//******************************************************************************************************
//  Common.cs - Gbtc
//
//  Copyright © 2012, Grid Protection Alliance.  All Rights Reserved.
//
//  Licensed to the Grid Protection Alliance (GPA) under one or more contributor license agreements. See
//  the NOTICE file distributed with this work for additional information regarding copyright ownership.
//  The GPA licenses this file to you under the MIT License (MIT), 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.opensource.org/licenses/MIT
//
//  Unless agreed to in writing, the subject software distributed under the License is distributed on an
//  "AS-IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. Refer to the
//  License for the specific language governing permissions and limitations.
//
//  Code Modification History:
//  ----------------------------------------------------------------------------------------------------
//  04/03/2006 - J. Ritchie Carroll
//       Generated original version of source code.
//  12/13/2007 - Darrell Zuercher
//       Edited code comments.
//  09/08/2008 - J. Ritchie Carroll
//       Converted to C#.
//  02/13/2009 - Josh L. Patterson
//       Edited Code Comments.
//  09/14/2009 - Stephen C. Wills
//       Added new header and license agreement.
//  09/17/2009 - Pinal C. Patel
//       Modified GetApplicationType() to remove dependency on HttpContext.Current.
//  09/28/2010 - Pinal C. Patel
//       Cached the current ApplicationType returned by GetApplicationType() for better performance.
//  12/05/2010 - Pinal C. Patel
//       Added an overload for TypeConvertToString() that takes CultureInfo as a parameter.
//  12/07/2010 - Pinal C. Patel
//       Updated TypeConvertToString() to return an empty string if the passed in value is null.
//  03/09/2011 - Pinal C. Patel
//       Moved UpdateType enumeration from GSF.Services.ServiceProcess namespace for broader usage.
//  04/07/2011 - J. Ritchie Carroll
//       Added ToNonNullNorEmptyString() and ToNonNullNorWhiteSpace() extensions.
//  12/14/2012 - Starlynn Danyelle Gilliam
//       Modified Header.
//
//******************************************************************************************************

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Diagnostics;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Web.Hosting;
using GSF.Collections;
using GSF.Console;
using GSF.IO;
using GSF.Reflection;
using Microsoft.Win32;

namespace GSF
{
    #region [ Enumerations ]

    /// <summary>
    /// Specifies the type of the application.
    /// </summary>
    public enum ApplicationType
    {
        /// <summary>
        /// Application is of unknown type.
        /// </summary>
        Unknown = 0,
        /// <summary>
        /// Application doesn't require a subsystem.
        /// </summary>
        Native = 1,
        /// <summary>
        /// Application runs in the Windows GUI subsystem.
        /// </summary>
        WindowsGui = 2,
        /// <summary>
        /// Application runs in the Windows character subsystem.
        /// </summary>
        WindowsCui = 3,
        /// <summary>
        /// Application runs in the OS/2 character subsystem.
        /// </summary>
        OS2Cui = 5,
        /// <summary>
        /// Application runs in the POSIX character subsystem.
        /// </summary>
        PosixCui = 7,
        /// <summary>
        /// Application is a native Win9x driver.
        /// </summary>
        NativeWindows = 8,
        /// <summary>
        /// Application runs in the Windows CE subsystem.
        /// </summary>
        WindowsCEGui = 9,
        /// <summary>
        /// The application is a web site or web application.
        /// </summary>
        Web = 100
    }

    /// <summary>
    /// Indicates the type of update.
    /// </summary>
    public enum UpdateType
    {
        /// <summary>
        /// Update is informational.
        /// </summary>
        Information,
        /// <summary>
        /// Update is a warning.
        /// </summary>
        Warning,
        /// <summary>
        /// Update is an alarm.
        /// </summary>
        Alarm
    }

    #endregion

    // This is the location for handy miscellaneous functions that are difficult to categorize elsewhere. For the most
    // part these functions may have the most value in a Visual Basic application which supports importing functions
    // down to a class level, e.g.: Imports GSF.Common

