using System;
using System.Diagnostics;
using System.Linq.Expressions;
using System.Reflection;
using Intromat.Interfaces;
using ReactiveUI;

namespace Intromat.ViewModels
{
    public class UndoItem<TObservable, TValue> : IUndoItem where TObservable : ReactiveObject
    {
        private readonly TValue _newValue;
        private readonly TObservable _observable;
        private readonly TValue _oldValue;
        private readonly PropertyInfo _propertyInfo;

        public UndoItem(IFile file, TObservable observable, Expression<Func<TObservable, TValue>> memberLamda, TValue oldValue, TValue newValue)
        {
            File = file;
            _observable = observable;
            _oldValue = oldValue;
            _newValue = newValue;
            if (memberLamda.Body is MemberExpression { Member: PropertyInfo propertyInfo }) _propertyInfo = propertyInfo;
            Debug.Assert(_propertyInfo != null);
        }

        public IFile File { get; }

        public void Redo()
        {
            _propertyInfo.SetValue(_observable, _newValue);
        }

        public void Undo()
        {
            _propertyInfo.SetValue(_observable, _oldValue);
        }
    }
}