Formatting: Trim base indentation off code block content

Author: vedxyz

TabletBot.Discord/Formatting.cs

@@ -1,5 +1,7 @@
 using System;
+using System.Linq;
 using System.Text;
+using System.Text.RegularExpressions;
 using Discord;
 
 namespace TabletBot.Discord
@@ -20,12 +22,46 @@ public static class Formatting
         public static string CodeBlock(string text, string? lang = null) =>
             $"{CODE_BLOCK}{lang}{Environment.NewLine}{text}{Environment.NewLine}{CODE_BLOCK}";
 
-        public static void AppendCodeBlock(this StringBuilder stringBuilder, string[] lines, string? lang = null)
+        public static void AppendCodeBlock(this StringBuilder stringBuilder, string text, string? lang = null)
         {
             stringBuilder.AppendLine(CODE_BLOCK + lang);
-            foreach (var line in lines)
-                stringBuilder.AppendLine(line);
+            stringBuilder.Append(TrimBaseIndentation(text));
             stringBuilder.AppendLine(CODE_BLOCK);
         }
+
+        public static void AppendCodeBlock(this StringBuilder stringBuilder, string[] lines, string? lang = null)
+            => AppendCodeBlock(stringBuilder, String.Join(Environment.NewLine, lines), lang);
+
+        public static string TrimBaseIndentation(string text)
+        {
+            var endsTrimmedContent = TrimStartRegex.Replace(text.TrimEnd(), "$1", 1);
+            var lines = endsTrimmedContent.Split(Environment.NewLine);
+            var baseIndentationLength = CountIndentation(lines[0]);
+
+            for (int i = 0; i != lines.Length; i++)
+            {
+                var line = lines[i];
+
+                var indentationLength = CountIndentation(line);
+                if (indentationLength < baseIndentationLength)
+                {
+                    if (indentationLength == line.Length)
+                    {
+                        lines[i] = "";
+                        continue;
+                    }
+
+                    return endsTrimmedContent;
+                }
+
+                lines[i] = line.Substring(Math.Min(baseIndentationLength, line.Length)).TrimEnd();
+            }
+
+            return String.Join(Environment.NewLine, lines);
+        }
+
+        private static readonly Regex TrimStartRegex = new Regex("^\\s*\n(\\s*)(?=\\S*)", RegexOptions.Compiled);
+
+        public static int CountIndentation(string line) => line.TakeWhile(Char.IsWhiteSpace).Count();
     }
 }