    /// <summary>
    /// Defines common global functions.
    /// </summary>
    public static class Common
    {
        private static ApplicationType? s_applicationType;
        private static string s_osPlatformName;
        private static PlatformID s_osPlatformID = PlatformID.Win32S;

        /// <summary>
        /// Determines if the current system is a POSIX style environment.
        /// </summary>
        /// <remarks>
        /// <para>
        /// Since a .NET application compiled under Mono can run under both Windows and Unix style platforms,
        /// you can use this property to easily determine the current operating environment.
        /// </para>
        /// <para>
        /// This property will return <c>true</c> for both MacOSX and Unix environments. Use the Platform property
        /// of the <see cref="System.Environment.OSVersion"/> to determine more specific platform type, e.g., 
        /// MacOSX or Unix. Note that all flavors of Linux will show up as <see cref="PlatformID.Unix"/>.
        /// </para>
        /// </remarks>        
        public static readonly bool IsPosixEnvironment = (Path.DirectorySeparatorChar == '/');   // This is how Mono source often checks this

        /// <summary>
        /// Determines if the code base is currently running under Mono.
        /// </summary>
        /// <remarks>
        /// This property can be used to make a run-time determination if Windows or Mono based .NET is being used. However, it is
        /// highly recommended to use the MONO compiler directive wherever possible instead of determining this at run-time.
        /// </remarks>
        public static bool IsMono = ((object)Type.GetType("Mono.Runtime") != null);

        /// <summary>Returns one of two strongly-typed objects.</summary>
        /// <returns>One of two objects, depending on the evaluation of given expression.</returns>
        /// <param name="expression">The expression you want to evaluate.</param>
        /// <param name="truePart">Returned if expression evaluates to True.</param>
        /// <param name="falsePart">Returned if expression evaluates to False.</param>
        /// <typeparam name="T">Return type used for immediate expression</typeparam>
        /// <remarks>
        /// <para>This function acts as a strongly-typed immediate if (a.k.a. inline if).</para>
        /// <para>
        /// It is expected that this function will only be used in languages that do not support ?: conditional operations, e.g., Visual Basic.NET.
        /// In Visual Basic this function can be used as a strongly-typed IIf replacement by specifying "Imports GSF.Common".
        /// </para>
        /// </remarks>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static T IIf<T>(bool expression, T truePart, T falsePart)
        {
            return (expression ? truePart : falsePart);
        }

        /// <summary>Creates a strongly-typed Array.</summary>
        /// <returns>New array of specified type.</returns>
        /// <param name="length">Desired length of new array.</param>
        /// <typeparam name="T">Return type for new array.</typeparam>
        /// <remarks>
        /// <para>It is expected that this function will only be used in Visual Basic.NET.</para>
        /// <para>
        /// The Array.CreateInstance provides better performance and more direct CLR access for array creation (not to
        /// mention less confusion on the matter of array lengths) in VB.NET, however the returned System.Array is not
        /// typed properly. This function properly casts the return array based on the type specification helping
        /// when Option Strict is enabled.
        /// </para>
        /// </remarks>
        /// <example>
        /// <code language="VB">
        ///     Dim buffer As Byte() = CreateArray(Of Byte)(12)
        ///     Dim matrix As Integer()() = CreateArray(Of Integer())(10)
        /// </code>
        /// </example>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static T[] CreateArray<T>(int length)
        {
            // The following provides better performance than "Return New T(length) {}".
            // ReSharper disable once UseArrayCreationExpression.1
            return (T[])Array.CreateInstance(typeof(T), length);
        }

        /// <summary>Creates a strongly-typed Array with an initial value parameter.</summary>
        /// <returns>New array of specified type.</returns>
        /// <param name="length">Desired length of new array.</param>
        /// <param name="initialValue">Value used to initialize all array elements.</param>
        /// <typeparam name="T">Return type for new array.</typeparam>
        /// <remarks>
        /// It is expected that this function will only be used in Visual Basic.NET.
        /// </remarks>
        /// <example>
        /// <code language="VB">
        ///     Dim elements As Integer() = CreateArray(12, -1)
        ///     Dim names As String() = CreateArray(100, "undefined")
        /// </code>
        /// </example>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static T[] CreateArray<T>(int length, T initialValue)
        {
            T[] typedArray = CreateArray<T>(length);

