Custom code before play

CustomPlayBehaviour.cs

using System;
using System.Collections.Generic;
using System.IO;
using UnityEditor;
using UnityEditor.SceneManagement;
using UnityEngine;

namespace blablalblalmao
{
    [InitializeOnLoad]
    public class CustomPlayBehaviour
    {
        private static PlayStateProcess playStateProcess;

        static CustomPlayBehaviour()
        {
            EditorApplication.playModeStateChanged += OnPlayModeStateChanging;
            EditorApplication.update += OnUpdate;
        }

        private static void OnUpdate()
        {
            if (!EditorApplication.isPlayingOrWillChangePlaymode)
            {
                if (playStateProcess == PlayStateProcess.PreStarting)
                {
                    float startTime = EditorPrefs.GetFloat("startTime");
                    if (EditorApplication.timeSinceStartup > startTime)
                    {
                        playStateProcess = PlayStateProcess.Starting;
                        OnAboutToEnterPlaymode();

                        playStateProcess = PlayStateProcess.Ready;
                        EditorApplication.isPlaying = true;
                    }
                }
                else
                {
                    playStateProcess = PlayStateProcess.Editing;
                }
            }
        }

        private static void OnPlayModeStateChanging(PlayModeStateChange playModeStateChange)
        {
            if (playModeStateChange == PlayModeStateChange.ExitingEditMode)
            {
                if (playStateProcess != PlayStateProcess.Ready)
                {
                    EditorApplication.isPlaying = false;
                }

                if (playStateProcess == PlayStateProcess.Editing)
                {
                    playStateProcess = PlayStateProcess.PreStarting;
                    EditorPrefs.SetFloat("startTime", (float)EditorApplication.timeSinceStartup + 0.15f);
                }
            }
            else if (playModeStateChange == PlayModeStateChange.EnteredEditMode)
            {
                if (playStateProcess == PlayStateProcess.Ready)
                {
                    playStateProcess = PlayStateProcess.Editing;
                }
            }
        }

        private static void OnAboutToEnterPlaymode()
        {
            //this will run just before play mode
        }

        public enum PlayStateProcess
        {
            Editing,
            PreStarting,
            Starting,
            Ready
        }
    }
}