using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using Cysharp.Threading.Tasks;
using Newtonsoft.Json.Linq;

namespace ShrinkDataSaver
{
    [Serializable]
    internal class SettingsData
    {
        public Dictionary<string, JToken> Values = new();
    }

    public static class ShrinkSettings
    {
        private const string BackupPrimarySuffix = ".bak1";
        private const string BackupSecondarySuffix = ".bak2";

        private static SettingsData _data = new();
        private static IStorageProvider _storage;
        private static string _filePath;

        private static CancellationTokenSource _debounceCts;
        private static readonly Dictionary<string, List<Action<object>>> _watchers = new();

        public static event Action<string, object> OnChanged;

        internal static void Initialize(IStorageProvider storage, string filePath)
        {
            _storage = storage; _filePath = filePath;
        }

        public static void Set<T>(string key, T value)
        {
            _data.Values[key] = JToken.FromObject(value);
            FireChanged(key, value);
            ScheduleWrite().Forget();
        }

        public static T Get<T>(string key, T defaultValue = default)
        {
            if (_data.Values.TryGetValue(key, out var token))
            {
                try { return token.ToObject<T>(); } catch { /* ignore */ }
            }
            return defaultValue;
        }

        public static bool Has(string key) => _data.Values.ContainsKey(key);

        public static IReadOnlyDictionary<string, JToken> GetAllRaw() => _data.Values;

        public static void Remove(string key)
        {
            if (_data.Values.Remove(key))
            {
                FireChanged(key, null);
                ScheduleWrite().Forget();
            }
        }

        public static void Watch<T>(string key, Action<T> callback)
        {
            if (!_watchers.ContainsKey(key)) _watchers[key] = new List<Action<object>>();
            _watchers[key].Add(raw => callback((T)Convert.ChangeType(raw, typeof(T))));
        }

        public static void Unwatch(string key, Action<object> callback)
        {
            if (_watchers.TryGetValue(key, out var list)) list.Remove(callback);
        }

        public static async UniTask SaveAsync(CancellationToken ct = default)
        {
            _debounceCts?.Cancel();
            if (_storage == null || string.IsNullOrWhiteSpace(_filePath))
            {
                // 未初始化（独立宿主/单测环境）时跳过持久化，与 LoadAsync 的守卫保持一致
                return;
            }

            var bytes = DataSerializer.Serialize(_data);
            await _storage.WriteAsync(_filePath, bytes, ct);
        }

        public static async UniTask LoadAsync(CancellationToken ct = default)
        {
            if (_storage == null || string.IsNullOrWhiteSpace(_filePath))
            {
                _data = new SettingsData();
                return;
            }

            var loadedData = await TryLoadWithFallbackAsync(ct);
            _data = loadedData ?? new SettingsData();
        }

        internal static void ResetForTesting()
        {
            _data = new SettingsData();
            _debounceCts?.Cancel();
            _debounceCts = null;
            _watchers.Clear();
            OnChanged = null;
        }

        private static void FireChanged(string key, object value)
        {
            OnChanged?.Invoke(key, value);

            if (_watchers.TryGetValue(key, out var list))
                foreach (var cb in list)
                    try { cb(value); } catch (Exception e) { ShrinkDataSaverPlatform.Exception(e); }
        }

        private static async UniTaskVoid ScheduleWrite()
        {
            _debounceCts?.Cancel();
            _debounceCts = new CancellationTokenSource();
            var token = _debounceCts.Token;

            try
            {
                var delay = (int)(ShrinkDataSaverPlatform.SettingsWriteDebounceSeconds * 1000);
                await Task.Delay(delay, token);
                await SaveAsync(token);
            }
            catch (OperationCanceledException) { }
            catch (Exception e) { ShrinkDataSaverPlatform.Exception(e); }
        }

        private static async UniTask<SettingsData> TryLoadWithFallbackAsync(CancellationToken ct)
        {
            var primaryPath = _filePath;
            Exception lastError = null;

            foreach (var candidatePath in EnumerateCandidatePaths(primaryPath))
            {
                if (!await _storage.ExistsAsync(candidatePath, ct))
                {
                    continue;
                }

                try
                {
                    var bytes = await _storage.ReadAsync(candidatePath, ct);
                    var loaded = DataSerializer.Deserialize<SettingsData>(bytes) ?? new SettingsData();
                    if (!string.Equals(candidatePath, primaryPath, StringComparison.Ordinal))
                    {
                        ShrinkDataSaverPlatform.Warning($"[ShrinkDataSaver] Settings 主文件损坏或缺失，已从备份恢复：{candidatePath}");
                        await _storage.WriteAsync(primaryPath, bytes, ct);
                    }

                    return loaded;
                }
                catch (Exception ex)
                {
                    lastError = ex;
                    ShrinkDataSaverPlatform.Warning($"[ShrinkDataSaver] 读取 Settings 副本失败：{candidatePath} / {ex.Message}");
                }
            }

            if (lastError != null)
            {
                ShrinkDataSaverPlatform.Warning("[ShrinkDataSaver] 所有 Settings 副本均不可用，已回退为空设置。");
            }

            return new SettingsData();
        }

        private static IEnumerable<string> EnumerateCandidatePaths(string primaryPath)
        {
            yield return primaryPath;
            yield return primaryPath + BackupPrimarySuffix;
            yield return primaryPath + BackupSecondarySuffix;
        }
    }
}