// ==++==
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--==
using System.Reflection;
using System.Text;
using System.Collections;
using System.Globalization;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Runtime.Versioning;
using System.Diagnostics.Contracts;

namespace System 
{
    [Serializable]
    [System.Runtime.InteropServices.ComVisible(true)]
    public abstract class Enum : ValueType, IComparable, IFormattable, IConvertible
    {
        #region Private Static Data Members
        private static readonly char [] enumSeperatorCharArray = new char [] {','};
        private const String enumSeperator = ", ";
        #endregion

        #region Private Static Methods
        [System.Security.SecuritySafeCritical]  // auto-generated
        private static ValuesAndNames GetCachedValuesAndNames(RuntimeType enumType, bool getNames)
        {
            ValuesAndNames entry = enumType.GenericCache as ValuesAndNames;

            if (entry == null || (getNames && entry.Names == null))
            {
                ulong[] values = null;
                String[] names = null;

#if MONO
                if (!GetEnumValuesAndNames (enumType, out values, out names))
                    Array.Sort (values, names, System.Collections.Generic.Comparer<ulong>.Default);
#else
                GetEnumValuesAndNames(
                    enumType.GetTypeHandleInternal(),
                    JitHelpers.GetObjectHandleOnStack(ref values),
                    JitHelpers.GetObjectHandleOnStack(ref names),
                    getNames);
#endif
                entry = new ValuesAndNames(values, names);
                enumType.GenericCache = entry;
            }

            return entry;
        }

        private static String InternalFormattedHexString(Object value)
        {
            TypeCode typeCode = Convert.GetTypeCode(value);

            switch (typeCode)
            {
                case TypeCode.SByte :
                    {
                        Byte result = (byte)(sbyte)value;

                        return result.ToString("X2", null);
                    }

                case TypeCode.Byte :
                    {
                        Byte result = (byte)value;

                        return result.ToString("X2", null);
                    }

                case TypeCode.Boolean:
                    {
                        // direct cast from bool to byte is not allowed
                        Byte result = Convert.ToByte((bool)value);

                        return result.ToString("X2", null);
                    }

                case TypeCode.Int16:
                    {
                        UInt16 result = (UInt16)(Int16)value;

                        return result.ToString("X4", null);
                    }

                case TypeCode.UInt16 :
                    {
                        UInt16 result = (UInt16)value;

                        return result.ToString("X4", null);
                    }

                case TypeCode.Char:
                    {
                        UInt16 result = (UInt16)(Char)value;

                        return result.ToString("X4", null);
                    }

                case TypeCode.UInt32:
                    {
                        UInt32 result = (UInt32)value;

                        return result.ToString("X8", null);
                    }

                case TypeCode.Int32 :
                    {
                        UInt32 result = (UInt32)(int)value;

                        return result.ToString("X8", null);
                    }

                case TypeCode.UInt64 :
                    {
                        UInt64 result = (UInt64)value;

                        return result.ToString("X16", null);
                    }

                case TypeCode.Int64 :
                    {
                        UInt64 result = (UInt64)(Int64)value;

                        return result.ToString("X16", null);
                    }

                // All unsigned types will be directly cast
                default :
                    Contract.Assert(false, "Invalid Object type in Format");
                    throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_UnknownEnumType"));
            }
        }

        private static String InternalFormat(RuntimeType eT, Object value)
        {
            Contract.Requires(eT != null);
            Contract.Requires(value != null);
            if (!eT.IsDefined(typeof(System.FlagsAttribute), false)) // Not marked with Flags attribute
            {
                // Try to see if its one of the enum values, then we return a String back else the value
                String retval = GetName(eT, value);
                if (retval == null)
                    return value.ToString();
                else
                    return retval;
            }
            else // These are flags OR'ed together (We treat everything as unsigned types)
            {
                return InternalFlagsFormat(eT, value);

            }
        }

        private static String InternalFlagsFormat(RuntimeType eT, Object value)
        {
            Contract.Requires(eT != null);
            Contract.Requires(value != null);
            ulong result = ToUInt64(value);

            // These values are sorted by value. Don't change this
            ValuesAndNames entry = GetCachedValuesAndNames(eT, true);

            String[] names = entry.Names;
            ulong[] values = entry.Values;
            Contract.Assert(names.Length == values.Length);

            int index = values.Length - 1;
            StringBuilder retval = new StringBuilder();
            bool firstTime = true;
            ulong saveResult = result;

            // We will not optimize this code further to keep it maintainable. There are some boundary checks that can be applied
            // to minimize the comparsions required. This code works the same for the best/worst case. In general the number of
            // items in an enum are sufficiently small and not worth the optimization.
            while (index >= 0)
            {
                if ((index == 0) && (values[index] == 0))
                    break;

                if ((result & values[index]) == values[index])
                {
                    result -= values[index];
                    if (!firstTime)
                        retval.Insert(0, enumSeperator);

                    retval.Insert(0, names[index]);
                    firstTime = false;
                }

                index--;
            }

            // We were unable to represent this number as a bitwise or of valid flags
            if (result != 0)
                return value.ToString();

