using System;
using System.Threading.Tasks;
using Firebase;
using Firebase.Auth;
using Firebase.Database;
using UnityEngine;

/// <summary>
///     the general managing class for handling communication with the firebase backend
///     (to be initialised by GameManager)
/// </summary>
public class Backend : MonoBehaviour
{
    /// <summary>
    ///     whether the backend is connected to the firebase backend
    /// </summary>
    public bool connected;

    /// <summary>
    ///     the firebase authentication object
    /// </summary>
    private FirebaseAuth _auth;

    /// <summary>
    ///     the firebase database reference
    /// </summary>
    private DatabaseReference _db;

    /// <summary>
    ///     callback function to be invoked when the user signs in
    /// </summary>
    private Action<FirebaseUser> _onSignInCallback = user => { Debug.Log("signed in as" + user.UserId); };

    /// <summary>
    ///     callback function to be invoked when the user signs out
    /// </summary>
    private Action<FirebaseUser> _onSignOutCallback = user => { Debug.Log("signed out" + user.UserId); };

    /// <summary>
    ///     the current user object, if authenticated
    /// </summary>
    private FirebaseUser _user;

    /// <summary>
    ///     script load function
    /// </summary>
    private void Awake()
    {
        Debug.Log("firing firebase Initialise() invocation");
        Initialise();
    }

    /// <summary>
    ///     deferred cleanup function
    /// </summary>
    private void OnDestroy()
    {
        SignOutUser();
    }

    /// <summary>
    ///     variable initialisation function
    /// </summary>
    private void Initialise()
    {
        FirebaseApp.CheckAndFixDependenciesAsync().ContinueWith(task =>
        {
            switch (task.Result)
            {
                case DependencyStatus.Available:
                    var app = FirebaseApp.DefaultInstance;
                    _auth = FirebaseAuth.GetAuth(app);
                    _auth.StateChanged += AuthStateChanged;
                    _db = FirebaseDatabase.DefaultInstance.RootReference;
                    connected = true;
                    Debug.Log("firebase initialised");
                    break;

                case DependencyStatus.UnavailableDisabled:
                case DependencyStatus.UnavailableInvalid:
                case DependencyStatus.UnavilableMissing:
                case DependencyStatus.UnavailablePermission:
                    Debug.LogError("firebase error outside of our control");
                    break;

                case DependencyStatus.UnavailableUpdaterequired:
                case DependencyStatus.UnavailableUpdating:
                    Debug.LogError("firebase is updating");
                    RetryInitialiseAfterDelay();
                    break;

                case DependencyStatus.UnavailableOther:
                default:
                    Debug.LogError("firebase ??? blew up or something," + task.Result);
                    break;
            }
        });
    }

    /// <summary>
    ///     function to handle the authentication state change event
    /// </summary>
    /// <param name="sender">the object that triggered the event</param>
    /// <param name="eventArgs">the event arguments</param>
    private void AuthStateChanged(object sender, EventArgs eventArgs)
    {
        if (_auth.CurrentUser == _user) return;
        var signedIn = _user != _auth.CurrentUser && _auth.CurrentUser != null;
        switch (signedIn)
        {
            case false when _user != null:
                _onSignOutCallback(_user);
                break;
            case true:
                _onSignInCallback(_auth.CurrentUser);
                break;
        }
    }

    /// <summary>
    ///     function to register a callback for when the user signs in
    /// </summary>
    /// <param name="callback">callback function that takes in a FirebaseUser argument</param>
    private void RegisterOnSignInCallback(Action<FirebaseUser> callback)
    {
        _onSignInCallback = callback;
    }

    /// <summary>
    ///     function to register a callback for when the user signs out
    /// </summary>
    /// <param name="callback">callback function that takes in a FirebaseUser argument</param>
    private void RegisterOnSignOutCallback(Action<FirebaseUser> callback)
    {
        _onSignOutCallback = callback;
    }

    /// <summary>
    ///     async function to retry initialisation after a delay
    /// </summary>
    private async void RetryInitialiseAfterDelay()
    {
        await Task.Delay(TimeSpan.FromSeconds(10));
        Initialise();
    }

    /// <summary>
    ///     abstraction function to authenticate the user
    /// </summary>
    /// <param name="username">user name string</param>
    /// <param name="password">user raw password string</param>
    /// <param name="callback">callback function that takes in an AuthenticationResult argument</param>
    /// <param name="registerUser">whether to treat authentication as registration</param>
    private void AuthenticateUser(
        string username,
        string password,
        Action<AuthenticationResult> callback,
        bool registerUser = false)
    {
        throw new NotImplementedException();
    }

    /// <summary>
    ///     abstraction function to retrieve the user
    /// </summary>
    /// <returns>the firebase user object</returns>
    private FirebaseUser GetUser()
    {
        return _user;
    }
    
    /// <summary>
    ///     abstraction function to sign out the user
    /// </summary>
    private void SignOutUser()
    {
        _auth.SignOut();
    }

    /// <summary>
    ///     abstraction function to submit a play to the database
    /// </summary>
    /// <param name="averageMatchAccuracy">the float percentage (0-100) of how accurate the user was when colour matching</param>
    /// <param name="callback">callback function that takes in one DatabaseTransactionResult argument</param>
    private void SubmitPlay(
        float averageMatchAccuracy,
        Action<DatabaseTransactionResult> callback)
    {
        throw new NotImplementedException();
    }

    /// <summary>
    ///     abstraction function to get and calculate the user's rating from the database
    ///     calculation is done locally, call UpdateUserRating to update the user's rating in the database
    /// </summary>
    /// <param name="callback">callback function that takes in a DatabaseTransactionResult and float (user rating) argument</param>
    private void CalculateUserRating(
        Action<DatabaseTransactionResult, float> callback)
    {
        throw new NotImplementedException();
    }

    /// <summary>
    ///     abstraction function to update the user's rating in the database
    /// </summary>
    /// <param name="newRating">new user rating value as a float</param>
    /// <param name="callback">callback function that takes in one DatabaseTransactionResult argument</param>
    private void UpdateUserRating(
        float newRating,
        Action<DatabaseTransactionResult> callback)
    {
        throw new NotImplementedException();
    }

    /// <summary>
    ///     abstraction function to get the leaderboard from the database
    /// </summary>
    /// <param name="callback"></param>
    /// <exception cref="NotImplementedException"></exception>
    private void GetLeaderboard(
        Action<DatabaseTransactionResult, LeaderboardEntry[]> callback)
    {
        throw new NotImplementedException();
    }

    /// <summary>
    ///     struct for a leaderboard entry
    /// </summary>
    // ReSharper disable once MemberCanBePrivate.Global
    public struct LeaderboardEntry
    {
        public string Username;
        public float Rating;
        public int PlayCount;
    }

    /// <summary>
    ///     enum for the result of the authentication process
    /// </summary>
    // ReSharper disable once MemberCanBePrivate.Global
    public enum AuthenticationResult
    {
        Ok,
        AlreadyAuthenticated,
        NonExistentUser,
        AlreadyExistingUser,
        InvalidCredentials,
        GenericError
    }

    /// <summary>
    ///     generic enum for the result of a database transaction
    /// </summary>
    // ReSharper disable once MemberCanBePrivate.Global
    public enum DatabaseTransactionResult
    {
        Ok,
        Unauthenticated,
        Error
    }
}