# Adapter pattern
- 써드파티 라이브러리에서 제공하는 것을 변형해서 사용하고 싶을 때
- legacy object
```swift
public struct GoogleUser {
  public var email: String
  public var password: String
  public var token: String
}

public class GoogleAuthenticator {

  public func login(email: String,
                    password: String,
                    completion: @escaping (GoogleUser?, Error?) -> Void) {
    let token = "special-token-value"
    let user = GoogleUser(email: email,
                          password: password,
                          token: token)
    completion(user, nil)
  }
}
```


- 내가 사용하고 싶은 것
```swift
public struct User {
  public let email: String
  public let password: String
}

public struct Token {
  public let value: String
}
```

- new protocol

```swift
public protocol AuthenticationService {
  func login(email: String,
             password: String,
             success: @escaping (User, Token) -> Void,
             failure: @escaping (Error?) -> Void)
}

```

- adapter

```swift
public class GoogleAuthenticatorAdapter: AuthenticationService {

  private var authenticator = GoogleAuthenticator()

  public func login(email: String, password: String, success: @escaping (User, Token) -> Void, failure: @escaping (Error?) -> Void) {
    authenticator.login(email: email, password: password) { (googleUser, error) in

      guard let googleUser = googleUser else {
        failure(error)
        return
      }

      let user = User(email: googleUser.email,
                      password: googleUser.password)
      let token = Token(value: googleUser.token)
      success(user, token)
    }
  }
}

```