using System;
using System.Linq;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Media;

namespace LinqToVisualTree
{
  /// <summary>
  /// Adapts a DependencyObject to provide methods required for generate
  /// a Linq To Tree API
  /// </summary>
  public class VisualTreeAdapter : ILinqTree<DependencyObject>
  {
    private DependencyObject _item;

    public VisualTreeAdapter(DependencyObject item)
    {
      _item = item;
    }

    public IEnumerable<DependencyObject> Children()
    {
      int childrenCount = VisualTreeHelper.GetChildrenCount(_item);
      for (int i = 0; i < childrenCount; i++)
      {
        yield return VisualTreeHelper.GetChild(_item, i);
      }
    }

    public DependencyObject Parent
    {
      get
      {
        return VisualTreeHelper.GetParent(_item);
      }
    }
  }
}

namespace LinqToVisualTree
{
  /// <summary>
  /// Defines an interface that must be implemented to generate the LinqToTree methods
  /// </summary>
  /// <typeparam name="T"></typeparam>
  public interface ILinqTree<T>
  {
    IEnumerable<T> Children();

    T Parent { get; }
  }

  public static class TreeExtensions
  {
    /// <summary>
    /// Returns a collection of descendant elements.
    /// </summary>
    public static IEnumerable<DependencyObject> Descendants(this DependencyObject item)
    {
      ILinqTree<DependencyObject> adapter = new VisualTreeAdapter(item);
      foreach (var child in adapter.Children())
      {
        yield return child;

        foreach (var grandChild in child.Descendants())
        {
          yield return grandChild;
        }
      }
    }

    /// <summary>
    /// Returns a collection containing this element and all descendant elements.
    /// </summary>
    public static IEnumerable<DependencyObject> DescendantsAndSelf(this DependencyObject item)
    {
      yield return item;

      foreach (var child in item.Descendants())
      {
        yield return child;
      }
    }

    /// <summary>
    /// Returns a collection of ancestor elements.
    /// </summary>
    public static IEnumerable<DependencyObject> Ancestors(this DependencyObject item)
    {
      ILinqTree<DependencyObject> adapter = new VisualTreeAdapter(item);

      var parent = adapter.Parent;
      while (parent != null)
      {
        yield return parent;
        adapter = new VisualTreeAdapter(parent);
        parent = adapter.Parent;
      }
    }

    /// <summary>
    /// Returns a collection containing this element and all ancestor elements.
    /// </summary>
    public static IEnumerable<DependencyObject> AncestorsAndSelf(this DependencyObject item)
    {
      yield return item;

      foreach (var ancestor in item.Ancestors())
      {
        yield return ancestor;
      }
    }

    /// <summary>
    /// Returns a collection of child elements.
    /// </summary>
    public static IEnumerable<DependencyObject> Elements(this DependencyObject item)
    {
      ILinqTree<DependencyObject> adapter = new VisualTreeAdapter(item);
      foreach (var child in adapter.Children())
      {
        yield return child;
      }
    }

    /// <summary>
    /// Returns a collection of the sibling elements before this node, in document order.
    /// </summary>
    public static IEnumerable<DependencyObject> ElementsBeforeSelf(this DependencyObject item)
    {
      if (item.Ancestors().FirstOrDefault() == null)
        yield break;
      foreach (var child in item.Ancestors().First().Elements())
      {
        if (child.Equals(item))
          break;
        yield return child;
      }
    }

    /// <summary>
    /// Returns a collection of the after elements after this node, in document order.
    /// </summary>
    public static IEnumerable<DependencyObject> ElementsAfterSelf(this DependencyObject item)
    {
      if (item.Ancestors().FirstOrDefault() == null)
        yield break;
      bool afterSelf = false;
      foreach (var child in item.Ancestors().First().Elements())
      {
        if (afterSelf)
          yield return child;

        if (child.Equals(item))
          afterSelf = true;
      }
    }

    /// <summary>
    /// Returns a collection containing this element and all child elements.
    /// </summary>
    public static IEnumerable<DependencyObject> ElementsAndSelf(this DependencyObject item)
    {
      yield return item;

      foreach (var child in item.Elements())
      {
        yield return child;
      }
    }

    /// <summary>
    /// Returns a collection of descendant elements which match the given type.
    /// </summary>
    public static IEnumerable<DependencyObject> Descendants<T>(this DependencyObject item)
    {
      return item.Descendants().Where(i => i is T).Cast<DependencyObject>();
    }

    /// <summary>
    /// Returns a collection of the sibling elements before this node, in document order
    /// which match the given type.
    /// </summary>
    public static IEnumerable<DependencyObject> ElementsBeforeSelf<T>(this DependencyObject item)
    {
      return item.ElementsBeforeSelf().Where(i => i is T).Cast<DependencyObject>();
    }

    /// <summary>
    /// Returns a collection of the after elements after this node, in document order
    /// which match the given type.
    /// </summary>
    public static IEnumerable<DependencyObject> ElementsAfterSelf<T>(this DependencyObject item)
    {
      return item.ElementsAfterSelf().Where(i => i is T).Cast<DependencyObject>();
    }

    /// <summary>
    /// Returns a collection containing this element and all descendant elements
    /// which match the given type.
    /// </summary>
    public static IEnumerable<DependencyObject> DescendantsAndSelf<T>(this DependencyObject item)
    {
      return item.DescendantsAndSelf().Where(i => i is T).Cast<DependencyObject>();
    }

    /// <summary>
    /// Returns a collection of ancestor elements which match the given type.
    /// </summary>
    public static IEnumerable<DependencyObject> Ancestors<T>(this DependencyObject item)
    {
      return item.Ancestors().Where(i => i is T).Cast<DependencyObject>();
    }

