using System;
using System.ComponentModel;
using System.Diagnostics;
using System.IO;
using System.Threading.Tasks;
using System.Windows;

// ReSharper disable once CheckNamespace
namespace DTS.Common.Base
{

    /// <summary>
    /// Base class used to create ViewModel objects that implement their own commands/verbs/actions.
    /// </summary>
    /// <typeparam name="T">Type of the Model object.</typeparam>
    public abstract class ViewModelBase<T> : DependencyObject, INotifyPropertyChanged, IViewModel
    {
        /// <summary>
        /// Gets or sets the Model object.
        /// </summary>
        public object Model { get; set; }


        /// <summary>
        /// Create new instance of base class used to create ViewModel objects that implement their own commands/verbs/actions.
        /// </summary>
        public ViewModelBase()
        {
            
        }

        /// <summary>
        /// Gets a value indicating whether this object is executing an asynchronous process. 
        /// </summary>
        public bool IsBusy { get; protected set; }

        /// <summary>
        /// Gets a value indicating whether the Model has been changed.
        /// </summary>
        public virtual bool IsDirty { get; protected set; }
    

        // Summary:
        //     Event raised when an error occurs during processing.
        /// <summary>
        /// 
        /// </summary>
        public virtual event EventHandler<ErrorEventArgs> ErrorOccurred;

        /// <summary>
        /// Event raised when a property changes.
        /// </summary>
        public virtual event PropertyChangedEventHandler PropertyChanged;


        /// <summary>
        ///     Override this method to implement async initialization of the model object.
        ///     The result of this method is used to set the Model property of the viewmodel.
        /// </summary>
        /// <returns>A Task that creates the model object.</returns>
        [DebuggerStepThrough]
        protected abstract Task<T> InitializeAsync();

        /// <summary>
        /// Creates or retrieves a new instance of the Model by invoking a static factory method.
        /// </summary>
        /// <param name="factoryMethod">Static factory method function.</param>
        protected abstract void DoRefresh(Func<T> factoryMethod);


        /// <summary>
        /// Raises ErrorOccurred event when an error occurs during processing.
        /// </summary>
        /// <param name="error"></param>
        protected abstract void OnError(Exception error);
        
        /// <summary>
        /// Invoked when the Model changes, allowing event handlers to be unhooked from the old object and hooked on the new object.
        /// </summary>
        /// <param name="oldValue">Previous Model reference.</param>
        /// <param name="newValue">New Model reference.</param>
        protected abstract void OnModelChanged(T oldValue, T newValue);
        
        /// <summary>
        /// Raise the PropertyChanged event.
        /// </summary>
        /// <param name="propertyName">Name of the changed property.</param>
        protected abstract void OnPropertyChanged(string propertyName);
        
    }
}