            // For the case when we have zero
            if (saveResult==0)
            {
                if (values.Length > 0 && values[0] == 0)
                    return names[0]; // Zero was one of the enum values.
                else
                    return "0";
            }
            else
            return retval.ToString(); // Return the string representation
        }

        internal static ulong ToUInt64(Object value)
        {
            // Helper function to silently convert the value to UInt64 from the other base types for enum without throwing an exception.
            // This is need since the Convert functions do overflow checks.
            TypeCode typeCode = Convert.GetTypeCode(value);
            ulong result;

            switch(typeCode)
            {
                case TypeCode.SByte:
                case TypeCode.Int16:
                case TypeCode.Int32:
                case TypeCode.Int64:
                    result = (UInt64)Convert.ToInt64(value, CultureInfo.InvariantCulture);
                    break;

                case TypeCode.Byte:
                case TypeCode.UInt16:
                case TypeCode.UInt32:
                case TypeCode.UInt64:
                case TypeCode.Boolean:
                case TypeCode.Char:
                    result = Convert.ToUInt64(value, CultureInfo.InvariantCulture);
                    break;

                default:
                // All unsigned types will be directly cast
                    Contract.Assert(false, "Invalid Object type in ToUInt64");
                    throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_UnknownEnumType"));
            }
            return result;
        }

#if !MONO
        [System.Security.SecurityCritical]  // auto-generated
        [ResourceExposure(ResourceScope.None)]
#endif
        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        private static extern int InternalCompareTo(Object o1, Object o2);

#if !MONO
        [System.Security.SecuritySafeCritical]
        [ResourceExposure(ResourceScope.None)]
#endif
        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        internal static extern RuntimeType InternalGetUnderlyingType(RuntimeType enumType);

#if MONO
        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        private static extern bool GetEnumValuesAndNames (RuntimeType enumType, out ulong[] values, out string[] names);
#else
        [System.Security.SecurityCritical]  // auto-generated
        [ResourceExposure(ResourceScope.None)]
        [DllImport(JitHelpers.QCall, CharSet = CharSet.Unicode)]
        [System.Security.SuppressUnmanagedCodeSecurity]
        private static extern void GetEnumValuesAndNames(RuntimeTypeHandle enumType, ObjectHandleOnStack values, ObjectHandleOnStack names, bool getNames);
#endif

#if !MONO
        [System.Security.SecurityCritical]  // auto-generated
        [ResourceExposure(ResourceScope.None)]
#endif
        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        private static extern Object InternalBoxEnum(RuntimeType enumType, long value);
        #endregion

        #region Public Static Methods
        private enum ParseFailureKind
        {
            None                  = 0,
            Argument              = 1,
            ArgumentNull          = 2,
            ArgumentWithParameter = 3,
            UnhandledException    = 4
        }

        // This will store the result of the parsing.
        private struct EnumResult
        {
            internal object parsedEnum;
            internal bool canThrow;
            internal ParseFailureKind m_failure;
            internal string m_failureMessageID;
            internal string m_failureParameter;
            internal object m_failureMessageFormatArgument;
            internal Exception m_innerException;

            internal void Init(bool canMethodThrow)
            {
                parsedEnum = 0;
                canThrow = canMethodThrow;
            }
            internal void SetFailure(Exception unhandledException)
            {
                m_failure = ParseFailureKind.UnhandledException;
                m_innerException = unhandledException;
            }
            internal void SetFailure(ParseFailureKind failure, string failureParameter)
            {
                m_failure = failure;
                m_failureParameter = failureParameter;
                if (canThrow)
                    throw GetEnumParseException();
            }
            internal void SetFailure(ParseFailureKind failure, string failureMessageID, object failureMessageFormatArgument)
            {
                m_failure = failure;
                m_failureMessageID = failureMessageID;
                m_failureMessageFormatArgument = failureMessageFormatArgument;
                if (canThrow)
                    throw GetEnumParseException();
            }
            internal Exception GetEnumParseException()
            {
                switch (m_failure)
                {
                    case ParseFailureKind.Argument:
                        return new ArgumentException(Environment.GetResourceString(m_failureMessageID));

                    case ParseFailureKind.ArgumentNull:
                        return new ArgumentNullException(m_failureParameter);

                    case ParseFailureKind.ArgumentWithParameter:
                        return new ArgumentException(Environment.GetResourceString(m_failureMessageID, m_failureMessageFormatArgument));

                    case ParseFailureKind.UnhandledException:
                        return m_innerException;

