for-carey.ts

interface HttpClient<Response, Options extends {} = {}> {
  get: (url: string, options: Options) => Promise<Response>;
  put: (url: string, options: Options) => Promise<Response>;
  post: (url: string, options: Options) => Promise<Response>;
}




interface CurrencyFormatter {
  format: (str: string) => string
}

class USCurrencyFormatter implements CurrencyFormatter {
  format = (str: string) => {
    return "$5.00"
  }
}

class CACurrencyFormatter implements CurrencyFormatter {
  format = (str: string) => {
    return "dfaksdfls"
  }
}

interface User {
  country: string
}


class CurrencyFormatterFactory {
  
  constructor(private user: User) {}

  getFormatter = (): CurrencyFormatter => {
    switch (this.user.country) {
      case "US":
        return new USCurrencyFormatter()
      case "CA":
        return new CACurrencyFormatter()
      default:
        throw Error("You fucked up")
    }
  }
}






class CurrencyFormatterBuilder {

  private selectedCurrency?: String

  withCurrencyType(currencyType: string): CurrencyFormatterBuilder {
    return this
  }

  build = (): CurrencyFormatter => {
    switch (this.selectedCurrency) {
      case "US":
        return new USCurrencyFormatter();
      case "CA":
        return new CACurrencyFormatter();
      default:
        throw Error("You fucked up");
    }
  };
}

















// business logic
//
const user = {country: "US"}

// const formatter = new CurrencyFormatterFactory(user).getFormatter()
const formatter = new CurrencyFormatterBuilder()
                       .withCurrencyType(user.country)
                       .build()

console.log(formatter.format("")) // $5.00