            // Initializes all elements with the default value.
            for (int x = 0; x < typedArray.Length; x++)
            {
                typedArray[x] = initialValue;
            }

            return typedArray;
        }


        /// <summary>
        /// Gets the type of the currently executing application.
        /// </summary>
        /// <returns>One of the <see cref="ApplicationType"/> values.</returns>
        public static ApplicationType GetApplicationType()
        {
            if (s_applicationType.HasValue)
                return s_applicationType.Value;

            if (HostingEnvironment.IsHosted)
            {
                s_applicationType = ApplicationType.Web;
            }
            else
            {
                try
                {
                    // References:
                    // - http://support.microsoft.com/kb/65122
                    // - http://support.microsoft.com/kb/90493/en-us
                    // - http://www.codeguru.com/cpp/w-p/system/misc/article.php/c2897/
                    // We will always have an entry assembly for windows application.
                    FileStream exe = new FileStream(AssemblyInfo.EntryAssembly.Location, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
                    byte[] dosHeader = new byte[64];
                    byte[] exeHeader = new byte[248];
                    byte[] subSystem = new byte[2];
                    exe.Read(dosHeader, 0, dosHeader.Length);
                    exe.Seek(BitConverter.ToInt16(dosHeader, 60), SeekOrigin.Begin);
                    exe.Read(exeHeader, 0, exeHeader.Length);
                    exe.Close();

                    Buffer.BlockCopy(exeHeader, 92, subSystem, 0, 2);

                    s_applicationType = ((ApplicationType)(LittleEndian.ToInt16(subSystem, 0)));
                }
                catch
                {
                    // We are unable to determine the application type.
                    s_applicationType = ApplicationType.Unknown;
                }
            }

            return s_applicationType.Value;
        }

        /// <summary>
        /// Gets the operating system <see cref="PlatformID"/>
        /// </summary>
        /// <returns>The operating system <see cref="PlatformID"/>.</returns>
        /// <remarks>
        /// This function will properly detect the platform ID, even if running on Mac.
        /// </remarks>
        public static PlatformID GetOSPlatformID()
        {
            if (s_osPlatformID != PlatformID.Win32S)
                return s_osPlatformID;

            s_osPlatformID = Environment.OSVersion.Platform;

            if (s_osPlatformID == PlatformID.Unix)
            {
                // Environment.OSVersion.Platform can report Unix when running on Mac OS X
                try
                {
                    s_osPlatformID = Command.Execute("uname").StandardOutput.StartsWith("Darwin", StringComparison.OrdinalIgnoreCase) ? PlatformID.MacOSX : PlatformID.Unix;
                }
                catch
                {
                    // Fall back on looking for Mac specific root folders:
                    if (Directory.Exists("/Applications") && Directory.Exists("/System") && Directory.Exists("/Users") && Directory.Exists("/Volumes"))
                        s_osPlatformID = PlatformID.MacOSX;
                }
            }

            return s_osPlatformID;
        }

        /// <summary>
        /// Gets the operating system product name.
        /// </summary>
        /// <returns>Operating system product name.</returns>
        public static string GetOSProductName()
        {
            if ((object)s_osPlatformName != null)
                return s_osPlatformName;

            switch (GetOSPlatformID())
            {
                case PlatformID.Unix:
                case PlatformID.MacOSX:
                    // Call sw_vers on Mac to get product name and version information, Linux could have this
                    try
                    {
                        string output = Command.Execute("sw_vers").StandardOutput;
                        Dictionary<string, string> kvps = output.ParseKeyValuePairs('\n', ':');
                        if (kvps.Count > 0)
                            s_osPlatformName = kvps.Values.Select(val => val.Trim()).ToDelimitedString(" ");
                    }
                    catch
                    {
                        s_osPlatformName = null;
                    }

                    if (string.IsNullOrEmpty(s_osPlatformName))
                    {
                        // Try some common ways to get product name on Linux, some might work on Mac
                        try
                        {
                            foreach (string fileName in FilePath.GetFileList("/etc/*release*"))
                            {
                                using (StreamReader reader = new StreamReader(fileName))
                                {
                                    string line = reader.ReadLine();