                    default:
                        Contract.Assert(false, "Unknown EnumParseFailure: " + m_failure);
                        return new ArgumentException(Environment.GetResourceString("Arg_EnumValueNotFound"));
                }
            }
        }

        public static bool TryParse<TEnum>(String value, out TEnum result) where TEnum : struct
        {
            return TryParse(value, false, out result);
        }

        public static bool TryParse<TEnum>(String value, bool ignoreCase, out TEnum result) where TEnum : struct
        {
            result = default(TEnum);
            EnumResult parseResult = new EnumResult();
            parseResult.Init(false);
            bool retValue;

            if (retValue = TryParseEnum(typeof(TEnum), value, ignoreCase, ref parseResult))
                result = (TEnum)parseResult.parsedEnum;           
            return retValue;
        }

        [System.Runtime.InteropServices.ComVisible(true)]
        public static Object Parse(Type enumType, String value)
        {
            return Parse(enumType, value, false);
        }

        [System.Runtime.InteropServices.ComVisible(true)]
        public static Object Parse(Type enumType, String value, bool ignoreCase)
        {
            EnumResult parseResult = new EnumResult();
            parseResult.Init(true);
            if (TryParseEnum(enumType, value, ignoreCase, ref parseResult))
                return parseResult.parsedEnum;
            else
                throw parseResult.GetEnumParseException();
        }

        private static bool TryParseEnum(Type enumType, String value, bool ignoreCase, ref EnumResult parseResult)
        {
            if (enumType == null)
                throw new ArgumentNullException("enumType");
            Contract.EndContractBlock();

            RuntimeType rtType = enumType as RuntimeType;
            if (rtType == null)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeType"), "enumType");

            if (!enumType.IsEnum)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeEnum"), "enumType");

            if (value == null) {
                parseResult.SetFailure(ParseFailureKind.ArgumentNull, "value");
                return false;
            }

            value = value.Trim();
            if (value.Length == 0) {
                parseResult.SetFailure(ParseFailureKind.Argument, "Arg_MustContainEnumInfo", null);
                return false;
            }

            // We have 2 code paths here. One if they are values else if they are Strings.
            // values will have the first character as as number or a sign.
            ulong result = 0;

            if (Char.IsDigit(value[0]) || value[0] == '-' || value[0] == '+')
            {
                Type underlyingType = GetUnderlyingType(enumType);
                Object temp;

                try
                {
                    temp = Convert.ChangeType(value, underlyingType, CultureInfo.InvariantCulture);
                    parseResult.parsedEnum = ToObject(enumType, temp);
                    return true;
                }
                catch (FormatException)
                { // We need to Parse this as a String instead. There are cases
                  // when you tlbimp enums that can have values of the form "3D".
                  // Don't fix this code.
                }
                catch (Exception ex)
                {
                    if (parseResult.canThrow)
                        throw;
                    else
                    {
                        parseResult.SetFailure(ex);
                        return false;
                    }
                }
            }

            String[] values = value.Split(enumSeperatorCharArray);

            // Find the field.Lets assume that these are always static classes because the class is
            //  an enum.
            ValuesAndNames entry = GetCachedValuesAndNames(rtType, true);

            String[] enumNames = entry.Names;
            ulong[] enumValues = entry.Values;
            
            for (int i = 0; i < values.Length; i++)
            {
                values[i] = values[i].Trim(); // We need to remove whitespace characters

                bool success = false;

                for (int j = 0; j < enumNames.Length; j++)
                {
                    if (ignoreCase)
                    {
                        if (String.Compare(enumNames[j], values[i], StringComparison.OrdinalIgnoreCase) != 0)
                            continue;
                    }
                    else
                    {
                        if (!enumNames[j].Equals(values[i]))
                            continue;
                    }

                    ulong item = enumValues[j];

                    result |= item;
                    success = true;
                    break;
                }

                if (!success)
                {
                    // Not found, throw an argument exception.
                    parseResult.SetFailure(ParseFailureKind.ArgumentWithParameter, "Arg_EnumValueNotFound", value);
                    return false;
                }
            }

            try
            {
                parseResult.parsedEnum = ToObject(enumType, result);
                return true;
            }
            catch (Exception ex)
            {
                if (parseResult.canThrow)
                    throw;
                else
                {
                    parseResult.SetFailure(ex);
                    return false;
                }
            }
        }

