practice/Model/FieldManager.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace WebApplication1
{

    public class FieldManager : IFieldManager
    {
        private List<Field> _fields = new List<Field>();

        public Field StartNewGame()
        {
            var ff = new RandomField(2);
            _fields.Add(ff);
            return ff;
        }
        public Field Move(string identifier)
        {
            var ff = _fields.FirstOrDefault(f => f.identifier.Equals(identifier));
            if (ff == null) return null;
            ff.MoveRandomFigure();
            return ff;
        }

        public Field List(string identifier)
        {
            var ff = _fields.FirstOrDefault(f => f.identifier.Equals(identifier));
            if (ff == null) return null;
            return ff;
        }
    }
}