using System;
using System.Linq;
using System.Collections.Generic;

using Avalonia;

using BFR.DataModels;

namespace BFR.Operations
{
    public abstract class Operation : AvaloniaObject
    {
        // Needs to be avalonia property to update UI with any potential error.
        private readonly AvaloniaProperty<string> errorProperty = AvaloniaProperty.Register<MainWindow, string>(nameof(Error), defaultValue: "");
        public string Error { get => GetValue(errorProperty); set => SetValue(errorProperty, value); }
        public bool IsEnabled { get; set; } = true;
        public abstract string Name { get; }
        public abstract string Description { get; }

        protected abstract void ApplyToInternal(IList<FileModel> files);
        
        public void ApplyTo(IList<FileModel> files)
        {
            // Backup of all changes thus far, in case something goes wrong
            var backup = files.Select(file => file.Path).ToList();
            try
            {
                if(IsEnabled)
                    ApplyToInternal(files); // Try to apply operation
                Error = "";                 // If successul, remove any previous error
            }  
            catch (OperationException e) { Error = e.Message; } // If expected, show user a concise and descriptive message
            catch (Exception e) { Error = $"Unexpected {e}"; }  // If not, hint with the exception thrown that this is unexpected behaviour
            finally
            {
                if (Error != "") // If something went wrong, restore backup
                    for (int i = 0; i < files.Count; i++)
                        files[i].Path = backup[i];
            }
        }
    }
}