Refactor table management to use a dedicated API and improve command handling.

internal/command/command.go

@@ -0,0 +1,37 @@
+package command
+
+import (
+	"errors"
+	"os/exec"
+)
+
+type NFT interface {
+	Run(arg ...string) error
+}
+
+type execNFT struct {
+	nftPath string
+}
+
+func New(path string) (NFT, error) {
+	if err := checkingNFT(path); err != nil {
+		return nil, err
+	}
+
+	return &execNFT{
+		nftPath: path,
+	}, nil
+}
+
+func (r *execNFT) Run(arg ...string) error {
+	cmd := exec.Command(r.nftPath, arg...)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		if len(out) > 0 {
+			return errors.New(string(out))
+		}
+		return err
+	}
+
+	return nil
+}