                                    while ((object)line != null)
                                    {
                                        if (line.StartsWith("PRETTY_NAME", StringComparison.OrdinalIgnoreCase) && !line.Contains('#'))
                                        {
                                            string[] parts = line.Split('=');

                                            if (parts.Length == 2)
                                            {
                                                s_osPlatformName = parts[1].Replace("\"", "");
                                                break;
                                            }
                                        }

                                        line = reader.ReadLine();
                                    }
                                }

                                if (!string.IsNullOrEmpty(s_osPlatformName))
                                    break;
                            }
                        }
                        catch
                        {
                            try
                            {
                                string output = Command.Execute("lsb_release", "-a").StandardOutput;
                                Dictionary<string, string> kvps = output.ParseKeyValuePairs('\n', ':');
                                if (kvps.TryGetValue("Description", out s_osPlatformName) && !string.IsNullOrEmpty(s_osPlatformName))
                                    s_osPlatformName = s_osPlatformName.Trim();

                            }
                            catch
                            {
                                s_osPlatformName = null;
                            }
                        }
                    }
                    break;
                default:
                    // Get Windows product name
                    try
                    {
                        s_osPlatformName = Registry.GetValue("HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion", "ProductName", null).ToString();
                    }
                    catch
                    {
                        s_osPlatformName = null;
                    }
                    break;
            }

            if (string.IsNullOrWhiteSpace(s_osPlatformName))
                s_osPlatformName = GetOSPlatformID().ToString();

            if (IsMono)
                s_osPlatformName += " using Mono";

            return s_osPlatformName;
        }

        /// <summary>
        /// Gets the memory usage by the current process.
        /// </summary>
        /// <returns>Memory usage by the current process.</returns>
        public static long GetProcessMemory()
        {
            long processMemory = Environment.WorkingSet;

            if (processMemory == 0 && IsPosixEnvironment)
            {
                try
                {
                    double percentOfTotal;
                    long totalMemory;

                    // Get total system memory
                    using (PerformanceCounter counter = new PerformanceCounter("Mono Memory", "Total Physical Memory"))
                        totalMemory = counter.RawValue;

                    // Get percent of total memory used by current process
                    string output = Command.Execute("ps", string.Format("-p {0} -o %mem", Process.GetCurrentProcess().Id)).StandardOutput;
                    string[] lines = output.Split('\n');

                    if (lines.Length > 1 && double.TryParse(lines[1].Trim(), out percentOfTotal))
                        processMemory = (long)Math.Round(percentOfTotal / 100.0D * totalMemory);
                }
                catch
                {
                    processMemory = -1;
                }
            }

            return processMemory;
        }

        // The following "ToNonNullString" methods extend all class based objects. Note that these extension methods can be
        // called even if the base object is null, hence the value of these methods. Our philosophy for this project has been
        // "not" to apply extensions to all objects (this to avoid general namespace pollution) and make sure extensions are
        // grouped together in their own source file (e.g., StringExtensions.cs); however these items do apply to all items
        // and are essentially type-less hence their location in the "Common" class. These extension methods are at least
        // limited to classes and won't show up on native types and custom structures.

        /// <summary>
        /// Converts value to string; null objects (or DBNull objects) will return an empty string (""). 
        /// </summary>
        /// <typeparam name="T"><see cref="Type"/> of <see cref="Object"/> to convert to string.</typeparam>
        /// <param name="value">Value to convert to string.</param>
        /// <returns><paramref name="value"/> as a string; if <paramref name="value"/> is null, empty string ("") will be returned. </returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static string ToNonNullString<T>(this T value) where T : class
        {
            return ((object)value == null || value is DBNull ? "" : value.ToString());
        }

