Move kubeconfig utility to a shared pkg

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>

internal/kubeconfig/contextmodify.go

@@ -0,0 +1,74 @@
+package kubeconfig
+
+import (
+	"github.com/pkg/errors"
+	"gopkg.in/yaml.v3"
+)
+
+func (k *Kubeconfig) DeleteContextEntry(deleteName string) error {
+	contexts := valueOf(k.rootNode, "contexts")
+	if contexts == nil {
+		return errors.New("there are no contexts in kubeconfig")
+	}
+	if contexts.Kind != yaml.SequenceNode {
+		return errors.New("'contexts' key is not a sequence")
+	}
+
+	i := -1
+	for j, ctxNode := range contexts.Content {
+		nameNode := valueOf(ctxNode, "name")
+		if nameNode != nil && nameNode.Kind == yaml.ScalarNode && nameNode.Value == deleteName {
+			i = j
+			break
+		}
+	}
+	if i >= 0 {
+		copy(contexts.Content[i:], contexts.Content[i+1:])
+		contexts.Content[len(contexts.Content)-1] = nil
+		contexts.Content = contexts.Content[:len(contexts.Content)-1]
+	}
+	return nil
+}
+
+func (k *Kubeconfig) ModifyCurrentContext(name string) error {
+	currentCtxNode := valueOf(k.rootNode, "current-context")
+	if currentCtxNode != nil {
+		currentCtxNode.Value = name
+		return nil
+	}
+
+	// if current-context field doesn't exist, create new field
+	keyNode := &yaml.Node{
+		Kind:  yaml.ScalarNode,
+		Value: "current-context",
+		Tag:   "!!str"}
+	valueNode := &yaml.Node{
+		Kind:  yaml.ScalarNode,
+		Value: name,
+		Tag:   "!!str"}
+	k.rootNode.Content = append(k.rootNode.Content, keyNode, valueNode)
+	return nil
+}
+
+func (k *Kubeconfig) ModifyContextName(old, new string) error {
+	contexts := valueOf(k.rootNode, "contexts")
+	if contexts == nil {
+		return errors.New("\"contexts\" entry is nil")
+	} else if contexts.Kind != yaml.SequenceNode {
+		return errors.New("\"contexts\" is not a sequence node")
+	}
+
+	var changed bool
+	for _, contextNode := range contexts.Content {
+		nameNode := valueOf(contextNode, "name")
+		if nameNode.Kind == yaml.ScalarNode && nameNode.Value == old {
+			nameNode.Value = new
+			changed = true
+			break
+		}
+	}
+	if !changed {
+		return errors.New("no changes were made")
+	}
+	return nil
+}