parses metadata collections using previous paths

src/internal/m365/collection/site/backup.go

@@ -150,7 +150,7 @@ func CollectLists(
 	su support.StatusUpdater,
 	counter *count.Bus,
 	errs *fault.Bus,
-) ([]data.BackupCollection, error) {
+) ([]data.BackupCollection, bool, error) {
 	logger.Ctx(ctx).Debug("Creating SharePoint List Collections")
 
 	var (
@@ -160,9 +160,19 @@ func CollectLists(
 		currPaths = map[string]string{}
 	)
 
+	dps, canUsePreviousBackup, err := parseMetadataCollections(ctx, path.ListsCategory, bpc.MetadataCollections)
+	if err != nil {
+		return nil, false, err
+	}
+
+	// [TODO] utilise deltapaths to determine list's state
+	_ = dps
+
+	ctx = clues.Add(ctx, "can_use_previous_backup", canUsePreviousBackup)
+
 	lists, err := bh.GetItems(ctx, acc)
 	if err != nil {
-		return nil, err
+		return nil, false, err
 	}
 
 	for _, list := range lists {
@@ -204,7 +214,7 @@ func CollectLists(
 		path.ListsCategory,
 		false)
 	if err != nil {
-		return nil, clues.WrapWC(ctx, err, "making metadata path prefix").
+		return nil, false, clues.WrapWC(ctx, err, "making metadata path prefix").
 			Label(count.BadPathPrefix)
 	}
 
@@ -216,12 +226,12 @@ func CollectLists(
 		su,
 		counter.Local())
 	if err != nil {
-		return nil, clues.WrapWC(ctx, err, "making metadata collection")
+		return nil, false, clues.WrapWC(ctx, err, "making metadata collection")
 	}
 
 	spcs = append(spcs, col)
 
-	return spcs, el.Failure()
+	return spcs, canUsePreviousBackup, el.Failure()
 }
 
 func idAnd(ss ...string) []string {

src/internal/m365/collection/site/backup_test.go

@@ -114,7 +114,7 @@ func (suite *SharePointSuite) TestCollectLists() {
 
 	bh := NewListsBackupHandler(bpc.ProtectedResource.ID(), ac.Lists())
 
-	col, err := CollectLists(
+	col, _, err := CollectLists(
 		ctx,
 		bh,
 		bpc,

src/internal/m365/collection/site/metadata.go

@@ -0,0 +1,99 @@
+package site
+
+import (
+	"context"
+	"encoding/json"
+
+	"github.com/alcionai/clues"
+
+	"github.com/alcionai/corso/src/internal/data"
+	"github.com/alcionai/corso/src/pkg/backup/metadata"
+	"github.com/alcionai/corso/src/pkg/fault"
+	"github.com/alcionai/corso/src/pkg/logger"
+	"github.com/alcionai/corso/src/pkg/path"
+)
+
+func parseMetadataCollections(
+	ctx context.Context,
+	cat path.CategoryType,
+	colls []data.RestoreCollection,
+) (metadata.DeltaPaths, bool, error) {
+	cdp := metadata.CatDeltaPaths{
+		cat: {},
+	}
+
+	found := map[path.CategoryType]map[string]struct{}{
+		cat: {},
+	}
+
+	errs := fault.New(true)
+
+	for _, coll := range colls {
+		var (
+			breakLoop bool
+			items     = coll.Items(ctx, errs)
+			category  = coll.FullPath().Category()
+		)
+
+		for {
+			select {
+			case <-ctx.Done():
+				return nil, false, clues.WrapWC(ctx, ctx.Err(), "parsing collection metadata")
+
+			case item, ok := <-items:
+				if !ok || errs.Failure() != nil {
+					breakLoop = true
+					break
+				}
+
+				var (
+					m                    = map[string]string{}
+					cdps, wantedCategory = cdp[category]
+				)
+
+				if !wantedCategory {
+					continue
+				}
+
+				err := json.NewDecoder(item.ToReader()).Decode(&m)
+				if err != nil {
+					return nil, false, clues.NewWC(ctx, "decoding metadata json")
+				}
+
+				if item.ID() == metadata.PreviousPathFileName {
+					if _, ok := found[category][metadata.PathKey]; ok {
+						return nil, false, clues.Wrap(clues.NewWC(ctx, category.String()), "multiple versions of path metadata")
+					}
+
+					for k, p := range m {
+						cdps.AddPath(k, p)
+					}
+
+					found[category][metadata.PathKey] = struct{}{}
+
+					cdp[category] = cdps
+				}
+			}
+
+			if breakLoop {
+				break
+			}
+		}
+	}
+
+	if errs.Failure() != nil {
+		logger.CtxErr(ctx, errs.Failure()).Info("reading metadata collection items")
+
+		return metadata.DeltaPaths{}, false, nil
+	}
+
+	for _, dps := range cdp {
+		for k, dp := range dps {
+			if len(dp.Path) == 0 {
+				delete(dps, k)
+			}
+		}
+	}
+
+	return cdp[cat], true, nil
+}

src/internal/m365/service/sharepoint/backup.go

@@ -58,7 +58,7 @@ func ProduceBackupCollections(
 		case path.ListsCategory:
 			bh := site.NewListsBackupHandler(bpc.ProtectedResource.ID(), ac.Lists())
 
-			spcs, err = site.CollectLists(
+			spcs, canUsePreviousBackup, err = site.CollectLists(
 				ctx,
 				bh,
 				bpc,
@@ -73,10 +73,6 @@ func ProduceBackupCollections(
 				continue
 			}
 
-			// Lists don't make use of previous metadata
-			// TODO: Revisit when we add support of lists
-			canUsePreviousBackup = true
-
 		case path.LibrariesCategory:
 			spcs, canUsePreviousBackup, err = site.CollectLibraries(
 				ctx,