ForgottenWawiTech/Content/Projectiles/Protogen/ProtogenOperativeNanite.cs

using Microsoft.Xna.Framework;
using Terraria;
using Terraria.ID;
using Terraria.ModLoader;

namespace ForgottenWawiTech.Content.Projectiles.Protogen
{
    public class ProtogenOperativeNanite : ModProjectile
    {
        private const float DetectionRange = 640f;
        private const float HomingStrength = 0.14f;
        private const float DesiredSpeed = 14f;

        public override string Texture => "ForgottenWawiTech/Assets/PlaceholderProj";
        
        public override void SetStaticDefaults()
        {
            ProjectileID.Sets.MinionShot[Type] = true;
            ProjectileID.Sets.MinionSacrificable[Type] = false;
        }

        public override void SetDefaults()
        {
            Projectile.width = 14;
            Projectile.height = 14;
            Projectile.friendly = true;
            Projectile.penetrate = 1;
            Projectile.timeLeft = 360;
            Projectile.tileCollide = false;
            Projectile.ignoreWater = true;
            Projectile.DamageType = DamageClass.Generic;
            Projectile.usesLocalNPCImmunity = true;
            Projectile.localNPCHitCooldown = 20;
            Projectile.extraUpdates = 1;
        }

        public override void AI()
        {
            Player owner = Main.player[Projectile.owner];
            if (!owner.active || owner.dead)
            {
                Projectile.Kill();
                return;
            }

            Projectile.rotation += 0.2f * Projectile.direction;
            Lighting.AddLight(Projectile.Center, 0.25f, 0.55f, 0.75f);

            NPC target = AcquireTarget(owner, Projectile.Center, DetectionRange);
            if (target != null)
            {
                Vector2 desiredVelocity = (target.Center - Projectile.Center).SafeNormalize(Vector2.Zero) * DesiredSpeed;
                Projectile.velocity = Vector2.Lerp(Projectile.velocity, desiredVelocity, HomingStrength);
            }
            else
            {
                Projectile.velocity *= 0.98f;
            }

            if (Main.rand.NextBool(4))
            {
                Dust dust = Dust.NewDustDirect(Projectile.position, Projectile.width, Projectile.height, DustID.Electric, 0f, 0f, 100, default, 1.1f);
                dust.noGravity = true;
            }
        }

        public override void OnHitNPC(NPC target, NPC.HitInfo hit, int damageDone)
        {
            if (Main.myPlayer != Projectile.owner)
            {
                return;
            }

            Player owner = Main.player[Projectile.owner];
            int healAmount = (int)(damageDone * 0.5f);
            if (healAmount <= 0)
            {
                return;
            }

            owner.statLife = Utils.Clamp(owner.statLife + healAmount, 0, owner.statLifeMax2);
            owner.HealEffect(healAmount);
        }

        private static NPC AcquireTarget(Player owner, Vector2 center, float range)
        {
            if (owner.HasMinionAttackTargetNPC)
            {
                NPC target = Main.npc[owner.MinionAttackTargetNPC];
                if (target.CanBeChasedBy())
                {
                    return target;
                }
            }

            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;
        }
    }
}