//
// EqualityComparer.cs
//
// Authors:
//	Ben Maurer (bmaurer@ximian.com)
//	Marek Safar (marek.safar@gmail.com)
//
// Copyright (C) 2004 Novell, Inc (http://www.novell.com)
// Copyright (C) 2014 Xamarin Inc (http://www.xamarin.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
// 
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

using System;
using System.Runtime.InteropServices;

namespace System.Collections.Generic {
	[Serializable]
	public abstract class EqualityComparer <T> : IEqualityComparer, IEqualityComparer <T> {
		
		static EqualityComparer ()
		{
			var t = typeof (T);
			if (t == typeof (string)) {
				_default = (EqualityComparer<T>) (object) new InternalStringComparer ();
				return;
			}

			if (t == typeof (int)) {
				_default = (EqualityComparer<T>) (object) new IntEqualityComparer ();
				return;
			}

			if (t.IsEnum && Enum.GetUnderlyingType (t) == typeof (int)) {
				_default = new EnumIntEqualityComparer<T> ();
				return;
			}

			if (typeof (IEquatable <T>).IsAssignableFrom (t))
				_default = (EqualityComparer <T>) Activator.CreateInstance (typeof (GenericEqualityComparer <>).MakeGenericType (t));
			else
				_default = new DefaultComparer<T> ();
		}
		
		public abstract int GetHashCode (T obj);
		public abstract bool Equals (T x, T y);
	
		static readonly EqualityComparer <T> _default;
		
		public static EqualityComparer <T> Default {
			get {
				return _default;
			}
		}

		int IEqualityComparer.GetHashCode (object obj)
		{
			if (obj == null)
				return 0;

			if (!(obj is T))
				throw new ArgumentException ("Argument is not compatible", "obj");

			return GetHashCode ((T)obj);
		}

		bool IEqualityComparer.Equals (object x, object y)
		{
			if (x == y)
				return true;

			if (x == null || y == null)
				return false;

			if (!(x is T))
				throw new ArgumentException ("Argument is not compatible", "x");
			if (!(y is T))
				throw new ArgumentException ("Argument is not compatible", "y");
			return Equals ((T)x, (T)y);
		}
		
		internal virtual int IndexOf (T[] array, T value, int startIndex, int endIndex)
		{
			for (int i = startIndex; i < endIndex; ++i) {
				if (Equals (Array.UnsafeLoad (array, i), value))
					return i;
			}

			return -1;
		}
	}

	[Serializable]
	sealed class DefaultComparer<T> : EqualityComparer<T> {
	
		public override int GetHashCode (T obj)
		{
			if (obj == null)
				return 0;
			return obj.GetHashCode ();
		}
	
		public override bool Equals (T x, T y)
		{
			if (x == null)
				return y == null;

			return x.Equals (y);
		}
	}

	[Serializable]
	sealed class InternalStringComparer : EqualityComparer<string> {
	
		public override int GetHashCode (string obj)
		{
			if (obj == null)
				return 0;
			return obj.GetHashCode ();
		}
	
		public override bool Equals (string x, string y)
		{
			if (x == null)
				return y == null;

			if ((object) x == (object) y)
				return true;
				
			return x.Equals (y);
		}

		internal override int IndexOf (string[] array, string value, int startIndex, int endIndex)
		{
			for (int i = startIndex; i < endIndex; ++i) {
				if (Array.UnsafeLoad (array, i) == value)
					return i;
			}

			return -1;
		}
	}

	[Serializable]
	sealed class IntEqualityComparer : EqualityComparer<int>
	{
		public override int GetHashCode (int obj)
		{
			return obj;
		}

		public override bool Equals (int x, int y)
		{
			return x == y;
		}

		internal override int IndexOf (int[] array, int value, int startIndex, int endIndex)
		{
			for (int i = startIndex; i < endIndex; ++i) {
				if (Array.UnsafeLoad (array, i) == value)
					return i;
			}

			return -1;
		}
	}

	[Serializable]
	sealed class EnumIntEqualityComparer<T> : EqualityComparer<T>
	{
		public override int GetHashCode (T obj)
		{
			return Array.UnsafeMov<T, int> (obj);
		}

		public override bool Equals (T x, T y)
		{
			return Array.UnsafeMov<T, int> (x) == Array.UnsafeMov<T, int> (y);
		}

		internal override int IndexOf (T[] array, T value, int startIndex, int endIndex)
		{
			int v = Array.UnsafeMov<T, int> (value);
			var a = Array.UnsafeMov<T[], int[]> (array);
			for (int i = startIndex; i < endIndex; ++i) {
				if (Array.UnsafeLoad (a, i) == v)
					return i;
			}

			return -1;
		}
	}

	[Serializable]
	sealed class GenericEqualityComparer <T> : EqualityComparer <T> where T : IEquatable <T> {

		public override int GetHashCode (T obj)
		{
			if (obj == null)
				return 0;
			return obj.GetHashCode ();
		}

		public override bool Equals (T x, T y)
		{
			if (x == null)
				return y == null;
			
			return x.Equals (y);
		}
	}
}