New Format.Escape method

src/Discord.Net/Format.cs

@@ -1,23 +1,91 @@
-using System.Text;
+using Discord.Net.API;
+using System.Text;
 using System.Text.RegularExpressions;
 
 namespace Discord
 {
-    public static class Format
+	public static class Format
 	{
-		private static readonly Regex _escapeRegex;
-		private static readonly MatchEvaluator _escapeEvaluator;
+		private static readonly string[] _patterns;
+		private static readonly StringBuilder _builder;
 
 		static Format()
 		{
-			const string innerPattern = "[_*]|~~";
-			_escapeRegex = new Regex($@"(?<=^|\W)(?:{innerPattern})|(?:{innerPattern})(?=\W|$)|\\", RegexOptions.Compiled);
-			_escapeEvaluator = new MatchEvaluator(e => '\\' + e.Value);
-		}
+			_patterns = new string[] { "__", "_", "**", "*", "~~" };
+			_builder = new StringBuilder(DiscordAPIClient.MaxMessageSize);
+        }
 
 		/// <summary> Removes all special formatting characters from the provided text. </summary>
 		private static string Escape(string text)
-			=> _escapeRegex.Replace(text, _escapeEvaluator);
+		{
+			lock (_builder)
+			{
+				_builder.Clear();
+
+				//Escape all backslashes
+				for (int i = 0; i < text.Length; i++)
+				{
+					_builder.Append(text[i]);
+					if (text[i] == '\\')
+						_builder.Append('\\');
+				}
+
+				EscapeSubstring(0, _builder.Length);
+
+				return _builder.ToString();
+			}
+		}
+		private static int EscapeSubstring(int start, int end)
+		{
+			int totalAddedChars = 0;
+			for (int i = start; i < end + totalAddedChars; i++)
+			{
+				for (int p = 0; p < _patterns.Length; p++)
+				{
+					string pattern = _patterns[p];
+					if (i + pattern.Length * 2 > _builder.Length)
+						continue;
+					int s = FindPattern(pattern, i, i + 1);
+					if (s == -1) continue;
+					int e = FindPattern(pattern, i + 1, end + totalAddedChars);
+					if (e == -1) continue;
+
+					if (e - s - pattern.Length > 0)
+					{
+						//By going right to left, we dont need to adjust any offsets
+						for (int k = pattern.Length - 1; k >= 0; k--)
+							_builder.Insert(e + k, '\\');
+						for (int k = pattern.Length - 1; k >= 0; k--)
+							_builder.Insert(s + k, '\\');
+                        int addedChars = pattern.Length * 2;
+						addedChars += EscapeSubstring(s + pattern.Length * 2, e + pattern.Length);
+						i = e + addedChars + pattern.Length - 1;
+						totalAddedChars += addedChars;
+						break;
+                    }
+				}
+			}
+			return totalAddedChars;
+		}
+		private static int FindPattern(string pattern, int start, int end)
+		{
+			for (int j = start; j < end; j++)
+			{
+				if (_builder[j] == '\\')
+				{
+					j++;
+					continue;
+				}
+				for (int k = 0; k < pattern.Length; k++)
+				{
+					if (_builder[j + k] != pattern[k])
+						goto nextpos;
+				}
+				return j;
+				nextpos:;
+			}
+			return -1;
+		}
 
 		/// <summary> Returns a markdown-formatted string with no formatting, optionally escaping the contents. </summary>
 		public static string Normal(string text, bool escape = true)