reduce go program in scope to just do the link processing

main.go

@@ -0,0 +1,70 @@
+package main
+
+import (
+	_ "embed"
+	"flag"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"regexp"
+	"strings"
+)
+
+func _main(o opts) error {
+	t, err := ioutil.ReadAll(o.In)
+	if err != nil {
+		return fmt.Errorf("could not read from stdin: %w", err)
+	}
+
+	r := regexp.MustCompile(`\(LINK ([^ ]+?) (.+?)\)`)
+	mms := r.FindAllSubmatch(t, -1)
+
+	if mms == nil {
+		fmt.Fprintf(o.Out, string(t))
+		return nil
+	}
+
+	output := string(t)
+
+	for _, ms := range mms {
+		switch o.Mode {
+		case "html":
+			output = strings.ReplaceAll(output, string(ms[0]),
+				fmt.Sprintf("<a href=\"%s\">%s</a>", string(ms[1]), string(ms[2])))
+		case "gopher":
+			break
+		case "gemini":
+			break
+		}
+	}
+
+	fmt.Fprintf(o.Out, output)
+
+	return nil
+}
+
+type opts struct {
+	In   io.Reader
+	Out  io.Writer
+	Mode string
+}
+
+func main() {
+	// TODO mode flag
+	var modeFlag = flag.String("mode", "", "one of html, gopher, gemini.")
+	flag.Parse()
+	if *modeFlag == "" || (*modeFlag != "html" && *modeFlag != "gopher" && *modeFlag != "gemini") {
+		fmt.Fprintln(os.Stderr, "--mode must be specified and one of: html, gopher, gemini")
+		os.Exit(1)
+	}
+	o := opts{
+		In:   os.Stdin,
+		Out:  os.Stdout,
+		Mode: *modeFlag,
+	}
+	if err := _main(o); err != nil {
+		fmt.Fprintln(os.Stderr, err.Error())
+		os.Exit(2)
+	}
+}