NPCFollowState.cs

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using System.IO;
using Microsoft.Xna.Framework;
 
namespace Terraria.DataStructures;
 
public class NPCFollowState
{
    private NPC _npc;
 
    private int? _playerIndexBeingFollowed;
 
    private Vector2 _floorBreadcrumb;
 
    public Vector2 BreadcrumbPosition => _floorBreadcrumb;
 
    public bool IsFollowingPlayer => _playerIndexBeingFollowed.HasValue;
 
    public Player PlayerBeingFollowed
    {
        get
        {
            if (_playerIndexBeingFollowed.HasValue)
            {
                return Main.player[_playerIndexBeingFollowed.Value];
            }
            return null;
        }
    }
 
    public void FollowPlayer(int playerIndex)
    {
        _playerIndexBeingFollowed = playerIndex;
        _floorBreadcrumb = Main.player[playerIndex].Bottom;
        _npc.netUpdate = true;
    }
 
    public void StopFollowing()
    {
        _playerIndexBeingFollowed = null;
        MoveNPCBackHome();
        _npc.netUpdate = true;
    }
 
    public void Clear(NPC npcToBelongTo)
    {
        _npc = npcToBelongTo;
        _playerIndexBeingFollowed = null;
        _floorBreadcrumb = default(Vector2);
    }
 
    private bool ShouldSync()
    {
        return _npc.isLikeATownNPC;
    }
 
    public void WriteTo(BinaryWriter writer)
    {
        int num = (_playerIndexBeingFollowed.HasValue ? _playerIndexBeingFollowed.Value : (-1));
        writer.Write((short)num);
    }
 
    public void ReadFrom(BinaryReader reader)
    {
        short num = reader.ReadInt16();
        if (Main.player.IndexInRange(num))
        {
            _playerIndexBeingFollowed = num;
        }
    }
 
    private void MoveNPCBackHome()
    {
        _npc.ai[0] = 20f;
        _npc.ai[1] = 0f;
        _npc.ai[2] = 0f;
        _npc.ai[3] = 0f;
        _npc.netUpdate = true;
    }
 
    public void Update()
    {
        if (IsFollowingPlayer)
        {
            Player playerBeingFollowed = PlayerBeingFollowed;
            if (!playerBeingFollowed.active || playerBeingFollowed.dead)
            {
                StopFollowing();
                return;
            }
            UpdateBreadcrumbs(playerBeingFollowed);
            Dust.QuickDust(_floorBreadcrumb, Color.Red);
        }
    }
 
    private void UpdateBreadcrumbs(Player player)
    {
        Vector2? vector = null;
        if (player.velocity.Y == 0f && player.gravDir == 1f)
        {
            vector = player.Bottom;
        }
        int num = 8;
        if (vector.HasValue && Vector2.Distance(vector.Value, _floorBreadcrumb) >= (float)num)
        {
            _floorBreadcrumb = vector.Value;
            _npc.netUpdate = true;
        }
    }
}