    /// <summary>
    /// Returns a collection containing this element and all ancestor elements
    /// which match the given type.
    /// </summary>
    public static IEnumerable<DependencyObject> AncestorsAndSelf<T>(this DependencyObject item)
    {
      return item.AncestorsAndSelf().Where(i => i is T).Cast<DependencyObject>();
    }

    /// <summary>
    /// Returns a collection of child elements which match the given type.
    /// </summary>
    public static IEnumerable<DependencyObject> Elements<T>(this DependencyObject item)
    {
      return item.Elements().Where(i => i is T).Cast<DependencyObject>();
    }

    /// <summary>
    /// Returns a collection containing this element and all child elements.
    /// which match the given type.
    /// </summary>
    public static IEnumerable<DependencyObject> ElementsAndSelf<T>(this DependencyObject item)
    {
      return item.ElementsAndSelf().Where(i => i is T).Cast<DependencyObject>();
    }

  }

  public static class EnumerableTreeExtensions
  {
    /// <summary>
    /// Applies the given function to each of the items in the supplied
    /// IEnumerable.
    /// </summary>
    private static IEnumerable<DependencyObject> DrillDown(this IEnumerable<DependencyObject> items,
        Func<DependencyObject, IEnumerable<DependencyObject>> function)
    {
      foreach (var item in items)
      {
        foreach (var itemChild in function(item))
        {
          yield return itemChild;
        }
      }
    }

    /// <summary>
    /// Applies the given function to each of the items in the supplied
    /// IEnumerable, which match the given type.
    /// </summary>
    public static IEnumerable<DependencyObject> DrillDown<T>(this IEnumerable<DependencyObject> items,
        Func<DependencyObject, IEnumerable<DependencyObject>> function)
        where T : DependencyObject
    {
      foreach (var item in items)
      {
        foreach (var itemChild in function(item))
        {
          if (itemChild is T)
          {
            yield return (T)itemChild;
          }
        }
      }
    }

    /// <summary>
    /// Returns a collection of descendant elements.
    /// </summary>
    public static IEnumerable<DependencyObject> Descendants(this IEnumerable<DependencyObject> items)
    {
      return items.DrillDown(i => i.Descendants());
    }

    /// <summary>
    /// Returns a collection containing this element and all descendant elements.
    /// </summary>
    public static IEnumerable<DependencyObject> DescendantsAndSelf(this IEnumerable<DependencyObject> items)
    {
      return items.DrillDown(i => i.DescendantsAndSelf());
    }

    /// <summary>
    /// Returns a collection of ancestor elements.
    /// </summary>
    public static IEnumerable<DependencyObject> Ancestors(this IEnumerable<DependencyObject> items)
    {
      return items.DrillDown(i => i.Ancestors());
    }

    /// <summary>
    /// Returns a collection containing this element and all ancestor elements.
    /// </summary>
    public static IEnumerable<DependencyObject> AncestorsAndSelf(this IEnumerable<DependencyObject> items)
    {
      return items.DrillDown(i => i.AncestorsAndSelf());
    }

    /// <summary>
    /// Returns a collection of child elements.
    /// </summary>
    public static IEnumerable<DependencyObject> Elements(this IEnumerable<DependencyObject> items)
    {
      return items.DrillDown(i => i.Elements());
    }

    /// <summary>
    /// Returns a collection containing this element and all child elements.
    /// </summary>
    public static IEnumerable<DependencyObject> ElementsAndSelf(this IEnumerable<DependencyObject> items)
    {
      return items.DrillDown(i => i.ElementsAndSelf());
    }

    /// <summary>
    /// Returns a collection of descendant elements which match the given type.
    /// </summary>
    public static IEnumerable<DependencyObject> Descendants<T>(this IEnumerable<DependencyObject> items)
        where T : DependencyObject
    {
      return items.DrillDown<T>(i => i.Descendants());
    }

    /// <summary>
    /// Returns a collection containing this element and all descendant elements.
    /// which match the given type.
    /// </summary>
    public static IEnumerable<DependencyObject> DescendantsAndSelf<T>(this IEnumerable<DependencyObject> items)
        where T : DependencyObject
    {
      return items.DrillDown<T>(i => i.DescendantsAndSelf());
    }

    /// <summary>
    /// Returns a collection of ancestor elements which match the given type.
    /// </summary>
    public static IEnumerable<DependencyObject> Ancestors<T>(this IEnumerable<DependencyObject> items)
        where T : DependencyObject
    {
      return items.DrillDown<T>(i => i.Ancestors());
    }

    /// <summary>
    /// Returns a collection containing this element and all ancestor elements.
    /// which match the given type.
    /// </summary>
    public static IEnumerable<DependencyObject> AncestorsAndSelf<T>(this IEnumerable<DependencyObject> items)
        where T : DependencyObject
    {
      return items.DrillDown<T>(i => i.AncestorsAndSelf());
    }

    /// <summary>
    /// Returns a collection of child elements which match the given type.
    /// </summary>
    public static IEnumerable<DependencyObject> Elements<T>(this IEnumerable<DependencyObject> items)
        where T : DependencyObject
    {
      return items.DrillDown<T>(i => i.Elements());
    }

    /// <summary>
    /// Returns a collection containing this element and all child elements.
    /// which match the given type.
    /// </summary>
    public static IEnumerable<DependencyObject> ElementsAndSelf<T>(this IEnumerable<DependencyObject> items)
        where T : DependencyObject
    {
      return items.DrillDown<T>(i => i.ElementsAndSelf());
    }
  }
}