        /// <summary>
        /// Converts value to string; null objects (or DBNull objects) will return specified <paramref name="nonNullValue"/>.
        /// </summary>
        /// <typeparam name="T"><see cref="Type"/> of <see cref="Object"/> to convert to string.</typeparam>
        /// <param name="value">Value to convert to string.</param>
        /// <param name="nonNullValue"><see cref="String"/> to return if <paramref name="value"/> is null.</param>
        /// <returns><paramref name="value"/> as a string; if <paramref name="value"/> is null, <paramref name="nonNullValue"/> will be returned.</returns>
        /// <exception cref="ArgumentNullException"><paramref name="nonNullValue"/> cannot be null.</exception>
        public static string ToNonNullString<T>(this T value, string nonNullValue) where T : class
        {
            if ((object)nonNullValue == null)
                throw new ArgumentNullException("nonNullValue");

            return ((object)value == null || value is DBNull ? nonNullValue : value.ToString());
        }

        // We handle strings as a special version of the ToNullNullString extension to handle documentation a little differently

        /// <summary>
        /// Makes sure returned string value is not null; if this string is null, empty string ("") will be returned. 
        /// </summary>
        /// <param name="value"><see cref="String"/> to verify is not null.</param>
        /// <returns><see cref="String"/> value; if <paramref name="value"/> is null, empty string ("") will be returned.</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static string ToNonNullString(this string value)
        {
            return ((object)value == null ? "" : value);
        }

        /// <summary>
        /// Converts value to string; null objects, DBNull objects or empty strings will return specified <paramref name="nonNullNorEmptyValue"/>.
        /// </summary>
        /// <typeparam name="T"><see cref="Type"/> of <see cref="Object"/> to convert to string.</typeparam>
        /// <param name="value">Value to convert to string.</param>
        /// <param name="nonNullNorEmptyValue"><see cref="String"/> to return if <paramref name="value"/> is null.</param>
        /// <returns><paramref name="value"/> as a string; if <paramref name="value"/> is null, DBNull or an empty string <paramref name="nonNullNorEmptyValue"/> will be returned.</returns>
        /// <exception cref="ArgumentException"><paramref name="nonNullNorEmptyValue"/> must not be null or an empty string.</exception>
        public static string ToNonNullNorEmptyString<T>(this T value, string nonNullNorEmptyValue = " ") where T : class
        {
            if (string.IsNullOrEmpty(nonNullNorEmptyValue))
                throw new ArgumentException("Must not be null or an empty string", "nonNullNorEmptyValue");

            if ((object)value == null || value is DBNull)
                return nonNullNorEmptyValue;

            string valueAsString = value.ToString();

            return (string.IsNullOrEmpty(valueAsString) ? nonNullNorEmptyValue : valueAsString);
        }

        /// <summary>
        /// Converts value to string; null objects, DBNull objects, empty strings or all white space strings will return specified <paramref name="nonNullNorWhiteSpaceValue"/>.
        /// </summary>
        /// <typeparam name="T"><see cref="Type"/> of <see cref="Object"/> to convert to string.</typeparam>
        /// <param name="value">Value to convert to string.</param>
        /// <param name="nonNullNorWhiteSpaceValue"><see cref="String"/> to return if <paramref name="value"/> is null.</param>
        /// <returns><paramref name="value"/> as a string; if <paramref name="value"/> is null, DBNull, empty or all white space, <paramref name="nonNullNorWhiteSpaceValue"/> will be returned.</returns>
        /// <exception cref="ArgumentException"><paramref name="nonNullNorWhiteSpaceValue"/> must not be null, an empty string or white space.</exception>
        public static string ToNonNullNorWhiteSpace<T>(this T value, string nonNullNorWhiteSpaceValue = "_") where T : class
        {
            if (string.IsNullOrWhiteSpace(nonNullNorWhiteSpaceValue))
                throw new ArgumentException("Must not be null, an empty string or white space", "nonNullNorWhiteSpaceValue");

            if ((object)value == null || value is DBNull)
                return nonNullNorWhiteSpaceValue;

            string valueAsString = value.ToString();

            return (string.IsNullOrWhiteSpace(valueAsString) ? nonNullNorWhiteSpaceValue : valueAsString);
        }

