Templates, Inversion of Control, Factories, and so on

using System.Linq;
using System.Windows;
using System.Windows.Controls;
using Pfz.Factoring;
using Pfz.WpfControls;
using System.Windows.Media;

namespace Pfz.Databasing.WpfControls
{
	/// <summary>
	/// Base lookup control. Use it only if you need a way to find
	/// LookupControls without knowing their specific generic 
	/// parameter type.
	/// </summary>
	public abstract class LookupControlBase:
		UserControl,
		IValueControl,
		IHasValueChanged,
		IHasDisplayName
	{
		internal KeyBoundControl _keyControl = new KeyBoundControl();
		internal TextBox _label = new TextBox { IsReadOnly = true, VerticalAlignment = VerticalAlignment.Bottom };

		private MenuItem _menuItemSearch;
		private MenuItem _menuItemCreate;
		internal MenuItem _menuItemEdit;
		private Button _button = new Button();
		
		/// <summary>
		/// Creates a new LookupControl instance.
		/// </summary>
		public LookupControlBase()
		{
			DockPanel.SetDock(_keyControl, Dock.Left);
			
			var panel = new DockPanel();
			panel.LastChildFill = true;
			var children = panel.Children;
			
			children.Add(_keyControl);
			children.Add(_label);
			
			var menuItemSearch = new MenuItem();
			_menuItemSearch = menuItemSearch;
			menuItemSearch.Header = "Search";
			menuItemSearch.Click +=	(sender, args) => Search();
			menuItemSearch.IsEnabled = CanSearch();

			bool canEdit = CanEdit();
			var menuItemCreateNew = new MenuItem();
			_menuItemCreate = menuItemCreateNew;
			menuItemCreateNew.Header = "Create New Record";
			menuItemCreateNew.Click += (sender, args) => CreateNewRecord();
			menuItemCreateNew.IsEnabled = canEdit;

			var menuItemEdit = new MenuItem();
			_menuItemEdit = menuItemEdit;
			menuItemEdit.Header = "Edit Actual Record";
			menuItemEdit.Click += (sender, args) => EditActualRecord();
			menuItemEdit.IsEnabled = false;

			var contextMenu = new ContextMenu();
			contextMenu.Items.Add(menuItemEdit);
			contextMenu.Items.Add(menuItemCreateNew);
			contextMenu.Items.Add(menuItemSearch);
			ContextMenu = contextMenu;

			_button.Content = "Lookup";
			var groupBox = new GroupBox();
			groupBox.Header = _button;
			groupBox.Content = panel;
			Content = groupBox;

			_button.Focusable = false;
			_button.Click += (a, b) => _ShowContextMenu();
			ContextMenu.Closed += (a, b) =>
			{
				ContextMenu.PlacementTarget = null;
				ContextMenu.VerticalOffset = 0;
			};
		}

		/// <summary>
		/// If key is Down, then open the menu.
		/// </summary>
		/// <param name="e"></param>
		protected override void OnPreviewKeyDown(System.Windows.Input.KeyEventArgs e)
		{
			base.OnPreviewKeyDown(e);

			if (e.Key == System.Windows.Input.Key.Down)
			{
				_ShowContextMenu();
				e.Handled = true;
			}
		}
		private void _ShowContextMenu()
		{
			ContextMenu.Placement = System.Windows.Controls.Primitives.PlacementMode.Relative;
			ContextMenu.PlacementTarget = _button;
			ContextMenu.VerticalOffset = _button.ActualHeight;
			ContextMenu.IsOpen = true;
		}

		/// <summary>
		/// Gets or sets a value indicating that this control is read-only.
		/// </summary>
		public bool IsReadOnly
		{
			get
			{
				return _keyControl._recordBoundControl.IsReadOnly;
			}
			set
			{
				bool canEdit = CanEdit();
				_menuItemCreate.IsEnabled = !value && canEdit;
				_menuItemSearch.IsEnabled = !value && CanSearch();
				_keyControl._recordBoundControl.IsReadOnly = value;
				_menuItemEdit.IsEnabled = !value && canEdit && Value != null;
			}
		}

		/// <summary>
		/// Gets or sets the button displayname.
		/// </summary>
		public string DisplayName
		{
			get
			{
				return _button.Content as string;
			}
			set
			{
				_button.Content = value;
			}
		}

		internal abstract bool CanSearch();
		internal abstract bool CanEdit();
		internal abstract void CreateNewRecord();
		internal abstract void EditActualRecord();
		internal abstract void Search();

		internal void OnValueChanged()
		{
			var handler = ValueChanged;
			if (handler != null)
				handler(this, null);
		}

		/// <summary>
		/// Event invoked when the value changes because of a search/new record.
		/// </summary>
		public event RoutedEventHandler ValueChanged;
		
		#region IValueContainer Members
			/// <summary>
			/// Gets or sets the value of this control.
			/// </summary>
			public abstract object Value { get; set; }
		#endregion
		#region IValueControl Members
			/// <summary>
			/// Clears the value of this control.
			/// </summary>
			public abstract void Clear();
		#endregion
	}
}