add Buffer::apply_change_{operation,unit}() for undo/redo

src/core/Buffer.cc

@@ -364,3 +364,25 @@ void Buffer::save_current_operation()
         m_current_change_operation_index = new_change_operation_index;
     }
 }
+
+void Buffer::apply_change_operation(const ChangeOperation & change_operation, bool forward)
+{
+    for (auto change_unit : change_operation.changes)
+    {
+        apply_change_unit(change_unit, forward);
+    }
+}
+
+void Buffer::apply_change_unit(const ChangeUnit & change_unit, bool forward)
+{
+    if (forward == change_unit.insert)
+    {
+        insert_data(change_unit.buffer_position,
+                m_change_buffer->address(change_unit.change_buffer_offset),
+                change_unit.length);
+    }
+    else
+    {
+        erase_data(change_unit.buffer_position, change_unit.length);
+    }
+}

src/core/Buffer.h

@@ -165,6 +165,8 @@ protected:
     void erase_data(size_t offset, size_t length);
     size_t lines_in_data(size_t offset, size_t length);
     void post_warp_cursors();
+    void apply_change_operation(const ChangeOperation & change_operation, bool forward);
+    void apply_change_unit(const ChangeUnit & change_unit, bool forward);
 };
 
 #endif