Add elprice table + JSON API (GET /api/elprice?date=...)

New `elprice` table with a simpler shape (time_dk, price_area,
price_dkk) backing a JSON endpoint that returns hourly DK1 + DK2
prices for any date. Cache-miss path fetches from the same
DayAheadPrices dataset as day_ahead_prices, upserts, and returns.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

resources/migrations/20260419010000-create-elprice.down.sql

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

resources/migrations/20260419010000-create-elprice.up.sql

@@ -0,0 +1,6 @@
+CREATE TABLE elprice (
+  time_dk    TIMESTAMP     NOT NULL,
+  price_area VARCHAR(3)    NOT NULL,
+  price_dkk  NUMERIC(10,2) NOT NULL,
+  PRIMARY KEY (time_dk, price_area)
+);

resources/queries.sql

@@ -65,3 +65,16 @@ ON CONFLICT (time_start, hour) DO NOTHING;
 INSERT INTO consumption (time_start, hour, kwh)
 VALUES (:time-start, :hour, :kwh)
 ON CONFLICT (time_start, hour) DO NOTHING;
+
+-- :name insert-elprice! :! :n
+-- :doc Insert an hourly el-price row; keep first value on conflict
+INSERT INTO elprice (time_dk, price_area, price_dkk)
+VALUES (:time-dk, :price-area, :price-dkk)
+ON CONFLICT (time_dk, price_area) DO NOTHING;
+
+-- :name get-elprice-for-date :? :*
+-- :doc Hourly prices for a DK local date, both areas
+SELECT time_dk, price_area, price_dkk
+FROM elprice
+WHERE time_dk::date = :date
+ORDER BY time_dk, price_area;

src/clj/pmagnus/elprice/web/controllers/elprice.clj

@@ -0,0 +1,93 @@
+(ns pmagnus.elprice.web.controllers.elprice
+  (:require
+    [clojure.data.json :as json]
+    [clojure.tools.logging :as log])
+  (:import
+    (java.net
+      URI
+      URLEncoder)
+    (java.net.http
+      HttpClient
+      HttpRequest
+      HttpResponse$BodyHandlers)
+    (java.sql
+      Timestamp)
+    (java.time
+      LocalDate
+      ZoneId)
+    (java.time.format
+      DateTimeFormatter)))
+
+
+(def ^:private dk-zone (ZoneId/of "Europe/Copenhagen"))
+(def ^:private date-fmt (DateTimeFormatter/ofPattern "yyyy-MM-dd"))
+(def ^:private eur-dkk-rate 7.46)
+
+
+(defn- build-url
+  [^LocalDate date]
+  (let [start (.format date date-fmt)
+        end   (.format (.plusDays date 1) date-fmt)]
+    (str "https://api.energidataservice.dk/dataset/DayAheadPrices"
+         "?start=" start
+         "&end=" end
+         "&filter=" (URLEncoder/encode (json/write-str {"PriceArea" ["DK1" "DK2"]}) "UTF-8")
+         "&sort=TimeDK%20asc"
+         "&limit=200")))
+
+
+(defn- fetch-json
+  [url]
+  (let [client   (HttpClient/newHttpClient)
+        request  (-> (HttpRequest/newBuilder)
+                     (.uri (URI/create url))
+                     (.header "Accept" "application/json")
+                     (.GET)
+                     (.build))
+        response (.send client request (HttpResponse$BodyHandlers/ofString))]
+    (when (= 200 (.statusCode response))
+      (json/read-str (.body response) :key-fn keyword))))
+
+
+(defn- parse-timestamp
+  [s]
+  (when s
+    (Timestamp/valueOf (.replace ^String s "T" " "))))
+
+
+(defn- dkk-price
+  [price-dkk price-eur]
+  (or price-dkk
+      (when price-eur (* price-eur eur-dkk-rate))))
+
+
+(defn- fetch-from-api
+  [^LocalDate date]
+  (let [url (build-url date)]
+    (log/info "Fetching el prices for" (.format date date-fmt) "from" url)
+    (:records (fetch-json url))))
+
+
+(defn- save-records!
+  [query-fn records]
+  (doseq [rec records]
+    (when-let [dkk (dkk-price (:DayAheadPriceDKK rec) (:DayAheadPriceEUR rec))]
+      (query-fn :insert-elprice!
+                {:time-dk    (parse-timestamp (:TimeDK rec))
+                 :price-area (:PriceArea rec)
+                 :price-dkk  dkk}))))
+
+
+(defn get-or-fetch!
+  "Return hourly el-price rows for the given LocalDate (DK local), fetching
+   from the upstream API and caching on a miss."
+  [query-fn ^LocalDate date]
+  (let [sql-date (java.sql.Date/valueOf date)
+        rows    (query-fn :get-elprice-for-date {:date sql-date})]
+    (if (seq rows)
+      rows
+      (let [records (fetch-from-api date)]
+        (when (seq records)
+          (log/info "Saving" (count records) "el-price records")
+          (save-records! query-fn records))
+        (query-fn :get-elprice-for-date {:date sql-date})))))

src/clj/pmagnus/elprice/web/routes/api.clj

@@ -1,6 +1,7 @@
 (ns pmagnus.elprice.web.routes.api
   (:require
     [integrant.core :as ig]
+    [pmagnus.elprice.web.controllers.elprice :as elprice]
     [pmagnus.elprice.web.controllers.health :as health]
     [pmagnus.elprice.web.middleware.exception :as exception]
     [pmagnus.elprice.web.middleware.formats :as formats]
@@ -8,7 +9,13 @@
     [reitit.ring.coercion :as coercion]
     [reitit.ring.middleware.muuntaja :as muuntaja]
     [reitit.ring.middleware.parameters :as parameters]
-    [reitit.swagger :as swagger]))
+    [reitit.swagger :as swagger]
+    [ring.util.http-response :as http-response])
+  (:import
+    (java.time
+      LocalDate)
+    (java.time.format
+      DateTimeParseException)))
 
 
 (def route-data
@@ -33,9 +40,24 @@
                 exception/wrap-exception]})
 
 
+(defn- elprice-handler
+  [query-fn {{{:keys [date]} :query} :parameters}]
+  (try
+    (let [d    (LocalDate/parse date)
+          rows (elprice/get-or-fetch! query-fn d)]
+      (http-response/ok
+        {:date   date
+         :prices (mapv (fn [r] {:time_dk    (str (:time_dk r))
+                                :price_area (:price_area r)
+                                :price_dkk  (:price_dkk r)})
+                       rows)}))
+    (catch DateTimeParseException _
+      (http-response/bad-request {:error "date must be YYYY-MM-DD"}))))
+
+
 ;; Routes
 (defn api-routes
-  [_opts]
+  [{:keys [query-fn]}]
   [["/swagger.json"
     {:get {:no-doc  true
            :swagger {:info {:title "pmagnus.elprice API"}}
@@ -44,7 +66,11 @@
     ;; note that use of the var is necessary
     ;; for reitit to reload routes without
     ;; restarting the system
-    {:get #'health/healthcheck!}]])
+    {:get #'health/healthcheck!}]
+   ["/elprice"
+    {:get {:summary    "Hourly DK1 + DK2 electricity prices for a date"
+           :parameters {:query [:map [:date :string]]}
+           :handler    (partial elprice-handler query-fn)}}]])
 
 
 (derive :reitit.routes/api :reitit/routes)