all: refactor router code to use interface

So the code is more modular, easier to read/maintain.

internal/router/ddwrt/ddwrt.go

@@ -0,0 +1,115 @@
+package ddwrt
+
+import (
+	"errors"
+	"fmt"
+	"os/exec"
+
+	"github.com/kardianos/service"
+
+	"github.com/Control-D-Inc/ctrld"
+	"github.com/Control-D-Inc/ctrld/internal/router/dnsmasq"
+	"github.com/Control-D-Inc/ctrld/internal/router/ntp"
+	"github.com/Control-D-Inc/ctrld/internal/router/nvram"
+)
+
+const Name = "ddwrt"
+
+//lint:ignore ST1005 This error is for human.
+var errDdwrtJffs2NotEnabled = errors.New(`could not install service without jffs, follow this guide to enable:
+
+https://wiki.dd-wrt.com/wiki/index.php/Journalling_Flash_File_System
+`)
+
+var nvramKvMap = map[string]string{
+	"dns_dnsmasq":     "1", // Make dnsmasq running but disable DNS ability, ctrld will replace it.
+	"dnsmasq_options": "",  // Configuration of dnsmasq set by ctrld, filled by setupDDWrt.
+	"dns_crypt":       "0", // Disable DNSCrypt.
+	"dnssec":          "0", // Disable DNSSEC.
+}
+
+type Ddwrt struct {
+	cfg *ctrld.Config
+}
+
+// New returns a router.Router for configuring/setup/run ctrld on ddwrt routers.
+func New(cfg *ctrld.Config) *Ddwrt {
+	return &Ddwrt{cfg: cfg}
+}
+
+func (d *Ddwrt) ConfigureService(config *service.Config) error {
+	if !ddwrtJff2Enabled() {
+		return errDdwrtJffs2NotEnabled
+	}
+	return nil
+}
+
+func (d *Ddwrt) Install(_ *service.Config) error {
+	return nil
+}
+
+func (d *Ddwrt) Uninstall(_ *service.Config) error {
+	return nil
+}
+
+func (d *Ddwrt) PreRun() error {
+	_ = d.Cleanup()
+	return ntp.Wait()
+}
+
+func (d *Ddwrt) Configure() error {
+	d.cfg.Listener["0"].IP = "127.0.0.1"
+	d.cfg.Listener["0"].Port = 5354
+	return nil
+}
+
+func (d *Ddwrt) Setup() error {
+	// Already setup.
+	if val, _ := nvram.Run("get", nvram.CtrldSetupKey); val == "1" {
+		return nil
+	}
+
+	data, err := dnsmasq.ConfTmpl(dnsmasq.ConfigContentTmpl, d.cfg)
+	if err != nil {
+		return err
+	}
+
+	nvramKvMap["dnsmasq_options"] = data
+	if err := nvram.SetKV(nvramKvMap, nvram.CtrldSetupKey); err != nil {
+		return err
+	}
+
+	// Restart dnsmasq service.
+	if err := restartDNSMasq(); err != nil {
+		return err
+	}
+	return nil
+}
+
+func (d *Ddwrt) Cleanup() error {
+	if val, _ := nvram.Run("get", nvram.CtrldSetupKey); val == "1" {
+		nvramKvMap["dnsmasq_options"] = ""
+		// Restore old configs.
+		if err := nvram.Restore(nvramKvMap, nvram.CtrldSetupKey); err != nil {
+			return err
+		}
+	}
+
+	// Restart dnsmasq service.
+	if err := restartDNSMasq(); err != nil {
+		return err
+	}
+	return nil
+}
+
+func restartDNSMasq() error {
+	if out, err := exec.Command("restart_dns").CombinedOutput(); err != nil {
+		return fmt.Errorf("restart_dns: %s, %w", string(out), err)
+	}
+	return nil
+}
+
+func ddwrtJff2Enabled() bool {
+	out, _ := nvram.Run("get", "enable_jffs2")
+	return out == "1"
+}