Handle event exceptions in caledar (#3589)

This ensures that we backup and restore and exceptions in the recurring events. One thing pending here is fixing up the attachments. I hope to create that as a separate PR. This can probably go in separately as well. --- #### Does this PR need a docs update or release note? - [x] ✅ Yes, it's included - [ ] 🕐 Yes, but in a later PR - [ ] ⛔ No #### Type of change  - [x] 🌻 Feature - [ ] 🐛 Bugfix - [ ] 🗺️ Documentation - [ ] 🤖 Supportability/Tests - [ ] 💻 CI/Deployment - [ ] 🧹 Tech Debt/Cleanup #### Issue(s)  * https://github.com/alcionai/corso/issues/2835 #### Test Plan  - [ ] 💪 Manual - [x] ⚡ Unit test - [x] 💚 E2E
2023-06-19 17:27:32 +05:30 · 2023-06-19 17:27:32 +05:30 · 9199db8f45
commit 9199db8f45
parent 9f7a6422a0
10 changed files with 580 additions and 51 deletions
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Added ProtectedResourceName to the backup list json output.  ProtectedResourceName holds either a UPN or a WebURL, depending on the resource type.
 - Rework base selection logic for incremental backups so it's more likely to find a valid base.
 - Improve OneDrive restore performance by paralleling item restores
+- Exceptions and cancellations for recurring events are now backed up and restored

 ### Fixed
 - Fix Exchange folder cache population error when parent folder isn't found.
@ -23,6 +24,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Changed
 - Do not display all the items that we restored at the end if there are more than 15. You can override this with `--verbose`.

+### Known Issues
+- Changes to attachments in instances of recurring events compared to the series master aren't restored
+
 ## [v0.8.0] (beta) - 2023-05-15

 ### Added
--- a/src/cmd/factory/impl/exchange.go
+++ b/src/cmd/factory/impl/exchange.go
@ -114,7 +114,10 @@ func handleExchangeCalendarEventFactory(cmd *cobra.Command, args []string) error
 		func(id, now, subject, body string) []byte {
 			return exchMock.EventWith(
 				User, subject, body, body,
-				now, now, exchMock.NoRecurrence, exchMock.NoAttendees, false)
+				exchMock.NoOriginalStartDate, now, now,
+				exchMock.NoRecurrence, exchMock.NoAttendees,
+				false, exchMock.NoCancelledOccurrences,
+				exchMock.NoExceptionOccurrences)
 		},
 		control.Defaults(),
 		errs)
--- a/src/internal/m365/exchange/events_restore.go
+++ b/src/internal/m365/exchange/events_restore.go
@ -2,11 +2,16 @@ package exchange

 import (
 	"context"
+	"fmt"
+	"strings"
+	"time"

 	"github.com/alcionai/clues"
 	"github.com/microsoftgraph/msgraph-sdk-go/models"

+	"github.com/alcionai/corso/src/internal/common/dttm"
 	"github.com/alcionai/corso/src/internal/common/ptr"
+	"github.com/alcionai/corso/src/internal/common/str"
 	"github.com/alcionai/corso/src/internal/m365/graph"
 	"github.com/alcionai/corso/src/pkg/backup/details"
 	"github.com/alcionai/corso/src/pkg/fault"
@ -82,12 +87,14 @@ func (h eventRestoreHandler) restore(

 	if ptr.Val(event.GetHasAttachments()) {
 		attachments = event.GetAttachments()
-		event.SetAttachments([]models.Attachmentable{})
+		// We cannot use `[]models.Attbachmentable{}` instead of nil
+		// for beta endpoint.
+		event.SetAttachments(nil)
 	}

 	item, err := h.ip.PostItem(ctx, userID, destinationID, event)
 	if err != nil {
-		return nil, graph.Wrap(ctx, err, "restoring mail message")
+		return nil, graph.Wrap(ctx, err, "restoring calendar item")
 	}

 	err = uploadAttachments(
@ -102,8 +109,181 @@ func (h eventRestoreHandler) restore(
 		return nil, clues.Stack(err)
 	}

