Initial commit: Auto-Charger Logging Web-App

MQTT-Collector (Python/paho-mqtt) speichert abgeschlossene go-e
Wallbox-Ladungen in SQLite; Next.js-Web-App zeigt sie als Tabelle mit
Energie-Summen (Monat/Jahr/gesamt) im werte-next-Design. Zwei
Docker-Container mit gemeinsamem DB-Volume.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/lib/db.ts

@@ -0,0 +1,86 @@
+import Database from "better-sqlite3";
+
+const DB_PATH = process.env.DB_PATH || "/data/charges.db";
+
+export interface Charge {
+  id: number;
+  start_time: string;
+  end_time: string;
+  duration_s: number;
+  energy_wh: number;
+}
+
+export interface Totals {
+  month_wh: number;
+  year_wh: number;
+  total_wh: number;
+  install_date: string | null;
+}
+
+let db: Database.Database | null = null;
+
+/**
+ * Öffnet die DB read-only. Gibt null zurück, falls die Datei noch nicht
+ * existiert (Collector legt sie beim ersten Start an) oder noch kein Schema
+ * vorhanden ist — die Seite bleibt dann leer statt zu crashen.
+ */
+function getDb(): Database.Database | null {
+  if (db) return db;
+  try {
+    const conn = new Database(DB_PATH, { readonly: true, fileMustExist: true });
+    const hasTable = conn
+      .prepare("SELECT name FROM sqlite_master WHERE type='table' AND name='charges'")
+      .get();
+    if (!hasTable) {
+      conn.close();
+      return null;
+    }
+    db = conn;
+    return db;
+  } catch {
+    return null;
+  }
+}
+
+export function getCharges(): Charge[] {
+  const conn = getDb();
+  if (!conn) return [];
+  return conn
+    .prepare(
+      `SELECT id, start_time, end_time, duration_s, energy_wh
+       FROM charges ORDER BY start_time DESC`,
+    )
+    .all() as Charge[];
+}
+
+export function getTotals(): Totals {
+  const conn = getDb();
+  if (!conn) {
+    return { month_wh: 0, year_wh: 0, total_wh: 0, install_date: null };
+  }
+  const month = conn
+    .prepare(
+      `SELECT COALESCE(SUM(energy_wh), 0) AS s FROM charges
+       WHERE strftime('%Y-%m', start_time) = strftime('%Y-%m', 'now', 'localtime')`,
+    )
+    .get() as { s: number };
+  const year = conn
+    .prepare(
+      `SELECT COALESCE(SUM(energy_wh), 0) AS s FROM charges
+       WHERE strftime('%Y', start_time) = strftime('%Y', 'now', 'localtime')`,
+    )
+    .get() as { s: number };
+  const total = conn
+    .prepare(`SELECT COALESCE(SUM(energy_wh), 0) AS s FROM charges`)
+    .get() as { s: number };
+  const install = conn
+    .prepare(`SELECT value FROM meta WHERE key = 'install_date'`)
+    .get() as { value: string } | undefined;
+
+  return {
+    month_wh: month.s,
+    year_wh: year.s,
+    total_wh: total.s,
+    install_date: install?.value ?? null,
+  };
+}