Bug fix: DoneTaskCommand undo/redo

src/main/java/seedu/address/logic/commands/task/DoneTaskCommand.java

@@ -35,41 +35,45 @@ public DoneTaskCommand(Index index) {
     @Override
     public CommandResult execute(Model model) throws CommandException {
         requireNonNull(model);
-        List<Task> taskList = model.getFilteredTaskList();
+        super.canExecute();
+        boolean isDone = changeTaskIsDone(model);
+        displayedString = isDone
+                ? MESSAGE_SUCCESS
+                : MESSAGE_UNDONE;
+
+        return new CommandResult(String.format(displayedString, completedTask));
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        return this == o || (o instanceof DoneTaskCommand && index.equals(((DoneTaskCommand) o).index));
+    }
+
+    @Override
+    public CommandResult undo(Model model) throws CommandException {
+        requireNonNull(model);
+        super.canUndo();
+        changeTaskIsDone(model);
+        return new CommandResult(String.format(displayedString, this.completedTask));
+    }
 
+    private boolean changeTaskIsDone(Model model) throws CommandException {
+        List<Task> taskList = model.getFilteredTaskList();
         if (index.getZeroBased() >= taskList.size()) {
             throw new CommandException(Messages.MESSAGE_INVALID_TASK_DISPLAYED_INDEX);
         }
-        super.canExecute();
 
         Task task = taskList.get(index.getZeroBased());
-        boolean isDone = task.isDone();
         Task completedTask = new Task(task.getTitle(),
                 task.getDescription().orElse(null),
                 task.getTimestamp().orElse(null),
                 task.getTags(),
                 !task.isDone(),
                 task.getContacts());
+
         this.completedTask = completedTask;
         model.setTask(task, completedTask);
 
-        displayedString = isDone
-                ? MESSAGE_UNDONE
-                : MESSAGE_SUCCESS;
-
-        return new CommandResult(String.format(displayedString, completedTask));
-    }
-
-    @Override
-    public boolean equals(Object o) {
-        return this == o || (o instanceof DoneTaskCommand && index.equals(((DoneTaskCommand) o).index));
-    }
-
-    @Override
-    public CommandResult undo(Model model) throws CommandException {
-        super.canUndo();
-        this.execute(model);
-        return new CommandResult(String.format(MESSAGE_SUCCESS,
-                this.completedTask));
+        return completedTask.isDone();
     }
 }