+	// Have to parse event again as we modified the original event and
+	// removed cancelled and exceptions events form it
+	event, err = api.BytesToEventable(body)
+	if err != nil {
+		return nil, clues.Wrap(err, "creating event from bytes").WithClues(ctx)
+	}
+
+	// Fix up event instances in case we have a recurring event
+	err = updateRecurringEvents(ctx, h.ac, userID, destinationID, ptr.Val(item.GetId()), event)
+	if err != nil {
+		return nil, clues.Stack(err)
+	}
+
 	info := api.EventInfo(event)
 	info.Size = int64(len(body))

 	return info, nil
 }
+
+func updateRecurringEvents(
+	ctx context.Context,
+	ac api.Events,
+	userID, containerID, itemID string,
+	event models.Eventable,
+) error {
+	if event.GetRecurrence() == nil {
+		return nil
+	}
+
+	// Cancellations and exceptions are currently in additional data
+	// but will get their own fields once the beta API lands and
+	// should be moved then
+	cancelledOccurrences := event.GetAdditionalData()["cancelledOccurrences"]
+	exceptionOccurrences := event.GetAdditionalData()["exceptionOccurrences"]
+
+	err := updateCancelledOccurrences(ctx, ac, userID, itemID, cancelledOccurrences)
+	if err != nil {
+		return clues.Wrap(err, "update cancelled occurrences")
+	}
+
+	err = updateExceptionOccurrences(ctx, ac, userID, itemID, exceptionOccurrences)
+	if err != nil {
+		return clues.Wrap(err, "update exception occurrences")
+	}
+
+	return nil
+}
+
+// updateExceptionOccurrences take events that have exceptions, uses
+// the originalStart date to find the instance and modify it to match
+// the backup by updating the instance to match the backed up one
+func updateExceptionOccurrences(
+	ctx context.Context,
+	ac api.Events,
+	userID string,
+	itemID string,
+	exceptionOccurrences any,
+) error {
+	if exceptionOccurrences == nil {
+		return nil
+	}
+
+	eo, ok := exceptionOccurrences.([]any)
+	if !ok {
+		return clues.New("converting exceptionOccurrences to []any").
+			With("type", fmt.Sprintf("%T", exceptionOccurrences))
+	}
+
+	for _, instance := range eo {
+		instance, ok := instance.(map[string]any)
+		if !ok {
+			return clues.New("converting instance to map[string]any").
+				With("type", fmt.Sprintf("%T", instance))
+		}
+
+		evt, err := api.EventFromMap(instance)
+		if err != nil {
+			return clues.Wrap(err, "parsing exception event")
+		}
+
+		start := ptr.Val(evt.GetOriginalStart())
+		startStr := dttm.FormatTo(start, dttm.DateOnly)
+		endStr := dttm.FormatTo(start.Add(24*time.Hour), dttm.DateOnly)
+
+		// Get all instances on the day of the instance which should
+		// just the one we need to modify
+		evts, err := ac.GetItemInstances(ctx, userID, itemID, startStr, endStr)
+		if err != nil {
+			return clues.Wrap(err, "getting instances")
+		}
+
+		// Since the min recurrence interval is 1 day and we are
+		// querying for only a single day worth of instances, we
+		// should not have more than one instance here.
+		if len(evts) != 1 {
+			return clues.New("invalid number of instances for modified").
+				With("instances_count", len(evts), "search_start", startStr, "search_end", endStr)
+		}
+
+		evt = toEventSimplified(evt)
+
+		// TODO(meain): Update attachments (might have to diff the
+		// attachments using ids and delete or add). We will have
+		// to get the id of the existing attachments, diff them
+		// with what we need a then create/delete items kinda like
+		// permissions
+		_, err = ac.PatchItem(ctx, userID, ptr.Val(evts[0].GetId()), evt)
+		if err != nil {
+			return clues.Wrap(err, "updating event instance")
+		}
+	}
+
+	return nil
+}
+
+// updateCancelledOccurrences get the cancelled occurrences which is a
+// list of strings of the format "<id>.<date>", parses the date out of
+// that and uses the to get the event instance at that date to delete.
