/**
 * Task 1771 — receivables and payables ageing.
 *
 * Buckets are inclusive-lower on whole days past the due date: 0-30 is
 * `current`, 31-60, 61-90, and 91 and above is `d90plus`. An invoice not yet
 * due has a negative age, which clamps to 0 and lands in `current`.
 *
 * Every bucket is a summed money amount, not a count of invoices. Summing is
 * done in minor units so a statement of many decimal amounts does not drift.
 */
import { toMinor, fromMinor } from './money.js'

const DAY_MS = 86_400_000

export interface OpenInvoice {
  ref: string
  dueDateMs: number
  outstanding: number
}

export interface AgeBuckets {
  current: number
  d31to60: number
  d61to90: number
  d90plus: number
  total: number
}

export function ageBuckets(invoices: readonly OpenInvoice[], now: number): AgeBuckets {
  let current = 0
  let d31to60 = 0
  let d61to90 = 0
  let d90plus = 0

  for (const inv of invoices) {
    const ageDays = Math.max(0, Math.floor((now - inv.dueDateMs) / DAY_MS))
    const minor = toMinor(inv.outstanding)
    if (ageDays <= 30) current += minor
    else if (ageDays <= 60) d31to60 += minor
    else if (ageDays <= 90) d61to90 += minor
    else d90plus += minor
  }

  return {
    current: fromMinor(current),
    d31to60: fromMinor(d31to60),
    d61to90: fromMinor(d61to90),
    d90plus: fromMinor(d90plus),
    total: fromMinor(current + d31to60 + d61to90 + d90plus),
  }
}