/**
 * Server-stamped phase timer math for the grand-finale ceremony.
 *
 * The cursor stores `phaseStartedAt` + `phaseDurationSeconds` plus a pause
 * accumulator; every client derives the countdown locally from those stamps,
 * so all screens agree and overtime is just a negative remainder.
 */

export type PhaseTimerState = {
  phaseStartedAt: Date | string | null
  phaseDurationSeconds: number | null
  phasePausedAt: Date | string | null
  phasePausedAccumMs: number
}

export function elapsedMs(t: PhaseTimerState, now: Date = new Date()): number {
  if (!t.phaseStartedAt) return 0
  const start = new Date(t.phaseStartedAt).getTime()
  const end = t.phasePausedAt ? new Date(t.phasePausedAt).getTime() : now.getTime()
  return Math.max(0, end - start - t.phasePausedAccumMs)
}

/** Seconds left on the phase timer; negative = overtime; null = no timer running. */
export function remainingSeconds(t: PhaseTimerState, now: Date = new Date()): number | null {
  if (!t.phaseStartedAt || t.phaseDurationSeconds == null) return null
  return t.phaseDurationSeconds - Math.floor(elapsedMs(t, now) / 1000)
}

/** `5:05` for positive seconds, `+1:23` for overtime. */
export function formatClock(seconds: number): string {
  const over = seconds < 0
  const abs = Math.abs(seconds)
  const m = Math.floor(abs / 60)
  const s = abs % 60
  return `${over ? '+' : ''}${m}:${s.toString().padStart(2, '0')}`
}