+func updateCancelledOccurrences(
+	ctx context.Context,
+	ac api.Events,
+	userID string,
+	itemID string,
+	cancelledOccurrences any,
+) error {
+	if cancelledOccurrences == nil {
+		return nil
+	}
+
+	co, ok := cancelledOccurrences.([]any)
+	if !ok {
+		return clues.New("converting cancelledOccurrences to []any").
+			With("type", fmt.Sprintf("%T", cancelledOccurrences))
+	}
+
+	// OPTIMIZATION: We can fetch a date range instead of fetching
+	// instances if we have multiple cancelled events which are nearby
+	// and reduce the number of API calls that we have to make
+	for _, instance := range co {
+		instance, err := str.AnyToString(instance)
+		if err != nil {
+			return err
+		}
+
+		splits := strings.Split(instance, ".")
+
+		startStr := splits[len(splits)-1]
+
+		start, err := dttm.ParseTime(startStr)
+		if err != nil {
+			return clues.Wrap(err, "parsing cancelled event date")
+		}
+
+		endStr := dttm.FormatTo(start.Add(24*time.Hour), dttm.DateOnly)
+
+		// Get all instances on the day of the instance which should
+		// just the one we need to modify
+		evts, err := ac.GetItemInstances(ctx, userID, itemID, startStr, endStr)
+		if err != nil {
+			return clues.Wrap(err, "getting instances")
+		}
+
+		// Since the min recurrence interval is 1 day and we are
+		// querying for only a single day worth of instances, we
+		// should not have more than one instance here.
+		if len(evts) != 1 {
+			return clues.New("invalid number of instances for cancelled").
+				With("instances_count", len(evts), "search_start", startStr, "search_end", endStr)
+		}
+
+		err = ac.DeleteItem(ctx, userID, ptr.Val(evts[0].GetId()))
+		if err != nil {
+			return clues.Wrap(err, "deleting event instance")
+		}
+	}
+
+	return nil
+}
--- a/src/internal/m365/exchange/mock/event.go
+++ b/src/internal/m365/exchange/mock/event.go
@ -25,11 +25,6 @@ import (
 //nolint:lll
 const (
 	eventTmpl = `{
-	"id":"AAMkAGZmNjNlYjI3LWJlZWYtNGI4Mi04YjMyLTIxYThkNGQ4NmY1MwBGAAAAAADCNgjhM9QmQYWNcI7hCpPrBwDSEBNbUIB9RL6ePDeF3FIYAAAAAAENAADSEBNbUIB9RL6ePDeF3FIYAAAAAG76AAA=",
-	"calendar@odata.navigationLink":"https://graph.microsoft.com/v1.0/users('foobar@8qzvrj.onmicrosoft.com')/calendars('AAMkAGZmNjNlYjI3LWJlZWYtNGI4Mi04YjMyLTIxYThkNGQ4NmY1MwAuAAAAAADCNgjhM9QmQYWNcI7hCpPrAQDSEBNbUIB9RL6ePDeF3FIYAAAAAAENAAA=')",
-	"calendar@odata.associationLink":"https://graph.microsoft.com/v1.0/users('foobar@8qzvrj.onmicrosoft.com')/calendars('AAMkAGZmNjNlYjI3LWJlZWYtNGI4Mi04YjMyLTIxYThkNGQ4NmY1MwAuAAAAAADCNgjhM9QmQYWNcI7hCpPrAQDSEBNbUIB9RL6ePDeF3FIYAAAAAAENAAA=')/$ref",
-	"@odata.etag":"W/\"0hATW1CAfUS+njw3hdxSGAAAJIxNug==\"",
-	"@odata.context":"https://graph.microsoft.com/v1.0/$metadata#users('foobar%%408qzvrj.onmicrosoft.com')/events/$entity",
 	"categories":[],
 	"changeKey":"0hATW1CAfUS+njw3hdxSGAAAJIxNug==",
 	"createdDateTime":"2022-03-28T03:42:03Z",
@ -46,7 +41,6 @@ const (
 		"timeZone":"UTC"
 	},
 	"hideAttendees":false,
-	"iCalUId":"040000008200E00074C5B7101A82E0080000000035723BC75542D801000000000000000010000000E1E7C8F785242E4894DA13AEFB947B85",
 	"importance":"normal",
 	"isAllDay":false,
 	"isCancelled":false,
@ -75,6 +69,7 @@ const (
 			"name":"Anu Pierson"
 		}
 	},
+	%s
 	"originalEndTimeZone":"UTC",
 	"originalStartTimeZone":"UTC",
 	"reminderMinutesBeforeStart":15,
@ -90,11 +85,13 @@ const (
 		"timeZone":"UTC"
 	},
 	"subject":"%s",
-	"type":"singleInstance",
+	"type":"%s",
 	"hasAttachments":%v,
 	%s
 	"webLink":"https://outlook.office365.com/owa/?itemid=AAMkAGZmNjNlYjI3LWJlZWYtNGI4Mi04YjMyLTIxYThkNGQ4NmY1MwBGAAAAAADCNgjhM9QmQYWNcI7hCpPrBwDSEBNbUIB9RL6ePDeF3FIYAAAAAAENAADSEBNbUIB9RL6ePDeF3FIYAAAAAG76AAA%%3D&exvsurl=1&path=/calendar/item",
 	"recurrence":%s,
+	%s
+	%s
 	"attendees":%s
 }`

