Factor out export command control flow

The export command works the same way for most (all?) types. I have
made it generic and moved it into export.go, then ported
{export,create}_auto_image{repository,policy}.go to use it.

Signed-off-by: Michael Bridgen <michael@weave.works>

cmd/flux/export.go

@@ -18,8 +18,15 @@ package main
 
 import (
 	"bytes"
+	"context"
+	"fmt"
 
 	"github.com/spf13/cobra"
+	"k8s.io/apimachinery/pkg/types"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+	"sigs.k8s.io/yaml"
+
+	"github.com/fluxcd/flux2/internal/utils"
 )
 
 var exportCmd = &cobra.Command{
@@ -38,6 +45,80 @@ func init() {
 	rootCmd.AddCommand(exportCmd)
 }
 
+// exportable represents a type that you can fetch from the Kubernetes
+// API, then tidy up for serialising.
+type exportable interface {
+	objectContainer
+	Export() interface{}
+}
+
+// exportableAt represents a type that has a list of values, each of
+// which is exportable.
+type exportableAt interface {
+	objectContainer
+	Len() int
+	ExportAt(i int) interface{}
+}
+
+type exportCommand struct {
+	object exportable
+	list   exportableAt
+}
+
+func (export exportCommand) run(cmd *cobra.Command, args []string) error {
+	if !exportAll && len(args) < 1 {
+		return fmt.Errorf("name is required")
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), timeout)
+	defer cancel()
+
+	kubeClient, err := utils.KubeClient(kubeconfig, kubecontext)
+	if err != nil {
+		return err
+	}
+
+	if exportAll {
+		err = kubeClient.List(ctx, export.list.AsClientObject(), client.InNamespace(namespace))
+		if err != nil {
+			return err
+		}
+
+		if export.list.Len() == 0 {
+			logger.Failuref("no objects found in %s namespace", namespace)
+			return nil
+		}
+
+		for i := 0; i < export.list.Len(); i++ {
+			if err = printExport(export.list.ExportAt(i)); err != nil {
+				return err
+			}
+		}
+	} else {
+		name := args[0]
+		namespacedName := types.NamespacedName{
+			Namespace: namespace,
+			Name:      name,
+		}
+		err = kubeClient.Get(ctx, namespacedName, export.object.AsClientObject())
+		if err != nil {
+			return err
+		}
+		return printExport(export.object.Export())
+	}
+	return nil
+}
+
+func printExport(export interface{}) error {
+	data, err := yaml.Marshal(export)
+	if err != nil {
+		return err
+	}
+	fmt.Println("---")
+	fmt.Println(resourceToString(data))
+	return nil
+}
+
 func resourceToString(data []byte) string {
 	data = bytes.Replace(data, []byte("  creationTimestamp: null\n"), []byte(""), 1)
 	data = bytes.Replace(data, []byte("status: {}\n"), []byte(""), 1)