Fetch and display day-ahead electricity spot prices from Energi Data Service

Adds a prices controller that fetches DK1/DK2 hourly spot prices via the
Energi Data Service API, stores them in PostgreSQL, and displays today's
and tomorrow's DK1 prices on the home page in øre/kWh. An HTMX "Refresh
Prices" button triggers the fetch-and-display cycle.

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

deps.edn

@@ -25,7 +25,8 @@
  io.github.kit-clj/kit-postgres {:mvn/version "1.0.7"}
  io.github.kit-clj/kit-sql-conman {:mvn/version "1.10.5"}
  io.github.kit-clj/kit-sql-migratus {:mvn/version "1.0.5"}
- hiccup/hiccup {:mvn/version "2.0.0"}}
+ hiccup/hiccup {:mvn/version "2.0.0"}
+ org.clojure/data.json {:mvn/version "2.5.1"}}
  :aliases {:build {:deps {io.github.clojure/tools.build {:mvn/version "0.10.11"}}
                    :ns-default build}
 

resources/migrations/20260214120000-create-day-ahead-prices.down.sql

@@ -0,0 +1 @@
+DROP TABLE IF EXISTS day_ahead_prices;

resources/migrations/20260214120000-create-day-ahead-prices.up.sql

@@ -0,0 +1,8 @@
+CREATE TABLE day_ahead_prices (
+  time_utc       TIMESTAMPTZ NOT NULL,
+  time_dk        TIMESTAMP   NOT NULL,
+  price_area     VARCHAR(3)  NOT NULL,
+  price_dkk      NUMERIC(10,2),
+  price_eur      NUMERIC(10,6),
+  PRIMARY KEY (time_utc, price_area)
+);

resources/queries.sql

@@ -1,2 +1,16 @@
--- place your sql queries here
+-- :name upsert-price! :! :n
--- see https://www.hugsql.org/ for documentation
+-- :doc Upsert a day-ahead price record
+INSERT INTO day_ahead_prices (time_utc, time_dk, price_area, price_dkk, price_eur)
+VALUES (:time-utc, :time-dk, :price-area, :price-dkk, :price-eur)
+ON CONFLICT (time_utc, price_area) DO UPDATE
+SET time_dk = EXCLUDED.time_dk,
+    price_dkk = EXCLUDED.price_dkk,
+    price_eur = EXCLUDED.price_eur;
+
+-- :name get-prices-for-date :? :*
+-- :doc Get all prices for a given date (time_dk local date) and price area
+SELECT time_utc, time_dk, price_area, price_dkk, price_eur
+FROM day_ahead_prices
+WHERE time_dk::date = :date
+  AND price_area = :price-area
+ORDER BY time_dk;

resources/system.edn

@@ -66,4 +66,5 @@
   :db {:datasource #ig/ref :db.sql/connection}
   :migrate-on-init? true}
  :reitit.routes/ui {:base-path "",
-                    :env #ig/ref :system/env}}
+                    :env #ig/ref :system/env
+                    :query-fn #ig/ref :db.sql/query-fn}}

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

@@ -0,0 +1,91 @@
+(ns pmagnus.elprice.web.controllers.prices
+  (:require
+   [clojure.data.json :as json]
+   [clojure.tools.logging :as log])
+  (:import
+   [java.net URI]
+   [java.net.http HttpClient HttpRequest HttpResponse$BodyHandlers]
+   [java.time LocalDate ZoneId]
+   [java.time.format DateTimeFormatter]
+   [java.sql Timestamp]))
+
+(def ^:private dk-zone (ZoneId/of "Europe/Copenhagen"))
+
+(def ^:private date-fmt (DateTimeFormatter/ofPattern "yyyy-MM-dd"))
+
+(defn- build-url
+  "Build the Energi Data Service API URL for day-ahead prices."
+  [start-date end-date]
+  (str "https://api.energidataservice.dk/dataset/DayAheadPrices"
+       "?start=" start-date
+       "&end=" end-date
+       "&filter=" (json/write-str {"PriceArea" ["DK1" "DK2"]})
+       "&sort=TimeDK%20asc"
+       "&limit=200"))
+
+(defn- fetch-json
+  "Fetch JSON from a URL using JDK HttpClient."
+  [url]
+  (let [client  (HttpClient/newHttpClient)
+        request (-> (HttpRequest/newBuilder)
+                    (.uri (URI/create url))
+                    (.header "Accept" "application/json")
+                    (.GET)
+                    (.build))
+        response (.send client request (HttpResponse$BodyHandlers/ofString))]
+    (when (= 200 (.statusCode response))
+      (json/read-str (.body response) :key-fn keyword))))
+
+(defn fetch-prices-from-api
+  "Fetch today's and tomorrow's prices from Energi Data Service."
+  []
+  (let [today    (LocalDate/now dk-zone)
+        tomorrow (.plusDays today 1)
+        ;; Fetch from start of today to end of tomorrow
+        start    (.format today date-fmt)
+        end      (.format (.plusDays tomorrow 1) date-fmt)
+        url      (build-url start end)]
+    (log/info "Fetching day-ahead prices from" url)
+    (when-let [data (fetch-json url)]
+      (:records data))))
+
+(defn- parse-timestamp
+  "Parse an ISO timestamp string to java.sql.Timestamp."
+  [s]
+  (when s
+    (Timestamp/valueOf
+     (.replace ^String s "T" " "))))
+
+(defn save-records!
+  "Upsert price records into the database."
+  [query-fn records]
+  (doseq [rec records]
+    (query-fn :upsert-price!
+              {:time-utc   (parse-timestamp (:TimeUTC rec))
+               :time-dk    (parse-timestamp (:TimeDK rec))
+               :price-area (:PriceArea rec)
+               :price-dkk  (:DayAheadPriceDKK rec)
+               :price-eur  (:DayAheadPriceEUR rec)})))
+
+(defn fetch-and-save!
+  "Fetch prices from API and save to database."
+  [query-fn]
+  (when-let [records (fetch-prices-from-api)]
+    (log/info "Saving" (count records) "price records")
+    (save-records! query-fn records)
+    (count records)))
+
+(defn get-prices-for-date
+  "Get prices for a given LocalDate and price area from the database."
+  [query-fn date price-area]
+  (query-fn :get-prices-for-date
+            {:date       (java.sql.Date/valueOf date)
+             :price-area price-area}))
+
+(defn get-today-prices
+  [query-fn]
+  (get-prices-for-date query-fn (LocalDate/now dk-zone) "DK1"))
+
+(defn get-tomorrow-prices
+  [query-fn]
+  (get-prices-for-date query-fn (.plusDays (LocalDate/now dk-zone) 1) "DK1"))