@ -151,13 +148,16 @@ const (
 		"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" +
 		"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=\"}],"

+	originalStartDateFormat = `"originalStart": "%s",`
+	NoOriginalStartDate     = ``
+
 	NoRecurrence   = `null`
 	recurrenceTmpl = `{
 		"pattern": {
 			"type": "absoluteYearly",
 			"interval": 1,
-			"month": 1,
-			"dayOfMonth": 1,
+			"month": %s,
+			"dayOfMonth": %s,
 			"firstDayOfWeek": "sunday",
 			"index": "first"
 		},
@ -170,6 +170,13 @@ const (
 		}
 	}`

+	cancelledOccurrencesFormat        = `"cancelledOccurrences": [%s],`
+	cancelledOccurrenceInstanceFormat = `"OID.AAMkAGJiZmE2NGU4LTQ4YjktNDI1Mi1iMWQzLTQ1MmMxODJkZmQyNABGAAAAAABFdiK7oifWRb4ADuqgSRcnBwBBFDg0JJk7TY1fmsJrh7tNAAAAAAENAABBFDg0JJk7TY1fmsJrh7tNAADHGTZoAAA=.%s"`
+	NoCancelledOccurrences            = ""
+
+	exceptionOccurrencesFormat = `"exceptionOccurrences": [%s],`
+	NoExceptionOccurrences     = ""
+
 	NoAttendees   = `[]`
 	attendeesTmpl = `[{
 		"emailAddress": {
@ -227,7 +234,8 @@ func EventWithSubjectBytes(subject string) []byte {
 	return EventWith(
 		defaultEventOrganizer, subject,
 		defaultEventBody, defaultEventBodyPreview,
-		atTime, endTime, NoRecurrence, NoAttendees, false,
+		NoOriginalStartDate, atTime, endTime, NoRecurrence, NoAttendees,
+		false, NoCancelledOccurrences, NoExceptionOccurrences,
 	)
 }

@ -239,7 +247,8 @@ func EventWithAttachment(subject string) []byte {
 	return EventWith(
 		defaultEventOrganizer, subject,
 		defaultEventBody, defaultEventBodyPreview,
-		atTime, atTime, NoRecurrence, NoAttendees, true,
+		NoOriginalStartDate, atTime, atTime, NoRecurrence, NoAttendees,
+		true, NoCancelledOccurrences, NoExceptionOccurrences,
 	)
 }

@ -251,6 +260,8 @@ func EventWithRecurrenceBytes(subject, recurrenceTimeZone string) []byte {

 	recurrence := string(fmt.Sprintf(
 		recurrenceTmpl,
+		strconv.Itoa(int(at.Month())),
+		strconv.Itoa(at.Day()),
 		timeSlice[0],
 		recurrenceTimeZone,
 	))
@ -258,7 +269,70 @@ func EventWithRecurrenceBytes(subject, recurrenceTimeZone string) []byte {
 	return EventWith(
 		defaultEventOrganizer, subject,
 		defaultEventBody, defaultEventBodyPreview,
-		atTime, atTime, recurrence, attendeesTmpl, true,
+		NoOriginalStartDate, atTime, atTime, recurrence, attendeesTmpl,
+		true, NoCancelledOccurrences, NoExceptionOccurrences,
+	)
+}
+
+func EventWithRecurrenceAndCancellationBytes(subject string) []byte {
+	tomorrow := time.Now().UTC().AddDate(0, 0, 1)
+	at := time.Date(tomorrow.Year(), tomorrow.Month(), tomorrow.Day(), tomorrow.Hour(), 0, 0, 0, time.UTC)
+	atTime := dttm.Format(at)
+	timeSlice := strings.Split(atTime, "T")
+	nextYear := tomorrow.AddDate(1, 0, 0)
+
+	recurrence := string(fmt.Sprintf(
+		recurrenceTmpl,
+		strconv.Itoa(int(at.Month())),
+		strconv.Itoa(at.Day()),
+		timeSlice[0],
+		`"UTC"`,
+	))
+
+	cancelledInstances := []string{fmt.Sprintf(cancelledOccurrenceInstanceFormat, dttm.FormatTo(nextYear, dttm.DateOnly))}
+	cancelledOccurrences := fmt.Sprintf(cancelledOccurrencesFormat, strings.Join(cancelledInstances, ","))
+
+	return EventWith(
+		defaultEventOrganizer, subject,
+		defaultEventBody, defaultEventBodyPreview,
+		NoOriginalStartDate, atTime, atTime, recurrence, attendeesTmpl,
+		true, cancelledOccurrences, NoExceptionOccurrences,
+	)
+}
+
+func EventWithRecurrenceAndExceptionBytes(subject string) []byte {
+	tomorrow := time.Now().UTC().AddDate(0, 0, 1)
+	at := time.Date(tomorrow.Year(), tomorrow.Month(), tomorrow.Day(), tomorrow.Hour(), 0, 0, 0, time.UTC)
+	atTime := dttm.Format(at)
+	timeSlice := strings.Split(atTime, "T")
+	newTime := dttm.Format(tomorrow.AddDate(0, 0, 1))
+	originalStartDate := dttm.FormatTo(at, dttm.TabularOutput)
+
+	recurrence := string(fmt.Sprintf(
+		recurrenceTmpl,
+		strconv.Itoa(int(at.Month())),
+		strconv.Itoa(at.Day()),
+		timeSlice[0],
+		`"UTC"`,
+	))
+
+	exceptionEvent := EventWith(
+		defaultEventOrganizer, subject+"(modified)",
+		defaultEventBody, defaultEventBodyPreview,
+		fmt.Sprintf(originalStartDateFormat, originalStartDate),
+		newTime, newTime, NoRecurrence, attendeesTmpl,
+		false, NoCancelledOccurrences, NoExceptionOccurrences,
+	)
+	exceptionOccurrences := fmt.Sprintf(
+		exceptionOccurrencesFormat,
+		strings.Join([]string{string(exceptionEvent)}, ","),
+	)
+
+	return EventWith(
+		defaultEventOrganizer, subject,
+		defaultEventBody, defaultEventBodyPreview,
+		NoOriginalStartDate, atTime, atTime, recurrence, attendeesTmpl,
+		true, NoCancelledOccurrences, exceptionOccurrences,
 	)
 }

