api: export mention event ticket references

Currently the JSON export does not set the `from_ticket` field for
events of type TICKET_MENTIONED. This commit implements writing out the
data as described in the legacy API docs:

https://man.sr.ht/todo.sr.ht/api.md#event-resource

Note that currently these events are not imported anyways (never have
been).

api/trackers/export.go

@@ -330,7 +330,34 @@ func exportTicketEvents(ctx context.Context, tx *sql.Tx, ticketID int) ([]Event,
 			}
 			evDump.ByUser = exportParticipant(byUser)
 		}
-		// TODO: populate FromTicket
+		if ev.EventType&model.EVENT_TICKET_MENTIONED != 0 {
+			var (
+				fromTicket             *model.Ticket
+				fromTicketTracker      *model.Tracker
+				fromTicketTrackerOwner *model.User
+				err                    error
+			)
+			// TODO write a custom loader, maybe?
+			fromTicket, err = loaders.ForContext(ctx).TicketsByID.Load(*ev.FromTicketID)
+			if err != nil {
+				return nil, err
+			}
+			if fromTicket != nil {
+				fromTicketTracker, err = loaders.ForContext(ctx).TrackersByID.Load(fromTicket.TrackerID)
+				if err != nil {
+					return nil, err
+				}
+			}
+			if fromTicketTracker != nil {
+				fromTicketTrackerOwner, err = loaders.ForContext(ctx).UsersByID.Load(fromTicketTracker.OwnerID)
+				if err != nil {
+					return nil, err
+				}
+			}
+			if fromTicketTrackerOwner != nil {
+				evDump.FromTicket = exportTicketRef(fromTicket, fromTicketTracker, fromTicketTrackerOwner)
+			}
+		}
 
 		l = append(l, evDump)
 	}
@@ -424,6 +451,23 @@ func exportParticipant(e model.Entity) *Participant {
 	panic(fmt.Errorf("unknown entity type %T", e))
 }
 
+func exportTicketRef(ticket *model.Ticket, tracker *model.Tracker, owner *model.User) *TicketRef {
+	return &TicketRef{
+		ID:  ticket.ID,
+		Ref: ticket.Ref(),
+		Tracker: TrackerRef{
+			Owner: User{
+				ID:            owner.ID,
+				CanonicalName: owner.CanonicalName(),
+				Name:          owner.Username,
+			},
+			Created: tracker.Created,
+			Updated: tracker.Updated,
+			Name:    tracker.Name,
+		},
+	}
+}
+
 func convertNullString(ns *string) string {
 	if ns == nil {
 		return ""

api/trackers/import.go

@@ -54,6 +54,19 @@ type Ticket struct {
 	Events     []Event     `json:"events,omitempty"`
 }
 
+type TrackerRef struct {
+	Owner   User      `json:"owner"`
+	Created time.Time `json:"created"`
+	Updated time.Time `json:"updated"`
+	Name    string    `json:"name"`
+}
+
+type TicketRef struct {
+	ID      int        `json:"id"`
+	Ref     string     `json:"ref"`
+	Tracker TrackerRef `json:"tracker"`
+}
+
 type Event struct {
 	ID            int          `json:"id"`
 	Created       time.Time    `json:"created"`
@@ -66,7 +79,7 @@ type Event struct {
 	Comment       *Comment     `json:"comment,omitempty"`
 	Label         *string      `json:"label,omitempty"`
 	ByUser        *Participant `json:"by_user,omitempty"`
-	FromTicket    *Ticket      `json:"from_ticket,omitempty"`
+	FromTicket    *TicketRef   `json:"from_ticket,omitempty"`
 	Upstream      string       `json:"upstream"`
 	Signature     string       `json:"X-Payload-Signature,omitempty"`
 	Nonce         string       `json:"X-Payload-Nonce,omitempty"`