[MM-59367] export: enable exporting thread followers for CRT (#27623)

server/channels/store/store.go

@@ -321,6 +321,7 @@ type ChannelMemberHistoryStore interface {
 }
 type ThreadStore interface {
 	GetThreadFollowers(threadID string, fetchOnlyActive bool) ([]string, error)
+	GetThreadMembershipsForExport(postID string) ([]*model.ThreadMembershipForExport, error)
 
 	Get(id string) (*model.Thread, error)
 	GetTotalUnreadThreads(userId, teamID string, opts model.GetUserThreadsOpts) (int64, error)
@@ -346,6 +347,9 @@ type ThreadStore interface {
 	DeleteOrphanedRows(limit int) (deleted int64, err error)
 	GetThreadUnreadReplyCount(threadMembership *model.ThreadMembership) (int64, error)
 	DeleteMembershipsForChannel(userID, channelID string) error
+
+	SaveMultipleMemberships(memberships []*model.ThreadMembership) ([]*model.ThreadMembership, error)
+	MaintainMultipleFromImport(memberships []*model.ThreadMembership) ([]*model.ThreadMembership, error)
 }
 
 type PostStore interface {
@@ -1103,6 +1107,9 @@ type ThreadMembershipOpts struct {
 	// UpdateParticipants indicates whether or not the thread's participants list
 	// should be updated.
 	UpdateParticipants bool
+	// ImportData contains the data only when the membership is imported.
+	// and triggers a different workflow.
+	ImportData *ThreadMembershipImportData
 }
 
 // PostReminderMetadata contains some info needed to send
@@ -1121,3 +1128,10 @@ type SidebarCategorySearchOpts struct {
 	ExcludeTeam bool
 	Type        model.SidebarCategoryType
 }
+
+type ThreadMembershipImportData struct {
+	// LastViewed is the timestamp to set the LastViewed field to.
+	LastViewed int64
+	// UnreadMentions is the number of unread mentions to set the UnreadMentions field to.
+	UnreadMentions int64
+}