tp/docs/DeveloperGuide.md at master · tsammeow/tp

layout	page
title	Developer Guide

Table of Contents {:toc}

Acknowledgements

{list here sources of all reused/adapted ideas, code, documentation, and third-party libraries -- include links to the original source as well}

Setting up, getting started

Refer to the guide Setting up and getting started.

Design

💡 Tip: The .puml files used to create diagrams in this document can be found in the diagrams folder. Refer to the PlantUML Tutorial at se-edu/guides to learn how to create and edit diagrams.

Architecture

The Architecture Diagram given above explains the high-level design of the App.

Given below is a quick overview of main components and how they interact with each other.

Main components of the architecture

Main has two classes called Main and MainApp. It is responsible for,

At app launch: Initializes the components in the correct sequence, and connects them up with each other.
At shut down: Shuts down the components and invokes cleanup methods where necessary.

Commons represents a collection of classes used by multiple other components.

The rest of the App consists of four components.

UI: The UI of the App.
Logic: The command executor.
Model: Holds the data of the App in memory.
Storage: Reads data from, and writes data to, the hard disk.

How the architecture components interact with each other

The Sequence Diagram below shows how the components interact with each other for the scenario where the user issues the command delete 1.

Each of the four main components (also shown in the diagram above),

defines its API in an interface with the same name as the Component.
implements its functionality using a concrete {Component Name}Manager class (which follows the corresponding API interface mentioned in the previous point.

For example, the Logic component defines its API in the Logic.java interface and implements its functionality using the LogicManager.java class which follows the Logic interface. Other components interact with a given component through its interface rather than the concrete class (reason: to prevent outside component's being coupled to the implementation of a component), as illustrated in the (partial) class diagram below.

The sections below give more details of each component.

UI component

The API of this component is specified in Ui.java

The UI consists of a MainWindow that is made up of parts e.g.CommandBox, ResultDisplay, PersonListPanel, StatusBarFooter etc. All these, including the MainWindow, inherit from the abstract UiPart class which captures the commonalities between classes that represent parts of the visible GUI.

The UI component uses the JavaFx UI framework. The layout of these UI parts are defined in matching .fxml files that are in the src/main/resources/view folder. For example, the layout of the MainWindow is specified in MainWindow.fxml

The UI component,

executes user commands using the Logic component.
listens for changes to Model data so that the UI can be updated with the modified data.
keeps a reference to the Logic component, because the UI relies on the Logic to execute commands.
depends on some classes in the Model component, as it displays Person object residing in the Model.

Logic component

API : Logic.java

Here's a (partial) class diagram of the Logic component:

How the Logic component works:

When Logic is called upon to execute a command, it uses the AddressBookParser class to parse the user command.
This results in a Command object (more precisely, an object of one of its subclasses e.g., AddCommand) which is executed by the LogicManager.
The command can communicate with the Model when it is executed (e.g. to add a person).
The result of the command execution is encapsulated as a CommandResult object which is returned back from Logic.

The Sequence Diagram below illustrates the interactions within the Logic component for the execute("delete 1") API call.

ℹ️ **Note:** The lifeline for `DeleteCommandParser` should end at the destroy marker (X) but due to a limitation of PlantUML, the lifeline reaches the end of diagram.

Here are the other classes in Logic (omitted from the class diagram above) that are used for parsing a user command:

How the parsing works:

When called upon to parse a user command, the AddressBookParser class creates an XYZCommandParser (XYZ is a placeholder for the specific command name e.g., AddCommandParser) which uses the other classes shown above to parse the user command and create a XYZCommand object (e.g., AddCommand) which the AddressBookParser returns back as a Command object.
All XYZCommandParser classes (e.g., AddCommandParser, DeleteCommandParser, ...) inherit from the Parser interface so that they can be treated similarly where possible e.g, during testing.

