using UnityEngine;
using UnityEngine.UI;
using BaseGames.Core;

namespace BaseGames.UI
{
    /// <summary>
    /// 将 <see cref="ISettingsService"/>.<c>Current.UIScale</c> 应用到挂载的
    /// <see cref="CanvasScaler"/>。挂在每个根 Canvas 上即可。
    ///
    /// 实现要点：
    ///   · 记录 Inspector 初始的 <c>scaleFactor</c> / <c>referenceResolution</c> 作为基准值，
    ///     避免反复缩放导致的累积漂移；
    ///   · 订阅 <see cref="SettingsManager.SettingsChanged"/> 在玩家调整后即时刷新；
    ///   · 兼容 <see cref="CanvasScaler.ScaleMode.ScaleWithScreenSize"/> 与
    ///     <see cref="CanvasScaler.ScaleMode.ConstantPixelSize"/> 两种模式。
    /// </summary>
    [DisallowMultipleComponent]
    [RequireComponent(typeof(CanvasScaler))]
    public class UIScaleApplier : MonoBehaviour
    {
        private CanvasScaler _scaler;
        private float        _baseScaleFactor;
        private Vector2      _baseReferenceResolution;

        private void Awake()
        {
            _scaler = GetComponent<CanvasScaler>();
            _baseScaleFactor         = _scaler.scaleFactor;
            _baseReferenceResolution = _scaler.referenceResolution;
        }

        private void OnEnable()
        {
            SettingsManager.SettingsChanged += OnSettingsChanged;
            Apply();
        }

        private void OnDisable()
        {
            SettingsManager.SettingsChanged -= OnSettingsChanged;
        }

        private void OnSettingsChanged(GlobalSettingsData _) => Apply();

        private void Apply()
        {
            var svc = ServiceLocator.GetOrDefault<ISettingsService>();
            float ui = svc?.Current?.UIScale ?? 1f;
            if (ui <= 0f) ui = 1f;

            switch (_scaler.uiScaleMode)
            {
                case CanvasScaler.ScaleMode.ConstantPixelSize:
                    _scaler.scaleFactor = _baseScaleFactor * ui;
                    break;
                case CanvasScaler.ScaleMode.ScaleWithScreenSize:
                    // 缩小参考分辨率 → 等价于放大 UI。
                    _scaler.referenceResolution = _baseReferenceResolution / ui;
                    break;
                default:
                    _scaler.scaleFactor = _baseScaleFactor * ui;
                    break;
            }
        }
    }
}