Add the --merge-graphs option

src/main/scala/eu/neverblink/jelly/cli/command/rdf/RdfFromJelly.scala

@@ -31,11 +31,11 @@ object RdfFromJellyPrint extends RdfCommandPrintUtil[RdfFormat.Writeable]:
     "If no input file is specified, the input is read from stdin.\n" +
     "If no output file is specified, the output is written to stdout.\n" +
     "If an error is detected, the program will exit with a non-zero code.\n" +
-    "Otherwise, the program will exit with code 0.\n" +
+    "Otherwise, the program will exit with code 0.\n\n" +
     "Note: this command works in a streaming manner where possible and scales well to\n" +
     "large files. Non-streaming formats (e.g. RDF/XML) by default work on a\n" +
     "frame-by-frame basis, but they can be combined into one dataset with the\n" +
-    "--combine option. RDF/XML will only serialize the default model.",
+    "--combine option.",
 )
 @ArgsName("<file-to-convert>")
 case class RdfFromJellyOptions(
@@ -56,10 +56,18 @@ case class RdfFromJellyOptions(
     )
     takeFrames: String = "",
     @HelpMessage(
-      "Add to combine the results into one dataset, when using a non-streaming output format. " +
-        "Ignored otherwise. Take care with input size, as this option will load everything into memory.",
+      "Add to combine all stream frames into one dataset, when using a non-streaming output format. " +
+        "Ignored otherwise. Take care with input size, as this option will load everything into memory. " +
+        "Default: false.",
     )
     combine: Boolean = false,
+    @HelpMessage(
+      "Discard the named graph information, treating the input as triples in the default graph. " +
+        "This allows you to convert a Jelly file containing quads to Turtle/N-Triples in a lossy manner. " +
+        "This option has no impact on frame boundaries. To merge frames, use the --combine option. " +
+        "Default: false.",
+    )
+    mergeGraphs: Boolean = false,
     @Recurse
     rdfPerformanceOptions: RdfPerformanceOptions = RdfPerformanceOptions(),
 ) extends HasJellyCommandOptions
@@ -72,8 +80,14 @@ object RdfFromJelly extends RdfSerDesCommand[RdfFromJellyOptions, RdfFormat.Writ
 
   lazy val printUtil: RdfCommandPrintUtil[RdfFormat.Writeable] = RdfFromJellyPrint
 
-  val defaultAction: (InputStream, OutputStream) => Unit =
-    (in, out) => jellyToLang(in, StreamRDFWriter.getWriterStream(out, RdfFormat.NQuads.jenaLang))
+  val defaultAction: WriteAction =
+    (in, out, opt) =>
+      jellyToLang(
+        in,
+        StreamRDFWriter.getWriterStream(out, RdfFormat.NQuads.jenaLang),
+        RdfFormat.NQuads,
+        opt,
+      )
 
   private def takeFrames: IndexRange = IndexRange(getOptions.takeFrames, "--take-frames")
 
@@ -84,34 +98,34 @@ object RdfFromJelly extends RdfSerDesCommand[RdfFromJellyOptions, RdfFormat.Writ
     takeFrames
     val (inputStream, outputStream) =
       this.getIoStreamsFromOptions(remainingArgs.remaining.headOption, options.outputFile)
-    parseFormatArgs(inputStream, outputStream, options.outputFormat, options.outputFile)
+    parseFormatArgs(inputStream, outputStream, options.outputFormat, options.outputFile, options)
 
   override def matchFormatToAction(
       format: RdfFormat.Writeable,
-  ): Option[(InputStream, OutputStream) => Unit] =
+  ): Option[WriteAction] =
     (format, getOptions.combine) match
       case (j: RdfFormat.Jena.StreamWriteable, _) =>
-        Some((in, out) => jellyToLang(in, StreamRDFWriter.getWriterStream(out, j.jenaLang)))
+        Some((in, out, opt) =>
+          jellyToLang(in, StreamRDFWriter.getWriterStream(out, j.jenaLang), j, opt),
+        )
       case (j: RdfFormat.Jena.BatchWriteable, true) =>
-        Some((in, out) =>
-          StreamRdfCombiningBatchWriter(out, j.jenaLang).runAndOutput(x => jellyToLang(in, x)),
+        Some((in, out, opt) =>
+          StreamRdfCombiningBatchWriter(out, j.jenaLang).runAndOutput(x =>
+            jellyToLang(in, x, j, opt),
+          ),
         )
       case (j: RdfFormat.Jena.BatchWriteable, false) =>
-        Some((in, out) => jellyToLang(in, StreamRdfBatchWriter(out, j.jenaLang)))
+        Some((in, out, opt) => jellyToLang(in, StreamRdfBatchWriter(out, j.jenaLang), j, opt))
       case (RdfFormat.JellyText, _) => Some(jellyBinaryToText)
 
