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Business Logic Layer

Responsibility Split​

  • Handlers SHOULD stay thin.
  • Business workflows SHOULD live in services.
  • Persistence logic MUST stay in models/repository helpers.

When to Introduce Services​

Create/expand service modules when logic includes:

  • multiple model operations in one use case
  • transaction coordination
  • external integrations (cache, email, AI, files)
  • domain validation beyond simple input checks

Interface and DI Patterns​

  • Use interfaces where behavior boundaries improve testing/replacement.
  • Keep interfaces minimal and behavior-oriented.
  • Prefer constructor injection for services.
  • Handlers MUST NOT create DB/Redis/external clients directly.
func NewTokenService(db *gorm.DB) (*TokenService, error) {
    if db == nil {
        return nil, ErrInvalidDependency
    }
    return &TokenService{db: db}, nil
}