Extract XCUI text editing core and window seam headers

tests/Core/UI/CMakeLists.txt

@@ -6,6 +6,7 @@ set(UI_TEST_SOURCES
     test_ui_core.cpp
     test_layout_engine.cpp
     test_ui_runtime.cpp
+    test_ui_text_editing.cpp
 )
 
 add_executable(core_ui_tests ${UI_TEST_SOURCES})

tests/Core/UI/test_ui_text_editing.cpp

@@ -0,0 +1,59 @@
+#include <gtest/gtest.h>
+
+#include <XCEngine/UI/Text/UITextEditing.h>
+
+#include <string>
+
+namespace {
+
+namespace UIText = XCEngine::UI::Text;
+
+TEST(UITextEditingTest, Utf8CountingAndCaretOffsetsRespectCodepointBoundaries) {
+    const std::string text = std::string("A") + "\xE4\xBD\xA0" + "B";
+
+    EXPECT_EQ(UIText::CountUtf8Codepoints(text), 3u);
+    EXPECT_EQ(UIText::AdvanceUtf8Offset(text, 0u), 1u);
+    EXPECT_EQ(UIText::AdvanceUtf8Offset(text, 1u), 4u);
+    EXPECT_EQ(UIText::AdvanceUtf8Offset(text, 4u), 5u);
+    EXPECT_EQ(UIText::RetreatUtf8Offset(text, text.size()), 4u);
+    EXPECT_EQ(UIText::RetreatUtf8Offset(text, 4u), 1u);
+    EXPECT_EQ(UIText::RetreatUtf8Offset(text, 1u), 0u);
+}
+
+TEST(UITextEditingTest, AppendUtf8CodepointEncodesCharactersAndSkipsInvalidSurrogates) {
+    std::string text = {};
+    UIText::AppendUtf8Codepoint(text, 'A');
+    UIText::AppendUtf8Codepoint(text, 0x4F60u);
+    UIText::AppendUtf8Codepoint(text, 0x1F642u);
+    UIText::AppendUtf8Codepoint(text, 0xD800u);
+
+    EXPECT_EQ(text, std::string("A") + "\xE4\xBD\xA0" + "\xF0\x9F\x99\x82");
+    EXPECT_EQ(UIText::CountUtf8Codepoints(text), 3u);
+}
+
+TEST(UITextEditingTest, SplitLinesAndLineHelpersTrackMultilineRanges) {
+    const std::string text = "alpha\nbeta\n";
+
+    const auto lines = UIText::SplitLines(text);
+    ASSERT_EQ(lines.size(), 3u);
+    EXPECT_EQ(lines[0], "alpha");
+    EXPECT_EQ(lines[1], "beta");
+    EXPECT_EQ(lines[2], "");
+    EXPECT_EQ(UIText::CountTextLines(text), 3u);
+    EXPECT_EQ(UIText::CountUtf8CodepointsInRange(text, 6u, 10u), 4u);
+    EXPECT_EQ(UIText::FindLineStartOffset(text, 7u), 6u);
+    EXPECT_EQ(UIText::FindLineEndOffset(text, 7u), 10u);
+}
+
+TEST(UITextEditingTest, MoveCaretVerticallyPreservesUtf8ColumnWhenPossible) {
+    const std::string text = std::string("A") + "\xE4\xBD\xA0" + "Z\nBC\n";
+    const std::size_t secondColumnCaret = UIText::AdvanceUtf8Offset(text, 1u);
+
+    const std::size_t movedDown = UIText::MoveCaretVertically(text, secondColumnCaret, 1);
+    const std::size_t movedBackUp = UIText::MoveCaretVertically(text, movedDown, -1);
+
+    EXPECT_EQ(movedDown, 8u);
+    EXPECT_EQ(movedBackUp, secondColumnCaret);
+}
+
+} // namespace