Model component

API : Model.java

The Model component,

stores the address book data i.e., all Person objects (which are contained in a UniquePersonList object).
stores the currently 'selected' Person objects (e.g., results of a search query) as a separate filtered list which is exposed to outsiders as an unmodifiable ObservableList<Person> that can be 'observed' e.g. the UI can be bound to this list so that the UI automatically updates when the data in the list change.
stores a UserPref object that represents the user’s preferences. This is exposed to the outside as a ReadOnlyUserPref objects.
does not depend on any of the other three components (as the Model represents data entities of the domain, they should make sense on their own without depending on other components)

ℹ️ **Note:** An alternative (arguably, a more OOP) model is given below. It has a `Tag` list in the `AddressBook`, which `Person` references. This allows `AddressBook` to only require one `Tag` object per unique tag, instead of each `Person` needing their own `Tag` objects.

Storage component

API : Storage.java

The Storage component,

can save both address book data and user preference data in json format, and read them back into corresponding objects.
inherits from both AddressBookStorage and UserPrefStorage, which means it can be treated as either one (if only the functionality of only one is needed).
depends on some classes in the Model component (because the Storage component's job is to save/retrieve objects that belong to the Model)

Common classes

Classes used by multiple components are in the seedu.addressbook.commons package.

Implementation

This section describes some noteworthy details on how certain features are implemented.

[Proposed] Undo/redo feature

Proposed Implementation

The proposed undo/redo mechanism is facilitated by VersionedAddressBook. It extends AddressBook with an undo/redo history, stored internally as an addressBookStateList and currentStatePointer. Additionally, it implements the following operations:

VersionedAddressBook#commit() — Saves the current address book state in its history.
VersionedAddressBook#undo() — Restores the previous address book state from its history.
VersionedAddressBook#redo() — Restores a previously undone address book state from its history.

These operations are exposed in the Model interface as Model#commitAddressBook(), Model#undoAddressBook() and Model#redoAddressBook() respectively.

Given below is an example usage scenario and how the undo/redo mechanism behaves at each step.

Step 1. The user launches the application for the first time. The VersionedAddressBook will be initialized with the initial address book state, and the currentStatePointer pointing to that single address book state.

Step 2. The user executes delete 5 command to delete the 5th person in the address book. The delete command calls Model#commitAddressBook(), causing the modified state of the address book after the delete 5 command executes to be saved in the addressBookStateList, and the currentStatePointer is shifted to the newly inserted address book state.

Step 3. The user executes add n/David … to add a new person. The add command also calls Model#commitAddressBook(), causing another modified address book state to be saved into the addressBookStateList.

ℹ️ **Note:** If a command fails its execution, it will not call `Model#commitAddressBook()`, so the address book state will not be saved into the `addressBookStateList`.

Step 4. The user now decides that adding the person was a mistake, and decides to undo that action by executing the undo command. The undo command will call Model#undoAddressBook(), which will shift the currentStatePointer once to the left, pointing it to the previous address book state, and restores the address book to that state.

ℹ️ **Note:** If the `currentStatePointer` is at index 0, pointing to the initial AddressBook state, then there are no previous AddressBook states to restore. The `undo` command uses `Model#canUndoAddressBook()` to check if this is the case. If so, it will return an error to the user rather than attempting to perform the undo.

The following sequence diagram shows how the undo operation works:

ℹ️ **Note:** The lifeline for `UndoCommand` should end at the destroy marker (X) but due to a limitation of PlantUML, the lifeline reaches the end of diagram.

The redo command does the opposite — it calls Model#redoAddressBook(), which shifts the currentStatePointer once to the right, pointing to the previously undone state, and restores the address book to that state.

ℹ️ **Note:** If the `currentStatePointer` is at index `addressBookStateList.size() - 1`, pointing to the latest address book state, then there are no undone AddressBook states to restore. The `redo` command uses `Model#canRedoAddressBook()` to check if this is the case. If so, it will return an error to the user rather than attempting to perform the redo.

