examples/open_world_city/Assets/Scripts/SaveSystem.cs

using System;
using System.IO;
using UnityEngine;

namespace UnityAgent
{
    /// <summary>
    /// JSON save system using <see cref="JsonUtility"/>. Stores a single
    /// save slot per profile in <c>Application.persistentDataPath</c>.
    /// </summary>
    public class SaveSystem : MonoBehaviour
    {
        public static SaveSystem Instance { get; private set; }

        public string profileName = "default";

        private void Awake()
        {
            if (Instance != null && Instance != this) { Destroy(gameObject); return; }
            Instance = this;
            DontDestroyOnLoad(gameObject);
        }

        private string SavePath => Path.Combine(Application.persistentDataPath, profileName + ".save");

        public void Save<T>(T data) where T : class
        {
            try
            {
                string json = JsonUtility.ToJson(new Wrapper<T> { payload = data }, true);
                File.WriteAllText(SavePath, json);
                Debug.Log($"[SaveSystem] Saved to {SavePath}");
            }
            catch (Exception e)
            {
                Debug.LogError($"[SaveSystem] Save failed: {e}");
            }
        }

        public T Load<T>() where T : class
        {
            if (!File.Exists(SavePath)) return null;
            try
            {
                string json = File.ReadAllText(SavePath);
                var w = JsonUtility.FromJson<Wrapper<T>>(json);
                return w?.payload;
            }
            catch (Exception e)
            {
                Debug.LogError($"[SaveSystem] Load failed: {e}");
                return null;
            }
        }

        public bool HasSave => File.Exists(SavePath);

        public void Delete()
        {
            if (File.Exists(SavePath)) File.Delete(SavePath);
        }

        [Serializable]
        private class Wrapper<T> { public T payload; }
    }
}