cache result getter

cacheResult.ts

/**
 * A cache result decorator means the value is lazily evaluated once and
 * the result is cached on the class instance.
 */
export const cacheResult = <T>(
  target: T,
  key: PropertyKey,
  descriptor: PropertyDescriptor
): void => {
  if (!descriptor) {
    descriptor = Object.getOwnPropertyDescriptor(
      target,
      key
    ) as PropertyDescriptor
  }
  const originalMethod = descriptor.get
  const isStatic = Object.getPrototypeOf(target) === Function.prototype
  if (isStatic) {
    throw new Error(`Don't use @cacheResult decorator on static properties`)
  }
  if (!originalMethod) {
    throw new Error('@cacheResult can only decorate getters!')
  } else if (!descriptor.configurable) {
    throw new Error('@cacheResult target must be configurable')
  } else {
    descriptor.get = function() {
      // eslint-disable-next-line
      const value = originalMethod.apply(this, arguments as any)
      const newDescriptor: PropertyDescriptor = {
        configurable: false,
        enumerable: false,
        value,
      }
      Object.defineProperty(this, key, newDescriptor)
      return value
    }
  }
}