🎉 init

shared/utils/split.ts

@@ -0,0 +1,21 @@
+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
+}