        [System.Runtime.InteropServices.ComVisible(true)]
        public static Type GetUnderlyingType(Type enumType)
        {
            if (enumType == null)
                throw new ArgumentNullException("enumType");
            Contract.Ensures(Contract.Result<Type>() != null);
            Contract.EndContractBlock();

            return enumType.GetEnumUnderlyingType();
        }

        [System.Runtime.InteropServices.ComVisible(true)]
        public static Array GetValues(Type enumType)
        {
            if (enumType == null)
                throw new ArgumentNullException("enumType");
            Contract.Ensures(Contract.Result<Array>() != null);
            Contract.EndContractBlock();

            return enumType.GetEnumValues();
        }

        internal static ulong[] InternalGetValues(RuntimeType enumType)
        {
            // Get all of the values
            return GetCachedValuesAndNames(enumType, false).Values;
        }
        
        [System.Runtime.InteropServices.ComVisible(true)]
        public static String GetName(Type enumType, Object value)
        {
            if (enumType == null)
                throw new ArgumentNullException("enumType");
            Contract.EndContractBlock();

            return enumType.GetEnumName(value);
        }

        [System.Runtime.InteropServices.ComVisible(true)]
        public static String[] GetNames(Type enumType)
        {
            if (enumType == null)
                throw new ArgumentNullException("enumType");
            Contract.Ensures(Contract.Result<String[]>() != null);
            Contract.EndContractBlock();

            return enumType.GetEnumNames();
        }

        internal static String[] InternalGetNames(RuntimeType enumType)
        {
            // Get all of the names
            return GetCachedValuesAndNames(enumType, true).Names;
        }

        [System.Runtime.InteropServices.ComVisible(true)]
        public static Object ToObject(Type enumType, Object value)
        {
            if (value == null)
                throw new ArgumentNullException("value");
            Contract.EndContractBlock();

            // Delegate rest of error checking to the other functions
            TypeCode typeCode = Convert.GetTypeCode(value);

#if !MONO
            // NetCF doesn't support char and boolean conversion
            if (CompatibilitySwitches.IsAppEarlierThanWindowsPhone8 &&
                ((typeCode == TypeCode.Boolean) || (typeCode == TypeCode.Char)))
            {
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeEnumBaseTypeOrEnum"), "value");
            }
#endif

            switch (typeCode)
            {
                case TypeCode.Int32 :
                    return ToObject(enumType, (int)value);

                case TypeCode.SByte :
                    return ToObject(enumType, (sbyte)value);

                case TypeCode.Int16 :
                    return ToObject(enumType, (short)value);

                case TypeCode.Int64 :
                    return ToObject(enumType, (long)value);

                case TypeCode.UInt32 :
                    return ToObject(enumType, (uint)value);

                case TypeCode.Byte :
                    return ToObject(enumType, (byte)value);

                case TypeCode.UInt16 :
                    return ToObject(enumType, (ushort)value);

                case TypeCode.UInt64 :
                    return ToObject(enumType, (ulong)value);

                case TypeCode.Char:
                    return ToObject(enumType, (char)value);

                case TypeCode.Boolean:
                    return ToObject(enumType, (bool)value);

                default:
                    // All unsigned types will be directly cast
                    throw new ArgumentException(Environment.GetResourceString("Arg_MustBeEnumBaseTypeOrEnum"), "value");
            }
        }

        [Pure]
        [System.Runtime.InteropServices.ComVisible(true)]
        public static bool IsDefined(Type enumType, Object value)
        {
            if (enumType == null)
                throw new ArgumentNullException("enumType");
            Contract.EndContractBlock();

            return enumType.IsEnumDefined(value);
        }
        
        [System.Runtime.InteropServices.ComVisible(true)]
        public static String Format(Type enumType, Object value, String format)
        {
            if (enumType == null)
                throw new ArgumentNullException("enumType");

            if (!enumType.IsEnum)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeEnum"), "enumType");

            if (value == null)
                throw new ArgumentNullException("value");

            if (format == null)
                throw new ArgumentNullException("format");
            Contract.EndContractBlock();

            RuntimeType rtType = enumType as RuntimeType;
            if (rtType == null)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeType"), "enumType");

            // Check if both of them are of the same type
            Type valueType = value.GetType();

            Type underlyingType = GetUnderlyingType(enumType);

            // If the value is an Enum then we need to extract the underlying value from it
            if (valueType.IsEnum) {
                Type valueUnderlyingType = GetUnderlyingType(valueType);

                if (!valueType.IsEquivalentTo(enumType))
                    throw new ArgumentException(Environment.GetResourceString("Arg_EnumAndObjectMustBeSameType", valueType.ToString(), enumType.ToString()));

                valueType = valueUnderlyingType;
                value = ((Enum)value).GetValue();
            }
            // The value must be of the same type as the Underlying type of the Enum
            else if (valueType != underlyingType) {
                throw new ArgumentException(Environment.GetResourceString("Arg_EnumFormatUnderlyingTypeAndObjectMustBeSameType", valueType.ToString(), underlyingType.ToString()));
            }

            if( format.Length != 1) {
                // all acceptable format string are of length 1
                throw new FormatException(Environment.GetResourceString("Format_InvalidEnumFormatSpecification"));
            }
            
            char formatCh = format[0];

            if (formatCh == 'D' || formatCh == 'd') {
                return value.ToString();
            }

            if (formatCh == 'X' || formatCh == 'x') {
                // Retrieve the value from the field.
                return InternalFormattedHexString(value);
            }

            if (formatCh == 'G' || formatCh == 'g') {
                return InternalFormat(rtType, value);
            }

            if (formatCh == 'F' || formatCh == 'f') {
                return InternalFlagsFormat(rtType, value);
            }

            throw new FormatException(Environment.GetResourceString("Format_InvalidEnumFormatSpecification"));
        }

