Implement basic update task feature to fulfill C-Update extension

User can now use update [task number] taskName [tokens] field value to
specify the fields within the task that they want to update.

For example: update 4 Hello /by 2024-05-11 changes the 4-th task's name
in the task list to Hello. If the task is Deadline, then change its
due date to May 11 2024, else a warning message will be prompted by
gopher

src/main/java/gopher/Gopher.java

@@ -133,6 +133,26 @@ public static String executeCreateTaskCommand(String userInput)
         }
     }
 
+    /**
+     * Executes the relevant actions when user input update task command.
+     *
+     * @param userInput command input by the user
+     * @return response by gopher after successful action
+     */
+    public static String executeUpdateTaskCommand(String userInput) {
+        try {
+            String[] tokens = userInput.split(" ");
+            if (tokens.length < 2) {
+                return "Update command cannot be empty";
+            }
+            int taskNumber = Integer.parseInt(tokens[1]);
+            taskList.update(taskNumber, tokens);
+            return "Hi I have updated this task for you already!";
+        } catch (DateTimeParseException e) {
+            return UI.getInvalidDateWarning();
+        }
+    }
+
     /**
      * Start the main event loop.
      */
@@ -152,6 +172,8 @@ public static String getResponse(String userInput)
             return executeFindTaskCommand(userInput);
         } else if (Parser.isValidTaskType(userInput.split(" ")[0])) {
             return executeCreateTaskCommand(userInput);
+        } else if (userInput.toLowerCase().startsWith("update")) {
+            return executeUpdateTaskCommand(userInput);
         } else {
             throw new UnknownCommandException(userInput);
         }

src/main/java/gopher/task/Deadline.java

@@ -22,6 +22,42 @@ public Deadline(String name, String dueDate) {
         this.dueDate = Parser.parseDateString(dueDate);
     }
 
+    @Override
+    public void update(String[] tokens) {
+        // Determine the position of /by token in update command tokens
+        int byTokenIndex = -1;
+        for (int i = 2; i < tokens.length; i++) {
+            if (tokens[i].equalsIgnoreCase("/by")) {
+                byTokenIndex = i;
+            }
+        }
+
+        // Update task name based on the position of /by token
+        StringBuilder taskName = new StringBuilder();
+        int taskNameIndexLimit = byTokenIndex != -1 ? byTokenIndex : tokens.length;
+        for (int i = 2; i < taskNameIndexLimit; i++) {
+            taskName.append(tokens[i]);
+            if (i < taskNameIndexLimit - 1) {
+                taskName.append(" ");
+            }
+        }
+        if (!taskName.isEmpty()) {
+            this.name = taskName.toString();
+        }
+
+        // Update due date if /by token is found in command tokens
+        if (byTokenIndex != -1) {
+            StringBuilder dueDateString = new StringBuilder();
+            for (int i = byTokenIndex + 1; i < tokens.length; i++) {
+                dueDateString.append(tokens[i]);
+                if (i < tokens.length - 1) {
+                    dueDateString.append(" ");
+                }
+            }
+            this.dueDate = Parser.parseDateString(dueDateString.toString());
+        }
+    }
+
     @Override
     public String getSaveMessage() {
         return String.format("D | %s | %s | %s",

src/main/java/gopher/task/Event.java

@@ -25,6 +25,65 @@ public Event(String name, String startDate, String endDate) {
         this.endDate = Parser.parseDateString(endDate);
     }
 
+    @Override
+    public void update(String[] tokens) {
+        // Determine the positions of from & to tokens if they exist in the command tokens
+        int fromTokenIndex = -1;
+        int toTokenIndex = -1;
+        for (int i = 2; i < tokens.length; i++) {
+            if (tokens[i].equalsIgnoreCase("/from")) {
+                fromTokenIndex = i;
+            }
+            if (tokens[i].equalsIgnoreCase("/to")) {
+                toTokenIndex = i;
+            }
+        }
+
+        // Update task name based on the position of /from and /to token
+        StringBuilder taskName = new StringBuilder();
+        int taskNameIndexLimit = fromTokenIndex != -1
+                ? fromTokenIndex
+                : toTokenIndex != -1
+                ? toTokenIndex
+                : tokens.length;
+        for (int i = 2; i < taskNameIndexLimit; i++) {
+            taskName.append(tokens[i]);
+            if (i < taskNameIndexLimit - 1) {
+                taskName.append(" ");
+            }
+        }
+        if (!taskName.isEmpty()) {
+            this.name = taskName.toString();
+        }
+
+        // Update start date if /from token exists in the command tokens
+        if (fromTokenIndex != -1) {
+            StringBuilder startDateString = new StringBuilder();
+            int startDateIndexLimit = toTokenIndex != -1
+                    ? toTokenIndex
+                    : tokens.length;
+            for (int i = taskNameIndexLimit + 1; i < startDateIndexLimit; i++) {
+                startDateString.append(tokens[i]);
+                if (i < startDateIndexLimit - 1) {
+                    startDateString.append(" ");
+                }
+            }
+            this.startDate = Parser.parseDateString(startDateString.toString());
+        }
+
+        // Update end date if /to token exists in the command tokens
+        if (toTokenIndex != -1) {
+            StringBuilder endDateString = new StringBuilder();
+            for (int i = toTokenIndex + 1; i < tokens.length; i++) {
+                endDateString.append(tokens[i]);
+                if (i < tokens.length - 1) {
+                    endDateString.append(" ");
+                }
+            }
+            this.endDate = Parser.parseDateString(endDateString.toString());
+        }
+    }
+
     @Override
     public String getSaveMessage() {
         return String.format("E | %s | %s | %s | %s",

src/main/java/gopher/task/Task.java

@@ -42,6 +42,11 @@ public static Task of(String command) throws UnknownCommandException,
         return Parser.parseCreateTaskCommand(command);
     }
 
+    /**
+     * Updates the relevant detail in the specified task.
+     */
+    public abstract void update(String[] tokens);
+
     /**
      * Gets the save file message representation of this task.
      *

src/main/java/gopher/task/TaskList.java

@@ -39,6 +39,17 @@ public void add(Task task) {
         TaskManager.saveTasks(tasks);
     }
 
+    /**
+     * Updates the task with the given task number with the relevant information.
+     *
+     * @param taskNumber number of the task to be updated
+     * @param tokens tokens from the update command
+     */
+    public void update(int taskNumber, String[] tokens) {
+        this.getTask(taskNumber).update(tokens);
+        TaskManager.saveTasks(tasks);
+    }
+
     /**
      * Deletes the task with the given task number from the task list.
      * Triggers the TaskManager to update the local saved tasks.

src/main/java/gopher/task/ToDo.java

@@ -14,6 +14,18 @@ public ToDo(String name) {
         super(name);
     }
 
+    @Override
+    public void update(String[] tokens) {
+        StringBuilder taskName = new StringBuilder();
+        for (int i = 2; i < tokens.length; i++) {
+            taskName.append(tokens[i]);
+            if (i < tokens.length - 1) {
+                taskName.append(" ");
+            }
+        }
+        this.name = taskName.toString();
+    }
+
     @Override
     public String getSaveMessage() {
         return String.format("T | %s | %s",