Fix bug for Undo command to mark and unmark tasks

Author: zhenglong1603

src/main/java/zbot/Parser.java

@@ -61,7 +61,8 @@ public class CommandFactory {
         public static Command getCommand(String input, TaskList taskList) throws Exception {
             String[] parts = input.split(" ", 2);
             final String supportedCommands =
-                    "- list\n- mark\n- unmark\n- find\n- delete\n- todo\n- deadline\n- event\n- undo\n- bye";
+                    "- list\n- mark\n- unmark\n- find\n- delete\n- todo\n- deadline\n- event\n- undo\n- bye\n\n"
+                    + "Date inputs are in the format of yyyy-MM-dd";
             switch (parts[0]) {
             case "list":
                 if (parts.length != 1) {

src/main/java/zbot/gui/MainWindow.java

@@ -25,9 +25,17 @@ public class MainWindow extends AnchorPane {
     private Image dukeImage = new
             Image(this.getClass().getResourceAsStream("/images/Cat.png"));
 
+    /**
+     * Initializes the Zbot GUI by setting up the dialog container and displaying an introductory message.
+     * This method is called during the initialization of the main window.
+     * It binds the scroll pane's vertical value property to the height of the dialog container
+     * and adds a welcome message from Zbot to the dialog container.
+     */
     @FXML
     public void initializeZbot() {
         scrollPane.vvalueProperty().bind(dialogContainer.heightProperty());
+        dialogContainer.getChildren().add(DialogBox.getZbotDialog(
+                "Hello! I'm ZoZo! How can I assist you today?", dukeImage));
     }
 
     /** Injects the Zbot instance */

src/main/java/zbot/tasks/DeadlineTask.java

@@ -43,6 +43,23 @@ public String getDeadline() {
         return this.deadline.format(inputFormatter);
     }
 
+    /**
+     * Creates a copy of the current task.
+     * This method is intended to return a new instance of the task with the same description and state.
+     *
+     * @return A new {@link Task} object with the same description and deadline as the current task.
+     */
+    @Override
+    public Task copy() {
+        DeadlineTask taskCopy = new DeadlineTask(this.getDescription(), this.getDeadline());
+        if (this.getDoneStatus()) {
+            taskCopy.markDone();
+        } else {
+            taskCopy.markUndone();
+        }
+        return taskCopy;
+    }
+
     /**
      * Returns a string representation of the {@code DeadlineTask}.
      * The string includes the task's description, completion status, and deadline.

src/main/java/zbot/tasks/EventTask.java

@@ -68,6 +68,23 @@ public String toDateString() {
         return this.toDate.format(outputFormatter);
     }
 
+    /**
+     * Creates a copy of the current task.
+     * This method is intended to return a new instance of the task with the same description and state.
+     *
+     * @return A new {@link Task} object with the same description and dates as the current task.
+     */
+    @Override
+    public Task copy() {
+        EventTask taskCopy = new EventTask(this.getDescription(), this.getFromDate(), this.getToDate());
+        if (this.getDoneStatus()) {
+            taskCopy.markDone();
+        } else {
+            taskCopy.markUndone();
+        }
+        return taskCopy;
+    }
+
     /**
      * Returns a string representation of the {@code EventTask}.
      * The string includes the task's description, completion status, and the event's date range.

src/main/java/zbot/tasks/Task.java

@@ -19,6 +19,15 @@ public Task(String description) {
         this.isDone = false;
     }
 
+    /**
+     * Creates a copy of the current task.
+     * This method is intended to be overridden by subclasses of {@link Task}.
+     * It should return a new instance of the task with the same description and relevant state.
+     *
+     * @return A new {@link Task} object with the same description and relevant state as the current task.
+     */
+    public abstract Task copy();
+
     /**
      * Marks the task as done.
      */

src/main/java/zbot/tasks/TaskList.java

@@ -160,7 +160,11 @@ public boolean restore() {
      *
      */
     private void saveStateForUndo() {
-        undoHistory.push(new ArrayList<>(taskList));
+        ArrayList<Task> taskListCopy = new ArrayList<>();
+        for (Task task : taskList) {
+            taskListCopy.add(task.copy());
+        }
+        undoHistory.push(taskListCopy);
     }
 
     /**

src/main/java/zbot/tasks/ToDoTask.java

@@ -15,6 +15,23 @@ public ToDoTask(String description) {
         super(description);
     }
 
+    /**
+     * Creates a copy of the current task.
+     * This method is intended to return a new instance of the task with the same description and state.
+     *
+     * @return A new {@link Task} object with the same description as the current task.
+     */
+    @Override
+    public Task copy() {
+        ToDoTask taskCopy = new ToDoTask(this.getDescription());
+        if (this.getDoneStatus()) {
+            taskCopy.markDone();
+        } else {
+            taskCopy.markUndone();
+        }
+        return taskCopy;
+    }
+
     /**
      * Returns a string representation of the to-do task.
      * The format is "[T][status] description".