@ -270,7 +344,8 @@ func EventWithAttendeesBytes(subject string) []byte {
 	return EventWith(
 		defaultEventOrganizer, subject,
 		defaultEventBody, defaultEventBodyPreview,
-		atTime, atTime, NoRecurrence, attendeesTmpl, true,
+		NoOriginalStartDate, atTime, atTime, NoRecurrence, attendeesTmpl,
+		true, NoCancelledOccurrences, NoExceptionOccurrences,
 	)
 }

@ -281,8 +356,8 @@ func EventWithAttendeesBytes(subject string) []byte {
 // Body must contain a well-formatted string, consumable in a json payload.  IE: no unescaped newlines.
 func EventWith(
 	organizer, subject, body, bodyPreview,
-	startDateTime, endDateTime, recurrence, attendees string,
-	hasAttachments bool,
+	originalStartDate, startDateTime, endDateTime, recurrence, attendees string,
+	hasAttachments bool, cancelledOccurrences, exceptionOccurrences string,
 ) []byte {
 	var attachments string
 	if hasAttachments {
@ -300,17 +375,26 @@ func EventWith(
 		endDateTime += ".0000000"
 	}

+	eventType := "singleInstance"
+	if recurrence != "null" {
+		eventType = "seriesMaster"
+	}
+
 	return []byte(fmt.Sprintf(
 		eventTmpl,
 		body,
 		bodyPreview,
 		endDateTime,
 		organizer,
+		originalStartDate,
 		startDateTime,
 		subject,
+		eventType,
 		hasAttachments,
 		attachments,
 		recurrence,
+		cancelledOccurrences,
+		exceptionOccurrences,
 		attendees,
 	))
 }
--- a/src/internal/m365/exchange/restore_test.go
+++ b/src/internal/m365/exchange/restore_test.go
@ -116,6 +116,14 @@ func (suite *RestoreIntgSuite) TestRestoreEvent() {
 			name:  "Test recurrenceTimeZone: Empty",
 			bytes: exchMock.EventWithRecurrenceBytes(subject, `""`),
 		},
+		{
+			name:  "Test cancelledOccurrences",
+			bytes: exchMock.EventWithRecurrenceAndCancellationBytes(subject),
+		},
+		{
+			name:  "Test exceptionOccurrences",
+			bytes: exchMock.EventWithRecurrenceAndExceptionBytes(subject),
+		},
 	}

 	for _, test := range tests {
--- a/src/internal/m365/exchange/transform.go
+++ b/src/internal/m365/exchange/transform.go
@ -70,7 +70,6 @@ func toEventSimplified(orig models.Eventable) models.Eventable {
 	newContent := insertStringToBody(origBody, attendees)
 	newBody := models.NewItemBody()
 	newBody.SetContentType(origBody.GetContentType())
-	newBody.SetAdditionalData(origBody.GetAdditionalData())
 	newBody.SetOdataType(origBody.GetOdataType())
 	newBody.SetContent(&newContent)
 	orig.SetBody(newBody)
@ -89,6 +88,14 @@ func toEventSimplified(orig models.Eventable) models.Eventable {
 		}
 	}

