import UIKit

// ---- [LoginManager.swift] ---- starts
enum LoginError: Error {
    case minUserNameLength(String), minPasswordLength(String), invalidUserName(String), invalidPassword(String)
}

enum LoginResult {
    case result([String: Any])
}

struct LoginManager {
    static func validate(user: String, pass: String, completion: (LoginResult) -> Void ) throws {
        guard (!user.isEmpty && user.count > 8) else { throw LoginError.minUserNameLength("A minimum username length is >= 8 characters.") }
        guard (!pass.isEmpty && pass.count > 8) else { throw LoginError.minPasswordLength("A minimum password length is >= 8 characters.") }

        //Call Login API to confirm the credentials with provided userName and password values.
        //Here we're checking locally for testing purpose.
        if user != "iosdevfromthenorthpole" { throw LoginError.invalidUserName("Invalid Username.") }
        if pass != "polardbear" { throw LoginError.invalidPassword("Invalid Password.") }

        //The actual result will be passed instead of below static result.
        completion(LoginResult.result(["userId": 1, "email": "nointernet@thenorthpole.com"]))
    }

    static func handle(error: LoginError, completion: (_ title: String, _ message: String) -> Void) {
        //Note that all associated values are of the same type for the LoginError cases.
        //Can we write it in more appropriate way?
        let title = "Login failed."
        switch error {
        case .minUserNameLength(let errorMessage):
            completion(title, errorMessage)
        case .minPasswordLength(let errorMessage):
            completion(title, errorMessage)
        case .invalidUserName(let errorMessage):
            completion(title, errorMessage)
        case .invalidPassword(let errorMessage):
            completion(title, errorMessage)
        }
    }
}
// ---- [LoginManager.swift] ---- ends

// ---- [LoginViewController.swift] ---- starts
//Confirming the user credentials when user taps on the "Login" button.

do {
    try LoginManager.validate(user: "iosdevfromthenorthpole", pass: "polardbear", completion: { (loginResult) in
        switch loginResult {
            case .result (let result):
                print("userId: ", result["userId"] ?? "Not available.")
                print("email: ", result["email"] ?? "Not available.")
        }
    })
} catch let error as LoginError {
    LoginManager.handle(error: error) { (title, message) in
        //Show an alert with title and message to the user.
        print(title + " " + message)
    }
}
// ---- [LoginViewController.swift] ---- ends