// Copyright 2004-2008 Castle Project - http://www.castleproject.org/
// 
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// 
//     http://www.apache.org/licenses/LICENSE-2.0
// 
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

namespace Castle.DynamicProxy.Generators
{
	using System;
	using System.Collections;
	using System.Reflection;
	using System.Collections.Generic;

	public class MethodSignatureComparer : IEqualityComparer<MethodInfo>
	{
		public static readonly MethodSignatureComparer Instance = new MethodSignatureComparer();

		public bool Equals(MethodInfo x, MethodInfo y)
		{
			if (x == null && y == null)
			{
				return true;
			}
			else if (x == null || y == null)
			{
				return false;
			}
			else
			{
				return x.Name == y.Name &&
				       EqualGenericParameters(x, y) &&
				       EqualSignatureTypes(x.ReturnType, y.ReturnType) &&
				       EqualParameters(x, y);
			}
		}

		private bool EqualGenericParameters(MethodInfo x, MethodInfo y)
		{
			if (x.IsGenericMethod != y.IsGenericMethod)
			{
				return false;
			}

			if (x.IsGenericMethod)
			{
				Type[] xArgs = x.GetGenericArguments();
				Type[] yArgs = y.GetGenericArguments();

				if (xArgs.Length != yArgs.Length)
				{
					return false;
				}

				for (int i = 0; i < xArgs.Length; ++i)
				{
					if (xArgs[i].IsGenericParameter != yArgs[i].IsGenericParameter)
					{
						return false;
					}

					if (!xArgs[i].IsGenericParameter && !xArgs[i].Equals(yArgs[i]))
					{
						return false;
					}
				}
			}

			return true;
		}

		private bool EqualParameters(MethodInfo x, MethodInfo y)
		{
			ParameterInfo[] xArgs = x.GetParameters();
			ParameterInfo[] yArgs = y.GetParameters();

			if (xArgs.Length != yArgs.Length)
			{
				return false;
			}

			for (int i = 0; i < xArgs.Length; ++i)
			{
				if (!EqualSignatureTypes(xArgs[i].ParameterType, yArgs[i].ParameterType))
				{
					return false;
				}
			}

			return true;
		}

		private static bool EqualSignatureTypes(Type x, Type y)
		{
			if (x.IsGenericParameter != y.IsGenericParameter)
			{
				return false;
			}

			if (x.IsGenericParameter)
			{
				if (x.GenericParameterPosition != y.GenericParameterPosition)
				{
					return false;
				}
			}
			else
			{
				if (!x.Equals(y))
				{
					return false;
				}
			}
			return true;
		}

		public int GetHashCode(MethodInfo obj)
		{
			return obj.Name.GetHashCode() ^ obj.GetParameters().Length; // everything else would be too cumbersome
		}
	}
}