using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;

namespace Nuclex.Support.Collections {

  /// <summary>Generic collection of progressions</summary>
  public class ObservableCollection<ItemType> : Collection<ItemType> {

    #region class ItemEventArgs

    /// <summary>Arguments class for events that need to pass a progression</summary>
    public class ItemEventArgs : EventArgs {

      /// <summary>Initializes a new event arguments supplier</summary>
      /// <param name="item">Item to be supplied to the event handler</param>
      public ItemEventArgs(ItemType item) {
        this.item = item;
      }

      /// <summary>Obtains the collection item the event arguments are carrying</summary>
      public ItemType Item {
        get { return this.item; }
      }

      /// <summary>Item that's passed to the event handler</summary>
      private ItemType item;

    }

    #endregion // class ItemEventArgs

    /// <summary>Raised when an item has been added to the collection</summary>
    public event EventHandler<ItemEventArgs> ItemAdded;
    /// <summary>Raised when an item is removed from the collection</summary>
    public event EventHandler<ItemEventArgs> ItemRemoved;
    /// <summary>Raised the collection is about to be cleared</summary>
    public event EventHandler Clearing;

    /// <summary>Removes all elements from the Collection</summary>
    protected override void ClearItems() {
      OnClearing();

      base.ClearItems();
    }

    /// <summary>
    ///   Inserts an element into the ProgressionCollection at the specified index
    /// </summary>
    /// <param name="index">
    ///   The object to insert. The value can be null for reference types.
    /// </param>
    /// <param name="item">The zero-based index at which item should be inserted</param>
    protected override void InsertItem(int index, ItemType item) {
      base.InsertItem(index, item);

      OnAdded(item);
    }

    /// <summary>
    ///   Removes the element at the specified index of the ProgressionCollection
    /// </summary>
    /// <param name="index">The zero-based index of the element to remove</param>
    protected override void RemoveItem(int index) {
      ItemType item = base[index];

      base.RemoveItem(index);

      OnRemoved(item);
    }

    /// <summary>Replaces the element at the specified index</summary>
    /// <param name="index">
    ///   The new value for the element at the specified index. The value can be null
    ///   for reference types
    /// </param>
    /// <param name="item">The zero-based index of the element to replace</param>
    protected override void SetItem(int index, ItemType item) {
      ItemType oldItem = base[index];

      base.SetItem(index, item);

      OnRemoved(oldItem);
      OnAdded(item);
    }

    /// <summary>Fires the 'ItemAdded' event</summary>
    /// <param name="item">Item that has been added to the collection</param>
    protected virtual void OnAdded(ItemType item) {
      if(ItemAdded != null)
        ItemAdded(this, new ItemEventArgs(item));
    }

    /// <summary>Fires the 'ItemRemoved' event</summary>
    /// <param name="item">Item that has been removed from the collection</param>
    protected virtual void OnRemoved(ItemType item) {
      if(ItemRemoved != null)
        ItemRemoved(this, new ItemEventArgs(item));
    }

    /// <summary>Fires the 'Clearing' event</summary>
    protected virtual void OnClearing() {
      if(Clearing != null)
        Clearing(this, EventArgs.Empty);
    }

  }

} // namespace Nuclex.Support.Collections