kg

var ConvertCmd = &cobra.Command{
	Use:   "convert",
	Short: "Convert between knowledge graph formats (e.g., TTL to NQ)",
	Long: `Convert between knowledge graph formats.

Supported inputs: .ttl (Turtle, via the knowledge-rdf parser), .nq
(N-Quads), .nt (N-Triples), .jsonld (JSON-LD). Supported outputs:
nquads (default), ntriples, jsonld.`,
	RunE: func(cmd *cobra.Command, args []string) error {

		f, err := os.Open(inFile)
		if err != nil {
			return fmt.Errorf("failed to open input file: %w", err)
		}
		defer f.Close()

		format := inFmt
		if format == "" {
			ext := filepath.Ext(inFile)
			switch ext {
			case ".ttl":

				format = "turtle"
			case ".nq":
				format = "nquads"
			case ".nt":
				format = "ntriples"
			case ".jsonld":
				format = "jsonld"
			default:
				return fmt.Errorf("unknown input extension %s, please specify --from (supported: .ttl, .nq, .nt, .jsonld)", ext)
			}
		}

		outF, err := os.Create(outFile)
		if err != nil {
			return fmt.Errorf("failed to create output file: %w", err)
		}
		defer outF.Close()

		// 4. Encoder
		var w quad.Writer
		switch outFmt {
		case "nquads", "ntriples":

			w = nquads.NewWriter(outF)
		case "jsonld":
			w = jsonld.NewWriter(outF)
		default:
			return fmt.Errorf("unsupported output format: %s", outFmt)
		}

		defer func() {
			if c, ok := w.(io.Closer); ok {
				c.Close()
			}
		}()

		// 5. Copy
		var n int
		if format == "turtle" || format == "ttl" {
			n, err = copyTurtle(w)
		} else {
			var r quad.Reader
			switch format {
			case "nquads", "ntriples":

				r = nquads.NewReader(f, false)
			case "jsonld":
				r = jsonld.NewReader(f)
			default:
				return fmt.Errorf("unsupported input format: %s (supported: turtle, nquads, ntriples, jsonld)", format)
			}
			n, err = quad.Copy(w, r)
		}
		if err != nil {
			return fmt.Errorf("conversion failed: %w", err)
		}

		cmd.Printf("Converted %d quads to %s\n", n, outFile)
		return nil
	},
}

var KgCmd = &cobra.Command{
	Use:   "kg",
	Short: "Knowledge Graph utilities",
	Run: func(cmd *cobra.Command, args []string) {
		cmd.Help()
	},
}