refactor: extract chat-input pure helpers for unit-testable submit + history math

ChatBox.SendMessage reads bytes from ValidateMessage so Encoding.UTF8.GetBytes
runs once per send. ValidateMessage takes an injectable sanitiser so xUnit can
exercise the length-equality gate without ClientStructs game memory.

CompactInputSubmitter and CompactInputHistoryNavigator lift the deterministic
parts of ChatInputBar's pop-out submit and history-up/down callback into POCO
helpers under HellionChat/_Helpers/. The ImGui buffer splice
(DeleteChars/InsertChars) stays at the call site because it needs the live
callback data.

Behavior is identical to the previous inline implementation; tests in the
local Build Suite repo pin the contracts.

HellionChat/GameFunctions/ChatBox.cs

@@ -16,6 +16,18 @@ public unsafe class ChatBox
     }
 
     public static void SendMessage(string message)
+    {
+        var bytes = ValidateMessage(message);
+        SendMessageUnsafe(bytes);
+    }
+
+    // Validation split out so the deterministic checks (UTF-8 length, sanitise
+    // round-trip) can run in xUnit without ClientStructs game memory. The
+    // sanitiser is injectable so tests can pin throw behaviour without invoking
+    // Utf8String->SanitizeString, which only resolves in-process. Returns the
+    // already-encoded bytes so SendMessage doesn't pay GetBytes twice.
+    // TEST-MIRROR: ../../../Hellion Build test/GameFunctions/ChatBoxTests.cs
+    internal static byte[] ValidateMessage(string message, Func<string, string>? sanitiserOverride = null)
     {
         var bytes = Encoding.UTF8.GetBytes(message);
         if (bytes.Length == 0)
@@ -24,10 +36,11 @@ public unsafe class ChatBox
         if (bytes.Length > 500)
             throw new ArgumentException(Language.ChatBox_Error_Too_Long, nameof(message));
 
-        if (message.Length != SanitiseText(message).Length)
+        var sanitiser = sanitiserOverride ?? SanitiseText;
+        if (message.Length != sanitiser(message).Length)
             throw new ArgumentException(Language.ChatBox_Error_Invalid, nameof(message));
 
-        SendMessageUnsafe(bytes);
+        return bytes;
     }
 
     private static string SanitiseText(string text)

HellionChat/Ui/ChatInputBar.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Numerics;
+using HellionChat._Helpers;
 using HellionChat.Code;
 using HellionChat.Util;
 using Dalamud.Bindings.ImGui;
@@ -89,60 +90,42 @@ public sealed class ChatInputBar
         }
     }
 
-    private void SubmitCompact(Tab tab)
+    // TEST-MIRROR: ../_Helpers/CompactInputSubmitter.cs
-    {
+    private void SubmitCompact(Tab tab) =>
-        if (string.IsNullOrWhiteSpace(_state.Buffer))
+        CompactInputSubmitter.TrySubmit(_state, tab, _host.SendChatBoxFromExternal);
-            return;
 
-        var text = _state.Buffer;
+    // History-navigation callback for the compact input. Cursor math is
-        _state.Buffer = string.Empty;
+    // delegated to CompactInputHistoryNavigator; only the ImGui buffer
-        _state.HistoryCursor = -1;
+    // splice stays here because it needs the live callback data.
-        _host.SendChatBoxFromExternal(tab, text);
+    // TEST-MIRROR: ../_Helpers/CompactInputHistoryNavigator.cs
-    }
-
-    // History-navigation callback for the compact input. Mirrors the main
-    // window's logic but operates on _state.HistoryCursor and the shared
-    // InputHistoryService. Index semantics match v0.5.x InputBacklog:
-    // 0 = oldest, Count-1 = newest.
     private int CompactCallback(scoped ref ImGuiInputTextCallbackData data)
     {
         if (data.EventFlag != ImGuiInputTextFlags.CallbackHistory)
             return 0;
 
-        var prev = _state.HistoryCursor;
+        var direction = data.EventKey switch
-        switch (data.EventKey)
         {
-            case ImGuiKey.UpArrow:
+            ImGuiKey.UpArrow => CompactInputHistoryNavigator.Direction.Up,
-                switch (_state.HistoryCursor)
+            ImGuiKey.DownArrow => CompactInputHistoryNavigator.Direction.Down,
-                {
+            _ => (CompactInputHistoryNavigator.Direction?)null,
-                    case -1:
+        };
-                        var offset = 0;
+        if (direction is null)
-                        if (!string.IsNullOrWhiteSpace(_state.Buffer))
-                        {
-                            InputHistoryService.Push(_state.Buffer);
-                            offset = 1;
-                        }
-                        _state.HistoryCursor = InputHistoryService.Count - 1 - offset;
-                        break;
-                    case > 0:
-                        _state.HistoryCursor--;
-                        break;
-                }
-                break;
-            case ImGuiKey.DownArrow:
-                if (_state.HistoryCursor != -1)
-                    if (++_state.HistoryCursor >= InputHistoryService.Count)
-                        _state.HistoryCursor = -1;
-                break;
-        }
-
-        if (prev == _state.HistoryCursor)
             return 0;
 
