NPOI/Code/Npoi.Core.Common/ExcelExtensions.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Xml;
using System.Xml.Linq;

namespace Npoi.Core
{
    public static class ExcelExtensions
    {
        public static XElement CreateElement(this XDocument element, string name)
        {
            return new XElement(name);
        }

        public static string GetAttribute(this XElement element, string name, string sub = null)
        {
            return element.Attribute(name)?.Value ?? sub;
        }

        public static void AppendChild(this XElement element, object content)
        {
            element.Add(content);
        }

        public static void AppendChild(this XDocument element, object content)
        {
            element.Add(content);
        }

        public static XElement CloneNode(this XElement element, bool deep)
        {
            return element;
        }

        public static XAttribute GetAttributeNode(this XElement root, string name)
        {
            return root.Attribute(name);
        }

        public static ConstructorInfo FilterConstructorsByType(this IEnumerable<ConstructorInfo> constructors, params Type[] types)
        {
            foreach (var item in constructors)
            {
                var paramsInfo = item.GetParameters().Select(x => x.ParameterType.FullName);
                var typesInfo = types.Select(x => x.FullName);
                var isThis = paramsInfo.Except(typesInfo).Count()==0;
                if (isThis)
                {
                    return item;
                }
            }
            return constructors.First();
        }

        // This function is duplicated in COMDateTime.cpp 
        // Number of 100ns ticks per time unit 
        private const long TicksPerMillisecond = 10000;
        private const long TicksPerSecond = TicksPerMillisecond * 1000;
        private const long TicksPerMinute = TicksPerSecond * 60;
        private const long TicksPerHour = TicksPerMinute * 60;
        private const long TicksPerDay = TicksPerHour * 24;

        // Number of milliseconds per time unit 
        private const int MillisPerSecond = 1000;
        private const int MillisPerMinute = MillisPerSecond * 60;
        private const int MillisPerHour = MillisPerMinute * 60;
        private const int MillisPerDay = MillisPerHour * 24;

        // Number of days in a non-leap year 
        private const int DaysPerYear = 365;
        // Number of days in 4 years 
        private const int DaysPer4Years = DaysPerYear * 4 + 1;
        // Number of days in 100 years
        private const int DaysPer100Years = DaysPer4Years * 25 - 1;
        // Number of days in 400 years
        private const int DaysPer400Years = DaysPer100Years * 4 + 1;
        private const int DaysTo1899 = DaysPer400Years * 4 + DaysPer100Years * 3 - 367;
        private const long DoubleDateOffset = DaysTo1899 * TicksPerDay;



        private const long OADateMinAsTicks = (DaysPer100Years - DaysPerYear) * TicksPerDay;

        private static double TicksToOADate(long value)
        {
            if (value == 0)
                return 0.0;  // Returns OleAut's zero'ed date value.
            if (value < TicksPerDay) // This is a fix for VB. They want the default day to be 1/1/0001 rathar then 12/30/1899.
                value += DoubleDateOffset; // We could have moved this fix down but we would like to keep the bounds check.
            if (value < OADateMinAsTicks)
                throw new OverflowException("Arg_OleAutDateInvalid");
            // Currently, our max date == OA's max date (12/31/9999), so we don't 
            // need an overflow check in that direction. 
            long millis = (value - DoubleDateOffset) / TicksPerMillisecond;
            if (millis < 0)
            {
                long frac = millis % MillisPerDay;
                if (frac != 0) millis -= (MillisPerDay + frac) * 2;
            }
            return (double)millis / MillisPerDay;
        }

#if !NET46
		public static double ToOADate(this DateTime root)
		{
			return TicksToOADate(root.Ticks);
		}
#endif

        public static string OuterXml(this XElement root)
        {
            using (var reader = root.CreateReader())
            {
                reader.MoveToContent();
                return reader.ReadOuterXml();
            }
        }

        public static string OuterXml(this XNode root)
        {
            using (var reader = root.CreateReader())
            {
                reader.MoveToContent();
                return reader.ReadOuterXml();
            }
        }

        public static string InnerXml(this XElement root)
        {
            using (var reader = root.CreateReader())
            {
                reader.MoveToContent();
                return reader.ReadInnerXml();
            }
        }
        public static string Prefix(this XElement root)
        {
            return root.GetPrefixOfNamespace(root.Name.Namespace);
        }

        public static IEnumerable<XElement> ChildElements(this XElement root)
        {
            foreach (XNode childNode in root.Nodes())
            {
                var elm = childNode as XElement;
                if (elm != null)
                {
                    yield return elm;
                }
            }
        }

        public static string AttributeValue(this XElement element, string attribute, string sub = null)
        {
            return element.Attribute(attribute).Value ?? sub;
        }

        //public static XElement SetAttribute(this XElement root, string name, string value)
        //{
        //	var nsAttribute =
        //		new XAttribute(name, value);
        //	root.Add(nsAttribute);
        //	return root;
        //}

        public static XmlNameTable NameTable(this XDocument doc)
        {
            using (var reader = doc.CreateReader())
            {
                return reader.NameTable;
            }
        }

        public static XElement SetAttribute(this XElement root, string name, XNamespace schema, string value)
        {
            var nsAttribute =
                new XAttribute(schema + name, value);
            root.Add(nsAttribute);
            return root;
        }
    }
}