert(ctx context.Context, logger *zap.Logger, format, inputPath, outputPath string) error
+	// Convert transforms a given PDF to the specified formats defined in
+	// PdfFormats. If no format, it does nothing.
+	Convert(ctx context.Context, logger *zap.Logger, formats PdfFormats, inputPath, outputPath string) error
 }
 
-// PDFEngineProvider is a module interface which exposes a method for creating a
-// PDFEngine for other modules.
+// PdfEngineProvider offers an interface to instantiate a [PdfEngine].
+// This is used to decouple the creation of a [PdfEngine] from its consumers.
+//
+// Example:
 //
 //	func (m *YourModule) Provision(ctx *gotenberg.Context) error {
-//		provider, _  := ctx.Module(new(gotenberg.PDFEngineProvider))
-//		pdfengines, _ := provider.(gotenberg.PDFEngineProvider).PDFEngine()
+//		provider, _ := ctx.Module(new(gotenberg.PdfEngineProvider))
+//		engine, _ := provider.(gotenberg.PdfEngineProvider).PdfEngine()
 //	}
-type PDFEngineProvider interface {
-	PDFEngine() (PDFEngine, error)
+type PdfEngineProvider interface {
+	// PdfEngine returns an instance of the PdfEngine interface for PDF operations.
+	PdfEngine() (PdfEngine, error)
 }