Adding kustomize mage utility (#38)

* Adding kustomize mage utility

* fix lint

* fix linting

kustomize/kustomize.go

@@ -0,0 +1,141 @@
+package kustomize
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"os/exec"
+	"path/filepath"
+	"regexp"
+
+	"github.com/cresta/magehelper/files"
+	"gopkg.in/yaml.v3"
+)
+
+var YAMLSeparator = regexp.MustCompile("---\n")
+var namespacelessKinds = map[string]bool{
+	"ClusterRole":        true,
+	"ClusterRoleBinding": true,
+	"StorageClass":       true,
+	"PersistentVolume":   true,
+}
+
+// Manifest represents a Kubernetes manifest YAML file
+type Manifest struct {
+	// YAML is the original YAML string
+	YAML string
+	// Parsed is the YAML string parsed as a map
+	Parsed map[string]any
+	// Name is the name of the manifest
+	Name string
+	// Namespace is the Kubernetes namespace this manifest is defined in.
+	Namespace string
+	// Kind is the kind of the manifest
+	Kind string
+}
+
+// ShortName returns a short display name of the Manifest, including on ly the kind and name
+func (m *Manifest) ShortName() string {
+	return fmt.Sprintf("[%s] %s", m.Kind, m.Name)
+}
+
+// LongName returns a long display name for the Manifest, including namespace, kind and name
+func (m *Manifest) LongName() string {
+	return m.Namespace + "-" + m.Kind + "-" + m.Name
+}
+
+// Init runs the `kuztomize init` command on a specified directory, returning the kustomize generated manifest.
+//
+// The returned map maps the Manifest long name to the manifest.
+func Init(ctx context.Context, path string) (map[string]Manifest, error) {
+	if !files.FileExists(filepath.Join(path, "kustomization.yaml")) {
+		_, err := shell(path, "kustomize", "init", ".", "--recursive", "--autodetect")
+		if err != nil {
+			return nil, fmt.Errorf("cannot init kustomize %s: %w", path, err)
+		}
+	}
+	output, err := shell(path, "kustomize", "build", "--load-restrictor=LoadRestrictionsNone")
+	if err != nil {
+		return nil, fmt.Errorf("failed to run kustomize at %s: %w", path, err)
+	}
+	yamls := YAMLSeparator.Split(output, -1)
+	documents := make(map[string]Manifest, len(yamls))
+	for _, content := range yamls {
+		var parsed map[string]any
+		err := yaml.Unmarshal([]byte(content), &parsed)
+		if err != nil {
+			return nil, fmt.Errorf("failed to unmarshal output:\n%s\n%w", content, err)
+		}
+		kind, ok := getString(parsed, true, "kind")
+		if !ok {
+			return nil, fmt.Errorf("missing kind in yaml document:\n%s", content)
+		}
+		name, ok := getString(parsed, true, "metadata", "name")
+		if !ok {
+			return nil, fmt.Errorf("missing metadata.name in yaml document:\n%s", content)
+		}
+		namespace := ""
+		if kind == "Namespace" {
+			namespace = name
+		} else {
+			namespace, ok = getString(parsed, true, "metadata", "namespace")
+			if !ok && !namespacelessKinds[kind] {
+				return nil, fmt.Errorf("missing metadata.namespace in yaml document:\n%s", content)
+			}
+		}
+		if namespace == "" {
+			namespace = "[no-namespace]"
+		}
+		m := Manifest{
+			YAML:      content,
+			Parsed:    parsed,
+			Name:      name,
+			Namespace: namespace,
+			Kind:      kind,
+		}
+		documents[m.LongName()] = m
+	}
+	return documents, nil
+}
+
+func shell(pwd string, cmdName string, args ...string) (stdout string, err error) {
+	cmd := exec.Command(cmdName, args...)
+	cmd.Dir = pwd
+	stderr := bytes.NewBuffer(nil)
+	cmd.Stderr = stderr
+	output, err := cmd.Output()
+	if err != nil {
+		return "", fmt.Errorf("%w. Stderr: %s", err, stderr.String())
+	}
+	return string(output), nil
+}
+
+func getString(m map[string]any, verbose bool, keys ...string) (string, bool) {
+	valueAny, ok := getValue(m, verbose, keys...)
+	if !ok {
+		return "", ok
+	}
+	value, ok := valueAny.(string)
+	return value, ok
+}
+
+func getValue(m map[string]any, verbose bool, keys ...string) (any, bool) {
+	var v any = m
+	for _, key := range keys {
+		m, ok := v.(map[string]any)
+		if !ok {
+			if verbose {
+				fmt.Printf("not a map: %v\n", v)
+			}
+			return "", false
+		}
+		v, ok = m[key]
+		if !ok {
+			if verbose {
+				fmt.Printf("%s not in %v\n", key, m)
+			}
+			return "", false
+		}
+	}
+	return v, true
+}