using System;

using System.Collections.Generic;

using System.Text;



namespace Otis

{

	/// <summary>

	/// Interface implemented by all aggregate functions which can be executed

	/// on path expressions

	/// </summary>

	/// <remarks>

	/// Client applications can implement additional functions by extending this interface

	/// and registering those classes with <see cref="Configuration"/>.

	/// </remarks>

	public interface IAggregateFunction<T> : IExpressionFormatProvider

	{

		/// <summary>

		/// Sets the starting value of the function

		/// </summary>

		/// <param name="initialValue">Initial value</param>

		void Initialize(T initialValue);



		/// <summary>

		/// Updates the function with specified value

		/// </summary>

		/// <param name="value">New value to be processed</param>

		void ProcessValue(T value);



		/// <summary>

		/// returns the number of items processed by the function

		/// </summary>

		int ProcessedItemCount { get; }



		/// <summary>

		/// Returns the current function result

		/// </summary>

		T Result { get; }



	}

}