Schedule Kraken OHLC polls at HH:01 UTC instead of fixed 5-min interval

Hourly candles only finalize on the hour, so polling every 5 minutes
was wasteful. Now the poller sleeps until 1 minute past each hour,
fetches immediately on first run when no data exists, and logs time
to next fetch on startup.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

resources/system.edn

@@ -59,5 +59,4 @@
   :uri      "wss://stream.binance.com:9443/ws/btcusdt@trade"}
 
  :kraken/ohlc
- {:query-fn    #ig/ref :db.sql/query-fn
-  :interval-ms 300000}}
+ {:query-fn #ig/ref :db.sql/query-fn}}

src/clj/pmagnus/btcprice/kraken/ohlc.clj

@@ -70,26 +70,49 @@
       (log/info "Fetched" (count candles) "completed Kraken hourly candles"))
     (count candles)))
 
+(defn- ms-until-next-poll
+  "Milliseconds from now until next HH:01:00 UTC."
+  []
+  (let [now    (java.time.ZonedDateTime/now java.time.ZoneOffset/UTC)
+        next   (-> now
+                   (.truncatedTo java.time.temporal.ChronoUnit/HOURS)
+                   (.plusMinutes 1))
+        target (if (.isAfter now next)
+                 (.plusHours next 1)
+                 next)]
+    (.toMillis (java.time.Duration/between now target))))
+
 (defn- start-poll-loop!
-  "Start a background future that polls Kraken every `interval-ms`.
-   Returns the future."
-  [client query-fn since-atom running? interval-ms]
+  "Start a background future that polls Kraken aligned to HH:01:00 UTC.
+   When `has-data?` is false, fetches immediately to backfill."
+  [client query-fn since-atom running? has-data?]
   (future
-    (while @running?
+    (when-not has-data?
       (try
         (poll! client query-fn since-atom)
         (catch Exception e
-          (log/error e "Kraken OHLC poll failed")))
-      (Thread/sleep interval-ms))))
+          (log/error e "Kraken OHLC initial poll failed"))))
+    (while @running?
+      (let [wait (ms-until-next-poll)]
+        (log/info "Next Kraken OHLC poll in" (quot wait 60000) "minutes")
+        (Thread/sleep wait)
+        (when @running?
+          (try
+            (poll! client query-fn since-atom)
+            (catch Exception e
+              (log/error e "Kraken OHLC poll failed"))))))))
 
 (defmethod ig/init-key :kraken/ohlc
-  [_ {:keys [query-fn interval-ms]}]
-  (log/info "Starting Kraken OHLC poller, interval:" interval-ms "ms")
+  [_ {:keys [query-fn]}]
   (let [client    (HttpClient/newHttpClient)
-        since     (atom (seed-since-from-db query-fn))
+        db-since  (seed-since-from-db query-fn)
+        since     (atom db-since)
         running?  (atom true)
-        fut       (start-poll-loop! client query-fn since running?
-                                    (or interval-ms 300000))]
+        has-data? (some? db-since)
+        fut       (start-poll-loop! client query-fn since running? has-data?)]
+    (if has-data?
+      (log/info "Starting Kraken OHLC poller, next fetch in" (quot (ms-until-next-poll) 60000) "minutes")
+      (log/info "Starting Kraken OHLC poller, fetching immediately (no data)"))
     {:running? running?
      :future   fut
      :since    since}))