Refactor and simplify member list code

PluralKit.Core/Utils/StringUtils.cs

@@ -1,5 +1,7 @@
 using System;
+using System.Collections.Generic;
 using System.Security.Cryptography;
+using System.Text;
 using System.Text.RegularExpressions;
 
 namespace PluralKit.Core
@@ -56,5 +58,36 @@ namespace PluralKit.Core
             // so we remove 'em all :)
             return Regex.Replace(input, " *\n", "\n");
         }
+
+        public static IReadOnlyList<string> JoinPages(IEnumerable<string> input, int characterLimit) =>
+            JoinPages(input, _ => characterLimit);
+
+        public static IReadOnlyList<string> JoinPages(IEnumerable<string> input, Func<int, int> characterLimitByPage)
+        {
+            var output = new List<string>();
+
+            var buf = new StringBuilder();
+            foreach (var s in input)
+            {
+                var limit = characterLimitByPage.Invoke(output.Count);
+                
+                // Would adding this string put us over the limit?
+                // (note: don't roll over if the buffer's already empty; this means an individual section is above the character limit. todo: truncate, then?)
+                if (buf.Length > 0 && buf.Length + s.Length > limit)
+                {
+                    // If so, "roll over" (before adding the string to the buffer)
+                    output.Add(buf.ToString());
+                    buf.Clear();
+                }
+
+                buf.Append(s);
+            }
+            
+            // We most likely have something left over, so add that in too
+            if (buf.Length > 0)
+                output.Add(buf.ToString());
+
+            return output;
+        } 
     }
 }