using System.Collections.Generic;
using UnityEngine;

namespace BaseGames.UI
{
    /// <summary>
    /// 全局伤害飘字 Tick 系统（架构 10_UIModule §10 优化）。
    ///
    /// 设计动机：原实现中每条飘字独立 StartCoroutine（FloatAndFade），
    /// Boss 战或大范围 AOE 时同时存在数十条会产生大量协程对象与调度开销。
    /// 本系统用单一 Update + 紧凑 List&lt;Entry&gt; 集中推进，
    /// 所有飘字共享同一份每帧调度（仅一次 Update 调用），并消除协程对象。
    ///
    /// 使用：FloatingDamageText.Show 不再 StartCoroutine，而是调用
    /// FloatingDamageTickSystem.Register(this, ...)；系统自动在动画结束时
    /// 调用 OnComplete 回调（飘字 SetActive(false) 回池）。
    /// </summary>
    [DefaultExecutionOrder(+100)]
    public class FloatingDamageTickSystem : MonoBehaviour
    {
        private struct Entry
        {
            public FloatingDamageText Target;
            public Vector2            StartWorld;
            public float              Elapsed;
            public float              Duration;
            public float              FloatDistance;
            public float              StartAlpha;
        }

        private static FloatingDamageTickSystem s_instance;
        private readonly List<Entry> _entries = new(64);

        public static FloatingDamageTickSystem Instance
        {
            get
            {
                if (s_instance != null) return s_instance;
                var go = new GameObject(nameof(FloatingDamageTickSystem));
                DontDestroyOnLoad(go);
                s_instance = go.AddComponent<FloatingDamageTickSystem>();
                return s_instance;
            }
        }

        private void Awake()
        {
            if (s_instance != null && s_instance != this) { Destroy(this); return; }
            s_instance = this;
        }

        public void Register(FloatingDamageText target, Vector2 startWorld,
                             float duration, float floatDistance, float startAlpha)
        {
            if (target == null || duration <= 0f) return;
            _entries.Add(new Entry
            {
                Target        = target,
                StartWorld    = startWorld,
                Elapsed       = 0f,
                Duration      = duration,
                FloatDistance = floatDistance,
                StartAlpha    = startAlpha
            });
        }

        /// <summary>取消指定目标的飘字动画（例如对象池回收）。</summary>
        public void Unregister(FloatingDamageText target)
        {
            for (int i = _entries.Count - 1; i >= 0; i--)
                if (_entries[i].Target == target) _entries.RemoveAt(i);
        }

        private void Update()
        {
            float dt = Time.deltaTime;
            // 倒序遍历，便于安全 RemoveAt
            for (int i = _entries.Count - 1; i >= 0; i--)
            {
                var e = _entries[i];
                if (e.Target == null) { _entries.RemoveAt(i); continue; }

                e.Elapsed += dt;
                float t    = e.Elapsed / e.Duration;
                bool done  = t >= 1f;
                if (done) t = 1f;

                e.Target.TickAnimation(e.StartWorld, t, e.StartAlpha, e.FloatDistance);

                if (done)
                {
                    e.Target.OnTickComplete();
                    _entries.RemoveAt(i);
                }
                else
                {
                    _entries[i] = e;
                }
            }
        }
    }
}