Portal.cs

using System;
using System.Collections;
using System.Linq;
using UnityEditor;
using UnityEngine;
using UnityEngine.AI;
using UnityEngine.SceneManagement;

namespace SceneManagement
{
    [Serializable]
    public class Portal : MonoBehaviour
    {
        [SerializeField] private Transform spawnPoint;
        [SerializeField, HideInInspector] private PortalSo portalData;

        public PortalSo SelectedPortal
        {
            get => portalData;
            set => portalData = value;
        }

        private void OnTriggerEnter(Collider other)
        {
            if (other.CompareTag("Player"))
            {
                StartCoroutine(Transition());
            }
        }

        private IEnumerator Transition()
        {
            DontDestroyOnLoad(gameObject);
            yield return SceneManager.LoadSceneAsync(portalData.SceneToLoad);

            Portal otherPortal = GetOtherPortal();
            UpdatePlayer(otherPortal);

            Destroy(gameObject);
        }

        private void UpdatePlayer(Portal otherPortal)
        {
            GameObject player = GameObject.FindWithTag("Player");
            player.GetComponent<NavMeshAgent>().Warp(otherPortal.spawnPoint.position);
            player.transform.rotation = otherPortal.spawnPoint.rotation;
        }

        private Portal GetOtherPortal()
        {
            var portals = FindObjectsOfType<Portal>();

            return portals.FirstOrDefault(portal => portal.portalData == portalData.DestinationPortal);
        }

        private void OnDrawGizmos()
        {
            BoxCollider col = GetComponent<BoxCollider>();
            DrawBoxCollider(new Color(0, 0, 255, .25f), col);
        }

        private void DrawBoxCollider(Color color, BoxCollider boxCollider)
        {
            Gizmos.matrix = Matrix4x4.TRS(transform.TransformPoint(boxCollider.center), transform.rotation, transform.lossyScale);
            Gizmos.color = color;
            Gizmos.DrawCube(Vector3.zero, boxCollider.size);
        }
    }

#if UNITY_EDITOR
    [CustomEditor(typeof(Portal))]
    public class PortalEditor : Editor
    {
        private PortalSo[] portals;
        private Portal portal;
        private int selectedIndex;
        private string[] portalNames;

        private void OnEnable()
        {
            portal = target as Portal;

            if (portal is null)
                return;

            portals = GetAllInstances<PortalSo>();

            portalNames = new string[portals.Length];
            selectedIndex = portals.ToList().IndexOf(portal.SelectedPortal);

            for (int i = 0; i < portals.Length; i++)
                portalNames[i] = portals[i].name;
        }

        public override void OnInspectorGUI()
        {
            base.OnInspectorGUI();

            selectedIndex = EditorGUILayout.Popup(new GUIContent("Portal Data"), selectedIndex, portalNames);
            portal.SelectedPortal = portals[selectedIndex];

            EditorUtility.SetDirty(target);
        }

        private T[] GetAllInstances<T>() where T : ScriptableObject
        {
            string[] guids = AssetDatabase.FindAssets("t:" + typeof(T).Name);
            var a = new T[guids.Length];

            for (int i = 0; i < guids.Length; i++)
            {
                string path = AssetDatabase.GUIDToAssetPath(guids[i]);
                a[i] = AssetDatabase.LoadAssetAtPath<T>(path);
            }

            return a;
        }
    }
#endif
}