Fix index lookup for minimal and maximal favorite id

src/computersandblues/lodestone/app.cljs

@@ -417,20 +417,9 @@
   "Returns a promise which resolves to the smallest or largest internal post id.
   This is useful to continue interrupted paginated requests."
   [max-or-min]
-  ; this may look like a horribly inefficient way to get these numbers, and it is!
-  ; there was an earlier version that simply used an index on :internal_id and
-  ; retrieved the first result in ascending or descending order; however, the
-  ; result that was returned was unexpected and unreliable. this may very well
-  ; have been my fault, because i'm only learning how the indexeddb api works as
-  ; i implement all of this here.
-  (let [xform (comp (keep (j/get :internal_id)))
-        rf (if (= max-or-min :min) min max)
-        init (if (= max-or-min :min) js/Number.POSITIVE_INFINITY js/Number.NEGATIVE_INFINITY)]
-    (. (->> (db/open-cursor! ::db/posts ::db/all)
-            (db/transduce-cursor xform rf init))
-       (then (fn [result]
-               (when-not (infinite? result)
-                 result))))))
+  (->> (db/open-cursor! ::db/posts ::db/all {:index ::db/post-internal-id
+                                             :direction (if (= max-or-min :min) :asc :desc)})
+       (db/first-result (keep (j/get :internal_id)))))
 
 (defn fetch-more-posts! [e]
   (.preventDefault e)