/**
 * Fetches a `years`-year window of Swedish calendar metadata (röda dagar,
 * klämdagar, weekends, workspace day overrides) starting at `startYear`.
 *
 * Backs both the Kalender page's shading + click-to-override (§3.4/§3.6) and
 * the Settings red-days list (§3.8) from the same `GET /api/calendar/days`
 * endpoint — see `app/routers/calendar.py` / ARCHITECTURE.md §13.3.
 *
 * There is no shared cache/invalidation layer (no TanStack Query) here, so a
 * day-override mutation elsewhere does not automatically make this window
 * stale — callers that mutate overrides (see `useDayOverrides`) must
 * explicitly call `refetch` afterwards or the calendar grid will keep
 * showing the pre-mutation shading until a full reload.
 */

import { useCallback, useEffect, useState } from 'react'
import * as api from '@/services/api'
import type { CalendarWindow } from '@/types'

interface UseCalendarDaysResult {
  data: CalendarWindow | null
  isLoading: boolean
  error: string | null
  refetch: () => Promise<void>
}

export function useCalendarDays(
  workspaceId: string,
  startYear: number,
  years: number = 4,
): UseCalendarDaysResult {
  const [data, setData] = useState<CalendarWindow | null>(null)
  const [isLoading, setIsLoading] = useState(false)
  const [error, setError] = useState<string | null>(null)

  const fetchWindow = useCallback(async () => {
    if (!workspaceId) return
    setIsLoading(true)
    setError(null)
    try {
      const result = await api.getCalendarDays(workspaceId, startYear, years)
      setData(result)
    } catch (err: unknown) {
      setError(err instanceof Error ? err.message : 'Failed to load calendar days')
    } finally {
      setIsLoading(false)
    }
  }, [workspaceId, startYear, years])

  useEffect(() => {
    void fetchWindow()
  }, [fetchWindow])

  return { data, isLoading, error, refetch: fetchWindow }
}