   /** This method reads the Jelly file, rewrites it to specified format and writes it to some output
     * stream
-    * @param jenaLang
-    *   Language that jelly should be converted to
-    * @param inputStream
-    *   InputStream
-    * @param outputStream
-    *   OutputStream
     */
   private def jellyToLang(
       inputStream: InputStream,
       writer: StreamRDF,
+      format: RdfFormat,
+      options: RdfFromJellyOptions,
   ): Unit =
     // Whether the output is active at this moment
     var outputEnabled = false
@@ -125,7 +139,18 @@ object RdfFromJelly extends RdfSerDesCommand[RdfFromJellyOptions, RdfFormat.Writ
       }
 
       override def handleQuad(subject: Node, predicate: Node, `object`: Node, graph: Node): Unit = {
-        if outputEnabled then writer.quad(Quad.create(graph, subject, predicate, `object`))
+        if outputEnabled then
+          if options.mergeGraphs then writer.triple(Triple.create(subject, predicate, `object`))
+          else if format.supportsQuads then
+            writer.quad(Quad.create(graph, subject, predicate, `object`))
+          else if Quad.isDefaultGraph(graph) then
+            writer.triple(Triple.create(subject, predicate, `object`))
+          else
+            throw new CriticalException(
+              f"Encountered a quad in the input ($subject $predicate ${`object`} $graph), " +
+                f"but the output format ($format) does not support quads. Either choose a different output format " +
+                "or use the --merge-graphs option to merge all named graphs into the default graph.",
+            )
       }
     }
 
@@ -153,13 +178,12 @@ object RdfFromJelly extends RdfSerDesCommand[RdfFromJellyOptions, RdfFormat.Writ
 
   /** This method reads the Jelly file, rewrites it to Jelly text and writes it to some output
     * stream
-    * @param inputStream
-    *   InputStream
-    * @param outputStream
-    *   OutputStream
     */
-  private def jellyBinaryToText(inputStream: InputStream, outputStream: OutputStream): Unit =
-
+  private def jellyBinaryToText(
+      inputStream: InputStream,
+      outputStream: OutputStream,
+      opt: RdfFromJellyOptions,
+  ): Unit =
     inline def writeFrameToOutput(f: RdfStreamFrame, frameIndex: Int): Unit =
       // we want to write a comment to the file before each frame
       val comment = f"# Frame $frameIndex\n"

src/main/scala/eu/neverblink/jelly/cli/command/rdf/RdfSerDesCommand.scala

@@ -17,52 +17,43 @@ abstract class RdfSerDesCommand[
     F <: RdfFormat: Typeable,
 ] extends JellyCommand[T]:
 
+  type WriteAction = (InputStream, OutputStream, T) => Unit
+
   override final def group = "rdf"
 
   /** What is the default action if no formats specified */
-  val defaultAction: (InputStream, OutputStream) => Unit
+  val defaultAction: WriteAction
 
   /** The print util responsible for handling the specific formats etc the command requires */
   lazy val printUtil: RdfCommandPrintUtil[F]
 
   /** The method responsible for matching the format to a given action */
-  def matchFormatToAction(format: F): Option[(InputStream, OutputStream) => Unit]
+  def matchFormatToAction(format: F): Option[WriteAction]
 
