FUE-T02: fix EditMeterForm timestamp parsing to use shared parseBackendTimestamp (handles offset form)

frontend/src/energy/MeterManager.tsx

@@ -38,7 +38,7 @@ import {
   type MeterReason,
 } from './hooks'
 import { ApiError } from '../api/client'
-import { formatLocalDate } from '../utils/datetime'
+import { formatLocalDate, parseBackendTimestamp } from '../utils/datetime'
 
 // ---------------------------------------------------------------------------
 // Helpers
@@ -60,6 +60,19 @@ function toLocalMidnightNaive(dateStr: string): string {
   return `${dateStr}T00:00:00`
 }
 
+/**
+ * Format a Date object as a "YYYY-MM-DD" string using the browser's local timezone.
+ * Used to populate <input type="date"> fields.
+ * Returns '' if the Date is invalid.
+ */
+function toLocalDateInputString(d: Date): string {
+  if (isNaN(d.getTime())) return ''
+  const y = d.getFullYear()
+  const m = String(d.getMonth() + 1).padStart(2, '0')
+  const day = String(d.getDate()).padStart(2, '0')
+  return `${y}-${m}-${day}`
+}
+
 // ---------------------------------------------------------------------------
 // Declare meter form (modal)
 // ---------------------------------------------------------------------------
@@ -204,19 +217,12 @@ interface EditMeterFormProps {
 function EditMeterForm({ meter, onClose, onSaved }: EditMeterFormProps) {
   const [label, setLabel] = useState(meter.label)
   const [note, setNote] = useState(meter.note ?? '')
-  // Convert UTC started_at to a local date string for the <input type="date">.
-  // We parse as UTC (appending Z if needed) and format to "YYYY-MM-DD" in local tz.
-  const initialDateStr = (() => {
-    const iso = meter.started_at.includes('T') && !meter.started_at.match(/[zZ+-]\d*$/)
-      ? meter.started_at + 'Z'
-      : meter.started_at
-    const d = new Date(iso)
-    if (isNaN(d.getTime())) return ''
-    const y = d.getFullYear()
-    const m = String(d.getMonth() + 1).padStart(2, '0')
-    const day = String(d.getDate()).padStart(2, '0')
-    return `${y}-${m}-${day}`
-  })()
+  // Convert started_at to a local date string for the <input type="date">.
+  // parseBackendTimestamp correctly handles naive strings (no tz marker → treated as UTC,
+  // matching the backend's storage convention), Z-suffixed strings, and strings with
+  // explicit offsets like +02:00.  We then extract the local-timezone date components
+  // so the displayed date matches the local wall-clock date of the meter start.
+  const initialDateStr = toLocalDateInputString(parseBackendTimestamp(meter.started_at))
   const [dateStr, setDateStr] = useState(initialDateStr)
   const [error, setError] = useState<string | null>(null)