Initial commit

Made-with: Cursor

frontend/src/hooks/useSiteStatus.ts

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+import { useCallback, useEffect, useState } from 'react'
+import { getJson } from '../api/postgrest'
+import type { SiteStatusRow } from '../types/ems'
+
+const POLL_MS = 5_000
+
+export function useSiteStatus() {
+  const [row, setRow] = useState<SiteStatusRow | null>(null)
+  const [ready, setReady] = useState(false)
+
+  const load = useCallback(async () => {
+    try {
+      const rows = await getJson<SiteStatusRow[]>('/vw_site_status')
+      setRow(Array.isArray(rows) && rows.length > 0 ? rows[0]! : null)
+    } catch {
+      setRow(null)
+    } finally {
+      setReady(true)
+    }
+  }, [])
+
+  useEffect(() => {
+    void load()
+    const id = window.setInterval(() => void load(), POLL_MS)
+    return () => window.clearInterval(id)
+  }, [load])
+
+  const hasTelemetry =
+    row != null &&
+    (row.pv_power_w != null ||
+      row.battery_power_w != null ||
+      row.grid_power_w != null ||
+      row.battery_soc_percent != null)
+
+  return {
+    site: row,
+    ready,
+    /** Máme řádek lokality a alespoň jednu telemetrickou hodnotu (jinak skeleton). */
+    hasLiveData: row != null && hasTelemetry,
+    reload: load,
+  }
+}