using System;
using System.Collections.Generic;

namespace SmartStore.Core
{
    public sealed partial class GenericEqualityComparer<T> : IEqualityComparer<T>
    {
		private readonly Func<T, T, bool> _equals;
		private readonly Func<T, int> _getHashcode;

		public GenericEqualityComparer(Func<T, T, bool> equals, Func<T, int> getHashcode)
		{
			_getHashcode = getHashcode;
			_equals = equals;
		}

		public static GenericEqualityComparer<T> CompareMember<TMember>(Func<T, TMember> memberExpression) where TMember : IEquatable<TMember>
		{
			return new GenericEqualityComparer<T>(
				(x, y) => memberExpression.Invoke(x).Equals((TMember)memberExpression.Invoke(y)),
				x =>
				{
					var invoked = memberExpression.Invoke(x);
					return !ReferenceEquals(invoked, default(TMember)) ? invoked.GetHashCode() : 0;
				});
		}

		/// <summary>
		/// Determines whether the specified objects are equal.
		/// </summary>
		/// <returns>
		/// true if the specified objects are equal; otherwise, false.
		/// </returns>
		/// <param name="x">The first object of type <paramref name="T"/> to compare.</param><param name="y">The second object of type <paramref name="T"/> to compare.</param>
		public bool Equals(T x, T y)
		{
			return _equals.Invoke(x, y);
		}

		/// <summary>
		/// Returns a hash code for the specified object.
		/// </summary>
		/// <returns>
		/// A hash code for the specified object.
		/// </returns>
		/// <param name="obj">The <see cref="T:System.Object"/> for which a hash code is to be returned.</param><exception cref="T:System.ArgumentNullException">The type of <paramref name="obj"/> is a reference type and <paramref name="obj"/> is null.</exception>
		public int GetHashCode(T obj)
		{
			return _getHashcode.Invoke(obj);
		}
	}
}
