Flat2DArray

 [Serializable]
    public class Flat2DArray<T> : ISerializationCallbackReceiver
    {
        [SerializeField] T[] _items;
        [SerializeField] int _x;
        [SerializeField] int _y;
        public int X => _x;
        public int Y => _y;
        public T[] Items
        {
            get => _items;
            private set => _items = value;
        }

        public Flat2DArray(int x = 0, int y = 0)
        {
            _x = x;
            _y = y;
            Items = new T[X * Y];
        }

        public void ForEach(Action<int, int> action)
        {
            for (int x = 0; x < X; x++)
            for (int y = 0; y < Y; y++)
                action?.Invoke(x, y);
        }

        public T this[int x, int y]
        {
            get => Items[(x * Y) + y];
            set => Items[(x * Y) + y] = value;
        }

        public void OnBeforeSerialize() { }

        public void OnAfterDeserialize()
        {
            Items ??= new T[X * Y];
            var newSize = X * Y;
            int oldSize = Items.Length;
            Array.Resize(ref _items, newSize);
            if (newSize <= oldSize) return;
            for (int i = oldSize; i < newSize; i++) Items[i] = default;
        }

        public void Populate(T[] items)
        {
            if (items.Length < Items.Length)
                Array.Copy(items, _items, items.Length);
        }

        public class Flat2DArrayConverter : JsonConverter<Flat2DArray<T>>
    {
        public override void WriteJson(JsonWriter writer, Flat2DArray<T> value, JsonSerializer serializer)
        {
            writer.WriteStartObject();
            writer.WritePropertyName("x");
            writer.WriteValue(value._x);
            writer.WritePropertyName("y");
            writer.WriteValue(value._y);
            writer.WritePropertyName("items");
            serializer.Serialize(writer, value._items);
            writer.WriteEndObject();
        }

        public override Flat2DArray<T> ReadJson(JsonReader reader, Type objectType, Flat2DArray<T> existingValue, bool hasExistingValue, JsonSerializer serializer)
        {
            var x = 0;
            var y = 0;
            T[] items = null;

            while (reader.Read())
            {
                if (reader.TokenType == JsonToken.PropertyName)
                {
                    var propertyName = reader.Value.ToString();
                    reader.Read();

                    switch (propertyName)
                    {
                        case "x":
                            x = Convert.ToInt32(reader.Value);
                            break;
                        case "y":
                            y = Convert.ToInt32(reader.Value);
                            break;
                        case "items":
                            items = serializer.Deserialize<T[]>(reader);
                            break;
                    }
                }
                else if (reader.TokenType == JsonToken.EndObject)
                    break;
            }
            return new Flat2DArray<T>(x, y) { _items = items };
        }
    }
    }