using System;
using System.Collections.Generic;
using Newtonsoft.Json.Linq;

namespace ShrinkDataSaver
{
    public static class MigrationChain
    {
        private static readonly SortedDictionary<int, Migration> Migrations = new();

        private struct Migration
        {
            public int ToVersion;
            public Func<JObject, JObject> Migrate;
        }

        public static void Register(int fromVersion, int toVersion, Func<JObject, JObject> migrate)
        {
            if (fromVersion >= toVersion)
                throw new ArgumentException(
                    $"[ShrinkDataSaver] fromVersion({fromVersion}) 必须小于 toVersion({toVersion})");

            Migrations[fromVersion] = new Migration { ToVersion = toVersion, Migrate = migrate };
        }

        internal static (JObject data, int finalVersion) Apply(JObject data, int currentVersion, int targetVersion)
        {
            var version = currentVersion;
            var backup = (JObject)data.DeepClone();

            while (version < targetVersion)
            {
                if (!Migrations.TryGetValue(version, out var migration))
                {
                    ShrinkDataSaverPlatform.Warning($"[ShrinkDataSaver] 未找到 v{version} → v{version + 1} 的迁移逻辑，数据可能不完整。");
                    break;
                }

                try
                {
                    var fromV = version;
                    data = migration.Migrate(data) ?? data;
                    version = migration.ToVersion;
                    ShrinkDataSaverPlatform.Info($"[ShrinkDataSaver] 存档已迁移 v{fromV} → v{version}");
                }
                catch (Exception e)
                {
                    ShrinkDataSaverPlatform.Error(
                        $"[ShrinkDataSaver] 迁移 v{version} → v{migration.ToVersion} 失败: {e.Message}，已回滚至 v{currentVersion}");
                    return (backup, currentVersion);
                }
            }

            return (data, version);
        }

        internal static void Clear() => Migrations.Clear();
    }
}