Step 5. The user then decides to execute the command list. Commands that do not modify the address book, such as list, will usually not call Model#commitAddressBook(), Model#undoAddressBook() or Model#redoAddressBook(). Thus, the addressBookStateList remains unchanged.

Step 6. The user executes clear, which calls Model#commitAddressBook(). Since the currentStatePointer is not pointing at the end of the addressBookStateList, all address book states after the currentStatePointer will be purged. Reason: It no longer makes sense to redo the add n/David … command. This is the behavior that most modern desktop applications follow.

The following activity diagram summarizes what happens when a user executes a new command:

Design considerations:

Aspect: How undo & redo executes:

Alternative 1 (current choice): Saves the entire address book.
- Pros: Easy to implement.
- Cons: May have performance issues in terms of memory usage.
Alternative 2: Individual command knows how to undo/redo by itself.
- Pros: Will use less memory (e.g. for delete, just save the person being deleted).
- Cons: We must ensure that the implementation of each individual command are correct.

{more aspects and alternatives to be added}

[Proposed] Data archiving

{Explain here how the data archiving feature will be implemented}

Documentation, logging, testing, configuration, dev-ops

Appendix: Requirements

Product scope

Target user profile:

is a university student who organizes many bulk purchases
has a need to manage a significant number of contacts
has a need to track who has paid him back
prefer desktop apps over other types
can type fast
prefers typing to mouse interactions
is reasonably comfortable using CLI apps

Value proposition:

track their debtors
view total money owed from all debtors
manage contacts faster than a typical mouse/GUI driven app

User stories

Priorities: High (must have) - * * *, Medium (nice to have) - * *, Low (unlikely to have) - *

Priority	As a …	I can …	So that …
`* * *`	user	save persons and their contact details	I do not need to remember these details
`* * *`	user	keep track of debts	I know who owes me money and for what
`* * *`	user	remove debts	I do not mistakenly think I have not yet been paid
`* * *`	user	see how much I am owed in total	I know how much I expect to be paid
`* * *`	user	close the application
`* *`	user	see an overview of all the debts owed	I am in better control of my overall financial situation
`* *`	user	search for a person’s contact	I can easily access his contact details
`* *`	user	save my contacts and debts over multiple usage sessions of the app	I do not need to key in data again when I exit and re-enter the app

{More to be added}

Use cases

(For all use cases below, the System is PayMeLah and the Actor is the user, unless specified otherwise)

Use case: Add a person

MSS

User requests to add a person
PayMeLah adds the person

Use case ends.

Extensions:

1a. The given input is invalid.
- 1a1. PayMeLah shows an error message.
  
  Use case ends.

Use case: Add a debt

MSS

User requests to list persons
PayMeLah shows a list of persons
User requests to add a debt to a specific person in the list
PayMeLah adds the debt to the person

Use case ends.

Extensions

1a. The given input is invalid.
- 1a1. PayMeLah shows an error message.
  
  Use case ends.
3a. The given input is invalid.
- 3a1. PayMeLah shows an error message.
  
  Use case resumes at step 2.

Use case: Delete a person

MSS

User requests to list persons
PayMeLah shows a list of persons
User requests to delete a specific person in the list
PayMeLah deletes the person

Use case ends.

Extensions

2a. The list is empty.

Use case ends.
3a. The given index is invalid.
- 3a1. PayMeLah shows an error message.
  
  Use case resumes at step 2.

Use case: Clear debts

MSS

User requests to list debtors
PayMeLah shows a list of debtors
User requests to clear the debts of a specific debtor in the list
PayMeLah clears the debts of that person
PayMeLah displays that the person’s debts are cleared

Extensions

3a. The given index is invalid.
- 3a1. PayMeLah shows an error message
  
  Use case resumes at step 3.

Use case: List persons with debts

MSS

User requests to list persons with debts
PayMeLah shows the list of persons

Use case ends.