   /** This method takes care of proper error handling and takes care of the parameter priorities in
     * matching the input to a given format conversion
-    *
-    * @param inputStream
-    *   InputStream
-    * @param outputStream
-    *   OutputStream
-    * @param format
-    *   Option[String]
-    * @param fileName
-    *   Option[String]
-    * @throws JellyDeserializationError
-    * @throws JenaRiotException
-    * @throws InvalidJellyFile
     */
   final def parseFormatArgs(
       inputStream: InputStream,
       outputStream: OutputStream,
       format: Option[String],
       fileName: Option[String],
+      opt: T,
   ): Unit =
     try {
       val explicitFormat = if (format.isDefined) RdfFormat.find(format.get) else None
       val implicitFormat =
         if (fileName.isDefined) RdfFormat.inferFormat(fileName.get) else None
       (explicitFormat, implicitFormat) match {
         case (Some(f: F), _) =>
-          matchFormatToAction(f).get(inputStream, outputStream)
+          matchFormatToAction(f).get(inputStream, outputStream, opt)
         // If format explicitly defined but does not match any available actions or formats, we throw an error
         case (_, _) if format.isDefined =>
           throw InvalidFormatSpecified(format.get, printUtil.validFormatsString)
         case (_, Some(f: F)) =>
-          matchFormatToAction(f).get(inputStream, outputStream)
+          matchFormatToAction(f).get(inputStream, outputStream, opt)
         // If format not explicitly defined but implicitly not understandable we default to this
-        case (_, _) => defaultAction(inputStream, outputStream)
+        case (_, _) => defaultAction(inputStream, outputStream, opt)
       }
     } catch
       case e: RiotException =>

src/main/scala/eu/neverblink/jelly/cli/command/rdf/RdfToJelly.scala

@@ -76,8 +76,8 @@ object RdfToJelly extends RdfSerDesCommand[RdfToJellyOptions, RdfFormat.Readable
 
   lazy val printUtil: RdfCommandPrintUtil[RdfFormat.Readable] = RdfToJellyPrint
 
-  val defaultAction: (InputStream, OutputStream) => Unit =
-    langToJelly(RdfFormat.NQuads, _, _)
+  val defaultAction: WriteAction =
+    langToJelly(RdfFormat.NQuads, _, _, _)
 
   private def loadOptionsFromFile(filename: String): RdfStreamOptions =
     val inputStream = new FileInputStream(filename)
@@ -108,13 +108,14 @@ object RdfToJelly extends RdfSerDesCommand[RdfToJellyOptions, RdfFormat.Readable
       outputStream,
       options.inputFormat,
       remainingArgs.remaining.headOption,
+      options,
     )
     if !isQuietMode then checkAndWarnTypeCombination()
 
   override def matchFormatToAction(
       format: RdfFormat.Readable,
-  ): Option[(InputStream, OutputStream) => Unit] = format match {
-    case f: RdfFormat.Jena.Readable => Some(langToJelly(f, _, _))
+  ): Option[WriteAction] = format match {
+    case f: RdfFormat.Jena.Readable => Some(langToJelly(f, _, _, _))
     case f: RdfFormat.JellyText.type => Some(jellyTextToJelly)
   }
 
@@ -130,6 +131,7 @@ object RdfToJelly extends RdfSerDesCommand[RdfToJellyOptions, RdfFormat.Readable
       format: RdfFormat.Jena,
       inputStream: InputStream,
       outputStream: OutputStream,
+      opt: RdfToJellyOptions,
   ): Unit =
     val jellyOpt = getOptions.jellySerializationOptions.asRdfStreamOptions
     // Configure the writer
@@ -202,7 +204,11 @@ object RdfToJelly extends RdfSerDesCommand[RdfToJellyOptions, RdfFormat.Readable
     * @param outputStream
     *   Jelly binary output stream
     */
-  private def jellyTextToJelly(inputStream: InputStream, outputStream: OutputStream): Unit =
+  private def jellyTextToJelly(
+      inputStream: InputStream,
+      outputStream: OutputStream,
+      opt: RdfToJellyOptions,
+  ): Unit =
     if !isQuietMode then
       printLine(
         "WARNING: The Jelly text format is not stable and may change in incompatible " +

src/main/scala/eu/neverblink/jelly/cli/command/rdf/util/RdfFormat.scala

@@ -7,6 +7,8 @@ sealed trait RdfFormat:
   val fullName: String
   val cliOptions: List[String]
   val supportsBaseIri: Boolean
+  val supportsQuads: Boolean
+  override final def toString: String = fullName
 
 object RdfFormat:
 
