DDD Tactical Patterns

// value object: immutable, compared by value, validates itself
export class Money {
  private constructor(readonly kobo: bigint, readonly currency: 'NGN' | 'USD') {}
  static of(kobo: bigint, c: 'NGN' | 'USD') { if (kobo < 0n) throw new Error('negative'); return new Money(kobo, c); }
  plus(o: Money) { this.same(o); return new Money(this.kobo + o.kobo, this.currency); }
  private same(o: Money) { if (o.currency !== this.currency) throw new Error('currency mismatch'); }
}
// aggregate root method: rules live here, not in controllers
hold(amount: Money, ref: string): void {
  if (this.available().lt(amount)) throw new InsufficientFunds(this.id, amount);
  this.holds.push(new Hold(ref, amount)); this.events.push({ type: 'FundsHeld', accountId: this.id, ref });
}