using System;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UIElements;

/// <summary>
///     singleton for a single source of truth game state and flow management
/// </summary>
public class GameManager : MonoBehaviour
{
    /// <summary>
    ///     singleton pattern: define instance field for accessing the singleton elsewhere
    /// </summary>
    public static GameManager Instance;

    /// <summary>
    ///     ui manager object for handling ui state and flow
    /// </summary>
    public UIManager ui;

    /// <summary>
    ///     the local player data object for storing player data
    /// </summary>
    private LocalPlayerData _data;

    /// <summary>
    ///     read-only property for accessing the local player data outside of this class
    /// </summary>
    public LocalPlayerData Data => _data;

    /// <summary>
    ///     list of callbacks to call when the local player data changes
    /// </summary>
    private readonly List<Action<LocalPlayerData>> _onLocalPlayerDataChangeCallbacks = new List<Action<LocalPlayerData>>();

    /// <summary>
    ///     backend object for handling communication with the firebase backend
    /// </summary>
    public Backend Backend;

    /// <summary>
    ///     enforces singleton behaviour; sets doesn't destroy on load and checks for multiple instances
    /// </summary>
    private void Awake()
    {
        // check if instance hasn't been set yet
        if (Instance == null)
        {
            Debug.Log("awake as singleton instance, setting self as the forever-alive instance");
            Instance = this;
            DontDestroyOnLoad(gameObject);
        }
        // check if instance is already set and it's not this instance
        else if (Instance != null && Instance != this)
        {
            Debug.Log("awake as non-singleton instance, destroying self");
            Destroy(gameObject);
        }
    }

    /// <summary>
    ///     called when the game object is enabled, initialises variables
    /// </summary>
    private void OnEnable()
    {
        ui = UIManager.Instance;
        
        // load the local player data and refresh the ui
        _data = new LocalPlayerData();

        Backend = new Backend();
        Backend.Initialise(status =>
        {
            Debug.Log("initialised backend, setting connection status text");

            ui.UI.Q<Label>("ConnectionStatusText").text = status switch
            {
                Backend.FirebaseConnectionStatus.Connected => "Status: Connected",
                Backend.FirebaseConnectionStatus.Updating => "Status: Updating... (Retrying in a bit!)",
                Backend.FirebaseConnectionStatus.NotConnected => "Status: Disconnected",
                Backend.FirebaseConnectionStatus.UpdateRequired =>
                    "Status: Disconnected (Device Component Update Required)",
                Backend.FirebaseConnectionStatus.ExternalError => "Status: Disconnected (External/Device Error)",
                Backend.FirebaseConnectionStatus.InternalError => "Status: Disconnected (Internal Error)",
                _ => "Status: Disconnected (unknown fcs state, this is unreachable and a bug)"
            };

            if (status == Backend.FirebaseConnectionStatus.Connected) return;

            // if we're not connected, hide any online 'features'
            ui.UI.Q<Button>("LeaderboardButton").style.display = DisplayStyle.None;
            ui.UI.Q<Button>("AccountButton").style.display = DisplayStyle.None;
        });
        
        // register a callback to refresh the ui when the player signs in
        Backend.RegisterOnSignInCallback(_ =>
        {
            Debug.Log("sign in callback, refreshing GameManager-controlled SideView UI");
            _data.LoadFromTheWorld(FireLocalPlayerDataChangeCallbacks);
        });
    }
    
    /// <summary>
    ///     load in stuff
    /// </summary>
    private void Start()
    {
        Debug.Log("GameManager starts here");
        _data.LoadFromTheWorld(FireLocalPlayerDataChangeCallbacks);
    }

    /// <summary>
    ///     called when the application is quitting, saves the local player data
    /// </summary>
    private void OnApplicationQuit()
    {
        Debug.Log("running deferred cleanup/save functions");
        Backend.Cleanup();
        _data.SaveToTheWorld();
    }
    
    /// <summary>
    ///     function to register a callback to be called when the local player data changes
    /// </summary>
    /// <param name="callback">callback function that takes a <c>LocalPlayerData</c> object</param>
    public void RegisterOnLocalPlayerDataChangeCallback(Action<LocalPlayerData> callback)
    {
        _onLocalPlayerDataChangeCallbacks.Add(callback);
        Debug.Log($"registering LocalPlayerDataChangeCallback ({_onLocalPlayerDataChangeCallbacks.Count})");
    }

    /// <summary>
    ///     function to fire all local player data change callbacks
    /// </summary>
    private void FireLocalPlayerDataChangeCallbacks(LocalPlayerData data)
    {
        Debug.Log($"firing LocalPlayerDataChangeCallbacks ({_onLocalPlayerDataChangeCallbacks.Count})");
        foreach (var callback in _onLocalPlayerDataChangeCallbacks)
        {
            try
            {
                callback.Invoke(data);
            }
            catch (Exception e)
            {
                Debug.LogError($"error invoking LocalPlayerDataChangeCallback: {e.Message}");
            }
        }
    }
}