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 _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);
        }
    }

    private void Start()
    {
        // load the local player data and refresh the ui
        _localPlayerData = new LocalPlayerData();
        _localPlayerData.LoadFromTheWorld();
        PopulateFields();

        // register a callback to refresh the ui when the player signs in
        Backend.RegisterOnSignInCallback(_ => { _localPlayerData.LoadFromTheWorld(); });
    }

    /// <summary>
    ///     called when the game object is enabled, initialises variables
    /// </summary>
    private void OnEnable()
    {
        Backend = new Backend();
        Backend.Initialise();
        ui = UIManager.Instance;
    }

    /// <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();
        _localPlayerData.SaveToTheWorld();
    }

    /// <summary>
    ///     populate the fields with the given username and email, used by GameManager after local player data is loaded
    /// </summary>
    public void PopulateFields()
    {
        ui.UI.Q<TextField>("UsernameField").value = _localPlayerData.LastKnownUsername;
        ui.UI.Q<TextField>("EmailField").value = _localPlayerData.LastKnownEmail;
    }
}