Calculator

A simple SwiftUI calculator app that performs basic arithmetic operations, logs session data to a Go server and SQLite database, and stores sessions locally on the iOS device using Core Data.

Screenshots:

Here are some screenshots showcasing the app's features:

Requirements

• macOS
• Xcode 16.2
• iOS 17.0+
• Go 1.21+

Setup

Backend:

1. Install Go (1.21+): brew install go (macOS)
2. Navigate to cd Backend
3. Run go mod tidy to install dependencies.
4. Run go run *.go to start the server on http://localhost:3000

iOS App:

1. Open Calculator.xcodeproj in Xcode.
2. Under Signing & Capabilities change the Team value to your development team.
3. Build and run on the iOS simulator. (Cannot be run on a real device because of the server local ip address. In a production scenario, the server would be publically accessible. In a dev environment, the server would be internally accessible.)
4. Perform a calculation or two.
5. Once you swipe the app so that it goes into the background, you will see a message in the Xcode debug console, in the terminal where you started the backend server, and the backend SQLite Calculator.db will be updated.
6. You can view past sessions by selecting the View Session Data in the app; it will show the current session and the previous sessions in descending order by last updated date.

Deliverables

Database Schema:

Table: sessions

Column	Data Type	Attributes	Description
session_id	TEXT	PRIMARY KEY	Unique identifier for each session
add_count	INTEGER	DEFAULT 0	Number of addition operations performed
subtract_count	INTEGER	DEFAULT 0	Number of subtraction operations performed
multiply_count	INTEGER	DEFAULT 0	Number of multiplication operations performed
divide_count	INTEGER	DEFAULT 0	Number of division operations performed
last_updated	DATETIME	DEFAULT CURRENT_TIMESTAMP	Timestamp of the last update

API Documentation:

POST /api/session

Request Body:

  {
      "sessionId": "string",
      "addCount": integer,
      "subtractCount": integer,
      "multiplyCount": integer,
      "divideCount": integer,
      "lastUpdated": "string"  // ISO 8601 format, e.g., "2025-02-27T12:00:00Z"
  }

Sample Data

{
    "sessionId": "550e8400-e29b-41d4-a716-446655440000",
    "addCount": 3,
    "subtractCount": 1,
    "multiplyCount": 2,
    "divideCount": 0,
    "lastUpdated": "2025-02-26T10:00:00Z"
}

Front-end Technical Details

• Written in Swift
• iOS
• SwiftUI
• MVVM Architecture
• SwiftLint
• Persists data locally via Core Data and sends each session’s data to the backend once the app is about to go into the background.
• Creates a new session each time the app launches.

Back-end Technical Details

• Written in Go
• Uses the Gin web framework for HTTP routing.
• Stores data in an SQLite database located at Backend/calculator.db.
• Implements basic authentication with hardcoded credentials (only done for this sample project, not something that would be done in development or production environments), though not currently applied to routes.
• Provides two endpoints:
  • POST /api/session: Saves session data to the database
  • GET /api/sessions: Retrieves all stored sessions (this was for my testing purposes)

If I had more time I would have:

• Added unit tests and mocks for both the Swift frontend and Go backend.
• Used Async/Await to handle concurrency.