Persist Frankfurter EUR/DKK rates in currencies table

Store daily exchange rates in PostgreSQL with EUR/DKK cross rate.
Seed rates atom from DB on startup so WebSocket works immediately
even if Frankfurter is unreachable.

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

resources/migrations/20260306200000-create-currencies.down.sql

@@ -0,0 +1 @@
+DROP TABLE currencies;

resources/migrations/20260306200000-create-currencies.up.sql

@@ -0,0 +1,7 @@
+CREATE TABLE currencies (
+  rate_date DATE PRIMARY KEY,
+  eur NUMERIC(12,6) NOT NULL,
+  dkk NUMERIC(12,6) NOT NULL,
+  eur_dkk NUMERIC(12,6) NOT NULL,
+  updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);

resources/queries.sql

@@ -50,3 +50,14 @@ INSERT INTO strike_price (rates, quote_sats) VALUES (:rates, :quote-sats)
 -- :name get-latest-strike-price :? :1
 -- :doc Get the most recent Strike ticker snapshot
 SELECT rates, recorded_at FROM strike_price ORDER BY id DESC LIMIT 1
+
+-- :name upsert-currency-rates! :! :n
+-- :doc Upsert daily currency rates from Frankfurter
+INSERT INTO currencies (rate_date, eur, dkk, eur_dkk, updated_at)
+VALUES (:rate-date, :eur, :dkk, :eur-dkk, NOW())
+ON CONFLICT (rate_date) DO UPDATE
+SET eur = EXCLUDED.eur, dkk = EXCLUDED.dkk, eur_dkk = EXCLUDED.eur_dkk, updated_at = NOW()
+
+-- :name get-latest-currency-rates :? :1
+-- :doc Get the most recent currency rates
+SELECT eur, dkk, eur_dkk, updated_at FROM currencies ORDER BY rate_date DESC LIMIT 1

resources/system.edn

@@ -61,7 +61,8 @@
  {:query-fn #ig/ref :db.sql/query-fn}
 
  :frankfurter/rates
- {:url #or [#env FRANKFURTER_URL "http://localhost:8080"]}
+ {:url      #or [#env FRANKFURTER_URL "http://localhost:8080"]
+  :query-fn #ig/ref :db.sql/query-fn}
 
  :strike/ticker
  {:query-fn        #ig/ref :db.sql/query-fn

src/clj/pmagnus/btcdata/frankfurter/rates.clj

@@ -6,7 +6,7 @@
   (:import
    [java.net URI]
    [java.net.http HttpClient HttpRequest HttpResponse$BodyHandlers]
-   [java.time Instant]))
+   [java.time Instant LocalDate]))
 
 (defn- fetch-rates
   "GET /latest?from=USD&to=EUR,DKK from Frankfurter. Returns {:EUR x :DKK y}."
@@ -22,23 +22,31 @@
     (:rates body)))
 
 (defn- poll!
-  "Fetch rates and update the atom."
-  [client base-url rates-atom]
+  "Fetch rates, update the atom, and persist to DB."
+  [client base-url rates-atom query-fn]
   (let [rates (fetch-rates client base-url)]
     (when (and (:EUR rates) (:DKK rates))
-      (reset! rates-atom
-              {:eur        (bigdec (str (:EUR rates)))
-               :dkk        (bigdec (str (:DKK rates)))
-               :updated-at (Instant/now)})
-      (log/info "Frankfurter rates — EUR:" (:EUR rates) "DKK:" (:DKK rates)))))
+      (let [eur (bigdec (str (:EUR rates)))
+            dkk (bigdec (str (:DKK rates)))
+            eur-dkk (.divide dkk eur 6 java.math.RoundingMode/HALF_UP)]
+        (reset! rates-atom
+                {:eur        eur
+                 :dkk        dkk
+                 :updated-at (Instant/now)})
+        (query-fn :upsert-currency-rates!
+                  {:rate-date (LocalDate/now)
+                   :eur       eur
+                   :dkk       dkk
+                   :eur-dkk   eur-dkk})
+        (log/info "Frankfurter rates — EUR:" eur "DKK:" dkk "EUR/DKK:" eur-dkk)))))
 
 (defn- start-poll-loop!
   "Fetch immediately, then poll every 60 minutes."
-  [client base-url rates-atom running?]
+  [client base-url rates-atom running? query-fn]
   (future
     (loop [retries 12]
       (let [ok? (try
-                  (poll! client base-url rates-atom)
+                  (poll! client base-url rates-atom query-fn)
                   true
                   (catch Exception e
                     (log/error e (str "Frankfurter fetch failed, retrying in 10s (" retries " left)"))
@@ -50,20 +58,34 @@
       (Thread/sleep 3600000)
       (when @running?
         (try
-          (poll! client base-url rates-atom)
+          (poll! client base-url rates-atom query-fn)
           (catch Exception e
             (log/error e "Frankfurter poll failed")))))))
 
+(defn- seed-from-db!
+  "Load latest rates from DB into the atom so we have data immediately."
+  [rates-atom query-fn]
+  (try
+    (when-let [row (query-fn :get-latest-currency-rates {})]
+      (reset! rates-atom
+              {:eur        (:eur row)
+               :dkk        (:dkk row)
+               :updated-at (:updated_at row)})
+      (log/info "Seeded Frankfurter rates from DB — EUR:" (:eur row) "DKK:" (:dkk row)))
+    (catch Exception e
+      (log/warn e "Could not seed rates from DB"))))
+
 (defmethod ig/init-key :frankfurter/rates
-  [_ {:keys [url]}]
+  [_ {:keys [url query-fn]}]
   (log/info "Starting Frankfurter rates poller:" url)
   (let [client   (HttpClient/newHttpClient)
         rates    (atom nil)
-        running? (atom true)
-        fut      (start-poll-loop! client url rates running?)]
-    {:rates    rates
-     :running? running?
-     :future   fut}))
+        running? (atom true)]
+    (seed-from-db! rates query-fn)
+    (let [fut (start-poll-loop! client url rates running? query-fn)]
+      {:rates    rates
+       :running? running?
+       :future   fut})))
 
 (defmethod ig/halt-key! :frankfurter/rates
   [_ {:keys [running? future]}]