Add UndoSystem implementation and refactor UndoNode for simplicity.

UndoNode.h

@@ -2,81 +2,25 @@
 #define KTE_UNDONODE_H
 
 #include <cstddef>
-#include <cstddef>
+#include <cstdint>
+#include <string>
 
 
-enum UndoKind {
-	UNDO_INSERT,
-	UNDO_DELETE,
+enum class UndoType : uint8_t {
+	Insert,
+	Delete,
+	Paste,
+	Newline,
+	DeleteRow,
 };
 
-
-class UndoNode {
-public:
-	explicit UndoNode(const UndoKind kind, const size_t row, const size_t col)
-		: kind_(kind), row_(row), col_(col) {}
-
-
-	~UndoNode() = default;
-
-
-	[[nodiscard]] UndoKind Kind() const
-	{
-		return kind_;
-	}
-
-
-	[[nodiscard]] UndoNode *Next() const
-	{
-		return next_;
-	}
-
-
-	void Next(UndoNode *next)
-	{
-		next_ = next;
-	}
-
-
-	[[nodiscard]] UndoNode *Child() const
-	{
-		return child_;
-	}
-
-
-	void Child(UndoNode *child)
-	{
-		child_ = child;
-	}
-
-
-	void SetRowCol(const std::size_t row, const std::size_t col)
-	{
-		this->row_ = row;
-		this->col_ = col;
-	}
-
-
-	[[nodiscard]] std::size_t Row() const
-	{
-		return row_;
-	}
-
-
-	[[nodiscard]] std::size_t Col() const
-	{
-		return col_;
-	}
-
-
-	void DeleteNext() const;
-
-private:
-	[[maybe_unused]] UndoKind kind_;
-	[[maybe_unused]] UndoNode *next_{nullptr};
-	[[maybe_unused]] UndoNode *child_{nullptr};
-
-	[[maybe_unused]] std::size_t row_{}, col_{};
+struct UndoNode {
+	UndoType type{};
+	int row{};
+	int col{};
+	std::string text;
+	UndoNode *child = nullptr; // next in current timeline
+	UndoNode *next  = nullptr; // redo branch
 };