civ14/Content.Shared/_RMC14/Projectiles/Penetration/RMCPenetratingProjectileSystem.cs

using Content.Shared.Physics;
using Content.Shared.Projectiles;
using Robust.Shared.Physics.Events;

namespace Content.Shared._RMC14.Projectiles.Penetration;

public sealed class RMCPenetratingProjectileSystem : EntitySystem
{
    private const int HardCollisionGroup = (int)(CollisionGroup.HighImpassable | CollisionGroup.Impassable);

    [Dependency] private readonly SharedTransformSystem _transform = default!;
    public override void Initialize()
    {
        SubscribeLocalEvent<RMCPenetratingProjectileComponent, MapInitEvent>(OnMapInit);
        SubscribeLocalEvent<RMCPenetratingProjectileComponent, PreventCollideEvent>(OnPreventCollide);
        SubscribeLocalEvent<RMCPenetratingProjectileComponent, StartCollideEvent>(OnStartCollide, after: [typeof(SharedProjectileSystem)]);
        SubscribeLocalEvent<RMCPenetratingProjectileComponent, ProjectileHitEvent>(OnProjectileHit);
        SubscribeLocalEvent<RMCPenetratingProjectileComponent, AfterProjectileHitEvent>(OnAllowAdditionalHits);
    }

    /// <summary>
    ///     Store the coordinates the projectile was shot from.
    /// </summary>
    private void OnMapInit(Entity<RMCPenetratingProjectileComponent> ent, ref MapInitEvent args)
    {
        ent.Comp.ShotFrom = _transform.GetMoverCoordinates(ent);
        Dirty(ent);
    }

    /// <summary>
    ///     Prevent collision with an already hit entity.
    /// </summary>
    private void OnPreventCollide(Entity<RMCPenetratingProjectileComponent> ent, ref PreventCollideEvent args)
    {
        if (!ent.Comp.HitTargets.Contains(args.OtherEntity))
            return;

        args.Cancelled = true;
    }

    /// <summary>
    ///     Add the hit target to a list of hit targets that won't be hit another time.
    /// </summary>
    private void OnProjectileHit(Entity<RMCPenetratingProjectileComponent> ent, ref ProjectileHitEvent args)
    {
        if (ent.Comp.HitTargets.Contains(args.Target))
        {
            args.Handled = true;
            return;
        }

        ent.Comp.HitTargets.Add(args.Target);
        Dirty(ent);
    }

    /// <summary>
    ///     Reduce the projectile damage and range based on what kind of target the projectile is colliding with.
    /// </summary>
    private void OnStartCollide(Entity<RMCPenetratingProjectileComponent> ent, ref StartCollideEvent args)
    {
        if (!TryComp(ent, out ProjectileComponent? projectile) || ent.Comp.ShotFrom == null)
            return;

        var rangeLoss = ent.Comp.RangeLossPerHit;
        var damageLoss = ent.Comp.DamageMultiplierLossPerHit;

        // Apply damage and range loss multipliers depending on target hit.
        if ((args.OtherFixture.CollisionLayer & HardCollisionGroup) != 0)
        {
            // Thick Membranes have a lower multiplier.
            if (TryComp(args.OtherEntity, out OccluderComponent? occluder) &&
                !occluder.Enabled)
            {
                rangeLoss *= ent.Comp.ThickMembraneMultiplier;
                damageLoss *= ent.Comp.ThickMembraneMultiplier;

            }
            else
            {
                rangeLoss *= ent.Comp.WallMultiplier;
                damageLoss *= ent.Comp.WallMultiplier;
            }
        }
        ent.Comp.Range -= rangeLoss;
        Dirty(ent);

        projectile.Damage *= 1 - damageLoss;
        Dirty(ent, projectile);
    }

    /// <summary>
    ///     Make sure additional hits are allowed if range is still above 0.
    /// </summary>
    private void OnAllowAdditionalHits(Entity<RMCPenetratingProjectileComponent> ent, ref AfterProjectileHitEvent args)
    {
        if (ent.Comp.ShotFrom == null)
            return;

        var distanceTravelled =
            (_transform.GetMoverCoordinates(ent).Position - ent.Comp.ShotFrom.Value.Position).Length();
        var range = ent.Comp.Range - distanceTravelled;

        ent.Comp.HitTargets.Add(args.Target);
        Dirty(ent);

        if (range < 0)
            return;

        args.Projectile.Comp.ProjectileSpent = false;
        Dirty(args.Projectile);
    }
}

/// <summary>
///     Raised on a projectile after it has hit an entity.
/// </summary>
[ByRefEvent]
public record struct AfterProjectileHitEvent(Entity<ProjectileComponent> Projectile, EntityUid Target);