        #endregion

        #region Definitions
        private class ValuesAndNames
        {
            // Each entry contains a list of sorted pair of enum field names and values, sorted by values
            public ValuesAndNames(ulong[] values, String[] names)
            {
                this.Values = values;
                this.Names = names;
            }

            public ulong[] Values;
            public String[] Names;
        }
        #endregion

#if MONO
        [MethodImplAttribute (MethodImplOptions.InternalCall)]
        extern object get_value ();
#endif

        #region Private Methods
        [System.Security.SecuritySafeCritical]
        internal unsafe Object GetValue()
        {
#if MONO
            return get_value ();
#else
            fixed (void* pValue = &JitHelpers.GetPinningHelper(this).m_data)
            {
                switch (InternalGetCorElementType())
                {
                    case CorElementType.I1:
                        return *(sbyte*)pValue;
                    case CorElementType.U1:
                        return *(byte*)pValue;
                    case CorElementType.Boolean:
                        return *(bool*)pValue;
                    case CorElementType.I2:
                        return *(short*)pValue;
                    case CorElementType.U2:
                        return *(ushort*)pValue;
                    case CorElementType.Char:
                        return *(char*)pValue;
                    case CorElementType.I4:
                        return *(int*)pValue;
                    case CorElementType.U4:
                        return *(uint*)pValue;
                    case CorElementType.R4:
                        return *(float*)pValue;
                    case CorElementType.I8:
                        return *(long*)pValue;
                    case CorElementType.U8:
                        return *(ulong*)pValue;
                    case CorElementType.R8:
                        return *(double*)pValue;
                    case CorElementType.I:
                        return *(IntPtr*)pValue;
                    case CorElementType.U:
                        return *(UIntPtr*)pValue;
                    default:
                        Contract.Assert(false, "Invalid primitive type");
                        return null;
                }
            }
#endif
        }

#if !MONO
        [System.Security.SecurityCritical]  // auto-generated
        [ResourceExposure(ResourceScope.None)]
#endif
        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        private extern bool InternalHasFlag(Enum flags);

        [MethodImplAttribute(MethodImplOptions.InternalCall)]
#if MONO
        private extern int get_hashcode ();
#else
        [System.Security.SecuritySafeCritical]  // auto-generated
        [ResourceExposure(ResourceScope.None)]
        private extern CorElementType InternalGetCorElementType();
#endif
        #endregion

        #region Object Overrides
#if MONO
        public override bool Equals (object obj)
        {
            return DefaultEquals (this, obj);
        }
#else
        [System.Security.SecuritySafeCritical]  // auto-generated
        [ResourceExposure(ResourceScope.None)]
        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        public extern override bool Equals(Object obj);
#endif
        [System.Security.SecuritySafeCritical]
        public override unsafe int GetHashCode()
        {
#if MONO
            return get_hashcode ();
#else
            // Avoid boxing by inlining GetValue()
            // return GetValue().GetHashCode();

            fixed (void* pValue = &JitHelpers.GetPinningHelper(this).m_data)
            {
                switch (InternalGetCorElementType())
                {
                    case CorElementType.I1:
                        return (*(sbyte*)pValue).GetHashCode();
                    case CorElementType.U1:
                        return (*(byte*)pValue).GetHashCode();
                    case CorElementType.Boolean:
                        return (*(bool*)pValue).GetHashCode();
                    case CorElementType.I2:
                        return (*(short*)pValue).GetHashCode();
                    case CorElementType.U2:
                        return (*(ushort*)pValue).GetHashCode();
                    case CorElementType.Char:
                        return (*(char*)pValue).GetHashCode();
                    case CorElementType.I4:
                        return (*(int*)pValue).GetHashCode();
                    case CorElementType.U4:
                        return (*(uint*)pValue).GetHashCode();
                    case CorElementType.R4:
                        return (*(float*)pValue).GetHashCode();
                    case CorElementType.I8:
                        return (*(long*)pValue).GetHashCode();
                    case CorElementType.U8:
                        return (*(ulong*)pValue).GetHashCode();
                    case CorElementType.R8:
                        return (*(double*)pValue).GetHashCode();
                    case CorElementType.I:
                        return (*(IntPtr*)pValue).GetHashCode();
                    case CorElementType.U:
                        return (*(UIntPtr*)pValue).GetHashCode();
                    default:
                        Contract.Assert(false, "Invalid primitive type");
                        return 0;
                }
            }
#endif
        }

