Update UrlUtility.cs

Add UrlUtility.Combine method

ZeroLevel/Services/Web/UrlUtility.cs

@@ -1,5 +1,7 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using System.Text;
+using System.Text.RegularExpressions;
 
 namespace ZeroLevel.Services.Web
 {
@@ -60,6 +62,78 @@ namespace ZeroLevel.Services.Web
             return str == null ? null : UrlEncodeUnicodeStringToStringInternal(str, false);
         }
 
+        /// <summary>
+        /// https://github.com/tmenier/Flurl
+        /// </summary>
+        public static string Combine(params string[] parts)
+        {
+            if (parts == null)
+                throw new ArgumentNullException(nameof(parts));
+
+            string result = "";
+            bool inQuery = false, inFragment = false;
+
+            string CombineEnsureSingleSeparator(string a, string b, char separator)
+            {
+                if (string.IsNullOrEmpty(a)) return b;
+                if (string.IsNullOrEmpty(b)) return a;
+                return a.TrimEnd(separator) + separator + b.TrimStart(separator);
+            }
+
+            foreach (var part in parts)
+            {
+                if (string.IsNullOrEmpty(part))
+                    continue;
+
+                if (result.EndsWith("?") || part.StartsWith("?"))
+                    result = CombineEnsureSingleSeparator(result, part, '?');
+                else if (result.EndsWith("#") || part.StartsWith("#"))
+                    result = CombineEnsureSingleSeparator(result, part, '#');
+                else if (inFragment)
+                    result += part;
+                else if (inQuery)
+                    result = CombineEnsureSingleSeparator(result, part, '&');
+                else
+                    result = CombineEnsureSingleSeparator(result, part, '/');
+
+                if (part.Contains("#"))
+                {
+                    inQuery = false;
+                    inFragment = true;
+                }
+                else if (!inFragment && part.Contains("?"))
+                {
+                    inQuery = true;
+                }
+            }
+            return EncodeIllegalCharacters(result);
+        }
+        /// <summary>
+        /// https://github.com/tmenier/Flurl
+        /// </summary>
+        public static string EncodeIllegalCharacters(string s, bool encodeSpaceAsPlus = false)
+        {
+            if (string.IsNullOrEmpty(s))
+                return s;
+
+            if (encodeSpaceAsPlus)
+                s = s.Replace(" ", "+");
+
+            // Uri.EscapeUriString mostly does what we want - encodes illegal characters only - but it has a quirk
+            // in that % isn't illegal if it's the start of a %-encoded sequence https://stackoverflow.com/a/47636037/62600
+
+            // no % characters, so avoid the regex overhead
+            if (!s.Contains("%"))
+                return Uri.EscapeUriString(s);
+
+            // pick out all %-hex-hex matches and avoid double-encoding 
+            return Regex.Replace(s, "(.*?)((%[0-9A-Fa-f]{2})|$)", c => {
+                var a = c.Groups[1].Value; // group 1 is a sequence with no %-encoding - encode illegal characters
+                var b = c.Groups[2].Value; // group 2 is a valid 3-character %-encoded sequence - leave it alone!
+                return Uri.EscapeUriString(a) + b;
+            });
+        }
+
         private static string UrlEncodeUnicodeStringToStringInternal(string s, bool ignoreAscii)
         {
             var l = s.Length;