From 81bc861085895216f48d43c42fc7c7dcd05ee1d1 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Sat, 8 May 2021 16:53:08 +0200
Subject: [PATCH] LibGUI: Implement merging of TextDocument's RemoveTextCommand

When deleting text by pressing backspace, the commands will be merged
into a single RemoveTextCommand.
---
 Userland/Libraries/LibGUI/TextDocument.cpp | 18 ++++++++++++++++++
 Userland/Libraries/LibGUI/TextDocument.h   |  1 +
 2 files changed, 19 insertions(+)

diff --git a/Userland/Libraries/LibGUI/TextDocument.cpp b/Userland/Libraries/LibGUI/TextDocument.cpp
index 78a23a30b0..bca690e3df 100644
--- a/Userland/Libraries/LibGUI/TextDocument.cpp
+++ b/Userland/Libraries/LibGUI/TextDocument.cpp
@@ -802,6 +802,24 @@ RemoveTextCommand::RemoveTextCommand(TextDocument& document, const String& text,
 {
 }
 
+bool RemoveTextCommand::merge_with(GUI::Command const& other)
+{
+    if (!is<RemoveTextCommand>(other))
+        return false;
+    auto& typed_other = static_cast<RemoveTextCommand const&>(other);
+    if (m_range.start() == typed_other.m_range.end()) {
+        // Merge backspaces
+        StringBuilder builder(m_text.length() + typed_other.m_text.length());
+        builder.append(typed_other.m_text);
+        builder.append(m_text);
+        m_text = builder.to_string();
+        m_range.set_start(typed_other.m_range.start());
+        return true;
+    }
+    // FIXME: Merge forward-deletes
+    return false;
+}
+
 void RemoveTextCommand::redo()
 {
     m_document.remove(m_range);
diff --git a/Userland/Libraries/LibGUI/TextDocument.h b/Userland/Libraries/LibGUI/TextDocument.h
index f3a4c9a0cf..1d0319f077 100644
--- a/Userland/Libraries/LibGUI/TextDocument.h
+++ b/Userland/Libraries/LibGUI/TextDocument.h
@@ -221,6 +221,7 @@ public:
     virtual void undo() override;
     virtual void redo() override;
     const TextRange& range() const { return m_range; }
+    virtual bool merge_with(GUI::Command const&) override;
 
 private:
     String m_text;