SwiftUI Firebase如何处理自定义错误

import SwiftUI
import Firebase

enum CustomError: Error {
    case invalidEmail
    case weakPassword
    case networkError
}

struct ContentView: View {
    @State private var errorMessage: String?

    var body: some View {
        VStack {
            TextField("Email", text: .constant("user@example.com"))
            TextField("Password", text: .constant("password"))
            Button(action: signIn) {
                Text("Sign In")
            }
            if let message = errorMessage {
                Text(message)
                    .foregroundColor(.red)
            }
        }
    }

    func signIn() {
        guard let email = "user@example.com", let password = "password" else { return }

        Auth.auth().signIn(withEmail: email, password: password) { result, error in
            if let error = error {
                switch error.code {
                case "ERROR_INVALID_EMAIL":
                    self.errorMessage = "Invalid email address."
                case "ERROR_WEAK_PASSWORD":
                    self.errorMessage = "Password is too weak."
                default:
                    self.errorMessage = "Network error. Please try again later."
                }
            } else {
                print("User signed in successfully.")
            }
        }
    }
}