+	// Remove exceptions for recurring events
+	// These will be present in objects once we start using the API
+	// that is currently in beta
+	additionalData := orig.GetAdditionalData()
+	delete(additionalData, "cancelledOccurrences")
+	delete(additionalData, "exceptionOccurrences")
+	orig.SetAdditionalData(additionalData)
+
 	return orig
 }

--- a/src/internal/m365/exchange/transform_test.go
+++ b/src/internal/m365/exchange/transform_test.go
@ -121,6 +121,32 @@ func (suite *TransformUnitTest) TestToEventSimplified_recurrence() {
 				return ptr.Val(e.GetRecurrence().GetRange().GetRecurrenceTimeZone()) == "Pacific Standard Time"
 			},
 		},
+		{
+			name: "Test cancelledOccurrences",
+			event: func() models.Eventable {
+				bytes := exchMock.EventWithRecurrenceAndCancellationBytes(subject)
+				event, err := api.BytesToEventable(bytes)
+				require.NoError(t, err, clues.ToCore(err))
+				return event
+			},
+
+			validateOutput: func(e models.Eventable) bool {
+				return e.GetAdditionalData()["cancelledOccurrences"] == nil
+			},
+		},
+		{
+			name: "Test exceptionOccurrences",
+			event: func() models.Eventable {
+				bytes := exchMock.EventWithRecurrenceAndExceptionBytes(subject)
+				event, err := api.BytesToEventable(bytes)
+				require.NoError(t, err, clues.ToCore(err))
+				return event
+			},
+
+			validateOutput: func(e models.Eventable) bool {
+				return e.GetAdditionalData()["exceptionOccurrences"] == nil
+			},
+		},
 	}

 	for _, test := range tests {
--- a/src/internal/operations/backup_integration_test.go
+++ b/src/internal/operations/backup_integration_test.go
@ -813,7 +813,10 @@ func testExchangeContinuousBackups(suite *BackupOpIntegrationSuite, toggles cont
 	eventDBF := func(id, timeStamp, subject, body string) []byte {
 		return exchMock.EventWith(
 			suite.user, subject, body, body,
-			now, now, exchMock.NoRecurrence, exchMock.NoAttendees, false)
+			exchMock.NoOriginalStartDate, now, now,
+			exchMock.NoRecurrence, exchMock.NoAttendees,
+			false, exchMock.NoCancelledOccurrences,
+			exchMock.NoExceptionOccurrences)
 	}

 	// test data set
--- a/src/pkg/services/m365/api/events.go
+++ b/src/pkg/services/m365/api/events.go
@ -3,8 +3,10 @@ package api
 import (
 	"bytes"
 	"context"
+	"encoding/json"
 	"fmt"
 	"io"
+	"strings"
 	"time"

 	"github.com/alcionai/clues"
@ -15,6 +17,7 @@ import (

 	"github.com/alcionai/corso/src/internal/common/dttm"
 	"github.com/alcionai/corso/src/internal/common/ptr"
+	"github.com/alcionai/corso/src/internal/common/str"
 	"github.com/alcionai/corso/src/internal/m365/graph"
 	"github.com/alcionai/corso/src/pkg/backup/details"
 	"github.com/alcionai/corso/src/pkg/fault"
@ -189,6 +192,14 @@ func (c Events) PatchCalendar(
 	return nil
 }

+const (
+	// Beta version cannot have /calendars/%s for get and Patch
+	// https://stackoverflow.com/questions/50492177/microsoft-graph-get-user-calendar-event-with-beta-version
+	eventExceptionsBetaURLTemplate = "https://graph.microsoft.com/beta/users/%s/events/%s?$expand=exceptionOccurrences"
+	eventPostBetaURLTemplate       = "https://graph.microsoft.com/beta/users/%s/calendars/%s/events"
+	eventPatchBetaURLTemplate      = "https://graph.microsoft.com/beta/users/%s/events/%s"
+)
+
 // ---------------------------------------------------------------------------
 // items
 // ---------------------------------------------------------------------------
@ -208,18 +219,168 @@ func (c Events) GetItem(
 		}
 	)

-	event, err = c.Stable.
-		Client().
-		Users().
-		ByUserId(userID).
-		Events().
-		ByEventId(itemID).
-		Get(ctx, config)
+	// Beta endpoint helps us fetch the event exceptions, but since we
+	// don't use the beta SDK, the exceptionOccurrences and
+	// cancelledOccurrences end up in AdditionalData
+	// https://learn.microsoft.com/en-us/graph/api/resources/event?view=graph-rest-beta#properties
+	rawURL := fmt.Sprintf(eventExceptionsBetaURLTemplate, userID, itemID)
+	builder := users.NewItemEventsEventItemRequestBuilder(rawURL, c.Stable.Adapter())
+
+	event, err = builder.Get(ctx, config)
 	if err != nil {
 		return nil, nil, graph.Stack(ctx, err)
 	}