        public override String ToString()
        {
            // Returns the value in a human readable format.  For PASCAL style enums who's value maps directly the name of the field is returned.
            // For PASCAL style enums who's values do not map directly the decimal value of the field is returned.
            // For BitFlags (indicated by the Flags custom attribute): If for each bit that is set in the value there is a corresponding constant
            //(a pure power of 2), then the  OR string (ie "Red | Yellow") is returned. Otherwise, if the value is zero or if you can't create a string that consists of
            // pure powers of 2 OR-ed together, you return a hex value
            return Enum.InternalFormat((RuntimeType)GetType(), GetValue());
        }
        #endregion

        #region IFormattable
        [Obsolete("The provider argument is not used. Please use ToString(String).")]        
        public String ToString(String format, IFormatProvider provider)
        {
            return ToString(format);
        }
        #endregion

        #region IComparable
        [System.Security.SecuritySafeCritical]  // auto-generated
        public int CompareTo(Object target)
        {
            const int retIncompatibleMethodTables = 2;  // indicates that the method tables did not match
            const int retInvalidEnumType = 3; // indicates that the enum was of an unknown/unsupported unerlying type
            
            if (this == null)
                throw new NullReferenceException();
            Contract.EndContractBlock();
        
            int ret = InternalCompareTo(this, target);

            if (ret < retIncompatibleMethodTables) 
            {
                // -1, 0 and 1 are the normal return codes
                return ret;
            }
            else if (ret == retIncompatibleMethodTables)
            {
                Type thisType = this.GetType();
                Type targetType = target.GetType();

                throw new ArgumentException(Environment.GetResourceString("Arg_EnumAndObjectMustBeSameType", 
                        targetType.ToString(), thisType.ToString()));
            }
            else
            {
                // assert valid return code (3)
                Contract.Assert(ret == retInvalidEnumType, "Enum.InternalCompareTo return code was invalid");
                
                throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_UnknownEnumType"));
            }
        }
        #endregion

        #region Public Methods
        public String ToString(String format) {
            if (format == null || format.Length == 0)
                format = "G";

            if (String.Compare(format, "G", StringComparison.OrdinalIgnoreCase) == 0)
                return ToString();

            if (String.Compare(format, "D", StringComparison.OrdinalIgnoreCase) == 0)
                return GetValue().ToString();

            if (String.Compare(format, "X", StringComparison.OrdinalIgnoreCase) == 0)
                return InternalFormattedHexString(GetValue());

            if (String.Compare(format, "F", StringComparison.OrdinalIgnoreCase) == 0)
                return InternalFlagsFormat((RuntimeType)GetType(), GetValue());

            throw new FormatException(Environment.GetResourceString("Format_InvalidEnumFormatSpecification"));
        }

        [Obsolete("The provider argument is not used. Please use ToString().")]
        public String ToString(IFormatProvider provider)
        {
            return ToString();
        }

        [System.Security.SecuritySafeCritical]
        public Boolean HasFlag(Enum flag) {
            if (flag == null)
                throw new ArgumentNullException("flag");
            Contract.EndContractBlock();
            
            if (!this.GetType().IsEquivalentTo(flag.GetType())) {
                throw new ArgumentException(Environment.GetResourceString("Argument_EnumTypeDoesNotMatch", flag.GetType(), this.GetType()));
            }

            return InternalHasFlag(flag);
        }

        #endregion

        #region IConvertable
        public TypeCode GetTypeCode()
        {
            Type enumType = this.GetType();
            Type underlyingType = GetUnderlyingType(enumType);

            if (underlyingType == typeof(Int32))
            {
                return TypeCode.Int32;
            }

            if (underlyingType == typeof(sbyte))
            {
                return TypeCode.SByte;
            }

            if (underlyingType == typeof(Int16))
            {
                return TypeCode.Int16;
            }

            if (underlyingType == typeof(Int64))
            {
                return TypeCode.Int64;
            }

            if (underlyingType == typeof(UInt32))
            {
                return TypeCode.UInt32;
            }

            if (underlyingType == typeof(byte))
            {
                return TypeCode.Byte;
            }

            if (underlyingType == typeof(UInt16))
            {
                return TypeCode.UInt16;
            }

            if (underlyingType == typeof(UInt64))
            {
                return TypeCode.UInt64;
            }

            if (underlyingType == typeof(Boolean))
            {
                return TypeCode.Boolean;
            }

            if (underlyingType == typeof(Char))
            {
                return TypeCode.Char;
            }

