events: add GET /v1/events/:eventId/followers

api/server.go

@@ -512,6 +512,7 @@ func NewApiServer(config config.Config) *ApiServer {
 		g.Get("/fan-club/feed", app.v1FanClubFeed)
 
 		g.Get("/events/:eventId/comments", app.v1EventComments)
+		g.Get("/events/:eventId/followers", app.v1EventsFollowers)
 		g.Get("/events/:eventId/follow_state", app.v1EventFollowState)
 		g.Get("/events/:eventId/follow-state", app.v1EventFollowState)
 		g.Post("/events/:eventId/follow", app.requireAuthMiddleware, app.requireWriteScope, app.postV1EventFollow)

api/v1_events_followers.go

@@ -110,6 +110,40 @@ func (app *ApiServer) deleteV1EventFollow(c *fiber.Ctx) error {
 	})
 }
 
+// v1EventsFollowers returns the list of users subscribed to a given
+// remix-contest event, ordered by each user's own follower count so the
+// most-followed fans surface first in the avatar stack / leaderboard. The
+// response shape matches /v1/users/:userId/followers so the same User
+// renderers can consume it.
+func (app *ApiServer) v1EventsFollowers(c *fiber.Ctx) error {
+	eventID, err := trashid.DecodeHashId(c.Params("eventId"))
+	if err != nil {
+		return fiber.NewError(fiber.StatusBadRequest, "invalid event id")
+	}
+
+	// `subscriptions.user_id` mirrors the event id (legacy column), so the
+	// `USING (user_id)` shortcut from v1UsersFollowers would be ambiguous
+	// here — qualify both joins explicitly against the user being looked
+	// up (subscriber_id).
+	sql := `
+	SELECT subscriptions.subscriber_id
+	FROM subscriptions
+	JOIN users ON users.user_id = subscriptions.subscriber_id
+	JOIN aggregate_user ON aggregate_user.user_id = subscriptions.subscriber_id
+	WHERE subscriptions.entity_type = 'Event'
+	  AND subscriptions.entity_id = @eventId
+	  AND subscriptions.is_current = true
+	  AND subscriptions.is_delete = false
+	  AND users.is_deactivated = false
+	ORDER BY aggregate_user.follower_count DESC
+	LIMIT @limit
+	OFFSET @offset
+	`
+	return app.queryUsers(c, sql, pgx.NamedArgs{
+		"eventId": eventID,
+	})
+}
+
 // v1EventFollowState returns { is_followed, follower_count } for an event.
 // Used by the contest page to render the follow button in the right state.
 func (app *ApiServer) v1EventFollowState(c *fiber.Ctx) error {

api/v1_events_followers_test.go

@@ -491,3 +491,112 @@ func TestPostEventFollow_DeletedEventIs404(t *testing.T) {
 	)
 	assert.Equal(t, 404, status)
 }
+
+func TestEventsFollowers_ReturnsOnlyLiveEventSubscribers(t *testing.T) {
+	// /v1/events/:eventId/followers returns the list of users subscribed
+	// to the event. Mirrors the shape + filtering rules of follow_state:
+	// entity_type='Event', is_current & !is_delete, and ignores legacy
+	// user-type subscriptions with a colliding numeric id.
+	app := emptyTestApp(t)
+
+	database.Seed(app.pool.Replicas[0], database.FixtureMap{
+		"users": testEventFollowersBaseUsers(),
+		"tracks": {
+			{
+				"track_id":   1,
+				"owner_id":   1,
+				"title":      "Original",
+				"created_at": "2020-01-01 00:00:00",
+			},
+		},
+		"events": {
+			{
+				"event_id":    200,
+				"event_type":  "remix_contest",
+				"user_id":     1,
+				"entity_type": "track",
+				"entity_id":   1,
+				"event_data":  map[string]any{"description": "remix"},
+				"created_at":  "2020-05-01 00:00:00",
+				"updated_at":  "2020-05-01 00:00:00",
+			},
+		},
+		"subscriptions": []map[string]any{
+			{
+				"subscriber_id": 2,
+				"user_id":       200,
+				"entity_type":   "Event",
+				"entity_id":     200,
+				"is_current":    true,
+				"is_delete":     false,
+				"blockhash":     "bh1",
+				"blocknumber":   101,
+				"txhash":        "tx1",
+			},
+			{
+				"subscriber_id": 3,
+				"user_id":       200,
+				"entity_type":   "Event",
+				"entity_id":     200,
+				"is_current":    true,
+				"is_delete":     false,
+				"blockhash":     "bh2",
+				"blocknumber":   101,
+				"txhash":        "tx2",
+			},
+			// Legacy user-type subscription with a colliding numeric id —
+			// must NOT show up.
+			{
+				"subscriber_id": 1,
+				"user_id":       200,
+				"entity_type":   "User",
+				"entity_id":     nil,
+				"is_current":    true,
+				"is_delete":     false,
+				"blockhash":     "bh3",
+				"blocknumber":   101,
+				"txhash":        "tx3",
+			},
+			// Deleted event subscription — must NOT show up.
+			{
+				"subscriber_id": 1,
+				"user_id":       200,
+				"entity_type":   "Event",
+				"entity_id":     200,
+				"is_current":    true,
+				"is_delete":     true,
+				"blockhash":     "bh4",
+				"blocknumber":   101,
+				"txhash":        "tx4",
+			},
+		},
+	})
+
+	encEvent, err := trashid.EncodeHashId(200)
+	require.NoError(t, err)
+	status, body := testGet(t, app, "/v1/events/"+encEvent+"/followers")
+	require.Equal(t, 200, status, string(body))
+
+	jsonAssert(t, body, map[string]any{
+		"data.#": 2,
+	})
+}
+
+func TestEventsFollowers_UnknownEventReturnsEmptyList(t *testing.T) {
+	app := emptyTestApp(t)
+
+	encEvent, err := trashid.EncodeHashId(9999)
+	require.NoError(t, err)
+	status, body := testGet(t, app, "/v1/events/"+encEvent+"/followers")
+	require.Equal(t, 200, status, string(body))
+	jsonAssert(t, body, map[string]any{
+		"data.#": 0,
+	})
+}
+
+func TestEventsFollowers_InvalidEventIdReturns400(t *testing.T) {
+	app := emptyTestApp(t)
+
+	status, _ := testGet(t, app, "/v1/events/not-a-hashid/followers")
+	assert.Equal(t, 400, status)
+}