-        var historyStr = InputHistoryService.GetByCursor(_state.HistoryCursor) ?? string.Empty;
+        var (cursor, replacement) = CompactInputHistoryNavigator.Navigate(
-        data.DeleteChars(0, data.BufTextLen);
+            direction.Value,
-        data.InsertChars(0, historyStr);
+            _state.HistoryCursor,
+            _state.Buffer,
+            () => InputHistoryService.Count,
+            InputHistoryService.Push,
+            InputHistoryService.GetByCursor);
 
+        _state.HistoryCursor = cursor;
+        if (replacement is null)
+            return 0;
+
+        data.DeleteChars(0, data.BufTextLen);
+        data.InsertChars(0, replacement);
         return 0;
     }
 

HellionChat/_Helpers/CompactInputHistoryNavigator.cs

@@ -0,0 +1,75 @@
+using System;
+
+namespace HellionChat._Helpers;
+
+// Pure-helper mirror of the compact pop-out history-navigation cursor
+// math. The original CompactCallback was tangled with ImGuiInputTextCallbackData
+// (DeleteChars/InsertChars), which can't be exercised in xUnit. The
+// ImGui buffer mutation stays at the call site; only the deterministic
+// cursor-and-replacement decision lives here.
+//
+// Index semantics match InputHistoryService:
+//   index 0          = oldest entry
+//   index Count - 1  = newest entry
+//   cursor == -1     = "not browsing history"
+//
+// TEST-MIRROR: ../../../Hellion Build test/Ui/CompactInputHistoryNavigatorTests.cs
+public static class CompactInputHistoryNavigator
+{
+    public enum Direction { Up, Down }
+
+    // replacement == null means: caller must NOT touch the buffer. This
+    // distinguishes "cursor unchanged, leave the user's typing alone"
+    // from "cursor moved to an empty slot, clear the buffer".
+    public static (int cursor, string? replacement) Navigate(
+        Direction direction,
+        int currentCursor,
+        string currentBuffer,
+        Func<int> getCount,
+        Action<string> push,
+        Func<int, string?> getByCursor)
+    {
+        ArgumentNullException.ThrowIfNull(getCount);
+        ArgumentNullException.ThrowIfNull(push);
+        ArgumentNullException.ThrowIfNull(getByCursor);
+
+        var prev = currentCursor;
+        var next = currentCursor;
+
+        switch (direction)
+        {
+            case Direction.Up:
+                if (currentCursor == -1)
+                {
+                    // First Up press from a fresh buffer: stash whatever
+                    // the user typed so they can recover it after browsing.
+                    var offset = 0;
+                    if (!string.IsNullOrWhiteSpace(currentBuffer))
+                    {
+                        push(currentBuffer);
+                        offset = 1;
+                    }
+                    next = getCount() - 1 - offset;
+                }
+                else if (currentCursor > 0)
+                {
+                    next--;
+                }
+                break;
+            case Direction.Down:
+                if (currentCursor != -1)
+                {
+                    next++;
+                    if (next >= getCount())
+                        next = -1;
+                }
+                break;
+        }
+
+        if (prev == next)
+            return (next, null);
+
+        var replacement = getByCursor(next) ?? string.Empty;
+        return (next, replacement);
+    }
+}

HellionChat/_Helpers/CompactInputSubmitter.cs

@@ -0,0 +1,29 @@
+using System;
+using HellionChat.Ui;
+
+namespace HellionChat._Helpers;
+
+// Pure-helper mirror of the compact pop-out submit flow. ChatInputBar's
+// SubmitCompact used to inline this against a sealed ChatLogWindow, which
+// blocks Moq-based isolation. Lifting the deterministic part into a POCO
+// keeps the production call site a one-liner while letting xUnit assert
+// the buffer/cursor reset and the sender contract directly.
+// TEST-MIRROR: ../../../Hellion Build test/Ui/CompactInputSubmitterTests.cs
+public static class CompactInputSubmitter
+{
+    public static bool TrySubmit(InputState state, Tab tab, Action<Tab, string> sender)
+    {
+        ArgumentNullException.ThrowIfNull(state);
+        ArgumentNullException.ThrowIfNull(tab);
+        ArgumentNullException.ThrowIfNull(sender);
+
+        if (string.IsNullOrWhiteSpace(state.Buffer))
+            return false;
+
+        var text = state.Buffer;
+        state.Buffer = string.Empty;
+        state.HistoryCursor = -1;
+        sender(tab, text);
+        return true;
+    }
+}