            Contract.Assert(false, "Unknown underlying type.");
            throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_UnknownEnumType"));
        }

        /// <internalonly/>
        bool IConvertible.ToBoolean(IFormatProvider provider) 
        {
            return Convert.ToBoolean(GetValue(), CultureInfo.CurrentCulture);
        }

        /// <internalonly/>
        char IConvertible.ToChar(IFormatProvider provider) 
        {
            return Convert.ToChar(GetValue(), CultureInfo.CurrentCulture);
        }

        /// <internalonly/>
        sbyte IConvertible.ToSByte(IFormatProvider provider) 
        {
            return Convert.ToSByte(GetValue(), CultureInfo.CurrentCulture);
        }

        /// <internalonly/>
        byte IConvertible.ToByte(IFormatProvider provider) 
        {
            return Convert.ToByte(GetValue(), CultureInfo.CurrentCulture);
        }

        /// <internalonly/>
        short IConvertible.ToInt16(IFormatProvider provider) 
        {
            return Convert.ToInt16(GetValue(), CultureInfo.CurrentCulture);
        }

        /// <internalonly/>
        ushort IConvertible.ToUInt16(IFormatProvider provider) 
        {
            return Convert.ToUInt16(GetValue(), CultureInfo.CurrentCulture);
        }

        /// <internalonly/>
        int IConvertible.ToInt32(IFormatProvider provider) 
        {
            return Convert.ToInt32(GetValue(), CultureInfo.CurrentCulture);
        }

        /// <internalonly/>
        uint IConvertible.ToUInt32(IFormatProvider provider) 
        {
            return Convert.ToUInt32(GetValue(), CultureInfo.CurrentCulture);
        }

        /// <internalonly/>
        long IConvertible.ToInt64(IFormatProvider provider) 
        {
            return Convert.ToInt64(GetValue(), CultureInfo.CurrentCulture);
        }

        /// <internalonly/>
        ulong IConvertible.ToUInt64(IFormatProvider provider) 
        {
            return Convert.ToUInt64(GetValue(), CultureInfo.CurrentCulture);
        }

        /// <internalonly/>
        float IConvertible.ToSingle(IFormatProvider provider) 
        {
            return Convert.ToSingle(GetValue(), CultureInfo.CurrentCulture);
        }

        /// <internalonly/>
        double IConvertible.ToDouble(IFormatProvider provider) 
        {
            return Convert.ToDouble(GetValue(), CultureInfo.CurrentCulture);
        }

        /// <internalonly/>
        Decimal IConvertible.ToDecimal(IFormatProvider provider) 
        {
            return Convert.ToDecimal(GetValue(), CultureInfo.CurrentCulture);
        }

        /// <internalonly/>
        DateTime IConvertible.ToDateTime(IFormatProvider provider) 
        {
            throw new InvalidCastException(Environment.GetResourceString("InvalidCast_FromTo", "Enum", "DateTime"));
        }

        /// <internalonly/>
        Object IConvertible.ToType(Type type, IFormatProvider provider) 
        {
            return Convert.DefaultToType((IConvertible)this, type, provider);
        }
        #endregion
    
        #region ToObject
        [System.Security.SecuritySafeCritical]  // auto-generated
        [CLSCompliant(false)]
        [System.Runtime.InteropServices.ComVisible(true)]
        public static Object ToObject(Type enumType, sbyte value)
        {
            if (enumType == null)
                throw new ArgumentNullException("enumType");
            if (!enumType.IsEnum)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeEnum"), "enumType");
            Contract.EndContractBlock();
            RuntimeType rtType = enumType as RuntimeType;
            if (rtType == null)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeType"), "enumType");
            return InternalBoxEnum(rtType, value);
        }

        [System.Security.SecuritySafeCritical]  // auto-generated
        [System.Runtime.InteropServices.ComVisible(true)]
        public static Object ToObject(Type enumType, short value)
        {
            if (enumType == null)
                throw new ArgumentNullException("enumType");
            if (!enumType.IsEnum)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeEnum"), "enumType");
            Contract.EndContractBlock();
            RuntimeType rtType = enumType as RuntimeType;
            if (rtType == null)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeType"), "enumType");
            return InternalBoxEnum(rtType, value);
        }

        [System.Security.SecuritySafeCritical]  // auto-generated
        [System.Runtime.InteropServices.ComVisible(true)]
        public static Object ToObject(Type enumType, int value)
        {
            if (enumType == null)
                throw new ArgumentNullException("enumType");
            if (!enumType.IsEnum)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeEnum"), "enumType");
            Contract.EndContractBlock();
            RuntimeType rtType = enumType as RuntimeType;
            if (rtType == null)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeType"), "enumType");
            return InternalBoxEnum(rtType, value);
        }

