Instruction file imported from massimilianolapuma/foodmap (.github/instructions/data.instructions.md). Copyright stays with the author.

Data layer review guidelines

Purpose

Rules for the Data layer that implements Domain protocols: DTOs, Mappers, Repositories (impl), DataSources, Persistence (SwiftData), Networking.

Mapping

• DTO ↔ entity conversion belongs only in Data/Mappers. Flag mapping logic anywhere else (repositories, view models, use cases).
• DTOs model the wire format; never leak DTOs out of the Data layer.

Networking (Open Food Facts)

• Networking lives only in Data/Networking. HTTPS only; ATS must stay enabled.
• Treat all API responses and scanned text as untrusted: validate and bound payloads, decode defensively, and handle missing/invalid fields without crashing.
• Surface failures as typed FoodMapError values; never force-unwrap decoded data.

// Avoid — trusts the response shape
let name = dto.product!.name!

// Prefer — defensive, bounded
guard let product = dto.product, let name = product.name, !name.isEmpty else {
    throw FoodMapError.notFound
}

Persistence

• Use SwiftData @Model types. In tests prefer in-memory stores.
• Be mindful of CloudKit constraints if sync is in scope (optional attributes / defaults, no unique constraints).

Privacy

• Never send allergies, diet types, or nutrition targets to third parties. Process sensitive data on-device.
• No secrets in source.