This reduces repeated code.

This is done by adding an overloaded echo() method to maintain the
functionality of existing code.

For improved readablity

Update startParse() to first split by spaces to handle commands with
multiple words, like mark x or unmark x, where x is the index of the
command.

This is to prevent Duke class from getting too bloated.

This is to prevent bloating of Duke class

Also removed usage of `this` where relevant to maintain consistency.

This is to handle the printing of extra information for the delete
command.

Move printing of error message to CliParserService

Update method signature of relevant methods.

This allows object persistence for Task by making it serializable.

Update method signature of relevant methods.

This class handles the read/write to files for object persistence,
specifically taskList.

StorageService now throws DukeStorageException instead of DukeException
for more specificity and different erorr handling.

The added complexity is not worth it for the increase in performance,
because the assumption was that the taskList would contain at most 100
Tasks only.

Add Tasks List persistence ability to Duke.

deadline commands must have an end date as argument, prefixed with 'by',
while event commands must have a start date prefixed with 'from', end
date prefixed with 'to' as arguments.

Fix parseDateTimeString() wrongly parsing yyyy-mm-dd, or inputs
containing Date only, as invalid inputs.

Update Duke to parse date inputs.

This class is responsible for the printing of messages to the console
output, and uses OutputService to handle the formatting and indentation
of Strings.

Operations on the TaskList like add, delete, mark etc will be handled by
TaskList.

"today" and "tomorrow" both return the end of their respective days.
Display formatting is updated to display minutes too.

Abstract methods and responsibilities into separate classes for
separation of concern.

This is to provide a logical grouping for different classes and their
responsibilities, improving readability.

Abstracts logic of inputs into individual Commands subclasses.

Add Gradle support to Duke project.

This is to allow for a more straightforward unit testing of
CliParserService.

Move from parse() to parseCommandAndArguments(). This is to allow for
better unit testing as well

Add JUnit tests for CliParserService and TimeUtil, as these are critical
service/util classes.

Adds JavaDocs to classes and methods. This improves maintainability.

Implement checkstyle and fix checkstyle violations.

Refactor printTask in OutputService to formatTaskList for increased
flexibility.

find searches the taskList for taskNames containing the given keyword,
then prints the matching tasks.

Add find command which allows users to search for tasks based on a
keyword.

Fixes CheckStyle violations

This is in preparation to integrate JavaFX with Duke, preventing the
Duke class from becoming too bloated.

Refactor existing classes, mainly changing the return type of UiService
to return a String which is displayed in the GUI window.

Add a GUI to Duke.

TaskFactory is responsible for the creation of new Tasks, and in no
cases does it return a null task.
Since there should only be one way of adding a task to TaskList, by
calling TaskList::add, there should be no null tasks added to the
TaskList. Neither should there by any null task retrieved by any
exposed methods.

This is to better reflect immutability.