        [System.Security.SecuritySafeCritical]  // auto-generated
        [System.Runtime.InteropServices.ComVisible(true)]
        public static Object ToObject(Type enumType, byte value)
        {
            if (enumType == null)
                throw new ArgumentNullException("enumType");
            if (!enumType.IsEnum)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeEnum"), "enumType");
            Contract.EndContractBlock();
            RuntimeType rtType = enumType as RuntimeType;
            if (rtType == null)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeType"), "enumType");
            return InternalBoxEnum(rtType, value);
        }

        [System.Security.SecuritySafeCritical]  // auto-generated
        [CLSCompliant(false)]
        [System.Runtime.InteropServices.ComVisible(true)]
        public static Object ToObject(Type enumType, ushort value)
        {
            if (enumType == null)
                throw new ArgumentNullException("enumType");
            if (!enumType.IsEnum)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeEnum"), "enumType");
            Contract.EndContractBlock();
            RuntimeType rtType = enumType as RuntimeType;
            if (rtType == null)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeType"), "enumType");
            return InternalBoxEnum(rtType, value);
        }

        [System.Security.SecuritySafeCritical]  // auto-generated
        [CLSCompliant(false)]
        [System.Runtime.InteropServices.ComVisible(true)]
        public static Object ToObject(Type enumType, uint value)
        {
            if (enumType == null)
                throw new ArgumentNullException("enumType");
            if (!enumType.IsEnum)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeEnum"), "enumType");
            Contract.EndContractBlock();
            RuntimeType rtType = enumType as RuntimeType;
            if (rtType == null)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeType"), "enumType");
            return InternalBoxEnum(rtType, value);
        }

        [System.Security.SecuritySafeCritical]  // auto-generated
        [System.Runtime.InteropServices.ComVisible(true)]
        public static Object ToObject(Type enumType, long value)
        {
            if (enumType == null)
                throw new ArgumentNullException("enumType");
            if (!enumType.IsEnum)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeEnum"), "enumType");
            Contract.EndContractBlock();
            RuntimeType rtType = enumType as RuntimeType;
            if (rtType == null)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeType"), "enumType");
            return InternalBoxEnum(rtType, value);
        }

        [System.Security.SecuritySafeCritical]  // auto-generated
        [CLSCompliant(false)]
        [System.Runtime.InteropServices.ComVisible(true)]
        public static Object ToObject(Type enumType, ulong value)
        {
            if (enumType == null)
                throw new ArgumentNullException("enumType");
            if (!enumType.IsEnum)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeEnum"), "enumType");
            Contract.EndContractBlock();
            RuntimeType rtType = enumType as RuntimeType;
            if (rtType == null)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeType"), "enumType");
            return InternalBoxEnum(rtType, unchecked((long)value));
        }

        [System.Security.SecuritySafeCritical]  // auto-generated
        private static Object ToObject(Type enumType, char value)
        {
            if (enumType == null)
                throw new ArgumentNullException("enumType");
            if (!enumType.IsEnum)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeEnum"), "enumType");
            Contract.EndContractBlock();
            RuntimeType rtType = enumType as RuntimeType;
            if (rtType == null)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeType"), "enumType");
            return InternalBoxEnum(rtType, value);
        }

        [System.Security.SecuritySafeCritical]  // auto-generated
        private static Object ToObject(Type enumType, bool value)
        {
            if (enumType == null)
                throw new ArgumentNullException("enumType");
            if (!enumType.IsEnum)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeEnum"), "enumType");
            Contract.EndContractBlock();
            RuntimeType rtType = enumType as RuntimeType;
            if (rtType == null)
                throw new ArgumentException(Environment.GetResourceString("Arg_MustBeType"), "enumType");
            return InternalBoxEnum(rtType, value ? 1 : 0);
        }
        #endregion

#if MONO
        public static TEnum Parse<TEnum>(string value) where TEnum : struct
        {
            return Parse<TEnum>(value, false);
        }

        public static TEnum Parse<TEnum>(string value, bool ignoreCase) where TEnum : struct
        {
            EnumResult parseResult = new EnumResult() { canThrow = true };
            if (TryParseEnum(typeof(TEnum), value, ignoreCase, ref parseResult))
                return (TEnum)parseResult.parsedEnum;
            else
                throw parseResult.GetEnumParseException();
        }

        public static bool TryParse(Type enumType, String value, bool ignoreCase, out object result)
        {
            result = null;
            EnumResult parseResult = new EnumResult();
            bool retValue;

            if (retValue = TryParseEnum(enumType, value, ignoreCase, ref parseResult))
                result = parseResult.parsedEnum;
            return retValue;
        }

        public static bool TryParse(Type enumType, String value, out object result)
        {
            return TryParse(enumType, value, false, out result);
        }
#endif
    }
}