Create helper functions/interfaces to retrieve next and delta links (#2308)

## Description

Create a shared set of helper functions and interfaces for getting next and delta links from Graph API responses. This helps standardize how they are handled with respect to nil/empty values and makes comparisons easier in other code

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

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

## Type of change

- [ ] 🌻 Feature
- [ ] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Test
- [ ] 💻 CI/Deployment
- [x] 🧹 Tech Debt/Cleanup

## Issue(s)

* #2264 

## Test Plan

- [ ] 💪 Manual
- [x] ⚡ Unit test
- [x] 💚 E2E

src/internal/connector/exchange/api/contacts.go

@@ -13,6 +13,7 @@ import (
 	"github.com/pkg/errors"
 
 	"github.com/alcionai/corso/src/internal/connector/graph"
+	"github.com/alcionai/corso/src/internal/connector/graph/api"
 	"github.com/alcionai/corso/src/internal/connector/support"
 	"github.com/alcionai/corso/src/pkg/backup/details"
 )
@@ -173,7 +174,7 @@ type contactPager struct {
 	options *users.ItemContactFoldersItemContactsDeltaRequestBuilderGetRequestConfiguration
 }
 
-func (p *contactPager) getPage(ctx context.Context) (pageLinker, error) {
+func (p *contactPager) getPage(ctx context.Context) (api.DeltaPageLinker, error) {
 	return p.builder.Get(ctx, p.options)
 }
 
@@ -181,7 +182,7 @@ func (p *contactPager) setNext(nextLink string) {
 	p.builder = users.NewItemContactFoldersItemContactsDeltaRequestBuilder(nextLink, p.gs.Adapter())
 }
 
-func (p *contactPager) valuesIn(pl pageLinker) ([]getIDAndAddtler, error) {
+func (p *contactPager) valuesIn(pl api.DeltaPageLinker) ([]getIDAndAddtler, error) {
 	return toValues[models.Contactable](pl)
 }
 

src/internal/connector/exchange/api/events.go

@@ -14,6 +14,7 @@ import (
 
 	"github.com/alcionai/corso/src/internal/common"
 	"github.com/alcionai/corso/src/internal/connector/graph"
+	"github.com/alcionai/corso/src/internal/connector/graph/api"
 	"github.com/alcionai/corso/src/internal/connector/support"
 	"github.com/alcionai/corso/src/pkg/backup/details"
 	"github.com/alcionai/corso/src/pkg/logger"
@@ -203,7 +204,7 @@ type eventPager struct {
 	options *users.ItemCalendarsItemEventsDeltaRequestBuilderGetRequestConfiguration
 }
 
-func (p *eventPager) getPage(ctx context.Context) (pageLinker, error) {
+func (p *eventPager) getPage(ctx context.Context) (api.DeltaPageLinker, error) {
 	resp, err := p.builder.Get(ctx, p.options)
 	return resp, err
 }
@@ -212,7 +213,7 @@ func (p *eventPager) setNext(nextLink string) {
 	p.builder = users.NewItemCalendarsItemEventsDeltaRequestBuilder(nextLink, p.gs.Adapter())
 }
 
-func (p *eventPager) valuesIn(pl pageLinker) ([]getIDAndAddtler, error) {
+func (p *eventPager) valuesIn(pl api.DeltaPageLinker) ([]getIDAndAddtler, error) {
 	return toValues[models.Eventable](pl)
 }
 

src/internal/connector/exchange/api/mail.go

@@ -13,6 +13,7 @@ import (
 	"github.com/pkg/errors"
 
 	"github.com/alcionai/corso/src/internal/connector/graph"
+	"github.com/alcionai/corso/src/internal/connector/graph/api"
 	"github.com/alcionai/corso/src/internal/connector/support"
 	"github.com/alcionai/corso/src/pkg/backup/details"
 	"github.com/alcionai/corso/src/pkg/logger"
@@ -198,7 +199,7 @@ type mailPager struct {
 	options *users.ItemMailFoldersItemMessagesDeltaRequestBuilderGetRequestConfiguration
 }
 
-func (p *mailPager) getPage(ctx context.Context) (pageLinker, error) {
+func (p *mailPager) getPage(ctx context.Context) (api.DeltaPageLinker, error) {
 	return p.builder.Get(ctx, p.options)
 }
 
@@ -206,7 +207,7 @@ func (p *mailPager) setNext(nextLink string) {
 	p.builder = users.NewItemMailFoldersItemMessagesDeltaRequestBuilder(nextLink, p.gs.Adapter())
 }
 
-func (p *mailPager) valuesIn(pl pageLinker) ([]getIDAndAddtler, error) {
+func (p *mailPager) valuesIn(pl api.DeltaPageLinker) ([]getIDAndAddtler, error) {
 	return toValues[models.Messageable](pl)
 }
 

src/internal/connector/exchange/api/shared.go

@@ -6,6 +6,7 @@ import (
 	"github.com/pkg/errors"
 
