using System;
using System.Collections;
using Ichni.Diagnostics;
using UnityEngine;
using UnityEngine.Localization.Settings;
using UnityEngine.ResourceManagement.AsyncOperations;

namespace Ichni
{
    /// <summary>
    /// Unity Localization 的统一启动入口。
    /// <para>
    /// 本类只包装 Unity 官方提供的 <see cref="LocalizationSettings.InitializationOperation"/>，
    /// 不自行初始化 Addressables、不查询 Locale Label，也不复制 Localization Package 的内部加载流程。
    /// 因此 Settings、Yarn 与其它本地化消费者始终等待同一个由 Unity 管理的初始化操作。
    /// </para>
    /// </summary>
    public static class LocalizationBootstrap
    {
        public enum InitializationState
        {
            NotStarted,
            Initializing,
            Ready,
            Failed
        }

        private static AsyncOperationHandle<LocalizationSettings> _initializationOperation;

        public static InitializationState State { get; private set; } = InitializationState.NotStarted;
        public static bool IsReady => State == InitializationState.Ready;
        public static bool HasFailed => State == InitializationState.Failed;
        public static string FailureReason { get; private set; }

        /// <summary>
        /// Unity Localization 官方初始化 Handle。
        /// 获取该属性会以幂等方式启动初始化，但不会同步阻塞主线程。
        /// </summary>
        public static AsyncOperationHandle<LocalizationSettings> InitializationOperation
        {
            get
            {
                BeginInitialization();
                return _initializationOperation;
            }
        }

        /// <summary>
        /// 在关闭 Domain Reload 的 Editor 配置下，清理上一次 Play Mode 留下的项目侧状态。
        /// Localization Package 会自行重建其内部 Handle，本类不持有也不释放 Package 的资源。
        /// </summary>
        [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.SubsystemRegistration)]
        private static void ResetState()
        {
            _initializationOperation = default;
            State = InitializationState.NotStarted;
            FailureReason = null;
        }

        /// <summary>
        /// 按 Unity 官方流程获取唯一的 Localization 初始化操作。
        /// 可以由多个系统重复调用；已经启动后不会创建第二条加载链。
        /// </summary>
        public static void BeginInitialization()
        {
            if (State != InitializationState.NotStarted)
            {
                return;
            }

            try
            {
                // 不设置 InitializeSynchronously，也不直接访问 SelectedLocale。
                // InitializationOperation 会异步完成 Locale 选择及所有配置为 Preload 的数据库初始化。
                _initializationOperation = LocalizationSettings.InitializationOperation;
                State = InitializationState.Initializing;
                Log("开始等待 Unity Localization 官方 InitializationOperation。");
                RefreshState();
            }
            catch (Exception exception)
            {
                Fail("无法创建 Unity Localization 初始化操作。", exception);
            }
        }

        /// <summary>
        /// 刷新初始化结果。供 YarnTask 等不能直接 yield AsyncOperationHandle 的异步流程调用。
        /// </summary>
        public static void RefreshState()
        {
            if (State != InitializationState.Initializing)
            {
                return;
            }

            if (!_initializationOperation.IsValid())
            {
                Fail("Unity Localization 返回了无效的 InitializationOperation Handle。");
                return;
            }

            if (!_initializationOperation.IsDone)
            {
                return;
            }

            if (_initializationOperation.Status != AsyncOperationStatus.Succeeded)
            {
                Fail("Unity Localization 初始化失败。", _initializationOperation.OperationException);
                return;
            }

            LocaleReady();
        }

        /// <summary>
        /// 供 MonoBehaviour 协程等待 Unity Localization 初始化。
        /// 此处直接 yield 官方 Handle，不使用轮询超时或自建 Addressables 状态机。
        /// </summary>
        public static IEnumerator WaitForInitialization()
        {
            BeginInitialization();

            if (State == InitializationState.Initializing)
            {
                yield return _initializationOperation;
                RefreshState();
            }
        }

        private static void LocaleReady()
        {
            State = InitializationState.Ready;
            FailureReason = null;

            // SelectedLocale 只有在完整 InitializationOperation 成功后才允许同步读取。
            string localeCode = LocalizationSettings.SelectedLocale != null
                ? LocalizationSettings.SelectedLocale.Identifier.Code
                : "<null>";
            Log($"Unity Localization 初始化完成。SelectedLocale={localeCode}");
        }

        private static void Fail(string message, Exception exception = null)
        {
            FailureReason = exception == null ? message : $"{message} Exception={exception}";
            State = InitializationState.Failed;

            Debug.LogError($"[LocalizationBootstrap] {FailureReason}");
            BuildHangTracer.Log("LOCALIZATION_BOOTSTRAP", $"[Failed] {FailureReason}");
        }

        private static void Log(string message)
        {
            Debug.Log($"[LocalizationBootstrap] {message}");
            BuildHangTracer.Log("LOCALIZATION_BOOTSTRAP", message);
        }
    }
}