feat(packer): restore packer-manifest.json state across blueprint regenerations

pkg/modulewriter/modulewriter_test.go

@@ -179,6 +179,44 @@ func (s *zeroSuite) TestRestoreTfState(c *C) {
 	c.Check(err, IsNil)
 }
 
+func (s *zeroSuite) TestRestorePackerState(c *C) {
+	// set up dir structure
+	//
+	// └── test_dir
+	//    ├── .ghpc
+	//       └── previous_deployment_groups
+	//          └── packer_group
+	//             └── image
+	//                └── packer-manifest.json
+	//    └── packer_group
+	//       └── image
+	depDir := c.MkDir()
+	groupName := "packer_group"
+	subPath := "image"
+	manifestContent := `{"builds": [{"artifact_id": "my-image"}]}`
+
+	prevGroup := filepath.Join(HiddenGhpcDir(depDir), prevGroupDirName, groupName, subPath)
+	curGroup := filepath.Join(depDir, groupName, subPath)
+	prevManifest := filepath.Join(prevGroup, packerManifestFileName)
+
+	c.Assert(os.MkdirAll(prevGroup, 0755), IsNil)
+	c.Assert(os.MkdirAll(curGroup, 0755), IsNil)
+	c.Assert(os.WriteFile(prevManifest, []byte(manifestContent), 0644), IsNil)
+
+	testWriter := PackerWriter{}
+	c.Check(testWriter.restoreState(depDir), IsNil)
+
+	// check manifest file was copied to current resource group dir
+	curManifest := filepath.Join(curGroup, packerManifestFileName)
+	_, err := os.Stat(curManifest)
+	c.Check(err, IsNil)
+
+	// check content is identical
+	gotContent, err := os.ReadFile(curManifest)
+	c.Check(err, IsNil)
+	c.Check(string(gotContent), Equals, manifestContent)
+}
+
 func TestGetTypeTokensRelaxed(t *testing.T) {
 	type test struct {
 		input cty.Type

pkg/modulewriter/packerwriter.go

@@ -19,9 +19,11 @@ package modulewriter
 import (
 	"fmt"
 	"io"
+	"os"
 	"path/filepath"
 
 	"hpc-toolkit/pkg/config"
+	"hpc-toolkit/pkg/logging"
 
 	"github.com/zclconf/go-cty/cty"
 )
@@ -85,8 +87,58 @@ func (w PackerWriter) writeGroup(
 	return nil
 }
 
+const packerManifestFileName = "packer-manifest.json"
+
 func (w PackerWriter) restoreState(deploymentDir string) error {
-	// TODO: restore packer-manifest.json if it exists
+	prevGroupPath := filepath.Join(HiddenGhpcDir(deploymentDir), prevGroupDirName)
+
+	// If the previous deployment groups directory doesn't exist, there is nothing to restore.
+	if _, err := os.Stat(prevGroupPath); os.IsNotExist(err) {
+		return nil
+	}
+
+	err := filepath.WalkDir(prevGroupPath, func(path string, d os.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+		if d.IsDir() || d.Name() != packerManifestFileName {
+			return nil
+		}
+
+		// Found a packer-manifest.json. Determine its relative path from prevGroupPath.
+		relPath, err := filepath.Rel(prevGroupPath, path)
+		if err != nil {
+			return fmt.Errorf("failed to get relative path for %s: %w", path, err)
+		}
+
+		dest := filepath.Join(deploymentDir, relPath)
+
+		// Ensure the destination directory exists before writing (it should have been created by writeGroup).
+		_, err = os.Stat(filepath.Dir(dest))
+		if err != nil {
+			if os.IsNotExist(err) {
+				return nil
+			}
+			return fmt.Errorf("failed to stat destination directory %s: %w", filepath.Dir(dest), err)
+		}
+
+		bytesRead, err := os.ReadFile(path)
+		if err != nil {
+			return fmt.Errorf("failed to read previous packer manifest %s: %w", path, err)
+		}
+		err = os.WriteFile(dest, bytesRead, 0644)
+		if err != nil {
+			return fmt.Errorf("failed to write previous packer manifest %s: %w", dest, err)
+		}
+		logging.Info("Restored packer manifest to %s", dest)
+
+		return nil
+	})
+
+	if err != nil {
+		return fmt.Errorf("error trying to restore packer manifests: %w", err)
+	}
+
 	return nil
 }