 	"github.com/alcionai/corso/src/internal/connector/graph"
+	"github.com/alcionai/corso/src/internal/connector/graph/api"
 	"github.com/alcionai/corso/src/internal/connector/support"
 )
 
@@ -14,14 +15,9 @@ import (
 // ---------------------------------------------------------------------------
 
 type itemPager interface {
-	getPage(context.Context) (pageLinker, error)
+	getPage(context.Context) (api.DeltaPageLinker, error)
 	setNext(string)
-	valuesIn(pageLinker) ([]getIDAndAddtler, error)
+	valuesIn(api.DeltaPageLinker) ([]getIDAndAddtler, error)
-}
-
-type pageLinker interface {
-	GetOdataDeltaLink() *string
-	GetOdataNextLink() *string
 }
 
 type getIDAndAddtler interface {
@@ -98,24 +94,24 @@ func getItemsAddedAndRemovedFromContainer(
 			}
 		}
 
+		nextLink, delta := api.NextAndDeltaLink(resp)
+
 		// the deltaLink is kind of like a cursor for overall data state.
 		// once we run through pages of nextLinks, the last query will
 		// produce a deltaLink instead (if supported), which we'll use on
 		// the next backup to only get the changes since this run.
-		delta := resp.GetOdataDeltaLink()
+		if len(delta) > 0 {
-		if delta != nil && len(*delta) > 0 {
+			deltaURL = delta
-			deltaURL = *delta
 		}
 
 		// the nextLink is our page cursor within this query.
 		// if we have more data to retrieve, we'll have a
 		// nextLink instead of a deltaLink.
-		nextLink := resp.GetOdataNextLink()
+		if len(nextLink) == 0 {
-		if nextLink == nil || len(*nextLink) == 0 {
 			break
 		}
 
-		pager.setNext(*nextLink)
+		pager.setNext(nextLink)
 	}
 
 	return addedIDs, removedIDs, deltaURL, nil

src/internal/connector/graph/api/api.go

@@ -0,0 +1,30 @@
+package api
+
+type PageLinker interface {
+	GetOdataNextLink() *string
+}
+
+type DeltaPageLinker interface {
+	PageLinker
+	GetOdataDeltaLink() *string
+}
+
+func NextLink(pl PageLinker) string {
+	next := pl.GetOdataNextLink()
+	if next == nil || len(*next) == 0 {
+		return ""
+	}
+
+	return *next
+}
+
+func NextAndDeltaLink(pl DeltaPageLinker) (string, string) {
+	next := NextLink(pl)
+
+	delta := pl.GetOdataDeltaLink()
+	if delta == nil || len(*delta) == 0 {
+		return next, ""
+	}
+
+	return next, *delta
+}

src/internal/connector/graph/api/api_test.go

@@ -0,0 +1,114 @@
+package api_test
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/suite"
+
+	"github.com/alcionai/corso/src/internal/connector/graph/api"
+)
+
+type mockNextLink struct {
+	nextLink *string
+}
+
+func (l mockNextLink) GetOdataNextLink() *string {
+	return l.nextLink
+}
+
+type mockDeltaNextLink struct {
+	mockNextLink
+	deltaLink *string
+}
+
+func (l mockDeltaNextLink) GetOdataDeltaLink() *string {
+	return l.deltaLink
+}
+
+type testInput struct {
+	name         string
+	inputLink    *string
+	expectedLink string
+}
+
+// Needs to be var not const so we can take the address of it.
+var (
+	emptyLink = ""
+	link      = "foo"
+	link2     = "bar"
+
+	nextLinkInputs = []testInput{
+		{
+			name:         "empty",
+			inputLink:    &emptyLink,
+			expectedLink: "",
+		},
+		{
+			name:         "nil",
+			inputLink:    nil,
+			expectedLink: "",
+		},
+		{
+			name:         "non_empty",
+			inputLink:    &link,
+			expectedLink: link,
+		},
+	}
+)
+
+type APIUnitSuite struct {
+	suite.Suite
+}
+
+func TestAPIUnitSuite(t *testing.T) {
+	suite.Run(t, new(APIUnitSuite))
+}
+
+func (suite *APIUnitSuite) TestNextLink() {
+	for _, test := range nextLinkInputs {
+		suite.T().Run(test.name, func(t *testing.T) {
+			l := mockNextLink{nextLink: test.inputLink}
+			assert.Equal(t, test.expectedLink, api.NextLink(l))
+		})
+	}
+}
+
+func (suite *APIUnitSuite) TestNextAndDeltaLink() {
+	deltaTable := []testInput{
+		{
+			name:         "empty",
+			inputLink:    &emptyLink,
+			expectedLink: "",
+		},
+		{
+			name:         "nil",
+			inputLink:    nil,
+			expectedLink: "",
+		},
+		{
+			name: "non_empty",
+			// Use a different link so we can see if the results get swapped or something.
+			inputLink:    &link2,
+			expectedLink: link2,
+		},
+	}
+
+	for _, next := range nextLinkInputs {
+		for _, delta := range deltaTable {
+			name := strings.Join([]string{next.name, "next", delta.name, "delta"}, "_")
+
+			suite.T().Run(name, func(t *testing.T) {
+				l := mockDeltaNextLink{
+					mockNextLink: mockNextLink{nextLink: next.inputLink},
+					deltaLink:    delta.inputLink,
+				}
+				gotNext, gotDelta := api.NextAndDeltaLink(l)
+
+				assert.Equal(t, next.expectedLink, gotNext)
+				assert.Equal(t, delta.expectedLink, gotDelta)
+			})
+		}
+	}
+}

src/internal/connector/onedrive/api/drive.go

@@ -9,12 +9,9 @@ import (
 	"github.com/pkg/errors"
 
