UnityTowerDefense/Assets/_Project/Scripts/Combat/Projectile.cs

// Assets/_Project/Scripts/Combat/Projectile.cs
using Unity.Netcode;
using UnityEngine;
using TD.Core;
using TD.Gameplay;

namespace TD.Combat
{
    /// <summary>
    /// A traveling projectile spawned by <see cref="TowerCombat"/> when a tower has
    /// a non-null <c>ProjectilePrefab</c> configured.
    /// </summary>
    /// <remarks>
    /// <b>Authority:</b> Movement and hit detection run server-only.
    /// <c>NetworkTransform</c> (required on the prefab) replicates the position to
    /// clients so the projectile is visible on all peers.
    ///
    /// <b>Initialization:</b> Mirrors the <c>TowerInstance.InitializeServer</c> pattern —
    /// <see cref="InitializeServer"/> is called by <c>TowerCombat</c> immediately after
    /// <c>Instantiate</c> and before <c>NetworkObject.Spawn()</c>, which avoids writing
    /// to NetworkVariables before spawn.
    ///
    /// <b>Target loss:</b> If the target dies or is destroyed before the projectile
    /// arrives, the projectile despawns silently (no hit, no damage).
    ///
    /// <b>Chain + Projectile:</b> By design, TargetType.Chain is hitscan. If a designer
    /// sets TargetType = Chain on a tower that has a ProjectilePrefab, the projectile
    /// will hit the primary target only and ignore the chain. Log a warning to surface
    /// the misconfiguration.
    ///
    /// <b>Prefab requirements:</b> Must have <c>NetworkObject</c>, <c>NetworkTransform</c>,
    /// and this <c>Projectile</c> component at the root.
    /// </remarks>
    [RequireComponent(typeof(NetworkObject))]
    public class Projectile : NetworkBehaviour
    {
        // Hit threshold: squared distance at which the projectile considers itself
        // to have reached the target. 0.09 = 0.3 world units; small enough to
        // feel accurate, large enough to survive a high-speed frame where the
        // projectile could skip past the target's transform in one step.
        private const float HitThresholdSq = 0.09f;

        // All fields are server-local. Set by InitializeServer before Spawn.
        private EnemyHealth target;
        private float       damage;
        private DamageType  damageType;
        private TargetType  targetType;
        private float       splashRadius;
        private float       slowFactor;
        private float       dotDamagePerSecond;
        private float       effectDuration;
        private float       speed;
        private LayerMask   enemyLayerMask;
        private bool        initialized;

        // Shared with TowerCombat's overlap calls. Both components run on the
        // server main thread so there is no concurrent access.
        private static readonly Collider[] s_overlapBuffer = new Collider[32];

        // ----- Initialization (server-only, called before Spawn) -----------

        /// <summary>
        /// Stores all data this projectile needs to travel and apply damage.
        /// Call this immediately after <c>Instantiate</c> and before
        /// <c>NetworkObject.Spawn()</c>.
        /// </summary>
        public void InitializeServer(
            EnemyHealth target,
            float       damage,
            DamageType  damageType,
            TargetType  targetType,
            float       splashRadius,
            float       slowFactor,
            float       dotDamagePerSecond,
            float       effectDuration,
            float       speed,
            LayerMask   enemyLayerMask)
        {
            this.target             = target;
            this.damage             = damage;
            this.damageType         = damageType;
            this.targetType         = targetType;
            this.splashRadius       = splashRadius;
            this.slowFactor         = slowFactor;
            this.dotDamagePerSecond = dotDamagePerSecond;
            this.effectDuration     = effectDuration;
            this.speed              = speed;
            this.enemyLayerMask     = enemyLayerMask;
            initialized             = true;

            if (targetType == TargetType.Chain)
                Debug.LogWarning("[Projectile] TargetType.Chain is hitscan-only. " +
                                 "This projectile will hit the primary target only. " +
                                 "Consider using hitscan (null ProjectilePrefab) for chain towers.");
        }

        // ----- Server movement + hit detection -----------------------------

        private void Update()
        {
            if (!IsServer || !initialized) return;

            // Target gone — silently despawn, no damage applied.
            if (target == null
                || target.IsDead
                || (target as UnityEngine.Object) == null)
            {
                NetworkObject.Despawn();
                return;
            }

            Vector3 toTarget = target.transform.position - transform.position;

            if (toTarget.sqrMagnitude <= HitThresholdSq)
            {
                ApplyHit();
                NetworkObject.Despawn();
                return;
            }

            // Rotate to face the target so the projectile mesh looks correct
            // on all clients (NetworkTransform replicates both position and rotation).
            transform.rotation = Quaternion.LookRotation(toTarget);
            transform.position += toTarget.normalized * (speed * Time.deltaTime);
        }

        // ----- Hit application ---------------------------------------------

        private void ApplyHit()
        {
            switch (targetType)
            {
                case TargetType.Single:
                case TargetType.Chain:  // chain falls back to single-target on projectiles
                    HitEnemy(target);
                    break;

                case TargetType.Splash:
                    HitEnemy(target);
                    if (splashRadius > 0f)
                    {
                        int count = Physics.OverlapSphereNonAlloc(
                            transform.position, splashRadius,
                            s_overlapBuffer, enemyLayerMask);

                        for (int i = 0; i < count; i++)
                        {
                            var eh = s_overlapBuffer[i].GetComponent<EnemyHealth>();
                            if (eh == null || eh.IsDead || (object)eh == (object)target) continue;
                            HitEnemy(eh);
                        }
                    }
                    break;
            }
        }

        private void HitEnemy(EnemyHealth eh)
        {
            eh.TakeDamage(damage, damageType);

            if (effectDuration > 0f)
            {
                float magnitude = damageType switch
                {
                    DamageType.Cold   => slowFactor,
                    DamageType.Fire   => dotDamagePerSecond,
                    DamageType.Poison => dotDamagePerSecond,
                    _                 => 0f,
                };

                if (magnitude > 0f)
                    eh.GetComponent<EnemyStatus>()
                      ?.ApplyEffect(damageType, magnitude, effectDuration);
            }
        }
    }
}