GC: Interface: Cache Refactor (#1043)

## Description
Code changed to support caching on the default folder of `exchange.Mail` as well as an independent node within the Inbox.
<!-- Insert PR description-->

## Type of change

- [x] 🌻 Feature

## Issue(s)

<!-- Can reference multiple issues. Use one of the following "magic words" - "closes, fixes" to auto-close the Github issue. -->
* related to Issue #1004<issue>

## Test Plan
- [x] ⚡ Unit test

src/internal/connector/exchange/mail_folder_cache.go

@@ -4,14 +4,15 @@ import (
 	"context"
 
 	multierror "github.com/hashicorp/go-multierror"
-	"github.com/microsoftgraph/msgraph-sdk-go/models"
-	msfolderdelta "github.com/microsoftgraph/msgraph-sdk-go/users/item/mailfolders/delta"
+	msfolderdelta "github.com/microsoftgraph/msgraph-sdk-go/users/item/mailfolders/item/childfolders/delta"
 	"github.com/pkg/errors"
 
 	"github.com/alcionai/corso/src/internal/connector/graph"
 	"github.com/alcionai/corso/src/pkg/path"
 )
 
+var _ cachedContainer = &mailFolder{}
+
 // cachedContainer is used for local unit tests but also makes it so that this
 // code can be broken into generic- and service-specific chunks later on to
 // reuse logic in IDToPath.
@@ -21,11 +22,16 @@ type cachedContainer interface {
 	SetPath(*path.Builder)
 }
 
+// mailFolder structure that implements the cachedContainer interface
 type mailFolder struct {
-	models.MailFolderable
-	p *path.Builder
+	folder container
+	p      *path.Builder
 }
 
+//=========================================
+// Required Functions to satisfy interfaces
+//=====================================
+
 func (mf mailFolder) Path() *path.Builder {
 	return mf.p
 }
@@ -34,15 +40,36 @@ func (mf *mailFolder) SetPath(newPath *path.Builder) {
 	mf.p = newPath
 }
 
-type mailFolderCache struct {
-	cache  map[string]cachedContainer
-	gs     graph.Service
-	userID string
+func (mf *mailFolder) GetDisplayName() *string {
+	return mf.folder.GetDisplayName()
 }
 
-// populateRoot fetches and populates the root folder in the cache so the cache
-// knows when to stop resolving the path.
-func (mc *mailFolderCache) populateRoot(ctx context.Context) error {
+//nolint:revive
+func (mf *mailFolder) GetId() *string {
+	return mf.folder.GetId()
+}
+
+//nolint:revive
+func (mf *mailFolder) GetParentFolderId() *string {
+	return mf.folder.GetParentFolderId()
+}
+
+// mailFolderCache struct used to improve lookup of directories within exchange.Mail
+// cache map of cachedContainers where the  key =  M365ID
+// nameLookup map: Key: DisplayName Value: ID
+type mailFolderCache struct {
+	cache          map[string]cachedContainer
+	gs             graph.Service
+	userID, rootID string
+}
+
+// populateMailRoot fetches and populates the "base" directory from user's inbox.
+// Action ensures that cache will stop at appropriate level.
+// @param directory: M365 ID of the root all intended inquiries.
+// Function should only be used directly when it is known that all
+// folder inquiries are going to a specific node. In all other cases
+// @error iff the struct is not properly instantiated
+func (mc *mailFolderCache) populateMailRoot(ctx context.Context, directoryID string) error {
 	wantedOpts := []string{"displayName", "parentFolderId"}
 
 	opts, err := optionsForMailFoldersItem(wantedOpts)
@@ -54,7 +81,7 @@ func (mc *mailFolderCache) populateRoot(ctx context.Context) error {
 		gs.
 		Client().
 		UsersById(mc.userID).
-		MailFoldersById(rootFolderAlias).
+		MailFoldersById(directoryID).
 		Get(ctx, opts)
 	if err != nil {
 		return errors.Wrapf(err, "fetching root folder")
@@ -62,18 +89,23 @@ func (mc *mailFolderCache) populateRoot(ctx context.Context) error {
 
 	// Root only needs the ID because we hide it's name for Mail.
 	idPtr := f.GetId()
+
 	if idPtr == nil || len(*idPtr) == 0 {
 		return errors.New("root folder has no ID")
 	}
 
-	mc.cache[*idPtr] = &mailFolder{
-		MailFolderable: f,
-		p:              &path.Builder{},
+	temp := mailFolder{
+		folder: f,
+		p:      &path.Builder{},
 	}
+	mc.cache[*idPtr] = &temp
+	mc.rootID = *idPtr
 
 	return nil
 }
 
+// checkRequiredValues is a helper function to ensure that
+// all the pointers are set prior to being called.
 func checkRequiredValues(c container) error {
 	idPtr := c.GetId()
 	if idPtr == nil || len(*idPtr) == 0 {
@@ -93,26 +125,33 @@ func checkRequiredValues(c container) error {
 	return nil
 }
 
-func (mc *mailFolderCache) Populate(ctx context.Context) error {
-	if mc.cache == nil {
-		mc.cache = map[string]cachedContainer{}
+// Populate utility function for populating the mailFolderCache.
+// Number of Graph Queries: 1.
+// @param baseID: M365ID of the base of the exchange.Mail.Folder
+// Use rootFolderAlias for input if baseID unknown
+func (mc *mailFolderCache) Populate(ctx context.Context, baseID string) error {
+	if len(baseID) == 0 {
+		return errors.New("populate function requires: M365ID as input")
 	}
 
