add-use-case

name	add-use-case
description	Add a use case to an existing context

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()
}

This is all the wiring the use case needs: the context factory is already exposed on AppServices (e.g. services.{context}Factory), so any feature can reach the new use case through it.

5. Consume from a Feature

There is no per-use-case dependency registration. A feature reaches the use case in its {Feature}Dependencies.live(services:) builder via the context factory on AppServices, mapping the domain result to a view model:

public extension {Feature}Dependencies {

    static func live(services: AppServices) -> {Feature}Dependencies {
        let useCase = services.{context}Factory.make{UseCaseName}UseCase()

        return {Feature}Dependencies(
            fetch: { id in
                let result = try await useCase.execute(id: id)
                return {Feature}Mapper().map(result)
            }
        )
    }

}

6. Write Unit Tests

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

• Create mock repository
• Test the happy path and the translation of each error type
• Use the Swift Testing framework

$ARGUMENTS