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

@@ -3,32 +3,85 @@
    [pmagnus.elprice.web.middleware.exception :as exception]
    [pmagnus.elprice.web.middleware.formats :as formats]
    [pmagnus.elprice.web.routes.utils :as utils]
-   [pmagnus.elprice.web.htmx :refer [page fragment] :as htmx]
+   [pmagnus.elprice.web.htmx :refer [page fragment]]
+   [pmagnus.elprice.web.controllers.prices :as prices]
    [integrant.core :as ig]
    [reitit.ring.middleware.muuntaja :as muuntaja]
-   [reitit.ring.middleware.parameters :as parameters]))
+   [reitit.ring.middleware.parameters :as parameters])
+  (:import
+   [java.time LocalDateTime]
+   [java.time.format DateTimeFormatter]))
 
-(defn home [request]
+(def ^:private hour-fmt (DateTimeFormatter/ofPattern "HH:00"))
+
+(defn- format-hour [time-dk]
+  (let [ldt (cond
+              (instance? LocalDateTime time-dk) time-dk
+              (instance? java.sql.Timestamp time-dk)
+              (.toLocalDateTime ^java.sql.Timestamp time-dk)
+              :else (LocalDateTime/parse (str time-dk)))]
+    (.format ldt hour-fmt)))
+
+(defn- dkk-mwh->ore-kwh
+  "Convert DKK/MWh to øre/kWh (divide by 10)."
+  [price-dkk]
+  (when price-dkk
+    (/ (double price-dkk) 10.0)))
+
+(defn- price-table [title prices]
+  [:div {:class "mt-6"}
+   [:h2 {:class "text-lg font-semibold text-gray-900"} title]
+   (if (seq prices)
+     [:table {:class "mt-2 w-full text-sm"}
+      [:thead
+       [:tr {:class "border-b border-gray-200 text-left text-gray-500"}
+        [:th {:class "py-2 pr-4"} "Time"]
+        [:th {:class "py-2 text-right"} "øre/kWh"]]]
+      [:tbody
+       (for [p prices]
+         [:tr {:class "border-b border-gray-100"}
+          [:td {:class "py-2 pr-4 text-gray-700"}
+           (format-hour (:time_dk p))]
+          [:td {:class "py-2 text-right font-mono text-gray-900"}
+           (if-let [ore (dkk-mwh->ore-kwh (:price_dkk p))]
+             (format "%.1f" ore)
+             "-")]])]]
+     [:p {:class "mt-2 text-sm text-gray-400"} "Not available yet"])])
+
+(defn- price-tables [query-fn]
+  (let [today    (prices/get-today-prices query-fn)
+        tomorrow (prices/get-tomorrow-prices query-fn)]
+    [:div {:id "price-tables"}
+     (price-table "Today — DK1" today)
+     (price-table "Tomorrow — DK1" tomorrow)]))
+
+(defn home [query-fn request]
   (page {:lang "en"}
    [:h1 {:class "text-2xl font-bold text-gray-900"}
-    "Welcome to elprice"]
+    "Electricity Prices"]
-   [:p {:class "mt-2 text-gray-600"}
+   [:p {:class "mt-1 text-sm text-gray-500"}
-    "Built with Kit, HTMX, Hiccup & Tailwind"]
+    "Day-ahead spot prices for DK1 in øre/kWh"]
    [:button {:class "mt-4 rounded-lg bg-blue-600 px-4 py-2 text-white font-medium
                      active:bg-blue-700 transition-colors"
-             :hx-post "/clicked"
+             :hx-post "/prices/fetch"
-             :hx-swap "outerHTML"}
+             :hx-target "#price-tables"
-    "Click me!"]))
+             :hx-swap "outerHTML"
+             :hx-indicator "#fetch-spinner"}
+    "Refresh Prices"]
+   [:span {:id "fetch-spinner"
+           :class "ml-2 htmx-indicator text-sm text-gray-400"}
+    "Loading..."]
+   (price-tables query-fn)))
 
-(defn clicked [request]
+(defn fetch-prices [query-fn request]
+  (prices/fetch-and-save! query-fn)
   (fragment
-   [:div {:class "mt-4 rounded-lg bg-green-100 p-4 text-green-800"}
+   (price-tables query-fn)))
-    "Congratulations! You just clicked the button!"]))
 
 ;; Routes
-(defn ui-routes [_opts]
+(defn ui-routes [{:keys [query-fn]}]
-  [["/" {:get home}]
+  [["/" {:get (partial home query-fn)}]
-   ["/clicked" {:post clicked}]])
+   ["/prices/fetch" {:post (partial fetch-prices query-fn)}]])
 
 (def route-data
   {:muuntaja   formats/instance