ForgottenWawiTech/Content/Projectiles/Protogen/ProtogenSentinelFragment.cs

using Microsoft.Xna.Framework;
using Terraria;
using Terraria.DataStructures;
using Terraria.ID;
using Terraria.ModLoader;
using ForgottenWawiTech.Content.GlobalProjectiles;

namespace ForgottenWawiTech.Content.Projectiles.Protogen
{
    public class ProtogenSentinelFragment : ModProjectile
    {
        private const float HomingRange = 560f;
        private const float HomingStrength = 0.18f;
        private const float DesiredSpeed = 15f;

        public override void SetStaticDefaults()
        {
            ProjectileID.Sets.MinionShot[Type] = true;
        }

        public override void SetDefaults()
        {
            Projectile.width = 14;
            Projectile.height = 14;
            Projectile.friendly = true;
            Projectile.penetrate = 1;
            Projectile.timeLeft = 240;
            Projectile.tileCollide = false;
            Projectile.ignoreWater = true;
            Projectile.DamageType = DamageClass.Generic;
            Projectile.extraUpdates = 1;
            Projectile.usesLocalNPCImmunity = true;
            Projectile.localNPCHitCooldown = 15;
        }

        public override void AI()
        {
            Projectile.rotation = Projectile.velocity.ToRotation();
            Lighting.AddLight(Projectile.Center, 0.3f, 0.8f, 1.15f);

            NPC target = AcquireTarget(Projectile.Center, HomingRange);
            if (target != null)
            {
                Vector2 desiredVelocity = (target.Center - Projectile.Center).SafeNormalize(Vector2.Zero) * DesiredSpeed;
                Projectile.velocity = Vector2.Lerp(Projectile.velocity, desiredVelocity, HomingStrength);
            }
            else
            {
                Projectile.velocity *= 0.99f;
            }

            if (Main.rand.NextBool(4))
            {
                Dust dust = Dust.NewDustDirect(Projectile.position, Projectile.width, Projectile.height, DustID.Electric, 0f, 0f, 120, default, 1.05f);
                dust.noGravity = true;
            }
        }

        public override void OnSpawn(IEntitySource source)
        {
            Projectile.GetGlobalProjectile<ProtogenSentinelGlobalProjectile>().DisableSentinelSplit = true;
        }

        private static NPC AcquireTarget(Vector2 center, float range)
        {
            NPC closest = null;
            float squaredRange = range * range;
            for (int i = 0; i < Main.maxNPCs; i++)
            {
                NPC npc = Main.npc[i];
                if (!npc.active || npc.friendly || npc.dontTakeDamage || npc.life <= 0)
                {
                    continue;
                }

                float distance = Vector2.DistanceSquared(npc.Center, center);
                if (distance <= squaredRange && Collision.CanHitLine(center, 0, 0, npc.Center, 0, 0))
                {
                    squaredRange = distance;
                    closest = npc;
                }
            }

            return closest;
        }
    }
}