Umbraco-CMS/src/Umbraco.Core/HashCodeCombiner.cs

using System;
using System.Globalization;
using System.IO;

namespace Umbraco.Cms.Core
{
    /// <summary>
    /// Used to create a .NET HashCode from multiple objects.
    /// </summary>
    /// <remarks>
    /// .Net has a class the same as this: System.Web.Util.HashCodeCombiner and of course it works for all sorts of things
    /// which we've not included here as we just need a quick easy class for this in order to create a unique
    /// hash of directories/files to see if they have changed.
    ///
    /// NOTE: It's probably best to not relying on the hashing result across AppDomains! If you need a constant/reliable hash value
    /// between AppDomains use SHA1. This is perfect for hashing things in a very fast way for a single AppDomain.
    /// </remarks>
    public class HashCodeCombiner
    {
        private long _combinedHash = 5381L;

        public void AddInt(int i)
        {
            _combinedHash = ((_combinedHash << 5) + _combinedHash) ^ i;
        }

        public void AddObject(object o)
        {
            AddInt(o.GetHashCode());
        }

        public void AddDateTime(DateTime d)
        {
            AddInt(d.GetHashCode());
        }

        public void AddString(string s)
        {
            if (s != null)
                AddInt((StringComparer.InvariantCulture).GetHashCode(s));
        }

        public void AddCaseInsensitiveString(string s)
        {
            if (s != null)
                AddInt((StringComparer.InvariantCultureIgnoreCase).GetHashCode(s));
        }

        public void AddFileSystemItem(FileSystemInfo f)
        {
            //if it doesn't exist, don't proceed.
            if (!f.Exists)
                return;

            AddCaseInsensitiveString(f.FullName);
            AddDateTime(f.CreationTimeUtc);
            AddDateTime(f.LastWriteTimeUtc);

            //check if it is a file or folder
            var fileInfo = f as FileInfo;
            if (fileInfo != null)
            {
                AddInt(fileInfo.Length.GetHashCode());
            }

            var dirInfo = f as DirectoryInfo;
            if (dirInfo != null)
            {
                foreach (var d in dirInfo.GetFiles())
                {
                    AddFile(d);
                }
                foreach (var s in dirInfo.GetDirectories())
                {
                    AddFolder(s);
                }
            }
        }

        public void AddFile(FileInfo f)
        {
            AddFileSystemItem(f);
        }

        public void AddFolder(DirectoryInfo d)
        {
            AddFileSystemItem(d);
        }

        /// <summary>
        /// Returns the hex code of the combined hash code
        /// </summary>
        /// <returns></returns>
        public string GetCombinedHashCode()
        {
            return _combinedHash.ToString("x", CultureInfo.InvariantCulture);
        }

    }
}