Software that outlives the team that built it.

/** A posting that has been written to the journal. */
export type Posted = Entry & { readonly postedAt: Date };

/**
 * Journal entries are append-only: correcting one means posting its
 * reversal, never editing the original. Balances are therefore a
 * fold over history rather than a mutable running total.
 */
export function post(journal: Journal, entry: Entry): Result<Posted> {
  if (sum(entry.lines) !== 0n) {
    return err("Entry does not balance", { lines: entry.lines });
  }
  if (journal.isClosed(entry.period)) {
    return err("Period is closed", { period: entry.period });
  }
  return ok(journal.append({ ...entry, postedAt: new Date() }));
}