package seedu.address.model;

import java.util.Set;

import seedu.address.commons.core.UnmodifiableObservableList;
import seedu.address.model.task.ReadOnlyTask;
import seedu.address.model.task.Task;
import seedu.address.model.task.UniqueTaskList;
import seedu.address.model.task.UniqueTaskList.DuplicateTaskException;

/**
 * The API of the Model component.
 */
public interface Model {
    /** Clears existing backing model and replaces with the provided new data. */
    void resetData(ReadOnlyAddressBook newData);

    /** Returns the AddressBook */
    ReadOnlyAddressBook getAddressBook();

    /** Deletes the given task. */
    void deleteTask(ReadOnlyTask target) throws UniqueTaskList.TaskNotFoundException;

    /** Adds the given task */
    void addTask(Task task) throws UniqueTaskList.DuplicateTaskException;

    /**
     * Updates the task located at {@code filteredTaskListIndex} with {@code editedTask}.
     *
     * @throws DuplicateTaskException if updating the task's details causes the task to be equivalent to
     *      another existing task in the list.
     * @throws IndexOutOfBoundsException if {@code filteredTaskListIndex} < 0 or >= the size of the filtered list.
     */
    void updateTask(int filteredTaskListIndex, ReadOnlyTask editedTask)
            throws UniqueTaskList.DuplicateTaskException;

    /** Returns the filtered task list as an {@code UnmodifiableObservableList<ReadOnlyTask>} */
    UnmodifiableObservableList<ReadOnlyTask> getFilteredTaskList();

    /** Updates the filter of the filtered person list to show all persons */
    void updateFilteredListToShowAll();

    /** Updates the filter of the filtered person list to filter by the given keywords*/
    void updateFilteredTaskList(Set<String> keywords);

}

@@ -44,16 +44,40 @@
 til.Set;
+%0Aimport java.util.Stack;
 %0A%0Aimport
@@ -404,20 +404,196 @@
 Model %7B%0A
-    
+%09%0A%09Stack%3CString%3E getUndoStack();%09%0A%09Stack%3CReadOnlyTask%3E getDeletedStackOfTasksAdd();%0A%09Stack%3CReadOnlyTask%3E getDeletedStackOfTasks();%0A%09Stack%3CInteger%3E getDeletedStackOfTasksIndex();%0A%0A%09
 /** Clea
@@ -829,20 +829,19 @@
  */%0A    
-void
+int
  deleteT
@@ -1956,12 +1956,17 @@
 ywords);
+%0A    
 %0A%0A%7D%0A

Update Model.java