services: add InputHistoryService for shared input history

ChatTwo/InputHistoryService.cs

@@ -0,0 +1,41 @@
+using System.Collections.Generic;
+
+namespace ChatTwo;
+
+// Hellion Chat — v0.6.0 shared input history. Replaces the embedded
+// ChatLogWindow.InputBacklog so that pop-out windows with their own
+// ChatInputBar can navigate the same Up/Down history as the main window.
+// Newest entry at index 0; consecutive duplicates are collapsed.
+public static class InputHistoryService
+{
+    private const int MaxSize = 30;
+    private static readonly List<string> _entries = new();
+
+    public static IReadOnlyList<string> Entries => _entries;
+
+    public static void Push(string entry)
+    {
+        if (string.IsNullOrWhiteSpace(entry))
+            return;
+
+        var trimmed = entry.Trim();
+
+        // Drop consecutive duplicates so spamming the same line does not
+        // pollute the history with repeats.
+        if (_entries.Count > 0 && _entries[0] == trimmed)
+            return;
+
+        _entries.Insert(0, trimmed);
+        if (_entries.Count > MaxSize)
+            _entries.RemoveAt(_entries.Count - 1);
+    }
+
+    public static string? GetByCursor(int cursor)
+    {
+        if (cursor < 0 || cursor >= _entries.Count)
+            return null;
+        return _entries[cursor];
+    }
+
+    public static int Count => _entries.Count;
+}