using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Linq;
using Chronos.Presentation.Core.Configuration;
using Chronos.Presentation.Core.VirtualDesktops;
using Chronos.Presentation.Core.Widgets;
using Chronos.Presentation.Core.Windows;
using Chronos.Presentation.ViewModel;
using nRoute.Components;

namespace Chronos.WidgetLibrary
{
  /// <summary>
  /// Widget library ViewModel
  /// </summary>
  public sealed class WidgetLibraryViewModel
      : WidgetViewModel
  {
    #region · Constants ·

    private static readonly string AllWidgetsKey = "All";

    #endregion

    #region · PropertyChangedEventArgs Cached Instances ·

    private static readonly PropertyChangedEventArgs FilterChangedArgs = CreateArgs<WidgetLibraryViewModel>(x => x.Filter);
    private static readonly PropertyChangedEventArgs WidgetsChangedArgs = CreateArgs<WidgetLibraryViewModel>(x => x.Widgets);
    private static readonly PropertyChangedEventArgs SelectedWidgetChangedArgs = CreateArgs<WidgetLibraryViewModel>(x => x.SelectedWidget);

    #endregion

    #region · Fields ·

    private string filter;
    private List<string> groups;
    private List<WidgetItemViewModel> widgets;
    private IWidget selectedWidget;
    private ActionCommand createWidgetCommand;

    #endregion

    #region · Commands ·

    /// <summary>
    /// Gets the create widget command.
    /// </summary>
    /// <value>The create widget command.</value>
    public ActionCommand CreateWidgetCommand
    {
      get
      {
        if (this.createWidgetCommand == null)
        {
          this.createWidgetCommand = new ActionCommand
          (
              () => OnCreateWidget(),
              () => CanCreateWidget()
          );
        }

        return this.createWidgetCommand;
      }
    }

    #endregion

    #region · Properties ·

    /// <summary>
    /// Gets/sets a fragment of the name to filter for.
    /// </summary>
    public string Filter
    {
      get { return this.filter; }
      set
      {
        if (value != filter)
        {
          this.filter = value;
          this.NotifyPropertyChanged(FilterChangedArgs);
          this.NotifyPropertyChanged(WidgetsChangedArgs);

          this.SelectedWidget = null;
        }
      }
    }

    /// <summary>
    /// Gets the list of widget groups.
    /// </summary>
    /// <value>The groups.</value>
    public IEnumerable<string> Groups
    {
      get { return this.groups; }
    }

    /// <summary>
    /// Gets the list of widgets
    /// </summary>
    public IList<WidgetItemViewModel> Widgets
    {
      get
      {
        if (String.IsNullOrEmpty(this.filter)
            || this.filter == AllWidgetsKey)
        {
          return this.widgets;
        }
        else
        {
          return new ReadOnlyCollection<WidgetItemViewModel>(this.widgets.Where(x => x.Group == this.filter).ToList());
        }
      }
    }

    /// <summary>
    /// Gets or sets the selected widget.
    /// </summary>
    /// <value>The selected widget.</value>
    public IWidget SelectedWidget
    {
      get { return this.selectedWidget; }
      set
      {
        if (this.selectedWidget != value)
        {
          this.selectedWidget = value;
          this.NotifyPropertyChanged(SelectedWidgetChangedArgs);
          this.CreateWidgetCommand.RequeryCanExecute();
        }
      }
    }

    #endregion

    #region · Constructors ·

    /// <summary>
    /// Initializes a new instance of the <see cref="WidgetLibrary"/> class.
    /// </summary>
    public WidgetLibraryViewModel()
      : base()
    {
      this.widgets = this.DiscoverWidgets();
      this.groups = this.DiscoverWidgetGroups();
    }

    #endregion

    #region · Overriden Methods ·

    /// <summary>
    /// Called when the related view is being closed.
    /// </summary>
    public override void Close()
    {
      base.Close();

      this.selectedWidget = null;
      this.createWidgetCommand = null;

      if (this.groups != null)
      {
        this.groups.Clear();
        this.groups = null;
      }

      if (this.widgets != null)
      {
        this.widgets.Clear();
        this.widgets = null;
      }
    }

    #endregion

    #region · Command Actions ·

    private bool CanCreateWidget()
    {
      return (this.selectedWidget != null);
    }

    /// <summary>
    /// Handles the create widget command.
    /// </summary>
    private void OnCreateWidget()
    {
      this.GetService<IVirtualDesktopManager>()
          .Show(this.selectedWidget.CreateView() as IDesktopElement);
    }

    #endregion

    #region · Private Methods ·

    private List<string> DiscoverWidgetGroups()
    {
      List<string> groups = new List<string>();
      var q = from widgetdef in this.widgets
              select widgetdef.Group;

      groups.Add(AllWidgetsKey);
      groups.AddRange(q.Distinct().ToList());

      return groups;
    }

    private List<WidgetItemViewModel> DiscoverWidgets()
    {
      IEnumerable<IWidget> widgetDefs = this.GetService<IWidgetConfigurationService>()
                                            .GetWidgets();

      if (widgetDefs != null)
      {
        var query = from widgetdef in widgetDefs
                    select new WidgetItemViewModel(widgetdef);

        return query.ToList();
      }

      return null;
    }

    #endregion
  }
}