// Assets/_Project/Scripts/Gameplay/BuilderSpells/SlowZoneRuntime.cs
using UnityEngine;
using TD.Core;

namespace TD.Gameplay.BuilderSpells
{
    /// <summary>
    /// Server-only runtime object for a Slow Area cast. Re-scans its radius every frame for the
    /// rest of the zone's lifetime, continuously refreshing the Cold status on whatever enemies
    /// currently overlap it.
    /// </summary>
    /// <remarks>
    /// <para><b>Zone, not a snapshot.</b> Replaces <see cref="SlowAreaSpellDefinition"/>'s old
    /// single <c>OverlapSphereNonAlloc</c> call at cast time, which slowed whoever was standing
    /// there for a fixed duration regardless of whether they walked out. This ticks continuously
    /// instead, so only enemies currently inside the radius are ever affected.</para>
    ///
    /// <para><b>Refresh, not enter/exit events.</b> Each tick re-applies
    /// <see cref="EnemyStatus.ApplyEffect"/> with a short fixed window (<see cref="RefreshWindow"/>),
    /// not the zone's remaining lifetime. An enemy that walks out of the zone simply stops being
    /// refreshed and the slow expires on its own <see cref="RefreshWindow"/> seconds later —
    /// no explicit exit detection needed.</para>
    ///
    /// <para><b>Not a NetworkObject.</b> It only ever runs where <see
    /// cref="SlowAreaSpellDefinition.ServerCast"/> runs (the server), and it never needs to exist
    /// on clients — the zone's visual is spawned independently on every peer via
    /// <see cref="SlowAreaSpellDefinition.ClientSpawnVfx"/>.</para>
    /// </remarks>
    public class SlowZoneRuntime : MonoBehaviour
    {
        // Comfortably longer than one frame so a single missed tick doesn't let the slow
        // visibly drop while an enemy is still inside, but short enough that leaving the
        // zone reads as an almost-immediate loss of the slow.
        private const float RefreshWindow = 0.35f;

        private static readonly Collider[] s_overlapBuffer = new Collider[64];

        private float radius;
        private float slowFactor;
        private float remainingLifetime;
        private LayerMask enemyLayerMask;
        private PlayerSlot owner;

        /// <summary>Positions and configures the zone. Call immediately after AddComponent.</summary>
        public void Initialize(Vector3 position, float radius, float slowFactor, float lifetime,
            LayerMask enemyLayerMask, PlayerSlot owner)
        {
            transform.position = position;
            this.radius = radius;
            this.slowFactor = slowFactor;
            this.remainingLifetime = lifetime;
            this.enemyLayerMask = enemyLayerMask;
            this.owner = owner;
        }

        private void Update()
        {
            remainingLifetime -= Time.deltaTime;
            if (remainingLifetime <= 0f)
            {
                Destroy(gameObject);
                return;
            }

            int count = Physics.OverlapSphereNonAlloc(
                transform.position, radius, s_overlapBuffer, enemyLayerMask);

            for (int i = 0; i < count; i++)
            {
                var enemyHealth = s_overlapBuffer[i].GetComponent<EnemyHealth>();
                if (enemyHealth == null || enemyHealth.IsDead) continue;

                var enemyStatus = s_overlapBuffer[i].GetComponent<EnemyStatus>();
                if (enemyStatus == null) continue;

                enemyStatus.ApplyEffect(DamageType.Cold, slowFactor, RefreshWindow, owner);
            }
        }
    }
}