using System.Collections.Generic;
using UnityEngine;

namespace BaseGames.Enemies.Abilities
{
    /// <summary>
    /// 多攻击选招器：从候选（category==Attack）里按"射程 + 冷却 + LOS + 着地"过滤，
    /// 再按 <see cref="AttackSelectionMode"/> 选一个。纯逻辑、无 MonoBehaviour 依赖，可单测。
    /// </summary>
    public sealed class EnemyAttackSelector
    {
        /// <summary>防重复折扣系数的默认值。EnemyStatsSO 字段初值与 EnemyBase 的兜底分支共用此常量。</summary>
        public const float DefaultAntiRepeatFactor = 0.3f;

        private readonly List<IAttackCandidate> _candidates;
        // 权重缓冲区（与 _candidates 等长，每次选招复用）：避免每次选招 new List 造成 GC
        private readonly List<float> _weightBuf;
        // 防重复折扣系数：0 = 有替代时绝不连续重复，1 = 不惩罚
        private float _antiRepeatFactor;

        private IAttackCandidate _lastPicked;

        public EnemyAttackSelector(IEnumerable<IAttackCandidate> candidates,
                                   float antiRepeatFactor = DefaultAntiRepeatFactor)
        {
            _candidates      = new List<IAttackCandidate>(candidates);
            _weightBuf       = new List<float>(_candidates.Count);
            AntiRepeatFactor = antiRepeatFactor; // 经属性赋值，夹紧逻辑只有一处
        }

        public int Count => _candidates.Count;

        /// <summary>防重复折扣系数。与 attackSelectionMode 一样每次选招前由调用方刷新，
        /// 使策划在播放模式下调参能立即生效。</summary>
        public float AntiRepeatFactor
        {
            get => _antiRepeatFactor;
            set => _antiRepeatFactor = Mathf.Clamp01(value);
        }

        /// <summary>上一次实际选中的招（防重复折扣的作用对象；供测试与调试面板读取）。</summary>
        public IAttackCandidate LastPicked => _lastPicked;

        /// <summary>对象池复用 / 阶段切换时清除防重复记忆。</summary>
        public void ResetRepeatMemory() => _lastPicked = null;

        private static bool Eligible(IAttackCandidate c, bool hasLOS, bool grounded)
            => c != null && c.CanUse && c.InAttackRange()
               && (!c.RequiresLineOfSight || hasLOS)
               && (!c.RequiresGrounded    || grounded);

        public bool HasEligible(bool hasLOS, bool grounded)
        {
            for (int i = 0; i < _candidates.Count; i++)
                if (Eligible(_candidates[i], hasLOS, grounded)) return true;
            return false;
        }

        public IAttackCandidate Select(bool hasLOS, bool grounded, AttackSelectionMode mode)
        {
            switch (mode)
            {
                case AttackSelectionMode.Priority:
                    return Remember(SelectByPriority(hasLOS, grounded));
                case AttackSelectionMode.WeightedRandomAntiRepeat:
                    return Remember(SelectByWeight(hasLOS, grounded, antiRepeat: true));
                default:
                    return Remember(SelectByWeight(hasLOS, grounded, antiRepeat: false));
            }
        }

        // 只在真选中了东西时更新记忆：选空时保留上一招，避免"空一帧就清掉防重复"。
        private IAttackCandidate Remember(IAttackCandidate pick)
        {
            if (pick != null) _lastPicked = pick;
            return pick;
        }

        private IAttackCandidate SelectByPriority(bool hasLOS, bool grounded)
        {
            IAttackCandidate best = null;
            for (int i = 0; i < _candidates.Count; i++)
            {
                var c = _candidates[i];
                if (!Eligible(c, hasLOS, grounded)) continue;
                if (best == null || c.Priority > best.Priority) best = c; // 并列取首个
            }
            return best;
        }

        private IAttackCandidate SelectByWeight(bool hasLOS, bool grounded, bool antiRepeat)
        {
            // 有效权重：不合格候选填 0（由共享原语保证零权重项绝不被选中）。缓冲区复用 → 选招零 GC。
            _weightBuf.Clear();
            for (int i = 0; i < _candidates.Count; i++)
            {
                var c = _candidates[i];
                float w = Eligible(c, hasLOS, grounded) ? Mathf.Max(0f, c.Weight) : 0f;
                // 防重复：上一招权重打折。折扣可把权重压到 0——此时若它是唯一候选，
                // 下面的 Priority 退化路径会把它选出来，不会出现"敌人永远不出手"。
                if (antiRepeat && w > 0f && ReferenceEquals(c, _lastPicked))
                    w *= _antiRepeatFactor;
                _weightBuf.Add(w);
            }

            int idx = BaseGames.Core.WeightedPick.Index(_weightBuf);
            if (idx >= 0) return _candidates[idx];

            // 无正权重（合格候选权重全 0，或全被防重复折扣压平）→ 退化为按 Priority 选(并列取首个)
            return SelectByPriority(hasLOS, grounded);
        }
    }
}