using UnityEngine;
using UnityEngine.UI;
using UnityEngine.EventSystems;
using BaseGames.Core;
using BaseGames.Core.Events;

namespace BaseGames.UI
{
    /// <summary>
    /// UI 面板基类：统一面板生命周期、焦点恢复、进场淡入与事件订阅清理。
    ///
    /// 消除各面板控制器（PauseMenu / Settings / InventoryHub 等）重复的样板：
    /// - OnEnable：取服务 / 订阅 / 设默认选中 / 播淡入
    /// - OnDisable：清理订阅（<see cref="_subs"/>）/ 停动画
    /// - <see cref="IFocusable.OnFocusRestored"/>：关闭子面板回到栈顶时聚焦首项
    ///
    /// 与 <see cref="UIManager"/> 面板栈完全兼容：UIManager 仍以 SetActive 驱动开关，
    /// 本基类只在 OnEnable/OnDisable 加钩子，不改变栈语义。
    ///
    /// 子类用法：重写 <see cref="OnPanelOpen"/>（订阅/刷新）与可选 <see cref="OnPanelClose"/>；
    /// 在 Inspector 指定 <see cref="_firstSelected"/>（手柄/键盘默认焦点）；可选挂 CanvasGroup 做淡入。
    /// </summary>
    [DisallowMultipleComponent]
    public abstract class UIPanelBase : MonoBehaviour, IFocusable
    {
        [Header("Panel Base")]
        [Tooltip("打开 / 焦点恢复时默认选中的控件（手柄/键盘导航起点）。可空。")]
        [SerializeField] protected Selectable _firstSelected;

        [Tooltip("进场淡入用的 CanvasGroup（可空；为空则不淡入）。")]
        [SerializeField] protected CanvasGroup _canvasGroup;

        [Tooltip("进场淡入时长（秒）。0 表示无淡入。")]
        [SerializeField] protected float _fadeInDuration = 0.15f;

        [Tooltip("打开时是否自动把焦点设到首项。")]
        [SerializeField] protected bool _selectFirstOnEnable = true;

        /// <summary>事件订阅容器，OnDisable 自动清理。子类订阅用 <c>channel.Subscribe(..).AddTo(_subs)</c>。</summary>
        protected readonly CompositeDisposable _subs = new();

        private Coroutine _fadeRoutine;

        // ── 生命周期 ──────────────────────────────────────────────────────────
        protected virtual void OnEnable()
        {
            OnPanelOpen();
            if (_canvasGroup != null && _fadeInDuration > 0f) PlayFadeIn();
            if (_selectFirstOnEnable) FocusFirst();
        }

        protected virtual void OnDisable()
        {
            _subs.Clear();
            if (_fadeRoutine != null) { StopCoroutine(_fadeRoutine); _fadeRoutine = null; }
            OnPanelClose();
        }

        /// <summary>面板打开时调用（OnEnable）。子类在此取服务、订阅事件、刷新内容。</summary>
        protected virtual void OnPanelOpen() { }

        /// <summary>面板关闭时调用（OnDisable，_subs 已清理之后）。子类在此释放非 _subs 资源。</summary>
        protected virtual void OnPanelClose() { }

        // ── 焦点 ──────────────────────────────────────────────────────────────
        /// <summary>关闭子面板、本面板恢复为栈顶时调用（<see cref="IUIManager.CloseTopPanel"/> 触发）。</summary>
        public virtual void OnFocusRestored() => FocusFirst();

        /// <summary>将 EventSystem 焦点设到首项（优先 <see cref="_firstSelected"/>，否则 <see cref="ResolveFirstSelected"/>）。</summary>
        protected void FocusFirst()
        {
            var go = _firstSelected != null ? _firstSelected.gameObject : ResolveFirstSelected();
            if (go != null && EventSystem.current != null)
                EventSystem.current.SetSelectedGameObject(go);
        }

        /// <summary>子类可重写：动态决定首个选中项（如列表第一行），当 <see cref="_firstSelected"/> 未指定时使用。</summary>
        protected virtual GameObject ResolveFirstSelected() => null;

        // ── 工具 ──────────────────────────────────────────────────────────────
        /// <summary>从 ServiceLocator 取服务（未注册返回 null）。</summary>
        protected static T GetService<T>() where T : class => ServiceLocator.GetOrDefault<T>();

        private void PlayFadeIn()
        {
            if (_fadeRoutine != null) StopCoroutine(_fadeRoutine);
            _canvasGroup.alpha = 0f;
            _fadeRoutine = StartCoroutine(UITween.FadeCanvasGroup(_canvasGroup, 1f, _fadeInDuration));
        }
    }
}