 	"github.com/alcionai/corso/src/internal/connector/graph"
+	"github.com/alcionai/corso/src/internal/connector/graph/api"
 )
 
-type PageLinker interface {
-	GetOdataNextLink() *string
-}
-
 type userDrivePager struct {
 	gs      graph.Servicer
 	builder *msusers.ItemDrivesRequestBuilder
@@ -41,7 +38,7 @@ func NewUserDrivePager(
 	return res
 }
 
-func (p *userDrivePager) GetPage(ctx context.Context) (PageLinker, error) {
+func (p *userDrivePager) GetPage(ctx context.Context) (api.PageLinker, error) {
 	return p.builder.Get(ctx, p.options)
 }
 
@@ -49,7 +46,7 @@ func (p *userDrivePager) SetNext(link string) {
 	p.builder = msusers.NewItemDrivesRequestBuilder(link, p.gs.Adapter())
 }
 
-func (p *userDrivePager) ValuesIn(l PageLinker) ([]models.Driveable, error) {
+func (p *userDrivePager) ValuesIn(l api.PageLinker) ([]models.Driveable, error) {
 	page, ok := l.(interface{ GetValue() []models.Driveable })
 	if !ok {
 		return nil, errors.Errorf(
@@ -87,7 +84,7 @@ func NewSiteDrivePager(
 	return res
 }
 
-func (p *siteDrivePager) GetPage(ctx context.Context) (PageLinker, error) {
+func (p *siteDrivePager) GetPage(ctx context.Context) (api.PageLinker, error) {
 	return p.builder.Get(ctx, p.options)
 }
 
@@ -95,7 +92,7 @@ func (p *siteDrivePager) SetNext(link string) {
 	p.builder = mssites.NewItemDrivesRequestBuilder(link, p.gs.Adapter())
 }
 
-func (p *siteDrivePager) ValuesIn(l PageLinker) ([]models.Driveable, error) {
+func (p *siteDrivePager) ValuesIn(l api.PageLinker) ([]models.Driveable, error) {
 	page, ok := l.(interface{ GetValue() []models.Driveable })
 	if !ok {
 		return nil, errors.Errorf(

src/internal/connector/onedrive/drive.go

@@ -14,6 +14,7 @@ import (
 	"golang.org/x/exp/maps"
 
 	"github.com/alcionai/corso/src/internal/connector/graph"
+	gapi "github.com/alcionai/corso/src/internal/connector/graph/api"
 	"github.com/alcionai/corso/src/internal/connector/onedrive/api"
 	"github.com/alcionai/corso/src/internal/connector/support"
 	"github.com/alcionai/corso/src/pkg/logger"
@@ -36,9 +37,9 @@ const (
 )
 
 type drivePager interface {
-	GetPage(context.Context) (api.PageLinker, error)
+	GetPage(context.Context) (gapi.PageLinker, error)
 	SetNext(nextLink string)
-	ValuesIn(api.PageLinker) ([]models.Driveable, error)
+	ValuesIn(gapi.PageLinker) ([]models.Driveable, error)
 }
 
 func PagerForSource(
@@ -64,7 +65,7 @@ func drives(
 ) ([]models.Driveable, error) {
 	var (
 		err             error
-		page            api.PageLinker
+		page            gapi.PageLinker
 		numberOfRetries = getDrivesRetries
 		drives          = []models.Driveable{}
 	)
@@ -111,12 +112,12 @@ func drives(
 
 		drives = append(drives, tmp...)
 
-		nextLink := page.GetOdataNextLink()
+		nextLink := gapi.NextLink(page)
-		if nextLink == nil || len(*nextLink) == 0 {
+		if len(nextLink) == 0 {
 			break
 		}
 
-		pager.SetNext(*nextLink)
+		pager.SetNext(nextLink)
 	}
 
 	logger.Ctx(ctx).Debugf("Found %d drives", len(drives))

src/internal/connector/onedrive/drive_test.go

@@ -14,7 +14,7 @@ import (
 
 	"github.com/alcionai/corso/src/internal/common"
 	"github.com/alcionai/corso/src/internal/connector/graph"
-	"github.com/alcionai/corso/src/internal/connector/onedrive/api"
+	"github.com/alcionai/corso/src/internal/connector/graph/api"
 	"github.com/alcionai/corso/src/internal/tester"
 	"github.com/alcionai/corso/src/pkg/control"
 	"github.com/alcionai/corso/src/pkg/logger"