CoverLetterGen

Project Overview

CoverLetterGen is a native iPad application that generates cover letters using the OpenAI API. It automates the formatting and drafting process while ensuring that personally identifiable information (PII) remains local to the device.

Technical Specifications

• Language: Swift 6
• Architecture: MVVM
• UI Framework: SwiftUI
• Persistence: SwiftData
• Concurrency: Swift Structured Concurrency (Async/Await, Actors)
• External API: OpenAI (Responses Endpoint)

Architecture & Implementation

Privacy Mechanism

To prevent PII leakage, the application separates generation from data assembly:

1. Generation: The OpenAIService sends only the anonymized resume text and job description to the LLM.
2. Assembly: The AppViewModel receives the raw text and prepends the user's contact details (name, address, phone) locally.
3. Storage: User profile data is persisted in UserDefaults, while generated content is stored in SwiftData.

Concurrency (Swift 6)

The project adopts strict concurrency checking to ensure thread safety:

• Actor Isolation: OpenAIService is defined as an actor to serialize network requests and manage session state.
• Main Actor: AppViewModel is isolated to @MainActor, ensuring all state mutations and UI updates occur on the main thread without manual dispatching.

Persistence Strategy

Data persistence is handled by SwiftData:

• Schema: The CoverLetter model stores the generated text along with the configuration state used at the time of generation (TextLengthOption, TextToneOption).
• State Restoration: Selecting a historical item re-initializes the application state (Input fields, Tone, Length) to match that record, enabling context switching.

Networking

Networking is implemented using URLSession and custom Codable structs.

• Schema Validation: The client maps the nested response structure of the GPT-5.2 API (output -> content -> text) to strongly typed models.
• Testing: Deterministic tests are implemented using a MockURLProtocol, allowing the service to be tested without live API calls.

Visuals

Code Examples

API Response Handling

File: OpenAIService.swift Parsing the nested response structure from the Responses API.

let decodedResponse = try JSONDecoder().decode(ResponsesResponse.self, from: data)

// Parse nested structure: output[0] -> content[0] -> text
if let firstOutput = decodedResponse.output.first,
   let textContent = firstOutput.content.first(where: { $0.type == "output_text" })?.text {
    return textContent
}

State Restoration

File: AppViewModel.swift Restoring configuration state from a persisted model. The usage of Enums prevents invalid state.

var selectedLetter: CoverLetter? {
    didSet {
        if let letter = selectedLetter {
            resumeInput = letter.resumeText
            jobInput = letter.jobDescription
            
            // Restore Settings from persisted raw values
            if let l = TextLengthOption(rawValue: letter.lengthOption) { length = l }
            if let t = TextToneOption(rawValue: letter.toneOption) { tone = t }
        }
    }
}

Setup

1. Clone the repository.
2. Open CoverLetterGen.xcodeproj (Xcode 26.2+).
3. Run on a simulator or device.
4. Configure the OpenAI API Key in the application settings.

License

MIT