Local-First Collaboration: Decentralized Consistency with CRDTs

// Abstract CRDT state merge demonstration
interface ElementTag<T> {
  value: T;
  tag: string; // Globally unique lamport timestamp + client id
}

class ORSet<T> {
  private addSet = new Map<string, ElementTag<T>>();
  private removeSet = new Set<string>();

  add(value: T, clientId: string): string {
    const tag = `${Date.now()}-${clientId}-${Math.random().toString(36).slice(2)}`;
    this.addSet.set(tag, { value, tag });
    return tag;
  }

  remove(tag: string): void {
    this.removeSet.add(tag);
  }

  read(): T[] {
    const items: T[] = [];
    for (const [tag, item] of this.addSet.entries()) {
      if (!this.removeSet.has(tag)) items.push(item.value);
    }
    return items;
  }

  merge(remote: ORSet<T>): void {
    // Commutative set union
    for (const [tag, item] of remote.addSet.entries()) {
      if (!this.addSet.has(tag)) this.addSet.set(tag, item);
    }
    for (const tag of remote.removeSet) {
      this.removeSet.add(tag);
    }
  }
}