adamayoung/add-use-case

Add a Use Case to Existing Context

Guide for adding a new use case following clean architecture patterns.

Required Information

Ask the user for:

• Context name (e.g., PopcornMovies, PopcornTVSeries)
• Use case name (e.g., FetchMovieCredits)
• Purpose of the use case

Steps

1. Create Use Case Directory

Contexts/{Context}/Sources/{Context}Application/UseCases/{UseCaseName}/

2. Create Three Files

{UseCaseName}UseCase.swift - Protocol definition:

public protocol {UseCaseName}UseCase: Sendable {
    func execute(...) async throws({UseCaseName}Error) -> ResultType
}

Default{UseCaseName}UseCase.swift - Implementation:

final class Default{UseCaseName}UseCase: {UseCaseName}UseCase {
    private let repository: any SomeRepository

    init(repository: some SomeRepository) {
        self.repository = repository
    }

    func execute(...) async throws({UseCaseName}Error) -> ResultType {
        // Implementation
    }
}

{UseCaseName}Error.swift - Error type:

public enum {UseCaseName}Error: Error, Equatable, Sendable {
    case notFound
    case unknown(Error? = nil)
}

3. Add Factory Method

In {Context}Application/{Context}ApplicationFactory.swift:

func make{UseCaseName}UseCase() -> some {UseCaseName}UseCase {
    Default{UseCaseName}UseCase(repository: repository)
}

4. Expose in Composition Layer

In {Context}Composition/Popcorn{Context}Factory.swift:

public func make{UseCaseName}UseCase() -> some {UseCaseName}UseCase {
    applicationFactory.make{UseCaseName}UseCase()
}

5. Add TCA Dependency

Create AppDependencies/{Context}/{UseCaseName}UseCase+TCA.swift:

enum {UseCaseName}UseCaseKey: DependencyKey {
    static var liveValue: any {UseCaseName}UseCase {
        @Dependency(\.{context}Factory) var factory
        return factory.make{UseCaseName}UseCase()
    }
}

public extension DependencyValues {
    var {useCaseName}: any {UseCaseName}UseCase {
        get { self[{UseCaseName}UseCaseKey.self] }
        set { self[{UseCaseName}UseCaseKey.self] = newValue }
    }
}

6. Write Unit Tests

Create tests in Contexts/{Context}/Tests/{Context}ApplicationTests/UseCases/{UseCaseName}/:

• Create mock repository
• Test success and error cases
• Use Swift Testing framework

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