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
    {
        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;

        public EnemyAttackSelector(IEnumerable<IAttackCandidate> candidates)
        {
            _candidates = new List<IAttackCandidate>(candidates);
            _weightBuf  = new List<float>(_candidates.Count);
        }

        public int Count => _candidates.Count;

        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)
            => mode == AttackSelectionMode.Priority
                ? SelectByPriority(hasLOS, grounded)
                : SelectByWeight(hasLOS, grounded);

        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)
        {
            // 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];
                _weightBuf.Add(Eligible(c, hasLOS, grounded) ? Mathf.Max(0f, c.Weight) : 0f);
            }

            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）→ 退化为按 Priority 选(并列取首个)
            return SelectByPriority(hasLOS, grounded);
        }
    }
}