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src/core/CommandHistory.h

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+#pragma once
+
+#include <memory>
+#include <vector>
+#include <string>
+
+namespace UsdLayerManager {
+
+/// Pure-virtual interface for all reversible operations.
+class ICommand {
+public:
+    virtual ~ICommand() = default;
+    virtual void Execute() = 0;
+    virtual void Undo() = 0;
+    virtual std::string GetDescription() const = 0;
+};
+
+/// Application-level undo/redo stack.
+///
+/// Push(cmd) executes the command, pushes it onto the undo stack,
+/// and clears the redo stack.  Undo() pops from the undo stack, calls
+/// Undo() on the command, and pushes it onto the redo stack (and vice
+/// versa for Redo()).
+///
+/// Call Clear() whenever the USD stage is replaced so stale USD object
+/// references (UsdPrim, UsdAttribute, SdfLayerHandle) cannot be dereferenced.
+class CommandHistory {
+public:
+    CommandHistory()  = default;
+    ~CommandHistory() = default;
+
+    /// Execute cmd and push onto undo stack; clears redo stack.
+    void Push(std::unique_ptr<ICommand> cmd);
+
+    /// Undo the top command (no-op if stack is empty).
+    void Undo();
+
+    /// Redo the top undone command (no-op if stack is empty).
+    void Redo();
+
+    /// Clear both stacks (must be called on stage close/open).
+    void Clear();
+
+    bool CanUndo() const { return !m_undoStack.empty(); }
+    bool CanRedo() const { return !m_redoStack.empty(); }
+
+    /// Description of the command that Undo() would reverse, or empty string.
+    std::string GetUndoDescription() const;
+
+    /// Description of the command that Redo() would replay, or empty string.
+    std::string GetRedoDescription() const;
+
+private:
+    std::vector<std::unique_ptr<ICommand>> m_undoStack;
+    std::vector<std::unique_ptr<ICommand>> m_redoStack;
+};
+
+} // namespace UsdLayerManager