        /// <summary>
        /// Converts <paramref name="value"/> to a <see cref="String"/> using an appropriate <see cref="TypeConverter"/>.
        /// </summary>
        /// <param name="value">Value to convert to a <see cref="String"/>.</param>
        /// <returns><paramref name="value"/> converted to a <see cref="String"/>.</returns>
        /// <remarks>
        /// <para>
        /// If <see cref="TypeConverter"/> fails, the value's <c>ToString()</c> value will be returned.
        /// Returned value will never be null, if no value exists an empty string ("") will be returned.
        /// </para>
        /// <para>
        /// You can use the <see cref="StringExtensions.ConvertToType{T}(string)"/> string extension method to
        /// convert the string back to its original <see cref="Type"/>.
        /// </para>
        /// </remarks>
        public static string TypeConvertToString(object value)
        {
            return TypeConvertToString(value, null);
        }

        /// <summary>
        /// Converts <paramref name="value"/> to a <see cref="String"/> using an appropriate <see cref="TypeConverter"/>.
        /// </summary>
        /// <param name="value">Value to convert to a <see cref="String"/>.</param>
        /// <param name="culture"><see cref="CultureInfo"/> to use for the conversion.</param>
        /// <returns><paramref name="value"/> converted to a <see cref="String"/>.</returns>
        /// <remarks>
        /// <para>
        /// If <see cref="TypeConverter"/> fails, the value's <c>ToString()</c> value will be returned.
        /// Returned value will never be null, if no value exists an empty string ("") will be returned.
        /// </para>
        /// <para>
        /// You can use the <see cref="StringExtensions.ConvertToType{T}(string)"/> string extension method to
        /// convert the string back to its original <see cref="Type"/>.
        /// </para>
        /// </remarks>
        public static string TypeConvertToString(object value, CultureInfo culture)
        {
            // Don't proceed further if value is null.
            if ((object)value == null)
                return string.Empty;

            // If value is already a string, no need to attempt conversion
            string valueAsString = value as string;

            if ((object)valueAsString != null)
                return valueAsString;

            // Initialize culture info if not specified.
            if ((object)culture == null)
                culture = CultureInfo.InvariantCulture;

            try
            {
                // Attempt to use type converter to set field value
                TypeConverter converter = TypeDescriptor.GetConverter(value);
                return converter.ConvertToString(null, culture, value).ToNonNullString();
            }
            catch
            {
                // Otherwise just call object's ToString method
                return value.ToNonNullString();
            }
        }

        /// <summary>Gets a high-resolution number of seconds, including fractional seconds, that have
        /// elapsed since 12:00:00 midnight, January 1, 0001.</summary>
        public static double SystemTimer
        {
            get
            {
                return Ticks.ToSeconds(DateTime.UtcNow.Ticks);
            }
        }

        /// <summary>Determines if given item is equal to its default value (e.g., null or 0.0).</summary>
        /// <param name="item">Object to evaluate.</param>
        /// <returns>Result of evaluation as a <see cref="bool"/>.</returns>
        /// <remarks>
        /// Native types default to zero, not null, therefore this can be used to evaluate if an item is its default (i.e., uninitialized) value.
        /// </remarks>
        public static bool IsDefaultValue(object item)
        {
            // Only reference types can be null, therefore null is its default value
            if ((object)item == null)
                return true;

            Type itemType = item.GetType();

            if (!itemType.IsValueType)
                return false;

            // Handle common types
            IConvertible convertible = item as IConvertible;

