import type { ParticipantId } from '../types';

/**
 * Splits amountCents equally among participantIds. Any remainder cents (from
 * integer division) go one-each to the first participants in the given
 * order, so the shares always sum exactly back to amountCents.
 */
export function computeSplit(
  amountCents: number,
  participantIds: ParticipantId[],
): Record<ParticipantId, number> {
  if (participantIds.length === 0) {
    throw new Error('computeSplit requires at least one participant');
  }

  const base = Math.floor(amountCents / participantIds.length);
  const remainder = amountCents - base * participantIds.length;

  const shares: Record<ParticipantId, number> = {};
  participantIds.forEach((id, index) => {
    shares[id] = base + (index < remainder ? 1 : 0);
  });
  return shares;
}