Store previous post ID in details

src/internal/m365/collection/groups/conversation_handler.go

@@ -124,13 +124,17 @@ func (bh conversationsBackupHandler) getItem(
 	containerIDs path.Elements, // expects: [conversationID, threadID]
 	postID string,
 ) (models.Postable, *details.GroupsInfo, error) {
+	cc := api.CallConfig{
+		Expand: []string{"inReplyTo"},
+	}
+
 	return bh.ac.GetConversationPost(
 		ctx,
 		groupID,
 		containerIDs[0],
 		containerIDs[1],
 		postID,
-		api.CallConfig{})
+		cc)
 }
 
 //lint:ignore U1000 false linter issue due to generics

src/pkg/backup/details/groups.go

@@ -65,6 +65,7 @@ type ConversationPostInfo struct {
 	Creator    string    `json:"creator,omitempty"`
 	Preview    string    `json:"preview,omitempty"`
 	Recipients []string  `json:"recipients,omitempty"`
+	InReplyTo  string    `json:"inReplyTo,omitempty"`
 	Size       int64     `json:"size,omitempty"`
 	Topic      string    `json:"topic,omitempty"`
 }

src/pkg/services/m365/api/conversations.go

@@ -69,8 +69,25 @@ func (c Conversations) GetConversationPost(
 		preview = "malformed or unparseable content body: " + preview
 	}
 
+	var inReplyToID string
+
+	prevPost := post.GetInReplyTo()
+	if prevPost != nil {
+		inReplyToID = ptr.Val(prevPost.GetId())
+	}
+
+	// Set prev post to nil to avoid storing it again in the backup. Storage is unnecessary
+	// since this is a read only property and graph doesn't support POSTing it. This is
+	// also safe to do since we do a full enumeration every time, so post and all its
+	// ancestors are guaranteed to exist.
+	//
+	// All we need to persist here is the prev post ID here so that we can build the
+	// reply tree during restore operation and restore posts top to bottom using
+	// POST /groups/{id}/conversations/{id}/threads/{id}/posts/{id}/reply
+	post.SetInReplyTo(nil)
+
 	if !ptr.Val(post.GetHasAttachments()) && !HasAttachments(post.GetBody()) {
-		return post, conversationPostInfo(post, contentLen, preview), nil
+		return post, conversationPostInfo(post, contentLen, preview, inReplyToID), nil
 	}
 
 	attachments, totalSize, err := c.getAttachments(
@@ -95,7 +112,9 @@ func (c Conversations) GetConversationPost(
 
 	post.SetAttachments(attachments)
 
-	return post, conversationPostInfo(post, contentLen, preview), graph.Stack(ctx, err).OrNil()
+	return post,
+		conversationPostInfo(post, contentLen, preview, inReplyToID),
+		graph.Stack(ctx, err).OrNil()
 }
 
 // ---------------------------------------------------------------------------
@@ -105,7 +124,7 @@ func (c Conversations) GetConversationPost(
 func conversationPostInfo(
 	post models.Postable,
 	size int64,
-	preview string,
+	preview, prevPostID string,
 ) *details.GroupsInfo {
 	if post == nil {
 		return nil
@@ -120,6 +139,7 @@ func conversationPostInfo(
 		CreatedAt: ptr.Val(post.GetCreatedDateTime()),
 		Creator:   sender,
 		Preview:   preview,
+		InReplyTo: prevPostID,
 		Size:      size,
 	}
 

src/pkg/services/m365/api/conversations_test.go

@@ -109,7 +109,7 @@ func (suite *ConversationsAPIUnitSuite) TestConversationPostInfo() {
 			t := suite.T()
 
 			post, expected := test.postAndInfo()
-			result := conversationPostInfo(post, 0, "")
+			result := conversationPostInfo(post, 0, "", "")
 
 			assert.Equal(t, expected, result)
 		})