Wire kage pack and kage open into the CLI

pack packs a mirror to a zim file or a runnable viewer, accepting a bare
host that it resolves against the default output directory. open serves a
zim over http like serve does for a folder. Execute checks for an appended
archive first, so a packed kage runs as an offline viewer on an ephemeral
port and ignores its arguments.

cli/open.go

@@ -0,0 +1,63 @@
+package cli
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"net/http"
+	"os"
+
+	"github.com/spf13/cobra"
+
+	"github.com/tamnd/kage/pack"
+	"github.com/tamnd/kage/zim"
+)
+
+func newOpenCmd() *cobra.Command {
+	var addr string
+	var openBrowser bool
+	cmd := &cobra.Command{
+		Use:   "open <file.zim>",
+		Short: "Serve a ZIM archive in your browser for offline reading",
+		Long: "open serves a packed ZIM file over a local HTTP server so you can browse the\n" +
+			"site exactly as it was cloned. It is the read side of kage pack --format zim.",
+		Args: cobra.ExactArgs(1),
+		RunE: func(cmd *cobra.Command, args []string) error {
+			return runOpen(cmd.Context(), args[0], addr, openBrowser)
+		},
+	}
+	cmd.Flags().StringVarP(&addr, "addr", "a", "127.0.0.1:8800", "address to listen on")
+	cmd.Flags().BoolVar(&openBrowser, "open", true, "open the default browser")
+	return cmd
+}
+
+func runOpen(ctx context.Context, path, addr string, openBrowser bool) error {
+	r, err := zim.Open(path)
+	if err != nil {
+		return fmt.Errorf("cannot open %q: %w", path, err)
+	}
+	defer r.Close()
+
+	ln, err := net.Listen("tcp", addr)
+	if err != nil {
+		return fmt.Errorf("cannot listen on %s: %w", addr, err)
+	}
+	url := "http://" + ln.Addr().String()
+
+	fmt.Fprintln(os.Stderr, styleTitle.Render("kage open")+" "+styleDim.Render(path))
+	fmt.Fprintln(os.Stderr, "  open "+styleAccent.Render(url))
+	fmt.Fprintln(os.Stderr, styleDim.Render("  press Ctrl-C to stop"))
+	if openBrowser {
+		_ = pack.OpenInBrowser(url)
+	}
+
+	srv := &http.Server{Handler: pack.Handler(r)}
+	go func() {
+		<-ctx.Done()
+		_ = srv.Close()
+	}()
+	if err := srv.Serve(ln); err != nil && err != http.ErrServerClosed {
+		return err
+	}
+	return nil
+}