using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Threading;
using AibisDream.Utility;
using Newtonsoft.Json;
using UnityEngine;

namespace AibisDream.SaveSystem
{
    /// <summary>
    /// 存档槽位目录与文件路径工具。
    /// </summary>
    public static class SlotDirectory
    {
        public static string GetSlotPath(int slotIndex)
        {
            return Path.Combine(ConstRef.SaveFilePath, $"{ConstRef.SaveSlotDirPrefix}{slotIndex}");
        }

        public static string GetSnapshotPath(int slotIndex)
        {
            return Path.Combine(GetSlotPath(slotIndex), $"{ConstRef.SaveSnapshotFileName}.json");
        }

        public static string GetMetaPath(int slotIndex)
        {
            return Path.Combine(GetSlotPath(slotIndex), $"{ConstRef.SaveMetaFileName}.json");
        }

        public static string GetThumbnailPath(int slotIndex)
        {
            return Path.Combine(GetSlotPath(slotIndex), $"{ConstRef.SaveThumbnailFileName}.png");
        }

        public static string GetLatestSlotIndexPath()
        {
            return Path.Combine(ConstRef.SaveFilePath, $"{ConstRef.LatestSlotFileName}.json");
        }

        public static bool Exists(int slotIndex)
        {
            return File.Exists(GetMetaPath(slotIndex));
        }

        public static IEnumerable<int> EnumerateExistingSlots()
        {
            if (!Directory.Exists(ConstRef.SaveFilePath))
            {
                yield break;
            }

            for (var i = SlotIndex.Auto; i <= SlotIndex.ManualEnd; i++)
            {
                if (Exists(i))
                {
                    yield return i;
                }
            }
        }

        public static void EnsureSlotDirectory(int slotIndex)
        {
            Directory.CreateDirectory(GetSlotPath(slotIndex));
        }
    }

    /// <summary>
    /// 槽位文件原子写工具。
    /// <para>先写入临时文件，再重命名为最终文件，避免写入过程中崩溃导致存档损坏。</para>
    /// </summary>
    public static class SlotAtomicWriter
    {
        public static void WriteJson<T>(T obj, string finalPath)
        {
            var json = JsonConvert.SerializeObject(obj, Formatting.Indented);
            WriteText(json, finalPath);
        }

        public static void WriteText(string text, string finalPath)
        {
            var tempPath = finalPath + ".tmp";
            var dir = Path.GetDirectoryName(finalPath);
            if (!string.IsNullOrEmpty(dir))
            {
                Directory.CreateDirectory(dir);
            }

            File.WriteAllText(tempPath, text);
            CommitTempFile(tempPath, finalPath);
        }

        public static void WriteBytes(byte[] data, string finalPath)
        {
            if (data == null)
            {
                return;
            }

            var tempPath = finalPath + ".tmp";
            var dir = Path.GetDirectoryName(finalPath);
            if (!string.IsNullOrEmpty(dir))
            {
                Directory.CreateDirectory(dir);
            }

            File.WriteAllBytes(tempPath, data);
            CommitTempFile(tempPath, finalPath);
        }

        private static void CommitTempFile(string tempPath, string finalPath)
        {
            const int maxAttempts = 5;

            for (var attempt = 0; attempt < maxAttempts; attempt++)
            {
                try
                {
                    if (File.Exists(finalPath))
                    {
                        // Unity 使用的 .NET Standard 2.0 无 File.Move(..., overwrite)；Replace 为原子覆盖。
                        File.Replace(tempPath, finalPath, null);
                    }
                    else
                    {
                        File.Move(tempPath, finalPath);
                    }

                    return;
                }
                catch (IOException) when (attempt < maxAttempts - 1)
                {
                    Thread.Sleep(20 * (attempt + 1));
                }
            }
        }
    }
}