Facebook user management for login and logout in Swift.

FacebookManager.swift

//
//  FacebookManager.swift
//
//  Created by Mathieu White on 2016-02-07.
//  Copyright © 2016 Mathieu White. All rights reserved.
//

import UIKit
import FBSDKCoreKit
import FBSDKLoginKit

let kFacebookLoggedOutNotification: String = "kFacebookLoggedOutNotification"
let kFacebookLoginSuccessNotification: String = "kFacebookLoginSuccessNotification"

/**
 *  Structure that holds the properties on the current Facebook user.
 */
struct FacebookUser
{
    var id: String = ""
    var firstName: String = ""
    var lastName: String = ""
    var email: String = ""
    var pictureURL: String = ""
}

/// Singleton class that handles all of Facebook's API calls in the app.
class FacebookManager: NSObject
{
    // MARK: - Constants
    
    /// The shared instance of the FacebookManager.
    static let sharedInstance: FacebookManager = FacebookManager()
    
    // The permissions to request from the Facebook API
    private let readPermissions: [AnyObject] = [
        "public_profile",
        "email",
    ]
    
    /// The parameters for fetching users.
    private let userParameters: [NSObject : AnyObject] = [
        "fields" : "id,first_name,last_name,email,picture{url}"
    ]
    
    /// The Facebook login manager for the application.
    private let loginManager: FBSDKLoginManager = FBSDKLoginManager()
    
    // MARK: - API Routes
    
    /// The API route to access the current user.
    private let currentUserPath: String = "me"
    
    // MARK: - Variables
    
    /// The current user logged in through Facebook.
    var currentUser: FacebookUser?
    
    // MARK: - Initializers
    
    private override init()
    {
        super.init()
        
        self.fetchCurrentUser()
    }
    
    // MARK: - User Access Methods
    
    /**
    This method checks if the app has access to the user's Facebook account.
    
    - returns: true if the app is connected to Facebook, false otherwise
    */
    func hasUserAccess() -> Bool
    {
        if let _ = FBSDKAccessToken.currentAccessToken()
        {
            return true
        }
        
        return false
    }
    
    /**
    This method handles the user's access inside the app. 
    It will either ask the user to connect with Facebook, 
    or logout, depending on the current status of the app.
    */
    func handleUserAccess()
    {
        // If the user is already connected, confirm the logout
        if (self.hasUserAccess())
        {
            self.loginManager.logOut()
            
            // Notify observers that the user logged out of their Facebook account
            NSNotificationCenter.defaultCenter().postNotificationName(kFacebookLoggedOutNotification, object: nil)
        }
        else
        {
            // Present the user with the Facebook login screen
            self.loginManager.logInWithReadPermissions(self.readPermissions,
                fromViewController: nil,
                handler: { [weak self] (result: FBSDKLoginManagerLoginResult!, error: NSError!) -> Void in
                    
                    // Check if the app received access to the Facebook account
                    if (self?.hasUserAccess() == true)
                    {
                        // Notify observers that the Facebook login was successful
                        NSNotificationCenter.defaultCenter().postNotificationName(kFacebookLoginSuccessNotification, object: nil)
                        
                        // Fetch the current user
                        if (self?.currentUser == nil)
                        {
                            self?.fetchCurrentUser()
                        }
                    }
                    
            })
        }
    }
    
    // MARK: - User Methods
    
    private func fetchCurrentUser()
    {
        // Initialize the request for the current user
        let request: FBSDKGraphRequest = FBSDKGraphRequest(graphPath: self.currentUserPath, parameters: self.userParameters)
        
        // Request the current user
        request.startWithCompletionHandler({ [weak self] (connection, result, error) -> Void in
            
            // Logged an error if we have one
            if let error = error
            {
                print("Error fetching Facebook user: \(error.localizedDescription)")
            }
            else
            {
                // Initialize the new facebook user info
                var currentUser: FacebookUser = FacebookUser()
                
                // Get the result as a dictionary
                if let result = result as? [NSObject : AnyObject]
                {
                    // Get the facebook user's id
                    if let id = result["id"] as? String
                    {
                        currentUser.id = id
                    }
                    
                    // Get the facebook user's first name
                    if let firstName = result["first_name"] as? String
                    {
                        currentUser.firstName = firstName
                    }
                    
                    // Get the facebook user's last name
                    if let lastName = result["last_name"] as? String
                    {
                        currentUser.lastName = lastName
                    }
                    
                    // Get the facebook user's email
                    if let email = result["email"] as? String
                    {
                        currentUser.email = email
                    }
                    
                    // Get the facebook user's picture URL
                    if
                        let picture = result["picture"] as? [NSObject : AnyObject],
                        let data = picture["data"] as? [NSObject : AnyObject],
                        let url = data["url"] as? String
                    {
                        currentUser.pictureURL = url
                    }
                }
                
                // Set the current user
                self?.currentUser = currentUser
            }
        })
    }
}