uprava FE pro multisite

frontend/src/context/SiteSelectionContext.tsx

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+import {
+  createContext,
+  useCallback,
+  useContext,
+  useEffect,
+  useMemo,
+  useState,
+  type ReactNode,
+} from 'react'
+
+import { getMySites, type MeSiteRow } from '../api/backend'
+
+export const SITE_STORAGE_KEY = 'ems.selected_site_id'
+
+export type SiteSelectionContextValue = {
+  sites: MeSiteRow[]
+  selectedSiteId: number | null
+  setSelectedSiteId: (id: number) => void
+  ready: boolean
+  error: string | null
+}
+
+const SiteSelectionContext = createContext<SiteSelectionContextValue | null>(null)
+
+export function SiteSelectionProvider({ children }: { children: ReactNode }) {
+  const [sites, setSites] = useState<MeSiteRow[]>([])
+  const [selectedSiteId, setSelectedSiteIdState] = useState<number | null>(null)
+  const [ready, setReady] = useState(false)
+  const [error, setError] = useState<string | null>(null)
+
+  useEffect(() => {
+    let cancelled = false
+    ;(async () => {
+      try {
+        const list = await getMySites()
+        if (cancelled) return
+        setSites(list)
+        if (list.length === 0) {
+          setError('Žádná aktivní lokalita')
+          setSelectedSiteIdState(null)
+        } else {
+          setError(null)
+          const raw = localStorage.getItem(SITE_STORAGE_KEY)
+          const parsed = raw != null ? Number.parseInt(raw, 10) : Number.NaN
+          const valid = Number.isFinite(parsed) && list.some((s) => s.id === parsed)
+          setSelectedSiteIdState(valid ? parsed : list[0]!.id)
+        }
+      } catch {
+        if (!cancelled) {
+          setSites([])
+          setSelectedSiteIdState(null)
+          setError('Lokality se nepodařilo načíst')
+        }
+      } finally {
+        if (!cancelled) setReady(true)
+      }
+    })()
+    return () => {
+      cancelled = true
+    }
+  }, [])
+
+  const setSelectedSiteId = useCallback((id: number) => {
+    setSelectedSiteIdState(id)
+    localStorage.setItem(SITE_STORAGE_KEY, String(id))
+  }, [])
+
+  const value = useMemo(
+    (): SiteSelectionContextValue => ({
+      sites,
+      selectedSiteId,
+      setSelectedSiteId,
+      ready,
+      error,
+    }),
+    [sites, selectedSiteId, setSelectedSiteId, ready, error],
+  )
+
+  return <SiteSelectionContext.Provider value={value}>{children}</SiteSelectionContext.Provider>
+}
+
+export function useSiteSelection(): SiteSelectionContextValue {
+  const ctx = useContext(SiteSelectionContext)
+  if (ctx == null) {
+    throw new Error('useSiteSelection must be used within SiteSelectionProvider')
+  }
+  return ctx
+}