//-----------------------------------------------------------------------------
// Copyright (c) Microsoft Corporation.  All rights reserved.
//-----------------------------------------------------------------------------

namespace System.Activities.Expressions
{
    using System;
    using System.Collections;
    using System.Collections.Generic;
    using System.Reflection;
    using System.Runtime;

    class AssemblyNameEqualityComparer : IEqualityComparer, IEqualityComparer<AssemblyName>
    {
        public AssemblyNameEqualityComparer()
        {
        }

        public new bool Equals(object xparam, object yparam)
        {
            if (xparam == null && yparam == null)
            {
                return true;
            }
            return this.Equals(xparam as AssemblyName, yparam as AssemblyName);
        }

        public bool Equals(AssemblyName x, AssemblyName y)
        {
            // this expects non-null AssemblyName
            if (x == null || y == null)
            {
                return false;
            }

            if (Object.ReferenceEquals(x, y))
            {
                return true;
            }

            if (x.Name != null && y.Name != null)
            {
                if (string.Compare(x.Name, y.Name, StringComparison.OrdinalIgnoreCase) != 0)
                {
                    return false;
                }
            }
            else if (!(x.Name == null && y.Name == null))
            {
                return false;
            }

            if (x.Version != null && y.Version != null)
            {
                if (x.Version != y.Version)
                {
                    return false;
                }
            }
            else if (!(x.Version == null && y.Version == null))
            {
                return false;
            }

            if (x.CultureInfo != null && y.CultureInfo != null)
            {
                if (!x.CultureInfo.Equals(y.CultureInfo))
                {
                    return false;
                }
            }
            else if (!(x.CultureInfo == null && y.CultureInfo == null))
            {
                return false;
            }

            byte[] xArray = x.GetPublicKeyToken();
            byte[] yArray = y.GetPublicKeyToken();
            if (!IsSameKeyToken(xArray, yArray))
            {
                return false;
            }

            return true;
        }

        public int GetHashCode(object objparam)
        {
            AssemblyName obj = objparam as AssemblyName;
            if (obj == null)
            {
                return 0;
            }
            return this.GetHashCode(obj);
        }

        public int GetHashCode(AssemblyName obj)
        {
            int hashcode = 0;

            if (obj.Name != null)
            {
                hashcode ^= obj.Name.GetHashCode();
            }

            if (obj.Version != null)
            {
                hashcode ^= obj.Version.GetHashCode();
            }

            if (obj.CultureInfo != null)
            {
                hashcode ^= obj.CultureInfo.GetHashCode();
            }

            byte[] objArray = obj.GetPublicKeyToken();
            if (objArray != null)
            {
                // distinguishing no PKToken from "PKToken = null" which is an array of length=0
                hashcode ^= objArray.Length.GetHashCode() + 1;
                if (objArray.Length > 0)
                {
                    hashcode ^= BitConverter.ToUInt64(objArray, 0).GetHashCode();
                }
            }
            return hashcode;
        }

        public static bool IsSameKeyToken(byte[] reqKeyToken, byte[] curKeyToken)
        {
            bool isSame = false;

            if (reqKeyToken == null && curKeyToken == null)
            {
                // Both Key Tokens are not set, treat them as same.
                isSame = true;
            }
            else if (reqKeyToken != null && curKeyToken != null)
            {
                // Both KeyTokens are set.
                if (reqKeyToken.Length == curKeyToken.Length)
                {
                    isSame = true;
                    for (int i = 0; i < reqKeyToken.Length; i++)
                    {
                        if (reqKeyToken[i] != curKeyToken[i])
                        {
                            isSame = false;
                            break;
                        }
                    }
                }
            }

            return isSame;
        }
    }
}