using System;
using System.IO;
using UnityEngine;

namespace ProjectM.Simulation
{
    /// <summary>
    /// Host-local persistence for the game save slice (<see cref="SaveData"/>) — single slot, versioned JSON at
    /// <c>Application.persistentDataPath/save_0.json</c>, atomic writes (temp + <c>File.Replace</c>). Read by the
    /// menu (to offer "Continue" + stage a <see cref="PendingSave"/>) and the server SaveWriteSystem (autosave).
    /// JsonUtility keeps it dependency-free. Returns null on a missing / corrupt / version-mismatched file —
    /// never throws to callers (a bad save degrades to "New Game", it never crashes boot).
    /// </summary>
    public static class SaveService
    {
        static string FilePath => Path.Combine(Application.persistentDataPath, "save_0.json");

        public static bool HasSave() => File.Exists(FilePath);

        public static SaveData Load()
        {
            try
            {
                if (!File.Exists(FilePath)) return null;
                var data = JsonUtility.FromJson<SaveData>(File.ReadAllText(FilePath));
                // EB-1: additive floor [MinLoadableVersion, CurrentVersion] so OLD v2 saves still load (a missing HP
                // field 0-defaults and the restore guard maps 0 -> baked Max); v0/v1 garbage is still rejected.
                if (data == null || data.Version < SaveData.MinLoadableVersion || data.Version > SaveData.CurrentVersion) return null;
                data.Ledger ??= Array.Empty<LedgerRow>();
                return data;
            }
            catch (Exception e)
            {
                Debug.LogWarning($"[SaveService] Load failed ({e.Message}); treating as no save.");
                return null;
            }
        }

        public static void Save(SaveData data)
        {
            if (data == null) return;
            data.Version = SaveData.CurrentVersion;
            try
            {
                var json = JsonUtility.ToJson(data, true);
                var tmp = FilePath + ".tmp";
                File.WriteAllText(tmp, json);
                if (File.Exists(FilePath)) File.Replace(tmp, FilePath, null);
                else File.Move(tmp, FilePath);
            }
            catch (Exception e)
            {
                Debug.LogWarning($"[SaveService] Save failed: {e.Message}");
            }
        }

        public static void Delete()
        {
            try { if (File.Exists(FilePath)) File.Delete(FilePath); }
            catch (Exception e) { Debug.LogWarning($"[SaveService] Delete failed: {e.Message}"); }
        }
    }
}