/** Pure math for the relationship-pulse ribbon (Client 360 overview). */

export interface PulseEvent {
  id: string
  lane: number
  date: string // ISO yyyy-mm-dd
  label: string
  tone: 'accent' | 'ok' | 'warn' | 'err'
}

export const LANES = ['Documents', 'Payments', 'Interactions', 'AMC & renewals'] as const

/** n month keys ('YYYY-MM') ending at todayIso's month, oldest first. */
export function lastMonths(todayIso: string, n = 12): string[] {
  const year = Number(todayIso.slice(0, 4))
  const month = Number(todayIso.slice(5, 7)) // 1-based
  const out: string[] = []
  for (let i = n - 1; i >= 0; i--) {
    const total = year * 12 + (month - 1) - i
    const y = Math.floor(total / 12)
    const m = total % 12 + 1
    out.push(`${y}-${String(m).padStart(2, '0')}`)
  }
  return out
}

/** Bucket events into `${lane}:${monthIndex}` cells; out-of-window events are dropped. */
export function groupPulse(events: PulseEvent[], months: string[]): Map<string, PulseEvent[]> {
  const index = new Map<string, number>()
  months.forEach((m, i) => index.set(m, i))
  const out = new Map<string, PulseEvent[]>()
  for (const ev of events) {
    const mi = index.get(ev.date.slice(0, 7))
    if (mi === undefined) continue
    const key = `${ev.lane}:${mi}`
    const cell = out.get(key)
    if (cell !== undefined) cell.push(ev)
    else out.set(key, [ev])
  }
  return out
}