-	if ptr.Val(event.GetHasAttachments()) || HasAttachments(event.GetBody()) {
+	err = validateCancelledOccurrences(event)
+	if err != nil {
+		return nil, nil, clues.Wrap(err, "verify cancelled occurrences")
+	}
+
+	err = fixupExceptionOccurrences(ctx, c, event, immutableIDs, userID)
+	if err != nil {
+		return nil, nil, clues.Wrap(err, "fixup exception occurrences")
+	}
+
+	attachments, err := c.getAttachments(ctx, event, immutableIDs, userID, itemID)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	event.SetAttachments(attachments)
+
+	return event, EventInfo(event), nil
+}
+
+// fixupExceptionOccurrences gets attachments and converts the data
+// into a format that gets serialized when storing to kopia
+func fixupExceptionOccurrences(
+	ctx context.Context,
+	client Events,
+	event models.Eventable,
+	immutableIDs bool,
+	userID string,
+) error {
+	// Fetch attachments for exceptions
+	exceptionOccurrences := event.GetAdditionalData()["exceptionOccurrences"]
+	if exceptionOccurrences == nil {
+		return nil
+	}
+
+	eo, ok := exceptionOccurrences.([]any)
+	if !ok {
+		return clues.New("converting exceptionOccurrences to []any").
+			With("type", fmt.Sprintf("%T", exceptionOccurrences))
+	}
+
+	for _, instance := range eo {
+		instance, ok := instance.(map[string]any)
+		if !ok {
+			return clues.New("converting instance to map[string]any").
+				With("type", fmt.Sprintf("%T", instance))
+		}
+
+		evt, err := EventFromMap(instance)
+		if err != nil {
+			return clues.Wrap(err, "parsing exception event")
+		}
+
+		// OPTIMIZATION: We don't have to store any of the
+		// attachments that carry over from the original
+		attachments, err := client.getAttachments(ctx, evt, immutableIDs, userID, ptr.Val(evt.GetId()))
+		if err != nil {
+			return clues.Wrap(err, "getting exception attachments").
+				With("exception_event_id", ptr.Val(evt.GetId()))
+		}
+
+		// This odd roundabout way of doing this is required as
+		// the json serialization at the end does not serialize if
+		// you just pass in a models.Attachmentable
+		convertedAttachments := []map[string]interface{}{}
+
+		for _, attachment := range attachments {
+			am, err := parseableToMap(attachment)
+			if err != nil {
+				return clues.Wrap(err, "converting attachment")
+			}
+
+			convertedAttachments = append(convertedAttachments, am)
+		}
+
+		instance["attachments"] = convertedAttachments
+	}
+
+	return nil
+}
+
+// Adding checks to ensure that the data is in the format that we expect M365 to return
+func validateCancelledOccurrences(event models.Eventable) error {
+	cancelledOccurrences := event.GetAdditionalData()["cancelledOccurrences"]
+	if cancelledOccurrences != nil {
+		co, ok := cancelledOccurrences.([]any)
+		if !ok {
+			return clues.New("converting cancelledOccurrences to []any").
+				With("type", fmt.Sprintf("%T", cancelledOccurrences))
+		}
+
+		for _, instance := range co {
+			instance, err := str.AnyToString(instance)
+			if err != nil {
+				return err
+			}
+
+			// There might be multiple `.` in the ID and hence >2
+			splits := strings.Split(instance, ".")
+			if len(splits) < 2 {
+				return clues.New("unexpected cancelled event format").
+					With("instance", instance)
+			}
+
+			startStr := splits[len(splits)-1]
+
+			_, err = dttm.ParseTime(startStr)
+			if err != nil {
+				return clues.Wrap(err, "parsing cancelled event date")
+			}
+		}
+	}
+
+	return nil
+}
+
+func parseableToMap(att serialization.Parsable) (map[string]any, error) {
+	var item map[string]any
+
+	writer := kjson.NewJsonSerializationWriter()
+	defer writer.Close()
+
+	if err := writer.WriteObjectValue("", att); err != nil {
+		return nil, err
+	}
+
+	ats, err := writer.GetSerializedContent()
+	if err != nil {
+		return nil, err
+	}
+
+	err = json.Unmarshal(ats, &item)
+	if err != nil {
+		return nil, clues.Wrap(err, "unmarshalling serialized attachment")
+	}
+
+	return item, nil
+}
+
+func (c Events) getAttachments(
+	ctx context.Context,
+	event models.Eventable,
+	immutableIDs bool,
+	userID string,
+	itemID string,
+) ([]models.Attachmentable, error) {
+	if !ptr.Val(event.GetHasAttachments()) && !HasAttachments(event.GetBody()) {
+		return nil, nil
+	}
+
 	config := &users.ItemEventsItemAttachmentsRequestBuilderGetRequestConfiguration{
 		QueryParameters: &users.ItemEventsItemAttachmentsRequestBuilderGetQueryParameters{
 			Expand: []string{"microsoft.graph.itemattachment/item"},
@ -236,13 +397,38 @@ func (c Events) GetItem(
 		Attachments().
 		Get(ctx, config)
 	if err != nil {
-			return nil, nil, graph.Wrap(ctx, err, "event attachment download")
+		return nil, graph.Wrap(ctx, err, "event attachment download")
 	}

