// Backend port of wages/frontend/src/lib/forecast.ts's forecastDayCost — keep both in sync.
const MAX_HOPS = 6 // 6 * 7 = 42 days back, comfortably within the 35-day actuals sync window

function addDaysStr(dateStr, n) {
  const d = new Date(dateStr + 'T00:00:00')
  d.setDate(d.getDate() + n)
  return `${d.getFullYear()}-${String(d.getMonth() + 1).padStart(2, '0')}-${String(d.getDate()).padStart(2, '0')}`
}

// Tiered forecast cost for a single department + date: actual (if present) → published
// rota → draft rota (if includeUnpublished) → same-weekday recurring fallback (7-day hops).
export function forecastDayCost(dateStr, actualDays, scheduledDays, includeUnpublished) {
  let probe = dateStr
  for (let hop = 0; hop <= MAX_HOPS; hop++) {
    const actual = actualDays?.[probe]
    if (actual != null) return { cost: actual.cost, tier: 'actual' }

    const sched = scheduledDays?.[probe]
    const hasPublished = (sched?.published_shift_count ?? 0) > 0
    const hasUnpublished = (sched?.unpublished_shift_count ?? 0) > 0
    if (hasPublished || (includeUnpublished && hasUnpublished)) {
      const cost = (sched?.published_cost ?? 0) + (includeUnpublished ? (sched?.unpublished_cost ?? 0) : 0)
      return { cost, tier: hasPublished ? 'rota-published' : 'rota-draft' }
    }

    probe = addDaysStr(probe, -7)
  }
  return { cost: 0, tier: 'none' }
}