From 054389b3d0eccd6767c8de2c6c848dd7798ab6d2 Mon Sep 17 00:00:00 2001
From: database64128 <free122448@hotmail.com>
Date: Thu, 9 Dec 2021 21:53:56 +0800
Subject: [PATCH] =?UTF-8?q?=E2=9A=A1=20Efficient=20command=20parsing?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Use ReadOnlySpan<char> for zero-copy string slicing.
---
 CubicBot.Telegram/Utils/ChatHelper.cs | 60 +++++++++++++++++----------
 1 file changed, 39 insertions(+), 21 deletions(-)

diff --git a/CubicBot.Telegram/Utils/ChatHelper.cs b/CubicBot.Telegram/Utils/ChatHelper.cs
index 9b2f5e0..7a8b381 100644
--- a/CubicBot.Telegram/Utils/ChatHelper.cs
+++ b/CubicBot.Telegram/Utils/ChatHelper.cs
@@ -318,52 +318,70 @@ public static string EscapeMarkdownV2CodeBlock(string code)
     /// Command is null if the text message is not a command to the bot.
     /// Argument can be null.
     /// </returns>
-    public static (string? command, string? argument) ParseMessageIntoCommandAndArgument(string? text, string botUsername)
+    public static (string? command, string? argument) ParseMessageIntoCommandAndArgument(ReadOnlySpan<char> text, string botUsername)
     {
         // Empty message
-        if (string.IsNullOrWhiteSpace(text))
+        if (text.IsEmpty)
             return (null, null);
 
         // Not a command
-        if (!text.StartsWith('/') || text.Length < 2)
+        if (text[0] != '/' || text.Length < 2)
             return (null, null);
 
         // Remove the leading '/'
         text = text[1..];
 
         // Split command and argument
-        var parsedText = text.Split(' ', 2);
-        string command;
-        string? argument = null;
-        switch (parsedText.Length)
+        ReadOnlySpan<char> command, argument;
+        var spacePos = text.IndexOf(' ');
+        if (spacePos == -1)
         {
-            case <= 0:
-                return (null, null);
-            case 2:
-                argument = parsedText[1];
-                goto default;
-            default:
-                command = parsedText[0];
-                break;
+            command = text;
+            argument = ReadOnlySpan<char>.Empty;
+        }
+        else if (spacePos == text.Length - 1)
+        {
+            command = text[..spacePos];
+            argument = ReadOnlySpan<char>.Empty;
+        }
+        else
+        {
+            command = text[..spacePos];
+            argument = text[(spacePos + 1)..];
         }
 
         // Verify and remove trailing '@bot' from command
         var atSignIndex = command.IndexOf('@');
         if (atSignIndex != -1)
         {
-            var atUsername = command[atSignIndex..];
-            if (atUsername != $"@{botUsername}")
-                return (null, null);
+            if (atSignIndex != command.Length - 1)
+            {
+                var atUsername = command[(atSignIndex + 1)..];
+                if (!atUsername.SequenceEqual(botUsername))
+                {
+                    return (null, null);
+                }
+            }
 
             command = command[..atSignIndex];
         }
 
         // Trim leading and trailing spaces from argument
-        if (argument is not null)
+        argument = argument.Trim();
+
+        // Convert back to string
+        string? commandString = null;
+        string? argumentString = null;
+        if (!command.IsEmpty)
         {
-            argument = argument.Trim();
+            commandString = command.ToString();
+
+            if (!argument.IsEmpty)
+            {
+                argumentString = argument.ToString();
+            }
         }
 
-        return (command, argument);
+        return (commandString, argumentString);
     }
 }