SKILL: Architecture & DDD Master Guide
This document defines the Domain-Driven Design (DDD) architecture and strict layer boundaries for the project.
🏛️ 1. Layered Architecture (The Law)
Dependencies must flow inward: Presentation → Application → Domain ← Infrastructure.
🔴 Domain Layer (src/app/domain/)
- Purity: Zero framework dependencies (No Angular, No Firebase, No RxJS).
- Entities: Minimal, intention-free models.
- Value Objects: Immutable, validated at creation.
- Repositories: Interfaces ONLY (ports).
- Aggregates: Transactional boundaries.
- Domain Events: Immutable "facts" that have occurred.
🟡 Application Layer (src/app/application/)
- Orchestration: Implements Use Cases (Handlers).
- State: NgRx Signals (Store) is the source of truth.
- Mappers: Domain ↔ DTO / ViewModel conversion.
- Ports: Defines repository and service interfaces.
🔵 Infrastructure Layer (src/app/infrastructure/)
- Adapters: Implements interfaces defined in the application/domain layers.
- Technical: Firebase, HTTP, persistence, logging, external SDKs.
- DTOs: Confined to this layer; never leaked to Presentation or Domain.
🟢 Presentation Layer (src/app/presentation/)
- UI Only: No business logic.
- Signals: Consumes signals from stores.
- Standalone: All components are standalone + zone-less.
🧩 2. Tactical DDD Patterns
Repository Pattern
- Interface defined in Domain or Application.
- Implementation hidden in Infrastructure.
- Injection via
InjectionTokento ensure loose coupling.
Domain Service
- Used when logic involves multiple entities or doesn't naturally fit into one.
- Must remain pure (no I/O).
Event-Driven Flow
- Append: Persist a command outcome to the store/database.
- Publish: Emit event via the
EventBus. - React: Other stores or capabilities listen and react.
📦 3. Project Structure & Naming
| Layer | Type | Pattern |
|---|---|---|
| Domain | Entity | {name}.entity.ts |
| Application | Store | {name}.store.ts |
| Infrastructure | Repository | {name}-firestore.repository.ts |
| Presentation | Component | {name}.component.ts |
- Alias Imports: Use
@domain/*,@application/*,@infrastructure/*. - No Relative Imports: Never import across layers using
../../.
🪒 4. Occam's Razor
- Minimalism: Do not add layers or abstractions without necessity.
- Cohesion: Keep related logic close.
- Decoupling: Minimize dependencies between modules.
Adjudication: TypeScript errors (TS2339, TS2345) regarding cross-layer imports or invalid field access in the Domain are architectural violations—fix the design, do not suppress the error.