chore: rework image-builder CLI (#151)

* chore: rework image-builder CLI

- split into reusable packages
- split image build stages into reusable actions

---------

Signed-off-by: Angelos Kolaitis <neoaggelos@gmail.com>

Author: neoaggelos

cmd/exp/image-builder/cmd_haproxy.go

@@ -0,0 +1,5 @@
+package action
+
+import "context"
+
+type Action func(context.Context) error

cmd/exp/image-builder/cmd_kubeadm.go

@@ -0,0 +1,18 @@
+package action
+
+import (
+	"context"
+	"fmt"
+)
+
+// Chain is a meta Action that runs multiple Action one after the other.
+func Chain(actions ...Action) Action {
+	return func(ctx context.Context) error {
+		for idx, action := range actions {
+			if err := action(ctx); err != nil {
+				return fmt.Errorf("action %d/%d failed: %w", idx, len(actions), err)
+			}
+		}
+		return nil
+	}
+}

cmd/exp/image-builder/cmd_root.go

@@ -0,0 +1,52 @@
+package action
+
+import (
+	"context"
+	"fmt"
+	"os"
+
+	incus "github.com/lxc/incus/v6/client"
+	"github.com/lxc/incus/v6/shared/ioprogress"
+	"sigs.k8s.io/controller-runtime/pkg/log"
+
+	"github.com/lxc/cluster-api-provider-incus/internal/lxc"
+)
+
+// ExportImage is an Action that downloads a unified image tarball and saves to a local file.
+func ExportImage(lxcClient *lxc.Client, imageAliasName string, outputFile string) Action {
+	return func(ctx context.Context) (rerr error) {
+		image, _, err := lxcClient.GetImageAlias(imageAliasName)
+		if err != nil {
+			return fmt.Errorf("failed to find image for alias %q: %w", imageAliasName, err)
+		}
+
+		output, err := os.Create(outputFile)
+		if err != nil {
+			return fmt.Errorf("failed to create output file: %w", err)
+		}
+		defer func() {
+			_ = output.Close()
+			if rerr != nil {
+				_ = os.Remove(outputFile)
+			}
+		}()
+
+		log.FromContext(ctx).V(1).Info("Downloading image")
+		resp, err := lxcClient.GetImageFile(image.Target, incus.ImageFileRequest{
+			MetaFile: output,
+			ProgressHandler: func(progress ioprogress.ProgressData) {
+				log.FromContext(ctx).V(2).WithValues("progress", progress.Text).Info("Downloading image")
+			},
+		})
+		if err != nil {
+			return fmt.Errorf("failed to download image: %w", err)
+		}
+
+		log.FromContext(ctx).V(1).WithValues("image", resp).Info("Downloaded image")
+		if err := output.Truncate(resp.MetaSize); err != nil {
+			return fmt.Errorf("failed to truncate output file: %w", err)
+		}
+
+		return nil
+	}
+}