using System.Collections.Generic;
using SepCore.Entity;

namespace SepCore.EnemyManager
{
    public class EnemyRegistry
    {
        private readonly Dictionary<int, EntityBase> _enemyById;

        public int Count => _enemyById.Count;
        public IReadOnlyCollection<EntityBase> Enemies => _enemyById.Values;

        public EnemyRegistry()
        {
            _enemyById = new Dictionary<int, EntityBase>();
        }

        public void Register(EnemyBase enemy)
        {
            if (enemy == null) return;
            _enemyById[enemy.Id] = enemy;
        }

        public void Remove(int entityId)
        {
            // 移除是幂等的。ClearEnemies 会同步清空 registry，而 HideEntity 的完成回调
            // 是异步的，晚几帧才到达，此时该 id 早已不在集合中，属正常情况，静默忽略即可。
            _enemyById.Remove(entityId);
        }

        public bool TryGet(int entityId, out EntityBase enemy)
        {
            return _enemyById.TryGetValue(entityId, out enemy);
        }

        public void PruneInvalidEntries()
        {
            var invalidIds = new List<int>();
            foreach (var kvp in _enemyById)
            {
                if (kvp.Value == null || !kvp.Value.Available)
                {
                    invalidIds.Add(kvp.Key);
                }
            }

            foreach (int id in invalidIds)
            {
                _enemyById.Remove(id);
            }
        }

        public void Clear()
        {
            _enemyById.Clear();
        }
    }
}