Alphanumeric sorting instead of numeric sorting

Pages/Index.cshtml.cs

@@ -1,4 +1,4 @@
-using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
@@ -36,7 +36,7 @@ namespace webmusic.Pages
             dirs.Sort();
             files = Directory.GetFiles(fullpath).Select(Path.GetFileName).ToList();
             files.RemoveAll(p => p.EndsWith(".m3u"));
-            files.Sort(new NumericComparer());
+            files.Sort(new AlphanumComparatorFast());
         }
 
         public string Encode(string str)
@@ -45,25 +45,96 @@ namespace webmusic.Pages
                 .Replace("?", "%3F").Replace("&", "%26")
                 .Replace(" ", "%20");
         }
-        
-        public class NumericComparer : IComparer<string>
+
+        public class AlphanumComparatorFast : IComparer<string>
         {
             public int Compare(string x, string y)
             {
-                var regex = new Regex(@"^\d+");
-
-                // run the regex on both strings
-                var xRegexResult = regex.Match(x);
-                var yRegexResult = regex.Match(y);
-
-                // check if they are both numbers
-                if (xRegexResult.Success && yRegexResult.Success)
+                string s1 = x;
+                if (s1 == null)
                 {
-                    return int.Parse(xRegexResult.Value).CompareTo(int.Parse(yRegexResult.Value));
+                    return 0;
                 }
 
-                // otherwise return as string comparison
-                return string.Compare(x, y, StringComparison.Ordinal);
+                if (!(y is string s2))
+                {
+                    return 0;
+                }
+
+                int len1 = s1.Length;
+                int len2 = s2.Length;
+                int marker1 = 0;
+                int marker2 = 0;
+
+                // Walk through two the strings with two markers.
+                while (marker1 < len1 && marker2 < len2)
+                {
+                    char ch1 = s1[marker1];
+                    char ch2 = s2[marker2];
+
+                    // Some buffers we can build up characters in for each chunk.
+                    char[] space1 = new char[len1];
+                    int loc1 = 0;
+                    char[] space2 = new char[len2];
+                    int loc2 = 0;
+
+                    // Walk through all following characters that are digits or
+                    // characters in BOTH strings starting at the appropriate marker.
+                    // Collect char arrays.
+                    do
+                    {
+                        space1[loc1++] = ch1;
+                        marker1++;
+
+                        if (marker1 < len1)
+                        {
+                            ch1 = s1[marker1];
+                        }
+                        else
+                        {
+                            break;
+                        }
+                    } while (char.IsDigit(ch1) == char.IsDigit(space1[0]));
+
+                    do
+                    {
+                        space2[loc2++] = ch2;
+                        marker2++;
+
+                        if (marker2 < len2)
+                        {
+                            ch2 = s2[marker2];
+                        }
+                        else
+                        {
+                            break;
+                        }
+                    } while (char.IsDigit(ch2) == char.IsDigit(space2[0]));
+
+                    // If we have collected numbers, compare them numerically.
+                    // Otherwise, if we have strings, compare them alphabetically.
+                    string str1 = new string(space1);
+                    string str2 = new string(space2);
+
+                    int result;
+
+                    if (char.IsDigit(space1[0]) && char.IsDigit(space2[0]))
+                    {
+                        int thisNumericChunk = int.Parse(str1);
+                        int thatNumericChunk = int.Parse(str2);
+                        result = thisNumericChunk.CompareTo(thatNumericChunk);
+                    }
+                    else
+                    {
+                        result = str1.CompareTo(str2);
+                    }
+
+                    if (result != 0)
+                    {
+                        return result;
+                    }
+                }
+                return len1 - len2;
             }
         }
     }