@@ -31,6 +33,7 @@ object RdfFormat:
     override val cliOptions: List[String] = List("nq", "nquads")
     override val jenaLang: Lang = RDFLanguages.NQUADS
     override val supportsBaseIri: Boolean = false
+    override val supportsQuads: Boolean = true
 
   case object NTriples
       extends RdfFormat.Jena.StreamWriteable,
@@ -40,18 +43,21 @@ object RdfFormat:
     override val cliOptions: List[String] = List("nt", "ntriples")
     override val jenaLang: Lang = RDFLanguages.NTRIPLES
     override val supportsBaseIri: Boolean = false
+    override val supportsQuads: Boolean = false
 
   case object Turtle extends RdfFormat.Jena.StreamWriteable, RdfFormat.Jena.Readable:
     override val fullName: String = "Turtle"
     override val cliOptions: List[String] = List("ttl", "turtle")
     override val jenaLang: Lang = RDFLanguages.TURTLE
     override val supportsBaseIri: Boolean = true
+    override val supportsQuads: Boolean = false
 
   case object TriG extends RdfFormat.Jena.StreamWriteable, RdfFormat.Jena.Readable:
     override val fullName: String = "TriG"
     override val cliOptions: List[String] = List("trig")
     override val jenaLang: Lang = RDFLanguages.TRIG
     override val supportsBaseIri: Boolean = true
+    override val supportsQuads: Boolean = true
 
   case object RdfProto
       extends RdfFormat.Jena.StreamWriteable,
@@ -61,6 +67,7 @@ object RdfFormat:
     override val cliOptions: List[String] = List("jenaproto", "jena-proto")
     override val jenaLang: Lang = RDFLanguages.RDFPROTO
     override val supportsBaseIri: Boolean = false
+    override val supportsQuads: Boolean = true
 
   case object Thrift
       extends RdfFormat.Jena.StreamWriteable,
@@ -70,18 +77,21 @@ object RdfFormat:
     override val cliOptions: List[String] = List("jenathrift", "jena-thrift")
     override val jenaLang: Lang = RDFLanguages.RDFTHRIFT
     override val supportsBaseIri: Boolean = false
+    override val supportsQuads: Boolean = true
 
   case object RdfXml extends RdfFormat.Jena.Readable, RdfFormat.Jena.BatchWriteable:
     override val fullName: String = "RDF/XML"
     override val cliOptions: List[String] = List("rdfxml", "rdf-xml")
     override val jenaLang: Lang = RDFLanguages.RDFXML
     override val supportsBaseIri: Boolean = true
+    override val supportsQuads: Boolean = false
 
   case object JsonLd extends RdfFormat.Jena.Readable, RdfFormat.Jena.BatchWriteable:
     override val fullName: String = "JSON-LD"
     override val cliOptions: List[String] = List("jsonld", "json-ld")
     override val jenaLang: Lang = RDFLanguages.JSONLD
     override val supportsBaseIri: Boolean = true
+    override val supportsQuads: Boolean = true
 
   // We do not ever want to write or read from Jelly to Jelly
   // So better not have it as Writeable or Readable, just mark that it's integrated into Jena
@@ -90,6 +100,7 @@ object RdfFormat:
     override val cliOptions: List[String] = List("jelly")
     override val jenaLang: Lang = JellyLanguage.JELLY
     override val supportsBaseIri: Boolean = false
+    override val supportsQuads: Boolean = true
 
   case object JellyText
       extends RdfFormat,
@@ -100,6 +111,7 @@ object RdfFormat:
     override val cliOptions: List[String] = List("jelly-text")
     val extension = ".jelly.txt"
     override val supportsBaseIri: Boolean = false
+    override val supportsQuads: Boolean = true
 
   private val rdfFormats: List[RdfFormat] =
     List(NQuads, NTriples, JellyBinary, JellyText, Turtle, TriG, RdfProto, Thrift, RdfXml, JsonLd)