// Assets/_Project/Scripts/Gameplay/EnemyUpgrades/AbilityEnemyUpgradeOption.cs
using UnityEngine;
using TD.Gameplay.EnemyAbilities;
using TD.Gameplay.Waves;

namespace TD.Gameplay.EnemyUpgrades
{
    /// <summary>
    /// The workhorse enemy-buff card: grants an <see cref="EnemyAbilityDefinition"/> to a wave
    /// slot. Every enemy spawned by that wave, in every later cycle of the phase, carries the
    /// ability.
    /// </summary>
    /// <remarks>
    /// There is nothing to do at vote-resolution time — recording the option id on the slot IS the
    /// effect, because the spawn path builds each enemy's ability set from the slot's recorded
    /// options. <see cref="Ability"/> is what that lookup resolves to.
    /// </remarks>
    [CreateAssetMenu(fileName = "EnemyUpgrade_Ability",
                     menuName = "TD/Enemy Upgrades/Ability Card", order = 20)]
    public class AbilityEnemyUpgradeOption : EnemyUpgradeOption
    {
        [Header("Payload")]
        [Tooltip("The ability every enemy in this wave gains. Must also be present in the scene's " +
                 "EnemyAbilityPool so it can be resolved at spawn time.")]
        public EnemyAbilityDefinition Ability;

        public override bool IsValidForSlot(RunState run, int slot)
        {
            if (Ability == null) return false;

            // Don't offer an ability the slot already has by another card's hand. Exact-id repeats
            // are filtered by the caller, but two different cards can grant the same ability, and
            // stacking one twice is a no-op the players would rightly feel cheated by.
            return !SlotAlreadyHasAbility(run, slot);
        }

        // Shared scratch: validation runs on the server during vote generation, which is
        // single-threaded, so one reused list beats allocating per candidate per slot.
        private static readonly System.Collections.Generic.List<int> s_idScratch
            = new System.Collections.Generic.List<int>();

        private bool SlotAlreadyHasAbility(RunState run, int slot)
        {
            var pool = EnemyUpgradePool.Instance;
            if (run == null || pool == null) return false;

            var ids = s_idScratch;
            run.GetUpgradesForSlot(slot, ids);

            foreach (int id in ids)
            {
                if (pool.Get(id) is AbilityEnemyUpgradeOption other && other.Ability == Ability)
                    return true;
            }
            return false;
        }

        /// <summary>Inherits nothing automatically — <see cref="EnemyAbilityDefinition"/> carries no
        /// icon, so the card's own <see cref="EnemyUpgradeOption.Icon"/> is the only source.</summary>
        public override Sprite ResolveIcon() => Icon;
    }
}