roadie/Roadie.Api.Library/Utility/FileSizeFormatProvider.cs

using System;

namespace Roadie.Library.Utility
{
    public class FileSizeFormatProvider : IFormatProvider, ICustomFormatter
    {
        private const string fileSizeFormat = "fs";

        private const decimal OneGigaByte = OneMegaByte * 1024M;

        private const decimal OneKiloByte = 1024M;

        private const decimal OneMegaByte = OneKiloByte * 1024M;

        private const decimal OneTeraByte = OneGigaByte * 1024M;

        public string Format(string format, object arg, IFormatProvider formatProvider)
        {
            if (format == null || !format.StartsWith(fileSizeFormat)) return defaultFormat(format, arg, formatProvider);

            if (arg is string) return defaultFormat(format, arg, formatProvider);

            decimal size;

            try
            {
                size = Convert.ToDecimal(arg);
            }
            catch (InvalidCastException)
            {
                return defaultFormat(format, arg, formatProvider);
            }

            string suffix;
            if (size > OneTeraByte)
            {
                size /= OneTeraByte;
                suffix = "TB";
            }
            else if (size > OneGigaByte)
            {
                size /= OneGigaByte;
                suffix = "GB";
            }
            else if (size > OneMegaByte)
            {
                size /= OneMegaByte;
                suffix = "MB";
            }
            else if (size > OneKiloByte)
            {
                size /= OneKiloByte;
                suffix = "kB";
            }
            else
            {
                suffix = " B";
            }

            var precision = format.Substring(2);
            if (string.IsNullOrEmpty(precision)) precision = "2";

            return string.Format("{0:N" + precision + "}{1}", size, suffix);
        }

        public object GetFormat(Type formatType)
        {
            if (formatType == typeof(ICustomFormatter)) return this;

            return null;
        }

        private static string defaultFormat(string format, object arg, IFormatProvider formatProvider)
        {
            var formattableArg = arg as IFormattable;
            if (formattableArg != null) return formattableArg.ToString(format, formatProvider);
            return arg.ToString();
        }
    }
}