export interface MonthlyBucket {
  month: string // YYYY-MM
  label: string // e.g. "Jul"
  total: number
  leading: number // hazard + near_miss
  lagging: number // injury
}

const LEADING_TYPES = ['hazard', 'near_miss']

export function bucketIncidentsByMonth(
  incidents: Array<{ reported_at: string; incident_type: string }>,
  months = 12,
  now = new Date(),
): MonthlyBucket[] {
  const buckets: MonthlyBucket[] = []
  const index = new Map<string, MonthlyBucket>()

  for (let i = months - 1; i >= 0; i--) {
    const d = new Date(Date.UTC(now.getUTCFullYear(), now.getUTCMonth() - i, 1))
    const month = `${d.getUTCFullYear()}-${String(d.getUTCMonth() + 1).padStart(2, '0')}`
    const bucket: MonthlyBucket = {
      month,
      label: d.toLocaleString('en', { month: 'short', timeZone: 'UTC' }),
      total: 0,
      leading: 0,
      lagging: 0,
    }
    buckets.push(bucket)
    index.set(month, bucket)
  }

  for (const inc of incidents) {
    const month = inc.reported_at.slice(0, 7)
    const bucket = index.get(month)
    if (!bucket) continue
    bucket.total++
    if (LEADING_TYPES.includes(inc.incident_type)) bucket.leading++
    if (inc.incident_type === 'injury') bucket.lagging++
  }

  return buckets
}

export interface RootCauseCount {
  cause: string
  count: number
}

// Root causes are free text (investigations.root_cause_summary); group on a
// normalized form so trivially different phrasings still collapse together.
export function topRootCauses(
  investigations: Array<{ root_cause_summary: string | null }>,
  top = 5,
): RootCauseCount[] {
  const counts = new Map<string, { cause: string; count: number }>()

  for (const inv of investigations) {
    const raw = (inv.root_cause_summary ?? '').trim()
    if (!raw) continue
    const key = raw.toLowerCase().replace(/\s+/g, ' ').replace(/[.。]$/, '')
    const entry = counts.get(key)
    if (entry) entry.count++
    else counts.set(key, { cause: raw, count: 1 })
  }

  return [...counts.values()]
    .sort((a, b) => b.count - a.count)
    .slice(0, top)
}