Decorator Patterns

function Log(target: any, propertyKey: string, descriptor: PropertyDescriptor) {
  const original = descriptor.value;

  descriptor.value = function (...args: any[]) {
    console.log(`Calling ${propertyKey} with:`, args);
    const result = original.apply(this, args);
    console.log(`Result:`, result);
    return result;
  };

  return descriptor;
}

class Calculator {
  @Log
  add(a: number, b: number): number {
    return a + b;
  }
}

function Memoize(target: any, propertyKey: string, descriptor: PropertyDescriptor) {
  const cache = new Map<string, any>();
  const original = descriptor.value;

  descriptor.value = function (...args: any[]) {
    const key = JSON.stringify(args);
    if (cache.has(key)) return cache.get(key);

    const result = original.apply(this, args);
    cache.set(key, result);
    return result;
  };

  return descriptor;
}

function Singleton<T extends new (...args: any[]) => any>(constructor: T) {
  let instance: InstanceType<T>;

  return class extends constructor {
    constructor(...args: any[]) {
      if (instance) return instance;
      super(...args);
      instance = this;
    }
  };
}

@Singleton
class Database {
  connect() {
    /* ... */
  }
}