Mark collections as Deleted if not available and invalid delta (#2503)

## Description

<!-- Insert PR description-->

## Does this PR need a docs update or release note?

- [ ] ✅ Yes, it's included
- [x] 🕐 Yes, but in a later PR
- [ ] ⛔ No 

## Type of change

<!--- Please check the type of change your PR introduces: --->
- [x] 🌻 Feature
- [ ] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Test
- [ ] 💻 CI/Deployment
- [ ] 🧹 Tech Debt/Cleanup

## Issue(s)

<!-- Can reference multiple issues. Use one of the following "magic words" - "closes, fixes" to auto-close the Github issue. -->
* Final entry : closes https://github.com/alcionai/corso/issues/2242

## Test Plan

<!-- How will this be tested prior to merging.-->
- [ ] 💪 Manual
- [x] ⚡ Unit test
- [ ] 💚 E2E

src/internal/connector/onedrive/collections.go

@@ -344,14 +344,59 @@ func (c *Collections) Get(
 		folderPaths[driveID] = map[string]string{}
 		maps.Copy(folderPaths[driveID], paths)
 
-		maps.Copy(excludedItems, excluded)
-
 		logger.Ctx(ctx).Infow(
 			"persisted metadata for drive",
 			"num_paths_entries",
 			len(paths),
 			"num_deltas_entries",
 			numDeltas)
+
+		if !delta.Reset {
+			maps.Copy(excludedItems, excluded)
+			continue
+		}
+
+		// Set all folders in previous backup but not in the current
+		// one with state deleted
+		modifiedPaths := map[string]struct{}{}
+		for _, p := range c.CollectionMap {
+			modifiedPaths[p.FullPath().String()] = struct{}{}
+		}
+
+		for i, p := range oldPaths {
+			_, found := paths[i]
+			if found {
+				continue
+			}
+
+			_, found = modifiedPaths[p]
+			if found {
+				// Original folder was deleted and new folder with the
+				// same name/path was created in its place
+				continue
+			}
+
+			delete(paths, i)
+
+			prevPath, err := path.FromDataLayerPath(p, false)
+			if err != nil {
+				return nil, map[string]struct{}{},
+					clues.Wrap(err, "invalid previous path").WithClues(ctx).With("deleted_path", p)
+			}
+
+			col := NewCollection(
+				c.itemClient,
+				nil,
+				prevPath,
+				driveID,
+				c.service,
+				c.statusUpdater,
+				c.source,
+				c.ctrl,
+				true,
+			)
+			c.CollectionMap[i] = col
+		}
 	}
 
 	observe.Message(ctx, observe.Safe(fmt.Sprintf("Discovered %d items to backup", c.NumItems)))

