using System;
using System.Threading.Tasks;
using System.Windows.Input;

namespace MVVM
{
    public class ActionCommandAsync : ICommand
    {
        private Func<object, Task> action;
        private Predicate<object> predicate;

        private bool executing = false;

        public ActionCommandAsync(Func<object, Task> action) : this(action, null)
        { }

        public ActionCommandAsync(Func<object, Task> action, Predicate<object> predicate)
        {
            this.action = action ?? throw new ArgumentNullException(nameof(action));
            this.predicate = predicate;
        }

        #region ICommand members:

        public event EventHandler CanExecuteChanged
        {
            add { CommandManager.RequerySuggested += value; }
            remove { CommandManager.RequerySuggested -= value; }
        }

        public bool CanExecute(object parameter) =>
            !executing && (predicate == null || predicate(parameter));

        public void Execute() =>
            Execute(null);

        public async void Execute(object parameter)
        {
            var task = action(parameter);

            if (task != null)
            {
                executing = true;

                await task;

                executing = false;
            }
        }

        #endregion
    }
}