using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.SceneManagement;

namespace IngameDebugConsole
{
    // Avoid multiple EventSystems in the scene by activating the embedded EventSystem only if one doesn't already exist in the scene
    [DefaultExecutionOrder(1000)]
    public class EventSystemHandler : MonoBehaviour
    {
#pragma warning disable 0649
        [SerializeField] private GameObject embeddedEventSystem;
#pragma warning restore 0649

        private void OnEnable()
        {
            SceneManager.sceneLoaded -= OnSceneLoaded;
            SceneManager.sceneLoaded += OnSceneLoaded;
            SceneManager.sceneUnloaded -= OnSceneUnloaded;
            SceneManager.sceneUnloaded += OnSceneUnloaded;

            ActivateEventSystemIfNeeded();
        }

        private void OnDisable()
        {
            SceneManager.sceneLoaded -= OnSceneLoaded;
            SceneManager.sceneUnloaded -= OnSceneUnloaded;

            DeactivateEventSystem();
        }

        private void OnSceneLoaded(Scene scene, LoadSceneMode mode)
        {
#if UNITY_2017_2_OR_NEWER
            DeactivateEventSystem();
#endif
            ActivateEventSystemIfNeeded();
        }

        private void OnSceneUnloaded(Scene current)
        {
            // Deactivate the embedded EventSystem before changing scenes because the new scene might have its own EventSystem
            DeactivateEventSystem();
        }

        private void ActivateEventSystemIfNeeded()
        {
            if (embeddedEventSystem && !EventSystem.current)
                embeddedEventSystem.SetActive(true);
        }

        private void DeactivateEventSystem()
        {
            if (embeddedEventSystem)
                embeddedEventSystem.SetActive(false);
        }
    }
}