src/internal/connector/onedrive/collections_test.go

@@ -1531,6 +1531,89 @@ func (suite *OneDriveCollectionsSuite) TestGet() {
 			expectedDelList: map[string]struct{}{"file": {}},
 			doNotMergeItems: false,
 		},
+		{
+			name:   "OneDrive_OneItemPage_InvalidPrevDelta_DeleteNonExistantFolder",
+			drives: []models.Driveable{drive1},
+			items: map[string][]deltaPagerResult{
+				driveID1: {
+					{
+						err: getDeltaError(),
+					},
+					{
+						items: []models.DriveItemable{
+							driveRootItem("root"),
+							driveItem("folder2", "folder2", driveBasePath1, "root", false, true, false),
+							driveItem("file", "file", driveBasePath1+"/folder2", "folder2", true, false, false),
+						},
+						deltaLink: &delta,
+					},
+				},
+			},
+			errCheck: assert.NoError,
+			prevFolderPaths: map[string]map[string]string{
+				driveID1: {
+					"root":   rootFolderPath1,
+					"folder": folderPath1,
+				},
+			},
+			expectedCollections: map[string]map[data.CollectionState][]string{
+				expectedPath1(""):         {data.NotMovedState: {"folder2"}},
+				expectedPath1("/folder"):  {data.DeletedState: {}},
+				expectedPath1("/folder2"): {data.NewState: {"file"}},
+			},
+			expectedDeltaURLs: map[string]string{
+				driveID1: delta,
+			},
+			expectedFolderPaths: map[string]map[string]string{
+				driveID1: {
+					"root":    rootFolderPath1,
+					"folder2": expectedPath1("/folder2"),
+				},
+			},
+			expectedDelList: map[string]struct{}{},
+			doNotMergeItems: true,
+		},
+		{
+			name:   "OneDrive_OneItemPage_InvalidPrevDelta_AnotherFolderAtDeletedLocation",
+			drives: []models.Driveable{drive1},
+			items: map[string][]deltaPagerResult{
+				driveID1: {
+					{
+						err: getDeltaError(),
+					},
+					{
+						items: []models.DriveItemable{
+							driveRootItem("root"),
+							driveItem("folder2", "folder", driveBasePath1, "root", false, true, false),
+							driveItem("file", "file", driveBasePath1+"/folder", "folder2", true, false, false),
+						},
+						deltaLink: &delta,
+					},
+				},
+			},
+			errCheck: assert.NoError,
+			prevFolderPaths: map[string]map[string]string{
+				driveID1: {
+					"root":   rootFolderPath1,
+					"folder": folderPath1,
+				},
+			},
+			expectedCollections: map[string]map[data.CollectionState][]string{
+				expectedPath1(""):        {data.NotMovedState: {"folder2"}},
+				expectedPath1("/folder"): {data.NewState: {"file"}},
+			},
+			expectedDeltaURLs: map[string]string{
+				driveID1: delta,
+			},
+			expectedFolderPaths: map[string]map[string]string{
+				driveID1: {
+					"root":    rootFolderPath1,
+					"folder2": expectedPath1("/folder"),
+				},
+			},
+			expectedDelList: map[string]struct{}{},
+			doNotMergeItems: true,
+		},
 	}
 	for _, test := range table {
 		suite.T().Run(test.name, func(t *testing.T) {
@@ -1574,6 +1657,7 @@ func (suite *OneDriveCollectionsSuite) TestGet() {
 			c.drivePagerFunc = drivePagerFunc
 			c.itemPagerFunc = itemPagerFunc
 
+			prevDelta := "prev-delta"
 			mc, err := graph.MakeMetadataCollection(
 				tenant,
 				user,
@@ -1583,8 +1667,8 @@ func (suite *OneDriveCollectionsSuite) TestGet() {
 					graph.NewMetadataEntry(
 						graph.DeltaURLsFileName,
 						map[string]string{
-							driveID1: "prev-delta",
+							driveID1: prevDelta,
-							driveID2: "prev-delta",
+							driveID2: prevDelta,
 						},
 					),
 					graph.NewMetadataEntry(
@@ -1605,7 +1689,13 @@ func (suite *OneDriveCollectionsSuite) TestGet() {
 			}
 
 			for _, baseCol := range cols {
-				folderPath := baseCol.FullPath().String()
+				var folderPath string
+				if baseCol.State() != data.DeletedState {
+					folderPath = baseCol.FullPath().String()
+				} else {
+					folderPath = baseCol.PreviousPath().String()
+				}
+
 				if folderPath == metadataPath.String() {
 					deltas, paths, err := deserializeMetadata(ctx, []data.RestoreCollection{
 						data.NotFoundRestoreCollection{Collection: baseCol},
@@ -1614,8 +1704,8 @@ func (suite *OneDriveCollectionsSuite) TestGet() {
 						continue
 					}
 
-					assert.Equal(t, test.expectedDeltaURLs, deltas)
+					assert.Equal(t, test.expectedDeltaURLs, deltas, "delta urls")
-					assert.Equal(t, test.expectedFolderPaths, paths)
+					assert.Equal(t, test.expectedFolderPaths, paths, "folder  paths")
 
 					continue
 				}

src/internal/connector/onedrive/drive.go

@@ -213,6 +213,7 @@ func collectItems(
 			logger.Ctx(ctx).Infow("Invalid previous delta link", "link", prevDelta)
 
 			invalidPrevDelta = true
+			newPaths = map[string]string{}
 
 			pager.Reset()