Extensions

2a. The list is empty (no persons with debts).

Use case ends.

Use case: Find a person by name

MSS

User requests to find a person by name.
PayMeLah shows a list of people with that name.

Use case ends.

Extensions

1a. There is no person with the given name.
- 1a1. PayMeLah shows an error message.
  
  Use case ends.

Use case: Find a person by debt description

MSS

User requests to find a person by debt description.
PayMeLah shows a list of people with a debt matching the debt description.

Use case ends.

Extensions

1a. There is no debt matching the given description.
- 1a1. PayMeLah shows an error message.
  
  Use case ends.

Use case: Get debt overview

MSS

User requests to get overview of all debts
PayMeLah shows the total sum of debts the user is owed.

Use case ends.

{More to be added}

Non-Functional Requirements

The software should work on any mainstream OS as long as it has Java 11 or above installed.
The software will not facilitate actual monetary transactions, nor any communications between persons.
The software should be able to hold up to 1000 persons and 10000 debts without a noticeable sluggishness in performance for typical usage.
The software should not result in noticeable lag for other applications.
The product should be for a single user only; multiple users cannot use the software on the same device simultaneously.
The data stored by the software should be stored locally and in a human editable text file, rather than stored using a DBMS.
The software should work without requiring an installer.
The software should not depend on a remote server.
The software should not require the user to create an account on a third-party service.
The software should follow the Object-oriented paradigm primarily.
The software should avoid implementing hard-to-test features or features that make the product hard-to-test.
The software should only make use of third-party frameworks/libraries/services if they are free, open-source, and have permissive license terms.
The software should be able to be packaged into a single JAR file.
The file sizes of the product and its documents should be reasonable, i.e. the JAR file itself should not exceed 100MB and the documents should not exceed 15MB per file.
The GUI should work well for standard screen resolutions 1920x1080 and higher, and, for screen scales 100% and 125%.
The GUI should be usable for resolutions 1280x720 and higher, and, for screen scales 150%.
The GUI should have a readable font, at least size 12.
The GUI should be able to respond to user inputs in 500 milliseconds.
The software and documentation should be accessible for users who have a basic command of the English language.
A user with above average typing speed for regular English text (i.e. not code, not system admin commands) should be able to accomplish most of the tasks faster using commands than using the mouse.

Glossary

Mainstream OS: Windows, Linux, Unix, OS-X
Debtor: The person who owes money.
Creditor: The person who is owed money.
Debt: The transaction event (e.g. group dinner, Grab food order) where money is owed between a debtor and a creditor

Appendix: Instructions for manual testing

Given below are instructions to test the app manually.

ℹ️ **Note:** These instructions only provide a starting point for testers to work on; testers are expected to do more *exploratory* testing.

Launch and shutdown

Initial launch
1. Download the jar file and copy into an empty folder
2. Double-click the jar file Expected: Shows the GUI with a set of sample contacts. The window size may not be optimum.
Saving window preferences
1. Resize the window to an optimum size. Move the window to a different location. Close the window.
2. Re-launch the app by double-clicking the jar file.
  Expected: The most recent window size and location is retained.
{ more test cases … }

Deleting a person

Deleting a person while all persons are being shown
1. Prerequisites: List all persons using the list command. Multiple persons in the list.
2. Test case: delete 1
  Expected: First contact is deleted from the list. Details of the deleted contact shown in the status message. Timestamp in the status bar is updated.
3. Test case: delete 0
  Expected: No person is deleted. Error details shown in the status message. Status bar remains the same.
4. Other incorrect delete commands to try: delete, delete x, ... (where x is larger than the list size)
  Expected: Similar to previous.
{ more test cases … }

Saving data

Dealing with missing/corrupted data files
1. {explain how to simulate a missing/corrupted file, and the expected behavior}
{ more test cases … }

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Acknowledgements

Setting up, getting started