-		event.SetAttachments(attached.GetValue())
+	return attached.GetValue(), nil
+}
+
+func (c Events) GetItemInstances(
+	ctx context.Context,
+	userID, itemID string,
+	startDate, endDate string,
+) ([]models.Eventable, error) {
+	config := &users.ItemEventsItemInstancesRequestBuilderGetRequestConfiguration{
+		QueryParameters: &users.ItemEventsItemInstancesRequestBuilderGetQueryParameters{
+			Select:        []string{"id"},
+			StartDateTime: ptr.To(startDate),
+			EndDateTime:   ptr.To(endDate),
+		},
 	}

-	return event, EventInfo(event), nil
+	events, err := c.Stable.
+		Client().
+		Users().
+		ByUserId(userID).
+		Events().
+		ByEventId(itemID).
+		Instances().
+		Get(ctx, config)
+	if err != nil {
+		return nil, graph.Stack(ctx, err)
+	}
+
+	return events.GetValue(), nil
 }

 func (c Events) PostItem(
@ -250,14 +436,10 @@ func (c Events) PostItem(
 	userID, containerID string,
 	body models.Eventable,
 ) (models.Eventable, error) {
-	itm, err := c.Stable.
-		Client().
-		Users().
-		ByUserId(userID).
-		Calendars().
-		ByCalendarId(containerID).
-		Events().
-		Post(ctx, body, nil)
+	rawURL := fmt.Sprintf(eventPostBetaURLTemplate, userID, containerID)
+	builder := users.NewItemCalendarsItemEventsRequestBuilder(rawURL, c.Stable.Adapter())
+
+	itm, err := builder.Post(ctx, body, nil)
 	if err != nil {
 		return nil, graph.Wrap(ctx, err, "creating calendar event")
 	}
@ -265,6 +447,22 @@ func (c Events) PostItem(
 	return itm, nil
 }

+func (c Events) PatchItem(
+	ctx context.Context,
+	userID, eventID string,
+	body models.Eventable,
+) (models.Eventable, error) {
+	rawURL := fmt.Sprintf(eventPatchBetaURLTemplate, userID, eventID)
+	builder := users.NewItemCalendarsItemEventsEventItemRequestBuilder(rawURL, c.Stable.Adapter())
+
+	itm, err := builder.Patch(ctx, body, nil)
+	if err != nil {
+		return nil, graph.Wrap(ctx, err, "updating calendar event")
+	}
+
+	return itm, nil
+}
+
 func (c Events) DeleteItem(
 	ctx context.Context,
 	userID, itemID string,
@ -472,3 +670,17 @@ func EventInfo(evt models.Eventable) *details.ExchangeInfo {
 		Modified:    ptr.OrNow(evt.GetLastModifiedDateTime()),
 	}
 }
+
+func EventFromMap(ev map[string]any) (models.Eventable, error) {
+	instBytes, err := json.Marshal(ev)
+	if err != nil {
+		return nil, clues.Wrap(err, "marshaling event exception instance")
+	}
+
+	body, err := BytesToEventable(instBytes)
+	if err != nil {
+		return nil, clues.Wrap(err, "converting exception event bytes to Eventable")
+	}
+
+	return body, nil
+}
--- a/website/docs/support/known-issues.md
+++ b/website/docs/support/known-issues.md
@ -26,3 +26,5 @@ included in backup and restore.
 * SharePoint document library data can't be restored after the library has been deleted.

 * Sharing information of items in OneDrive/SharePoint using sharing links aren't backed up and restored.
+
+* Changes to attachments in instances of recurring events compared to the series master aren't restored