import type { ReturnFunction } from '@/type';

const counter = 0;
function getNewFunction(
  originalMethod: ReturnFunction,
  hashFunction?: ReturnFunction,
): ReturnFunction {
  const identifier = counter + 1;
  // The function returned here gets called instead of originalMethod.
  return function Func(this: any, ...args: string[]) {
    const propValName = `__memoized_value_${identifier}`;
    const propMapName = `__memoized_map_${identifier}`;

    let returnedValue;

    if (hashFunction || args.length > 0) {
      // Get or create map
      if (!('propMapName' in this)) {
        Reflect.defineProperty(this, propMapName, {
          configurable: false,
          enumerable: false,
          writable: false,
          value: new Map<any, any>(),
        });
      }
      const myMap: Map<any, any> = Reflect.get(this, propMapName);

      let [hashKey] = args;

      if (hashFunction) {
        hashKey = hashFunction.apply(this, args);
      }

      if (myMap.has(hashKey)) {
        returnedValue = myMap.get(hashKey);
      } else {
        returnedValue = originalMethod.apply(this, args);
        myMap.set(hashKey, returnedValue);
      }
    } else if ('propValName' in this) {
      returnedValue = Reflect.get(this, propValName);
    } else {
      returnedValue = originalMethod.apply(this, args);
      Reflect.defineProperty(this, propValName, {
        configurable: false,
        enumerable: false,
        writable: false,
        value: returnedValue,
      });
    }
    return returnedValue;
  };
}

export const Memoize =
  (hashFunction?: ReturnFunction): MethodDecorator =>
  (_target: Object, _propertyKey: string | symbol, descriptor: TypedPropertyDescriptor<any>) => {
    if (descriptor.value != null) {
      Reflect.set(descriptor, 'value', getNewFunction(descriptor.value, hashFunction));
    } else if (descriptor.get != null) {
      Reflect.set(descriptor, 'get', getNewFunction(descriptor.value, hashFunction));
    } else {
      throw new Error('Only put a Memoize() decorator on a method or get accessor.');
    }
  };