gather-and-defend/Assets/LevelEditor/LevelEditorEditor.cs

using UnityEditor;
using UnityEngine.Tilemaps;
using UnityEngine;
using System.IO;

namespace GatherAndDefend.LevelEditor
{
    [CustomEditor(typeof(LevelEditor))]
    public class LevelEditorEditor : Editor
    {
        const string defaultName = "Level";
        const string extension = ".asset";
        string Path => "Assets/";
        public override void OnInspectorGUI()
        {
            DrawDefaultInspector();

            var targ = (LevelEditor)target;
            if (GUILayout.Button("Save"))
            {
                string name;
                if (targ.Level) name = targ.Level.name;
                else name = defaultName;
                if (File.Exists(Path + name + extension))
                {
                    File.Delete(Path + name + extension);
                }
                
                var map = CreateInstance<Map>();
                map.name = name;

                foreach (Tilemap tilemap in targ.GetComponentsInChildren<Tilemap>())
                {
                    map.Write(tilemap);
                }

                AssetDatabase.CreateAsset(map, Path + name + extension);
                targ.Level = map;
                AssetDatabase.ImportAsset(Path + name + extension);
            }
            if (GUILayout.Button("Load"))
            {
                if (!targ.Level) return;

                foreach (Tilemap tilemap in targ.GetComponentsInChildren<Tilemap>())
                {
                    tilemap.ClearAllTiles();
                    targ.Level.Read(tilemap);
                }
            }
        }
    }
}