-	if err := mc.populateRoot(ctx); err != nil {
+	err := mc.Init(ctx, baseID)
+	if err != nil {
 		return err
 	}
 
-	builder := mc.
+	query := mc.
 		gs.
 		Client().
 		UsersById(mc.userID).
-		MailFolders().
+		MailFoldersById(mc.rootID).ChildFolders().
 		Delta()
 
 	var errs *multierror.Error
 
+	// TODO: Cannot use Iterator for delta
+	// Awaiting resolution: https://github.com/microsoftgraph/msgraph-sdk-go/issues/272
 	for {
-		resp, err := builder.Get(ctx, nil)
+		resp, err := query.Get(ctx, nil)
 		if err != nil {
 			return err
 		}
@@ -123,7 +162,9 @@ func (mc *mailFolderCache) Populate(ctx context.Context) error {
 				continue
 			}
 
-			mc.cache[*f.GetId()] = &mailFolder{MailFolderable: f}
+			mc.cache[*f.GetId()] = &mailFolder{
+				folder: f,
+			}
 		}
 
 		r := resp.GetAdditionalData()
@@ -134,7 +175,7 @@ func (mc *mailFolderCache) Populate(ctx context.Context) error {
 		}
 
 		link := *(n.(*string))
-		builder = msfolderdelta.NewDeltaRequestBuilder(link, mc.gs.Adapter())
+		query = msfolderdelta.NewDeltaRequestBuilder(link, mc.gs.Adapter())
 	}
 
 	return errs.ErrorOrNil()
@@ -164,3 +205,14 @@ func (mc *mailFolderCache) IDToPath(
 
 	return fullPath, nil
 }
+
+// Init ensures that the structure's fields are initialized.
+// Fields Initialized when cache == nil:
+// [mc.cache, mc.rootID]
+func (mc *mailFolderCache) Init(ctx context.Context, baseNode string) error {
+	if mc.cache == nil {
+		mc.cache = map[string]cachedContainer{}
+	}
+
+	return mc.populateMailRoot(ctx, baseNode)
+}

src/internal/connector/exchange/mail_folder_cache_test.go

@@ -22,6 +22,8 @@ const (
 	//nolint:lll
 	testFolderID = "AAMkAGZmNjNlYjI3LWJlZWYtNGI4Mi04YjMyLTIxYThkNGQ4NmY1MwAuAAAAAADCNgjhM9QmQYWNcI7hCpPrAQDSEBNbUIB9RL6ePDeF3FIYAABl7AqpAAA="
 
+	//nolint:lll
+	topFolderID = "AAMkAGZmNjNlYjI3LWJlZWYtNGI4Mi04YjMyLTIxYThkNGQ4NmY1MwAuAAAAAADCNgjhM9QmQYWNcI7hCpPrAQDSEBNbUIB9RL6ePDeF3FIYAAAAAAEIAAA="
 	// Full folder path for the folder above.
 	expectedFolderPath = "toplevel/subFolder/subsubfolder"
 )
@@ -303,19 +305,35 @@ func TestMailFolderCacheIntegrationSuite(t *testing.T) {
 }
 
 func (suite *MailFolderCacheIntegrationSuite) TestDeltaFetch() {
-	ctx := context.Background()
-	t := suite.T()
-	userID := tester.M365UserID(t)
-
-	mfc := mailFolderCache{
-		userID: userID,
-		gs:     suite.gs,
+	tests := []struct {
+		name string
+		root string
+	}{
+		{
+			name: "Default Root",
+			root: rootFolderAlias,
+		},
+		{
+			name: "Node Root",
+			root: topFolderID,
+		},
 	}
+	ctx := context.Background()
+	userID := tester.M365UserID(suite.T())
 
-	require.NoError(t, mfc.Populate(ctx))
+	for _, test := range tests {
+		suite.T().Run(test.name, func(t *testing.T) {
+			mfc := mailFolderCache{
+				userID: userID,
+				gs:     suite.gs,
+			}
 
-	p, err := mfc.IDToPath(ctx, testFolderID)
-	require.NoError(t, err)
+			require.NoError(t, mfc.Populate(ctx, test.root))
 
-	assert.Equal(t, expectedFolderPath, p.String())
+			p, err := mfc.IDToPath(ctx, testFolderID)
+			require.NoError(t, err)
+
+			assert.Equal(t, expectedFolderPath, p.String())
+		})
+	}
 }

src/internal/connector/exchange/service_functions.go

@@ -395,7 +395,7 @@ func maybeGetAndPopulateFolderResolver(
 		return nil, nil
 	}
 
-	if err := res.Populate(ctx); err != nil {
+	if err := res.Populate(ctx, rootFolderAlias); err != nil {
 		return nil, errors.Wrap(err, "populating directory resolver")
 	}
 

src/internal/connector/graph/service.go

@@ -36,6 +36,9 @@ type ContainerResolver interface {
 	// to that container. The path has a similar format to paths on the local
 	// file system.
 	IDToPath(ctx context.Context, m365ID string) (*path.Builder, error)
-	// Populate performs any setup logic the resolver may need.
-	Populate(context.Context) error
+	// Populate performs initialization steps for the resolver
+	// @param ctx is necessary param for Graph API tracing
+	// @param baseFolderID represents the M365ID base that the resolver will
+	// conclude its search. Default input is "".
+	Populate(ctx context.Context, baseFolderID string) error
 }