            if ((object)convertible != null)
            {
                try
                {
                    switch (convertible.GetTypeCode())
                    {
                        case TypeCode.Boolean:
                            return ((bool)item == default(bool));
                        case TypeCode.SByte:
                            return ((sbyte)item == default(sbyte));
                        case TypeCode.Byte:
                            return ((byte)item == default(byte));
                        case TypeCode.Int16:
                            return ((short)item == default(short));
                        case TypeCode.UInt16:
                            return ((ushort)item == default(ushort));
                        case TypeCode.Int32:
                            return ((int)item == default(int));
                        case TypeCode.UInt32:
                            return ((uint)item == default(uint));
                        case TypeCode.Int64:
                            return ((long)item == default(long));
                        case TypeCode.UInt64:
                            return ((ulong)item == default(ulong));
                        case TypeCode.Single:
                            return ((float)item == default(float));
                        case TypeCode.Double:
                            return ((double)item == default(double));
                        case TypeCode.Decimal:
                            return ((decimal)item == default(decimal));
                        case TypeCode.Char:
                            return ((char)item == default(char));
                        case TypeCode.DateTime:
                            return ((DateTime)item == default(DateTime));
                    }
                }
                catch (InvalidCastException)
                {
                    // An exception here indicates that the item is a custom type that
                    // lied about its type code. The type should still be instantiable,
                    // so we can ignore this exception
                }
            }

            // Handle custom value types
            return ((ValueType)item).Equals(Activator.CreateInstance(itemType));
        }

        /// <summary>Determines if given item is a reference type.</summary>
        /// <param name="item">Object to evaluate.</param>
        /// <returns>Result of evaluation as a <see cref="bool"/>.</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static bool IsReference(object item)
        {
            return !(item is ValueType);
        }

        /// <summary>Determines if given item is a reference type but not a string.</summary>
        /// <param name="item">Object to evaluate.</param>
        /// <returns>Result of evaluation as a <see cref="bool"/>.</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static bool IsNonStringReference(object item)
        {
            return (IsReference(item) && !(item is string));
        }

        /// <summary>Determines if given item is numeric.</summary>
        /// <param name="item">Object to evaluate.</param>
        /// <returns>Result of evaluation as a <see cref="bool"/>.</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static bool IsNumeric(object item)
        {
            IConvertible convertible = item as IConvertible;

            if ((object)convertible != null)
            {
                switch (convertible.GetTypeCode())
                {
                    case TypeCode.Boolean:
                    case TypeCode.SByte:
                    case TypeCode.Byte:
                    case TypeCode.Int16:
                    case TypeCode.UInt16:
                    case TypeCode.Int32:
                    case TypeCode.UInt32:
                    case TypeCode.Int64:
                    case TypeCode.UInt64:
                    case TypeCode.Single:
                    case TypeCode.Double:
                    case TypeCode.Decimal:
                        return true;
                    case TypeCode.Char:
                    case TypeCode.String:
                        double result;
                        return double.TryParse(convertible.ToString(null), out result);
                }
            }

            return false;
        }

        /// <summary>Returns the smallest item from a list of parameters.</summary>
        /// <typeparam name="T">Return type <see cref="Type"/> that is the minimum value in the <paramref name="itemList"/>.</typeparam>
        /// <param name="itemList">A variable number of parameters of the specified type.</param>
        /// <returns>Result is the minimum value of type <see cref="Type"/> in the <paramref name="itemList"/>.</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static T Min<T>(params T[] itemList)
        {
            return itemList.Min();
        }

        /// <summary>Returns the largest item from a list of parameters.</summary>
        /// <typeparam name="T">Return type <see cref="Type"/> that is the maximum value in the <paramref name="itemList"/>.</typeparam>
        /// <param name="itemList">A variable number of parameters of the specified type .</param>
        /// <returns>Result is the maximum value of type <see cref="Type"/> in the <paramref name="itemList"/>.</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static T Max<T>(params T[] itemList)
        {
            return itemList.Max();
        }

        /// <summary>Returns the value that is neither the largest nor the smallest.</summary>
        /// <typeparam name="T"><see cref="Type"/> of the objects passed to and returned from this method.</typeparam>
        /// <param name="value1">Value 1.</param>
        /// <param name="value2">Value 2.</param>
        /// <param name="value3">Value 3.</param>
        /// <returns>Result is the value that is neither the largest nor the smallest.</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static T Mid<T>(T value1, T value2, T value3) where T : IComparable<T>
        {
            if ((object)value1 == null)
                throw new ArgumentNullException("value1");

            if ((object)value2 == null)
                throw new ArgumentNullException("value2");

            if ((object)value3 == null)
                throw new ArgumentNullException("value3");

            int comp1to2 = value1.CompareTo(value2);
            int comp1to3 = value1.CompareTo(value3);
            int comp2to3 = value2.CompareTo(value3);

            // If 3 is the smallest, pick the smaller of 1 and 2
            if (comp1to3 >= 0 && comp2to3 >= 0)
                return (comp1to2 <= 0) ? value1 : value2;

            // If 2 is the smallest, pick the smaller of 1 and 3
            if (comp1to2 >= 0 && comp2to3 <= 0)
                return (comp1to3 <= 0) ? value1 : value3;

            // 1 is the smallest so pick the smaller of 2 and 3
            return (comp2to3 <= 0) ? value2 : value3;
        }

        #region [ Old Code ]

        ///// <summary>Returns the smallest item from a list of parameters.</summary>
        ///// <param name="itemList">A variable number of parameters of type <see cref="Object"/></param>
        ///// <returns>Result is the minimum value of type <see cref="Object"/> in the <paramref name="itemList"/>.</returns>
        //public static object Min(params object[] itemList)
        //{
        //    return itemList.Min<object>(CompareObjects);
        //}

        ///// <summary>Returns the largest item from a list of parameters.</summary>
        ///// <param name="itemList">A variable number of parameters of type <see cref="Object"/></param>
        ///// <returns>Result is the maximum value of type <see cref="Object"/> in the <paramref name="itemList"/>.</returns>
        //public static object Max(params object[] itemList)
        //{
        //    return itemList.Max<object>(CompareObjects);
        //}

        ///// <summary>Compares two elements of any type.</summary>
        ///// <param name="x">Object which is compared to object <paramref name="y"/>.</param>
        ///// <param name="y">Object which is compared against.</param>
        ///// <returns>Result of comparison as an <see cref="int"/>.</returns>
        //public static int CompareObjects(object x, object y)
        //{
        //    // Just using Visual Basic runtime to compare two objects of unknown types - this can be a very
        //    // complex process and the VB runtime library is distributed with .NET anyway, so why not use it:

        //    // Note that comparison is based on VB object comparison rules:
        //    // ms-help://MS.VSCC.v80/MS.MSDN.v80/MS.VisualStudio.v80.en/dv_vbalr/html/d6cb12a8-e52e-46a7-8aaf-f804d634a825.htm
        //    return (Microsoft.VisualBasic.CompilerServices.Operators.ConditionalCompareObjectLess(x, y, false) ? -1 :
        //        (Microsoft.VisualBasic.CompilerServices.Operators.ConditionalCompareObjectGreater(x, y, false) ? 1 : 0));
        //}
        // This function is probably not that useful

        ///// <summary>Time zone names enumeration used to look up desired time zone in GetWin32TimeZone function.</summary>
        //public enum TimeZoneName
        //{
        //    DaylightName,
        //    DisplayName,
        //    StandardName
        //}

        ///// <summary>Returns the specified Win32 time zone, using specified name.</summary>
        ///// <param name="name">Value of name used for time zone lookup.</param>
        ///// <param name="lookupBy">Type of name used for time zone lookup.</param>
        //public static TimeZoneInfo GetTimeZone(string name, TimeZoneName lookupBy)
        //{
        //    foreach (TimeZoneInfo timeZone in TimeZoneInfo.GetSystemTimeZones())
        //    {
        //        if (lookupBy == TimeZoneName.DaylightName)
        //        {
        //            if (string.Compare(timeZone.DaylightName, name, true) == 0)
        //                return timeZone;
        //        }
        //        else if (lookupBy == TimeZoneName.DisplayName)
        //        {
        //            if (string.Compare(timeZone.DisplayName, name, true) == 0)
        //                return timeZone;
        //        }
        //        else if (lookupBy == TimeZoneName.StandardName)
        //        {
        //            if (string.Compare(timeZone.StandardName, name, true) == 0)
        //                return timeZone;
        //        }
        //    }

        //    throw new ArgumentException("Windows time zone with " + lookupBy + " of \"" + name + "\" was not found!");
        //}

        #endregion
    }
}